Production of Mink

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Production of Mink

The influence of various management,

environment and nutritional elements on behaviour, physiology and production in mink

Steen H. Møller, Steffen W. Hansen, Outi Lohi,

Asbjørn Brandt, Palle V. Rasmussen Lone Vejgaard Jensen

Beretning Foulum 1991

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Statens flusdvrbrujisforsøR har til formål at gem.- ¡ " v . m m - nz opbygge viden at betydning for erhvervsmæssig husdyrbrug i D a n m a r k og bi-

' , h'l f L 'L J " i i i , ) k ^ < i ->ri, . il UlligCillC.

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T h e a, f «ir > j n - . r .-search and accumulate L v a h <ice .T impor i ZiJin c « .m m ¡i f » ^L »i and contribute to an cliidf"«, iu \>

m e n t a iei . r - i r^{t i r e} i i h r ud i ^ s.

T h e rt r ki :i u > i . n/ation of resources, e n v i r o n m e n t and a n i m a ' «-' n» n ! - jn i t o «« . 'mpetitiveness of the agricultural prod- ucts.

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" " "ow d e p a r t m e n t s :

nistry Research in Fur Animals Central Laboratory

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ISSN 0105-8883

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Beretning fra

Statens Husdyrbrugsforsøg

Report from the National InstUute øf Animal Science, Denmark

Steen H. Møller, Steffen W. Hansen,

Outi Loh i, Asbjørn Brandt, Palle V. Rasmussen Department of Research in Fur Aeimals Lone Vejgaard Jensen

Biotechnical Institute

Production of Mink

The influence of various management, environment and nutritional elements on behaviour, physiology and production in mink Indflydelse af forskellig driftsledelse,

miljø og ernæring på adfærd, fysiologi og produktion hos mink

Med dansk sammendrag

Manuskriptet afleveret december 1990

Special-Trykkeriet Viborg a-s efter WordPerfect dokument

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P R E F A C E

T h j c r p n o r t r e p r e s e *1 t s c u i r n r p a n e ^ tiiiu CUÍávlujlOllo o f Uli €-A|Jtii-

mental sections of the largest single p r o j e c t this d e p a r t m e n t has carried out T h e p r o j e c t was en titled: Production f a c t o r s and production control. T h e results of the investigations on the f a r m s regarding m a n a g e m e n t a n d environment will be published in a special report.

The p r o j e c t was f i n a n c e d b y tne Ministry of Agricultu«e t h r o u g h T h e J o i n r C o m m i t r e e f o r A g n -

"uUuial Research a.^i E r p e n ments as part of the research Oí e g i :;rn Pi . j d n r d o n > 2 e m in Agriculture (1984-88), T h e Danish F u r Bleeders Association and the app'opriation& allocated

co the d e p a r t m e n t by the g o v e r n - ment.

The o f f i c i a l title of t h e very broad p r o j e c t was: T h e i n f l u e n c e of management and e n v i r o n m e n - tal factors on b e h a v i o u r , health and productivity of f u r animals, illustration of the applicability of various blood p a r a m e t e r s f o r health control as well as an i n - vestigation of the i n f l u e n c e of minerals on f u r characteristics and blood parameters in m i n k . Investigations regarding f o x e s were, h o w e v e r , f r o m the b e g i n - ning separated into an i n d e p e n -

rjf»nt intPrn^rHir prnjpcf

T h e work w i t h i n the d i f f e r e n t areas of the p r o j e c t has been di /ersified Within en / i r o n m e n t , behaviour and production the experimental work has primarily b e e r concentrating on behaviour and reaction« of the mink to d i f - f e r e n t production environments A considerable part of this work has included development and te ting of measuring methods A method f o r determination of behaviour b / a »"tick test, sampling and analysis of blood as well as methods f o r d e t e r m i n a - tion of light reduction were developed. Choice of drinking water teinpv r a t a i e w i s tested und^r experimental cond tions Greatest irr>po~Tancc was. h o w - ever placed o i experiments witn mink in d i f f e r e n t environments.

The comparaci e *vork with m m eral content in "eed and hairs included a great deal ef method development as regards analysis of mineral: in m n k hairs. M o r - phological methods ier< applied 1 or description or hair type., and used f o r basic studies on normal

" ^ n a t i o n between t a r m j

T h e work with haematology 3 i d clinical-chemical parameters ha„

mainly consisted of development

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and implementation of analyses on m i n k and d e t e r m i n a t i o n of normal values.

A c o m m o n f a c t o r f o r the parts of the p r o j e c t included in the p r e s - ent report has t h e r e f o r e been the high degree of d e v e l o p m e n t work. This is an illustration of the status of f u r animal research when we are talking a b o u t areas outside the traditional subjects.

In areas like n u t r i t i o n , disease control, breeding and r e p r o d u c - tion, methods and tools are a v a i - lable, as well as knowledge about the normal reactions and c h a r a c - teristics of the animals.

In new fields such as e n v i r o n - ment, behaviour and p r o d u c t i o n , hair and skins as well as health control, tools and methods were sparsely developed. K n o w l e d g e of the normal condition of the animals and the variations herein was t h e r e f o r e sparsely or not at all d o c u m e n t e d .

Besides leading to a n u m b e r of other projects, this p r o j e c t gave the following main results and effects:

1. Behavioural research within the f u r animal field started early enough f o r the debate regarding the w e l f a r e of f u r animals to be based on facts instead of assumptions. T h e results of these investiga-

tlOES ll^VC IbCdl USed- CX.tGÜ*

sively as d o c u m e n t a t i o n in discussions and legislation in this field. T h e team r e s p o n - sible f o r this part of the research is today i n t e r n a - tionally well r e c o g n i z e d when f u r animal w e l f a r e is discussed.

2. The m a n a g e m e n t and e n v i - r o n m e n t section has clearly tevealed i m p o r t a n t area^ to be covered and cleared u p a n u m b e r of "myths" as r e - gards m i n k p r o d u c t i o n , (screening of females, w a - tering conditions, kit b e - haviour b e f o r e weaning, light conditions etc). T h e results of these investigations were also included in the above mentioned w o r k of elucidation and legislation.

3. T h e genetic examinations related to pelt properties and blood parameters have c o n t r i b u t e d considerably to the u n d e r s t a n d i n g of the importance of o b j e c t i v e criteria in the breeding work. T h e results have also c o n f i r m e d that genetics play an i m p o r t a n t role in the variations between m i n k f a r m s (mink populations).

4. T h e h a e m a t o l o g i c a l a n d clinical-chemical section of the p r o j e c t has helped to

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develop and strengthen this very important tool as an aid in research as well as in health control.

It has not been possible to establish a complete check- up system f o r health control - if such a system can at all be f o u n d .

An important result of the e f f o r t s of the department in this area has been that in cooperation with The Soviet Union and Finland, and edited by A s b j ø r n Brandt, we have been able to p u b - lish a book of 150 pages entitled: "Haernatology and Clinical Chemistry of Fur Animals - A Current T r e a - tise (SCIENTIFUR, 1989).

