The mean values of daily carbondioxide production and oxygen consumption in the different balance periods are shown for each period in the Main Tables.
The values are either means of the individual measurements (series G) or means of groups (series H, K and J) expressed per one hen. In series H and K, 4 battery cages with 3 hens/cage were placed in each respiration chamber while in series J, 6 hens were placed freely in each respiration chamber. The gas ex-change was measured totally for all hens in the chamber and then it was divided between groups (series H and K) or between individuals (series J) in relation to their metabolic body weight (W,kg075). In order to describe the course of gas exchange during the laying period from 26 to 47 weeks of age, the CO2 produc-tion was related to age of the hens in each series. An attempt was made to calcu-late functions of CO2 production and O2 consumption in relation to W,kg°75, metabolizable energy (ME) and egg production using the individual observa-tions from series G. Finally the effect of temperature, origin and housing on the gas exchange was inspected.
î
43 ZO
oo oco.
O*o
39
37
35
33
7
26 30 34 38
AGE
42 46 week
Figure 5.1. Mean values of CO2 production in relation to age. Series G and H.
o Ser. G 21°C, ^ Ser. H ITC, ^ Ser. H 21°C.
Middelværdier for CO2 i relation til alder. Serie G og H.
5.1 The course of CO2 production and the predictions of gas exchange Course. The relations between mean daily CO2 production and the age of hens are shown graphically in Fig. 5.1 for series G and H and in Fig. 5.2 for series K and J.
The CO2 production in series G in which the hens were kept at 21°C increased from 35 to a maximum of 37 1 by an age of 35 weeks and then it decreased to about 35. The hens in series H, kept at 17°C or 21°C showed the same pattern with increasing CO2 production from 37 to 42 (17°C) and from 34 to 41 (21°C) by an age of 35 weeks and then levels of about 41 and 40 1 were maintained in the following weeks. In series K in which the highest CO2 production was ob-served, levels of about 43 and 45 1 were kept from 33 weeks of age and during the whole experimental time. In series J increments from 41 to 42 (17°C) and from 37 to 41 1 (21°C) were measured.
Predictions. In order to establish functions for gas exchange in laying hens, the individual values of CO2 production and O2 consumption from series G were related to W,kg° 75, ME and egg production. The multiple regressions of gas exchange were calculated according to the following model:
45
43
41
a o
£ 3 9
OO 37
35 26 30 34 38
AGE
42 46 week
Figure 5.2. Mean values of CO2 production in relation to age. Series K and J. • Ser. K 17°C, o Ser. K 21°C, A Ser. J 17°C, ^ Ser. J 21°C.
Middelværdier for CO2 i relation til alder. Serie K og J.
CO2 or O2,l = a + bj x W,kg075 + b2 x ME,kJ + b3 x Eggs,g
Where a is an intercept and b1?b2,b3 are the regression coefficients. The follow-ing equations were obtained:
(1) CO2,1= 5.56+ 12.7 x W,kg075 + 0.0084 x ME,kJ + 0.047 x Eggs,g se: 3.218 2.94 0.00214 0.0539 t-test: 1.73 4.32*** 3.92*** 0.87 n = 81, RSD = 2.49, CV = 7.08%, R2 = 0.564
(2) O2,l= 3.54+ 18.3xW,kgO75 + 0.0048 x ME,kJ + 0.095 x Eggs,g se: 3.616 3.31 0.00241 0.0605 t-test: 0.98 5.54*** 2.01* 1.57 n = 81, RSD = 2.80, CV = 7.11%, R2 = 0.584
A t-test for the »null« hypothesis of the intercepts and regression coefficients showed that the intercepts and the regression coefficients for egg production were not significant (P > 0.05). Consequently the variable egg production was excluded from the further calculations and multiple regressions of CO2 and O2 were calculated in relation to W,kg°75 and ME. The intercepts were not signifi-cant and the following equations through the origin (cf. Chapter 2.7) for CO2
production and O2 consumption in series G were obtained:
(3) CO2,1= 17.3xW,kgo75+ 0.0094 xME,kJ se: 1.61 0.00200 t-test: 10.6*** 5.00**
n = 81, RSD = 2.51, CV = 7.15%
(4) o2, l = 22.7xW,kgO75+ 0.0063 x ME,kJ se: 1.80 0.00231 t-test: 12.5*** 2.95**
n = 81, RSD = 2.82, CV = 7.17%
Compared with the first set of equations (1,2) the residual standard deviation (RSD) and the coefficient of variation (CV = RSD/y x 100) increased only slightly but the values of R2 from the regressions with intercept were markedly improved ((3) R2 = 0.682, (4) R2 = 0.720) when the information about egg pro-duction was excluded. Thereby indicating that daily CO2 production and O2
consumption in series G could be predicted with a satisfactory accuracy when based on metabolic body weight and metabolizable energy.
5.2 Gas exchange in different series
The grand means of all measurements of daily gas exchange in each experi-mental series for 17°C and