5. The subproject concerning mineral substances revealed considerable variation in the mineral content of feed and illustrated in which cases the mineral content in hair depended on the feed. F u r - thermore, correlations b e - tween mineral content in the hair and pelt characteristics were illustrated.

6. The establishment of hair morphological research in connection with this project has made it possible to start

up basic research in this area. In f u r animals as well as in rabbits it has proved to be an important tool in the research as well as in the breeding work. The i m m e - diate result of this project has been the description of genetic differences in hair types f r o m scanblack mink.

In the areas mentioned, the p r o - ject has given considerable c o n - tributions as regards practical methods and actual experimental results. As the weighing of m e - thod development and applica- tions has varied between the three d i f f e r e n t parts of the p r o - ject, it is difficult to make a combined discussion about all subprojects. The broad aim of the project has also made it d i f f i c u l t to get an overall view or to make a common conclusion.

Discussion as well as summaries and conclusions have therefore been given within each of the 4 main sections of the report. Be- sides, we r e f e r to the more than 70 publications incl. papers at congresses and meetings, on which this report is based.

The project has been carried out in cooperation with Bioteknisk Institut, The Government Veteri- nary Serum Laboratory, The University of Copenhagen, dept.

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of Population Biology, and T h e Danish F u r Breeders Association.

Besides, we have been in contact with a n u m b e r of institutions and persons in D e n m a r k and abroad.

All tecb"iteal employees of tHe depai tment on *he f a r m as we'* as

¡1 Qui laboratories have «.¿ken part in this p r o j e c t .

T h e m a n u i c r i p t has been typed by H a n n e A rived and Dorthe V Nielsen. The m a j o r part of the editorial and lay out work has been done by Steen H. Moller.

T h e d e p a r t m e n t wants to thank all collaborators and employees f o r a f i n e cooperation as regards the implementation of the p r o j e c t and the preparation of the report.

F o u l u m , December 1990

G u n n a r Jørgensen

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C O N T E N T S

Page

PREFACE 3

1. MANA

m ML

œ E

T I O Î

> N M E N T

teen M o l l e r , . 13

S S

13

16

1.1 Background 19

1.2 General f a r m conditions and management . . . 19

1.3 Light conditions in mink sheds . . . 21

1.3.1 Introduction . . . 21

1.3.2 Material and methods . . . 22

1.3.3 Results and discussion . . . 22

1.3.4 Conclusion . . . 22

1.4 Drinking water temperature . . . 23

1.4.1 Introduction . . . 23

1.4.3 Results . . . 24

1.4.3.1 Males . . . . . . 24

1.4.3.2 Kits . . . 27

1.4.3.3 Females . . . 29

1.4.4 Discussion . . . 31

1.5 Supplementary watering system . . . 33

1.5.1 Introduction . . . 33

1.5.3 Results . . . 34

1.5.4 Discussion . . . 37

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1.6 Visual isolation of m i n k f e m a l e s during t h e repioduction

period . . . 39

1.6.1 Introduction . . . 39

1.6.3 Results . . . 40

1.6.4 Discussion . . . . . . 44

1.7 Scent communication . . . 46

1.7.1 I n t r o d u c t i o n . . . 46

1.8 Weighing a n d behavioural response . . . 46

1.8.1 I n t r o d u c t i o n . . . 4 6 1.8.2 Material and methods . . . 47

1.9 Weight development, body length skin l e n g t h and pelt quality . . . 50

1.9.1 I n t r o d u c t i o n . . . 50

1.9.2 Material and methods 51 1.9.3 Results and discussion . . . 51

1.10 Development of body l e n g t h and weight In relation to time of birth ami litter size . . . 5 5 1.10.1 I n t r o d u c t i o n . . . 55

1.10.2 Material and methods 55 1.10.3 Results and discussion . . . 55

1.10.4 Conclusion . . . 59

R e f e r e n c e s 60

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2 B E H A V I O U R AND ENVIRONMENT OF MINK.

By Steffen W. Hansen . . . . . . 63

Summary 63 Sammendrag 65 2.1 Introduction 66 2 • 2 Research topics oo 2.3 Importance of cage sizes and nest boxes . . . 67

2.3.1 Experiment I . . . 67

2.3.2 Experiment 2 . . . 67

• 2.3.3.1 Behaviour . . . 69

2.3.3.2 Haematology . . . 69

2.3.3.3 Physical-chemical parameters . . . 69

2 3 . 3 . 4 Eosinophil leucocytes . . . 69

2 3.3 5 D i f f e r e n t i a l leucocyte count . . . 70

2 3 . 3 . 6 Adrenal cortex functional test . . . 2.3.3.7 Production results 71 2.3.4 Conclusion 71 2.4 Activity pattern of lactating females and t h e Importance of water trays and resting place . . . 71

2.4.1 Introduction . . . 71

2.4.2 Materials and methods . . . 72

2.4.4 Conclusion 76 2.5 E f f e c t of water trays f o r farmed mink . . . 77

2.5.2 Materials and methods . . . 77

2.5.3.1 Weight development 78 2.5.3.2 Skin qualities . . . 80

2.5.3.3 Behaviour 82 2.5.3.4 Level of eosinophil leucocytes . . . 84

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2.6 Correlation between behavioural response a t stick test

a n d eosinophil level of m i n k f e m a l e s . . . 85

2.6.2 Results a n d discussion . . . 86

2.7 T h e Importance of weaning lime on mating success and temperament of mink . . . . . . . . . . . 90

2.8 Theses from the Luwersiiy cl Ccpea*iagea, I t m cf Population Biology connected with this project v . . . . . . 92

2.8.1 T h e i m p o r t a n c e of early weaning and handling . . . 92

2.8.2 The ontogeny of mink kits . . . . . . 93

2 8.3 The development ct behaviour of juvenile inmk in cages and the importance of stress to beha/icur, physiology and fur quality . . . 93

References . . . 94

3. MINERAL CONTENT OF FEED AND HAIR AND MICROSCOPIC STUDIES ON HAIR. By Outi Lohi, Palle V. Rasmussen and Lone Vejgaard Jensen . . . 97

Summary 97 Sammendrag . . . 98

3.1 MINERAL COMPOSITION OF MINK FEED AND MINK HAIR . . . 99

3.1.1 Introduction . . . 99

3.1.2 Material and methods . . . 99

3.1.3 Results and discussion . . . 101

3.1.3.1 Mineral composition of Danish mink feed . . . 101

3.1.3.2 Minerals in drinking water . . . 106

3.1.3.3 Minerals in hair and correlation between feed and hair . . . 108

3.1.3.4 Minerals in hair and grading characteristics . . 112

3.1.3.5 Correlation between minerals in the hair . . . . 112

3.1.4 Conclusions . . . 114

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3.2.1 Introduction

3.2.4 Conclusions

4 » 2 • 1

4^a2 ®2

4.2.3

4.2.5 Data analysis

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4.3 Results and discussion . . . 4.3.1 _ Haematology, enzymology, vitaminology

and metabolites . . . 144

4.3.1.1 Method development . . . 144

4.3.1.2 R e f e r e n c e value determination . . . 148

4 . 3 J . 3 Investigations on heritability . . . 156

4.3.2 Evaluation of clinico-pachological parameters as (subclinical) disease predictors in mink. . . . 156

4.3.3 Experimental investigations . . . 159

4 . 4 C o n c l u s i o n J 6 References . . . . 163

Appendix . . . 16/

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1. M A N A G E M E N T AND E N V I R O N M E N T IN MINK P R O D U C T I O N b y Steen Møller

S u m m a r y

In this part of the p r o j e c t " M a n - agement and E n v i r o n m e n t " e x - periments w e r e conducted c o n - cerning light, t e m p e r a t u r e of d r i n k i n g w a t e r , water s u p p l y , visual isolation, scent c o m m u n i - cation, reaction to r e p e a t e d weighings, a n d the correlation between time of b i r t h , litter size, w e i g h t d e v e l o p m e n t . b o d y length, skin size and pelt q u a h ty.

A method f o r evaluation of light conditions in m i n k sheds was developed a n d tested. This method measures the q u a n t i t y of light in the shed in relation to the quantity of light outside, a n d the d i f f e r e n c e expresses the light reducing e f f e c t of the shed. T h e light reduction is connected w i t h the n u m b e r of light panels in the roof and the cleanliness of these panels. T h e m e t h o d gives the same results u n d e r d i f f e r e n t weather conditions. The m e t h o d is t h e r e f o r e f o u n d to be a p p l i c - able in practice. T h e s i g n i f i c a n c e of the light r e d u c t i o n is d i s c u s - sed, and it is f o u n d that m i n k can be kept u n d e r very d a r k conditions w i t h o u t any negative

consequences as regards p r o d u c - tion. Negative consequences are more likely to occur w h e n m o v - ing animals between varying light conditions or w h e n using artificial light.

T h e intake of 40° C w a r m water by m i n k in comparison to water f r o m the tap has been e x a m i n e d with adult males, with kits, and with p r e g n a n t a n d n u r s i n g f e - males. In all cases the w a r m w a - ter was d r u n k in the same q u a n - tities as the cold water. If the adult males were o f f e r e d one t e m p e r a t u r e at a time, they d r a n k more w a r m water. If both temperatures were o f f e r e d at the same time, they d r a n k the same quantities, or in one case more cold water. T h e m i n k d r a n k more f r e q u e n t l y b u t less per session of cold water if both temperatures were available. If there was only one t e m p e r a t u r e at a time, no d i f f e r e n c e in the intake pattern was seen. In all cases a higher q u a n t i t y of cold water was spilled, both totally and per drinking session. M i n k kits d r a n k equal a m o u n t s of w a r m and cold w a t e r , b u t wasted

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moie cold water Before giving birth the females preferred warm water, but a f t e r b'rth they drank mostly cold water. The physiological significance of the lemperarure of drinking v ate: h

dibClisted It h coi' w l u d e a cnai mink like to dnnk water up to

40 c . The w i.ste o^r warei ib lowest if the water is warm.

In the latter part of the lactation period a supplement to the ordi- nary - upp\-. of drsakjr g w . t f r i- often used. A drip watering sy?~

fem was tested throughout^fw o lactation periods, and the weight development, drinking behaviour and activity of the animals were recoided. In the cold and wet lactation period of the first year the system had no e f f e c t . In the warm and dry lactation period of the second year, the weight loss of the females was reduced, and the weight gain of the kits was faster in the group with drip watering system. Kits with drip water supply take in water earlier than the control group, by licking water f r o m the tongue of the valve. However, they do not learn to release the valve earlier, Saliva licking occurred most f r e - quently in the group without drip water supply. A d i f f e r e n c e of approx 2 weeks was observed f r o m the kits start eating and until they start drinking. It is

concluded that rhe opportunity of the kits to take in water early improves with dnp watering. In warm and dry lactation periods this will increase gain and reduce the stress on the females,

Pr^-vio'is experiment1: wi*t • »sual

isolation o, rr inx vemsies -n^The gestation and lactation periods have indicated a positive e f f e c t on the whelping result. The ex- pcnm^nM ¿r-rj^i b j . e howe- ver, been too small to d e m o n - strate any enable J d i c i e n c e s in reproduction results. Therefore, f o u r experiments with v^:sual screening of mink females were carried out. The females were isolated before mating or before whelping. The separation consisted of an empty cage or a cage filled with straw Whelping results, weight development, and activity were recorded. Mo sys- tematic differences in whelping results were found that could be related to the screening, and kit gam was not affected The f e - males In the control group were more active than the separated groups. The whelping results are discussed. Thev conflict with previous results but are confirmed by later investigations It is concluded that visual isolation of mink females does not i n f l u - ence whelping result or kit gain but reduces the activity of the females in the lactation period.

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T h e significance of scent c o m - munication b e t w e e n males and females was investigated by spraying male u r i n e on the cages of the f e m a l e s b e f o r e mating.

T h e period of latency f r o m the time animals are put together until mating starts, was 4 m i n - utes shorter in the group s t i m u - lated by scent, b u t no d i f f e r e n c e was f o u n d in mating success or whelping result. It is concluded that scent stimulation is of no practical i m p o r t a n c e as regards the way in w h i c h males and f e - males are placed b e f o r e mating.

T h e reaction of m i n k kits to r e - peated weighing,; was examined by means of a stick test on 17

rd"TT distrit.K aV js r r J \ n - marK. l i g ^ e r a1 The weig ,ed animals reacted mor^ timidly than the n o t - w e i g h e d animals.

Females reacted in general more timidly t h a n males On a f e w f a r m s the w e i g h e d anima's were less timid w h i c h shows that handling can be regarded as a positive e x p e r i e n c e .

T h e correlation between weight development body length, skin size, and pelt quality was e x a m i - ned on scanblack malej. Already

at the age of 9 days weight Is correlated to body length, skin length and weight at pelting.

A f t e r weaning, the correlations are increasing until pelting. T h e correlations between size m e a - s u r e m e n t s and quality of the skins show that weight is r e - sponsible f o r the decrease in quality, whereas body length plays a secondary role. It is c o n - cluded that a long skin f r o m a long m i n k is of better quality than a long skin f r o m a f a t m i n k . T h e body length can t h e r e f o r e with advantage be i n - cluded in the breeding w o r k , instead of body weight.

Body length and weight d e v e l o p - m e n t w e r e examined in relation to t i m e of birth and litter size.

T h e importance of lime of oirih decreased quickly and had a l - most been balanced out in A u - g u s t - S e p t e m b e r . Litter size was s i g n i f i c a n t f o r both body length a n d weight all the time until pelting- and the biggest kits c a m e f r o m litters of 3 - 7 kits.

K i t s f r o m large litters do catch u p somewhat in size a f t e r w e a n - ing, whereas kits f r o m small litters have no compensatory gain.

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Sammendrag

U n d e r delprojektet "Management og Miljø" er der g e n n e m f ø r t undersøgelser vedrørende lysforhold, temperatur af drikkevand, vandforsyning, visuel adskillelse, duf tkommunikation, betydning af gentagne vejninger og sam- menhænge mellem fødselstids- p u n k t , kuldstørrelse, vægtudvik- ling, kropslængde, skindlængde og kvalitet.

En metode til vurdering af lys- forholdene i minkhaller blev udviklet og a f p r ø v e t . Ved m e t o - den måles lysstyrken i hallen i forhold til u d e n f o r , og forskellen tages som udtryk f o r hallens dæmpende e f f e k t . L y s d æ m p n i n - gen står i relation til antallet af lysplader i taget og pladernes renhed. Metoden giver samme resultater under forskellige v e j r - forhold, og den skønnes d e r f o r anvendelig i praksis. L y s d æ m p - ningens betydning diskuteres, og det skønnes, at mink kan holdes under meget mørke forhold uden negative p r o d u k t i o n s m æ s s i g e konsekvenser. Disse kan snarere forventes ved flytning af dyr mellem forskellige lysforhold, eller ved brug af kunstigt lys.

Minkens optagelse af 40° C varmt drikkevand i forhold til vand f r a hanen er undersøgt med udvoksede hanner, med

hvalpe samt med drægtige og diegivende tæver. 1 alle tilfælde blev det varme vand d r u k k e t i samme mængder som det kolde vand. Hvis de voksne hanner blev tilbudt en temperatur ad gangen, drak de mest varmt vand. Hvis begge temperaturer blev givet samtidig, drak de lige meget eller, i et tilfælde, mest koldt vand. Minkene drak h y p - pigere men mindre per gang af koldt vand, hvis begge t e m p e r a - turer var tilgængelige. Hvis der kun var en temperatur ad g a n - gen, var der ingen forskel i o p - tagelsesmønsteret. Der blev i alle tilfælde spildt mest koldt vand, både i alt og per drikkesekvens.

Minkhvalpe drak lige meget varmt og koldt vand, men spildte mest koldt vand. Indtil fødsel foretrak tæverne varmt vand, men efter fødslen drak de mest koldt vand. Den fysiologiske betydning af drikkevandets t e m - peratur diskuteres. Det k o n k l u - deres, at mink gerne drikker vand op til 40°C, og at v a n d - spildet er mindst, hvis vandet er varmt.

I sidste del af diegivningsperio- den anvendes ofte et supplement til den almindelige drikkevands- forsyning. Et drypvandingssy- stem blev afprøvet gennem to diegivningsperioder, og dyrenes

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17

vægtudvikling, drikkeadfærd og aktivitet blev registreret. I det første års kolde og fugtige dieperiode havde systemet ingen e f f e k t . I andet års varme og tørre dieperiode var tævernes vægttab reduceret og hvalpenes vægtudvikling hurtigere i holdet med drypvand. Hvalpe med drypvand optager vand tidligere ved at slikke vand f r a ventilens læbe, men de lærer ikke at u d - løse ventilen tidligere end kon- trolholdet. Spytslikning forekom hyppigst i holdet uden drypvand.

Der blev observeret en forskel på ca. to uger, f r a hvalpene begynder at æde, til de begynder at drikke. Det konkluderes, at hvalpenes mulighed f o r tidligt at optage vand forbedres ved d r y p - vand. I varme og tørre dieperio- der vil dette forøge tilvæksten og reducere belastningen af t æ - ven.

Visuel adskillelse af minktæver i drægtigheds- og diegivnings- perioden har ved tidligere forsøg med meget f å tæver tydet på en positiv e f f e k t på hvalperesulta- tet. Der blev derfor g e n n e m f ø r t fire forsøg med visuel adskillelse af minktæver. Tæverne blev isoleret f ø r parring eller f ø r hvalpning, og adskillelsen bestod af et tomt eller et halmfyldt bur.

Hvalperesultater, vægtudvikling og aktivitet blev registreret. Der var ingen systematiske forskelle i

hvalperesultaterne, der kunne henføres til adskillelsen, og hvalpenes tilvækst var ikke på- virket, Tæverne i kontrolholdet var mere aktive end i de adskilte grupper. Baggrunden for hval- peresultaterne diskuteres. De er i strid med tidligere resultater, men bekræftes af senere under- søgelser. Det konkluderes, at visuel isolation af minktæver ikke har betydning for hvalpe re- sultat eller hvalpenes tilvækst, men reducerer tævernes aktivi- tet.

Betydningen af duftkommunika- tion mellem hanner og tæver blev undersøgt ved at sprøjte urin fra hanner på tævernes bur forud for parring. Latenstiden fra dyrene sættes sammen, til parringen begynder, var 4 mi- nutter kortere i den duftstimu- lerede gruppe, men der var in- gen forskel i parringssucces eller hvalperesultat. Det konkluderes, at duftstimulering ikke har no- gen praktisk betydning med hensyn til, hvordan hanner og tæver skal gå i forhold til hinan- den op til parring.

Minkhvalpenes reaktion på gen- tagne vejninger blev undersøgt ved en pindetest på 17 farme fordelt over hele Danmark. De vejede dyr reagerede generelt mere frygtsomt end ikke vejede, og tæver reagerede generelt mere

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f r y g t s o m t e n d h a n n e r . P å e n k e l t e

farme var de vejede ayr mindst frygtsomme, hvilket viser, at håndteringen kan opfaites som noget positivt.

Sammenhængen n.ellem vægtud- vikling. kropslængde skindstør- icise og pelskvai.tei biev undei - jøgc pa. scar-'>iack hanntr. Al- lerede ved 9 dage e^r vægten korreleret til kropslængden, sk'nd'ærgden og vægten ved peLniiig. Efter fravænning ei korrelationerne stigende f rem til pelsning. Sammenhængene mel- lem størrelsesmålene og kvalite- ten af skindene viser, at vægten er ansvarlig for den faldende kvalitet, mens kropslængden spiller en underordnet rolle. Det konkluderes derfor, at et langt

skind fra en lang mink er af bedre kvalitet end et langt skind fra en fed mink. Kropslængden vil derfor med fordel kunne inddrages i avlsarbejdet i stedet for vægten.

Kropslængde og vægtudvikling blev undersøgt ; relation til f ø d - selstidspunkt og kuldstørrelse.

Fødselstidspunktets betydning aftog hurtigt og var stort set ud- lignet i august-september.

Kuldstørrelsen havde betydning for både kropslængde og vægt helt frem til pelsning, og de største hvalpe kom fra kuld på 3 til 7 hvalpe. Hvalpe fra store kuld indhenter noget i størrelse efter fravænning, mens hvalpe fra små kuld ikke har nogen kompensatorisk vækst.

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19

1.1 Background

The purpose of the management and environment section of the p i o j e U was iu desci ibe the v a c - ation in physical f a r m conditions and management on the partici- pating mink farms. Based on an evaluation of the importance of these differences in relation to production, individual items were chosen f o r experimental investigation, either on a r e - search f a r m or in practice.

Furthermore an examination of routines for management and control of the production was included as an essential element

in the project.

As the project has been split up into many subjects and sections, results and discussion will be divided into paragraphs on each subject.

1.2 General f a r m conditions and management.

The physical f r a m e s of f u r a n i - mal production are standardized to a very high degree in D e n - mark. Within the field of sheds and cages a f e w types are totally dominant on the market. This is primarily due to a very rational standard of the buildings, where farmers - contrary to other

countries - buy readymade sheds instead of developing and build- ing the sheds themselves. The design is based on a well operat- ing type developed on basis of practical experiences. On the other hand the many different housing conditions used in mink farming around the world reflect that mink are very robust with regard to housing in general.

The type of shed most often used is the open double-row shed with an "Eternit" asbestos roof. Another much used type is the closed multi-row shed. This type exists in many different designs, but most often It con- sists of f j rows and is mainly used for breeding animals during the winter. Afterwards the kits are placed in double-row sheds at weaning. The construction of the sheds is divided into 2.00 m wide sections, on which the cage sections are suspended.

The cage sections consist of either 6 or 8 cages. Typically 6 - room cages measure 36 x 12 x 18 inches (approx 90 x 30 x 45 cm) (1 x w x h) and are used for breeding, birth, lactation and kits after weaning. The 8-room cages measure 36 x 8 x 18 inches (approx 90 x 20 x 45 cm) and are used for breeding animals kept individually. Each cage has a nest box, placed outside the

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cage of the same width as the cage, 8 - 1 0 inches (20-25 cm) long and 6 - 8 inches (15-20 cm) deep. F u r t h e r m o r e , there are cages with the nesters placed in the upper part of the cage.

These cages are o f t e n shorter but taller than the standard 6 - and 8 - r o o m cages. Design of cages and nest boxes has been described in "Guidelines of f u r animal production* prepared and recom- mended by the Fur Breeders' Associations of the f o u r Nordic countries. These common Nordic regulations which also deal with feed and water, hygiene, health, transportation, and killing, e x - press the wish f o r a common, justifiable standard of f u r a n i - mal production in the countries selling under the Saga l a b e l During the whelping period most breeders place a d r o p - i n bottom in the nest box. T h e purpose is to help the female build the nest and to prevent the kits f r o m getting lost in the comers. The drop-in bottom varies f r o m a wooden plate and a brick to a moulded plastic or a hollowed wooden bottom with windscreen.

Fresh feed is delivered every day f r o m f e e d kitchens. The feed is placed on top of the cage and the mink eat the wet feed through the wire netting.

The watering system consists of a hose running along the back- side of the cages. The mink get water by releasing a drinking valve and sucking water. The valves are of d i f f e r e n t makes, but only details d i f f e r . An older system consisted of a cup with f r e e water, but chis type is not in u»e very much any more. The water hoses may be either insulated, screened or uninsulated, and the water may be circulating a n d / o r heated in order to secure the water supply in frosty weather.

Management can be divided into the various production periods throughout the year.

The main impression f r o m the project is that there is not only one correct way of doing things.

What is important is that all jobs are carried out at the right time which means that many d i f f e r e n t systems may very well work perfectly. The most important thing is that the f a r m e r has a system which suits him and which he knows will work.

The farms can be divided into d i f f e r e n t types or groups according to their way of handling each production period. This division is to a high degree ge- ographical and is presumably the result of the local advisory ser-

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21

vice and of communication with colleagues where f a r m e r s learn how things are done on other farms. The same goes f o r special cage and watering systems like for instance the use of nester cages and circulating watering systems.

The physical f a r m conditions and management on the project farms are described m a later Report f r o m the Natl. Inst, of Anim. Scii

Physical f a r m conditions as well as management have been the objects of experimental investigations. These have been p u b - lished currently and will be presented in short here, to o b - tain a total presentation of the results of the project.

The following investigations are presented in this chapter:

Investigations of physical f a r m conditions:

1.3 Light conditions in mink sheds.

1.4 Drinking water t e m p e r a - ture.

1.5 S u p p l e m e n t a r y w a t e r i n g systems.

Investigations of management conditions:

1.6 Visual isolation of females.

1.7 Scent communication in the mating season.

1.8 Weighing and behavioural response.

1.9 Weight development, body length, size and quality of f u r .

1.10 D e v e l o p m e n t of b o d y length and weight in relation to time of birth and litter size.

1.3 Light conditions In mink sheds

1.3.1 -

jd

The time of f u r development and the reproduction cycle of the mink are primarily control- led by light conditions.

Mink breeders therefore have a natural interest in being familiar with these and the importance of the changes caused by d i f f e r e n t housing arrangements in relation to normal daylight.

The objective of almost all light experiments has been to change the production towards earlier f u r development (e.g. Adair &

Stout, 1972) or to induce more heat cycles per year (e.g. A u - lerich et al., 1963; Williams &

T u r b a k , 1970; Reiten, 1977).

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sion. The d i f f e r e n c e s in the re- d u . t . j n ¿ic criincc.cd .vuh amount of light panels in the roof, windows in the walls, the cleanliness of the light panels and windows, and the strength of the light outside the shed. In two-row sheds light conditions are much better in the cages than ii* »lit* fu'uuie. l%!it iailc

ti-row

very low intensities of light (Travis et al. 19/1) Moving

1.3

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23

determination of light conditions in mink sheds. Within the limits of measured r e d u c t i o n there is no detectable e f f e c t on the p r o - duction, and 3 reduction of u p to 6 Iw is t h e r e f o r e f o u n d a c - ceptable. Light panels covering 10-15% of the roof give a satis- f a c t o r y a m o u n t of light, if they are k e p t clean. Moving mink f r o m good to p o o r light c o n d i - tions or vice versa, may e f f e c t the production by altering the day length e x p e r i e n c e d by the mink. Light problems in d o u b l e - row houses are r e g a r d e d as very rare, as the light falls in through the side of the shed.

The results have b e e n presented and published at the annual meeting of the Natl. Inst, of A n i m . Sci. (Møller, 1989).

1.4 D r i n k i n g w a t e r t e m p e r a t u r e 1.4.1 I n t r o d u c t i o n

In D e n m a r k , w a t e r i n g systems f o r m i n k consist almost e x c l u - sively of automatic e q u i p m e n t where a d r i n k i n g valve at the rear end of the cage is screwed into a water hose r u n n i n g along the cage rows. Traditionally the water hose is a black 3/4" plastic hose. In sunlit hoses the water will quickly be heated u p to 45°C or more, w h e r e a s In frosty weather it will quickly freeze.

Yarlous m e t h o d s have been d e - veloped to r e m e d y t h e s e problems.

1 h*» wqfpr in rb e h o w rn^y b ° circulating and the hoses may be screened or insulated. O f t e n heating possibilities are installed in the hoses a n d / o r the c i r c u l a t - ing water.

While the water Intake of the mink stops suddenly w h e n the water f r e e z e s , no knowledge existed r e g a r d i n g the water In- take of the m i n k when the water t e m p e r a t u r e was rising. A n u m - ber of e x p e r i m e n t s f o r c l a r i f i c a - tion of this pro b l e m have been carried out.

1.4.2 M a t e r i a l and methods In all experiments the t e m p e r a - t u r e of the w a r m water was 40°C, whereas the cold water f r o m the tap varied f r o m 6 -

17°C.

Experiments have been carried out according to two d i f f e r e n t methods. In one method the a n i - mals were o f f e r e d both t e m p e r a • tures f o r 8 days. The animals could thus choose between two temperatures at the same time.

T h e d r i n k i n g nipples with the two t e m p e r a t u r e s were switched around at certain intervals in order to avoid habituation to

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placement. In the other method the animals were o f f e r e d the two temperatures alternately every second day, o f f e r i n g each t e m - perature f o r 4 days.

The experiment ran over 5 p e - riods of approx 8 days. In p e r i - ods 1, 3 and 5 warm and cold wate- was o f f e r e d according to the c wo methods. In periods 2 and 4 only warm and cold water, respectively, was o f f e r e d .

Experiments have been carried out with adult males in Febru- ary-March, with pairs of male and female kits f r o m weaning, and with lactating females.

1.4.3 Results 1.4.3.1 .Males

The adult males were given cold water of 6°C and warm water of 40°C according to both methods.

In both methods the waste of

cold water was significantly higher than the waste of warm water (tables LI a and b). In the method with changing temperatures a higher amount of warm water was drunk in all three periods (P<0.01). At the method with both temperatures equal amounts of warm and cold water were d r u n k in periods 1 and 3.

In period 5 a significant p r e - ference for cold drinking water was registered. The results of the habituation periods are summar- ized in table 1.1c. With great certainty it can be said that in both methods warm water was p r e f e r r e d (P<0.001).

The total water intake amounted to approx 90 m l / d a y except f o r the periods with only cold water, where smaller amounts were drunk. The individual variation between mink is considerable with regard to water intake waste of water and tem

preference.

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25

Table 1.1 Grams of water at 40°C or 6°C ingested and wasted by a group of five male mink.

a. One temperature at a time, changing from day to day. Each temperature o f f e r e d f o r 4 days.

Period g of water 40°C 6°C P<

1 Wasted 50 17S 0.01

Ingested 103 81 0 001

3 Wasted

j j ss

122 0.001

Ingested 121 87 0.01

5 Wasted 56 250 0.001

Ingested 121 M> éaø A 69 0 001

b. Both temperatures o f f e r e d simultaneously for 8 days.

Period e of water 40° C 6° C P<

1 Wasted 26 0.001

Ingested 53 ns

i j Wasted 18 0.001

Ingested 49 ns

5 Wasted 15 0.001

Incested 38 0.001

c. Each temperature o f f e r e d f o r 7 days between experimental periods 1, 3 and 5.

Method s of water

Period 2 40° C

Period 4 6°C P<

Changing Wasted 30 261 0 001

Ingested 93 76 0 0 1

Both \ 51 256 ^0.001

Ingested 89 71 0 001

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A video recording of the experi- ment with males was carried out in order to examine activity and

Table 1.2

Behaviour Drinking sessions g ingested g wasted

T g/

Wasted g / session

Hours of sleep

The table shows that there was no d i f f e r e n c e in water intake on the days with video recording.

Nevertheless, there was a d i f - ference in drinking behaviour at the two temperatures. Each time the mink drink, they take in twice as much warm as cold wa-

drinking behaviour of the two methods and temperatures. T h e results appear f r o m table 1.2.

18 17 17

ter if both temperatures are o f - fered. There is no d i f f e r e n c e when only one temperature is o f f e r e d . Both methods showed that the waste of cold water was 5 times as high per drinking session as the waste of warm water.

Activity and oeha tloui i f eita't m i l k n ¿elation

» a t a l c jiPti at water at 4 | i^cr or b'L Rtgi* iered 2-4 \ c u Z with eacn empeia.ure.

Changing

6Ö€ 40° C Total 6°C 40°C

18 7 25 28 30

41 37 78 79 81

138 11 149 230 35

2.4 5.1 - 2.9 2.8

7.9 1.4 - 8.4 1.2

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2 7

In both experimental m e t h o d s the mink d r a n k 2 5 - 3 0 times and took in a p p r o x 80 ml of water altogether. T h e mink ate 6 - 1 2 t<jyjp<5 poj- y/j tio>jrs fnlIowpH Hv 1 - 2 d r i n k i n g sessions a n d 1 - 2 hours of sleep. One of t h e m i n k played with the cold w a t e r valve but the d i f f e r e n c e in waste of water applied to all 4 m i n k . If the results b e f o r e a n d a f t e r a period of habituation w i t h only one water t e m p e r a t u r e , or the start and ending of such a p e r i - od are analysed, the results will give an idea of the h a b i t u a t i o n to water t e m p e r a t u r e . T h e results b e f o r e and a f t e r an e x c h a n g e of

U -.ipc< Jla. c ' wil x«vc an ir.'JiCd^

•ion of hab'Kuation to placement.

The waste and intake of cold water (6°C) are not a f f e c t e d by habituation in the males. A p - parently habituation has a small influence on waste and intake of warm water (40° C).

A f t e r 8 days with w a r m water, the intake of w a r m water is higher than b e f o r e the period (P<0.05) when both temperatures are offered. When the tempera- tures are offered alternately, the same tendency towards increased intake is found (P=0.12), and the waste of warm water has also increased (P=0.06).

Eight days with cold water did not influence waste or intake of water regardless ol temperature at the method with both tem- perature«: of tpreri cimultaneo'i«;! v The method with changing water temperatures showed a tendency towards a reduction of the in- take of cold water after the 8 days (P=0.13).

From the start to the end of the g day period with warm water there was a tendency towards a reduction in both intake and waste of water, when both tem- peratures were offered (P=0 I7) and similar for the intake when temperatures were changing (P<0.05). In none of the methods we'e 'here any d i f f e r e n c e s in v-ater intake or waste ai the be- ginning or the end of the period with cold water.

The waste of water was inde- pendent of the placement of the drinking valves, whereas the water intake showed a moderate tendency towards changing after the exchange of the valves and therefore a possible habituation to placement (P=0.14).

1.4.3.2 Kits

Mink kits were offered water of 40°C and 17°C simultaneously.

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d u r i n g the e x p e r i m e n t a l period ( f i g u r e 1.1). T h e statistical p r o - cessing showed no d i f f e r e n c e in water Intake at the two t e m p e r a - tures. T h e r e was a s i g n i f i c a n t d i f f e r e n c e in water Intake b e - tween the f i v e p a k s of kits (PcO.Ol).

T h e water waste also increased a little with age, and the Increase

significantly m o r e cold t h a n w a r m w a t e r w a s w a s t e d (PcO.OOl). T h e r e was also a significant d i f f e r e n c e In water waste between the 5 pairs of kits.

T h e r e seemed to be an cffecc of habituation of periods 2 and 4 with reg'ird to w act e of water.

Figure 1.1 Daily i n t a k e of 40°C ( H ) and 17°C ( C ) d r i n k i n g water by 5 p a i r s of mink kits a f t e r weaning. Periods I, I I I and ¥ include both temperatures simultaneously, period I I with w a r m and IV with cold water.

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29

1.4.3.3 Females

In the e x p e r i m e n t with females in the latter part of the gestation and lactation periods water of 40°C and 8 - 1 5 ° C was o f f e r e d simultaneously d u r i n g the entire e x p e r i m e n t . This is d u e to the f a c t that d i f f e r e n c e s in time of birth a n d n u m b e r of kits makes an e x p e r i m e n t a l plan w i t h the previously used 5 periods i m p o s - sible.

The w h e l p i n g result was poor, and m a n y kits were lost d u r i n g the e x p e r i m e n t . This cannot be caused by the water t e m p e r a t u r e , as the f e m a l e s could still d r i n k cold water as they were used to.

The e x p e r i m e n t with the females started on April 27th, the f i r s t f e m a l e gave b i r t h on April 30th and the last on May 7th. On average t h e females had 6 live kits and 0.5 stillborn. Within the first w e e k the females lost 4 of the 6 kits which must be a result of the t r a n s f e r to the u n k n o w n

e n v i r o n m e n t indoors. T h e r e f o r e the experiment will have to be repeated in the normal f a r m e n v i r o n m e n t b e f o r e any f i n a l l o n d u s i o i i a can be d r a w n .

D u e to the low n u m b e r of kits and the many deaths it is i m p o s - sible to calculate water c o n - s u m p t i o n per kit or per g of kit gain.

T w o females had 3 and 4 kits, respectively, d u r i n g the entire experimental period. The results of these two females are lllu—

strated in f i g u r e 1.2. It appears that the total water intake d e c r e - ases until birth in order to i n - crease again until weaning. U n t i l the time of b i r t h the females d r a n k mostly w a r m water, b u t a f t e r the birth mostly cold water was d r u n k . T h e waste of water followed the curve of water intake, and a f t e r b i r t h almost exclusively cold water was w a - sted (figure 1.3).

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Figure 1.2 Daily intake of 40°C and 8 - 1 5 ° C drinking water from 4 days before till 7 weeks a f t e r birth. Two females with 3 and 4 kits.

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31

DAYS AFTER BIRTH

WATER TEMPERATURE 40 C 8 - 1 5 C BOTH

Figure 1.3 Daily waste of 40°C and 8 - 1 5 ° C drinking water f r o m 4 days before till 7 weeks a f t e r b i r t h . Two females with 3 and 4 kits.

1.4.4 Discussion

Both test methods work well and the choice of method must be based on the actual investigation.

The method with both temperatures is a logical way to deter- mine preferences, while the method with changing t e m p e r a -

tures is realistic in relation to practice, where only one t e m - perature is available at the time.

Physiologically it is understand- able that mink like to drink 40"C warm water. Cold water is only let out of the stomach slowly, and the stomach will be

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filled quickly. The feeling of thirst Is thereby put out without removing the physiological res™

son f o r thirst (Deaux, 1973).

Drinking water at body t e m p e r a - ture passes through the stomach, allowing a greater volume to be Ingested b e f o r e stomach disten- tion signals a satiation of thirst.

Blood tests In rats have shown that drinking water at body t e m - perature lead to a faster decrease In serum osmolarity than cold water (Deaux, 1973). Warm water Is therefore a better thirst quencher, as it is absorbed more quickly in the body, and a higher amount Is absorbed b e f o r e the feeling of thirst is put out. This may be the explanation why mink p r e f e r warm water, If the cold water Is only 6°C, whereas there Is no d i f f e r e n c e If it is over approx 10°C.

Waste of water Is in all cases significantly higher f o r cold w a - ter. Of course there Is a correlation between the Intake and the waste, but also In relation to In- take there Is always more waste of cold water. There seems to be an Insignificant habituation to water of u n k n o w n temperature, i.e. 40° C f o r adult m i n k , but

also to cold water as f a r as the kits are concerned.

1.4.5 Conclusion

On basis of the experiments p e r - f o r m e d , It can be concluded that mink do not r e f r a i n f r o m d r i n k - ing 40°C hot water. In some cases the warm water is p r e f e r - red, but in most cases no p r e f e - rence is noted. In a single e x - perimental period cold water was preferred. It is still too early to say precisely, whether the d i f - ference In results is due to a d i f f e r e n c e In sex and age of the animals, In time of year a n d / o r In differences In ambient t e m p e - rature or temperature of the

"cold" water. Waste of water Is In all cases significantly higher f o r cold water than f o r warm water.

The results of the water t e m p e - rature experiments were presented at the Annual Meeting of the Natl. lest, of Anim. Sci., and at the 4th Int. Sci. Congr. in Fur Animal Prod., Toronto, as well as in the Danish Fur Breeders Journal (Møller, 1986, 1987,

1988b, 1988c; Møller & Lohi, 1989b).

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1.5 S u p p l e m e n t a r y w a t e r i n g system

1.5.1 Introduction

Mink kits start eating and d r i n k - ing in the latter part of the lactation period. In the same period loss of weight and dehydration of some females are seen, espe- cially in hot summers. Both kits and females can therefore be relieved if the kits start to drink as soon as possible. Mink have no natural qualifications f o r drinking f r o m a valve. Various devices have been developed to help the kits f i n d the drinking valve and learn to drink. One type is a clamp intended to help the kits release the valve more easily. Another principle is valves supplied with a tongue which can either be tilted so that water will stay on the tongue or it can be equipped with drip watering to secure that there is water on the tongue all the time.

A clamp with a bowl combines these two ideas.

1.5.2 Material and methods During two lactation periods experiments have been carried out with a drip watering system.

The drip watering equipment was turned on on May 3rd and set at 25-40 drips per minute to

secure maximum e f f e c t of the system. Among 60 scanblack females with drip watering and 60 females in the control group, 15 female« with 4-8 kits w r p chosen f o r weighing.

The animals were weighed at the age of 10, 20, 30, 40 and 50 days. T h e first year the kits were distributed at weaning with 60 pairs (male + female) in the drip watering system and 60 pairs in the control group. They were weighed every fortnight until August 26th when the e x - periment ended.

Activity and drinking behaviour of the Mis were registered 6 times with short observations in two daily periods f r o m June 9th until weaning. Until June 9th, the animals were observed once a day, and registrations started when the first kits became active near the drinking valve.

In the f i r s t year it was registered whether the kits were out in the cage, active, in which part of the cage compared to the d r i n k - ing valve, and whether they were drinking or trying to drink.

In the second year the observations were concentrated on the actual drinking behaviour and specifying whether the kits got water and whether they released the valve themselves. F u r t h e r -

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more. saliva liciriny f i o m the córner of toe temaie's mouth was observed.

system had significantly less u n - successful atteiiip a to d n k (P<0.05) and more attempts tended to be successful. There were no other d i f f e r e n c e s in b e - haviour between systems.

The results f r o m the second year showed that the females in the drip watering group lost less

•7 Iglr' kf 1> r v t ln i 1 £ l u U f

(P<0.05). The weights are shown in table 1.3, f r o m which it appears that the d i f f e r e n c e was most significant around June 10th.

Table 1.3 Weight of female mink with normal and drip watering system. F i f t e e n females weighed five times between birth ami weaning.

11/5 2 0 / 5 30/5 10/6 21/6 G r o u p n — - - w e i g h t g ± sd

Control 15 1026± 79 1006± 89 986± 72 889± 67 Dripwater 15 1156+130 1146±114 1113±121 1054±109

'>3

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35

Males

Control 42 48±12 99±l8 176±25 295±53 505±75 Drlpwater 47 4 M 9 98±J5 185±23 294±42 541±78 Females

Control 37 42±9 91±16 157±27 263±57 430±93 Dripwater 40 43±9 95+17 170±l9 263±33 451±58

As far as the gain of the kits (table 1.4) is concerned there was a clear effect of drip wa- tering (P<0.001). The effect started showing already between the age of 20 and 30 days and increased until weaning. As the kits in the experimental group are born one day later than the kits in the control group, the difference is actually larger than shown in tables 1.3 and 1.4.

Behavioural observations showed that kits with drip watering start sucking water from the age of 40 days, whereas kits without drip watering rarely have this opportunity. On the contrary more kits in the control group find the valve without getting any water from it.

All in all the kits with drip wa- tering start taking in water earli- er no matter whether they re- lease the nipple or not which is shown in figure 1.4. This is due to the fact that they suck the dripping water. They do not learn to release the valve earlier than the control group. Saliva licking is significantly more common in the control group than in the drip watering group already from the age of 35 days as shown in figure 1.5. The wa- ter temperature in the hoses was

19.6 ± 4.0°C in the drip water- ing system and 20.4 ± 5.6°C in the control row. The difference was significant (P<0.05).

Observations of eating and drinking behaviour showed that

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the kits start eating at the age of 4 weeks but only start d r i n k i n g approx 14 days later. These terms have been c o n f i r m e d by observing the time of eating and d r i n k i n g d u r i n g the whelping period 1585 on the research f a r m . Of 272 litters observed.

3.3% were seen eating bet ore 4

weeks of age. whereas 73.9%

started eating in their 5th w e e k , between 28 and 35 days of age.

T h e f i r s t time drinking was only registered in 42 litters. Of these 81% started d r i n k i n g in the 7th week f r o m 42 to 48 days, whereas 7.1% (3 litters) started the week b e f o r e .

K 1 30 T S

B S E 20

R V E D 15 D N K ' 5 N G

0

30 35 40 45 50 55 60

ns — — ns — — p < 0 . 0 0 1— — ns — ns — — p < 0.06 —

GROUP - - . C O N T R O L - - - DRIP WATER AGE IN DAYS

Figure 1.4 Development of d r i n k i n g behavior of m i n k kits with a n d w i t h o u t drip watering system. P e r c e n t a g e of k i t s o b - served d r i n k i n g , releasing t h e nipple or not.

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37

o

1.5.4 Discussion

The d i f f e r e n c e between the r e - sults of the two years is presumably due to the large d i f f e r e n - ce in weather conditions during the lactation periods. In 1987 it was very cold with medium t e m - peratures of 9.1 °C against n o r - mally 11.2°C. The maximum temperature during daytime was

around 15°C. In 1988 it was hot and dry with a medium t e m - perature of 11.9° C and t e m p e r a - tures above 2 0 ° € during daytime in the month of May.

Even though an analysis of co- variance shows a d i f f e r e n c e in the weight development of f e - males of the two groups, the weight curves run almost paral-

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lelly, except at the weighing on June 10th. Females in moderate condition around birth have earlier proved to keep their weight best during the lactation period (Tauson & Alden, 1985).

It was therefore to be expected that the rather heavy females in the drip watering group would s u f f e r a heavier weight loss towards the end of the lactation period. This is not the case, which is probably due to the drip watering system and c o n - firms the e f f e c t showed by the analysis of co-variance.

The weight of the kits is already d i f f e r i n g at the age of 30 days.

The gain has thus been quicker in the drip watering group, b e - fore the kits have started eating solid feed at the age of approx 4 weeks. This seems to indicate that the female somehow b e n e - fits f r o m the d r i p watering system and passes this on to the kits. As the drinking behaviour of the females has not been i n - vestigated, the reason cannot be explained.

The improved weight development of the majority of the f e - males as well elS of the kits can be explained by their drinking behaviour. As the kits take in water earlier and more f r e q u e n t - ly In the drip watering group, they take in more feed and b e - come less dependent on the f e -

male. This Is confirmed by the redaction in saliva licking The di'ierence in water temperature can be explained by an increased flow In the drip watering sys- stera. The d i f f e r e n c e of approx

1°C is, however, quite insignifi- cant f o r the vater intake as doc

uriieiiiCvi ii< afti'aph ' 4 o n

water temperature experiments.

The difference of 2 weeks in the

t i m e wnen^-h* ki\> s t a r t m a t i n g

and drinking illustrates why this period is so critical for the f e - male as well as for the kits During this period the kits must cover their need for liquid through water from the feed milk and the saliva licking from the female. During this period the milk production of the f e - male starts to decrease and nursing disease in the female and cannibalism among the kits are seen.

1.5.5 Co

All in all, it can be concluded that the water intake of mink kits is improved with access to free water. In hot and dry weather during the lactation pe- riods this will improve their weight gain and reduce the weight loss of the females. The female herself may also profit from auxiliary installations at the water valves. The drip watering

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39

system w h i c h was tested h e l p e d the kits take in water at an e a r - lier stage, b u t they did not learn to release the valve themselves b e f o r e the kits in the control group. K i t s only start t a k i n g in water when they are a p p r o x 35 days old, and the first of t h e m can release the valve at the age of 40 days. When they start e a t - ing at the age of a p p r o x 4 weeks, there is a period of 1 - 2 weeks a f t e r they have started eating w h e n they have not yet learned to d r i n k . It is t h e r e f o r e important to do a n y t h i n g p o s - sible to help them d u r i n g this period.

Tlu result; » f w'-ierh'g e x p e r i m e n t have b*»en published

as a Short Comm f r o m t h e Natl Inst, of Anim Sci. and in the annual report of the Danish F u r Breeders Association (Møller &

Lohi, 1988, 1989a) T h e i m p o r - tance of good m a n a g e m e n t d u r - ing the lactation period has been discussed in the Danish Fur Breeders Journal (Møller & L o - hi, 1989b).

1.6 Visual isolation of mink females during the repro- duction period.

1.1

Wild mink are known to be soli- tary animals, and presumably in

most cases the females are rear- ing the kits alone. It could therefore be expected that the close presence of other mink would influence mink in captivl ty, and in the reproduction p e - riod be the cause of inferior parental care. Previous investiga- tions have found that a screening from neighbouring females may influence breeding result and kit gain favourably (Gilbert & Bai- ley, 1967, 1970, Hernesniemi, 1976; Vestergård, 19??a) These investigations are, however, 10- 20 years old and were performed with only very f e w animals (10- 20 females per group) An in- vestigation with large groups of

M u u k v- v. .di

t h e - efore needed in ord^r

c ' z r i f y , if a favourable e f f e c t can be obtained.

1.6.2 Material and methods The experiments were performed over two years with scanblack and scanbrown females on two private farms. In 1985 3 experi- ments were carried out. In expe- riment I 79 scanbrown females were isolated immediately before mating by means of an empty cage, whereas the control group of 70 females occupied all the cages. In experiment II 198 f e - males were separated by means of an empty cage during the latter part of the gestation peri-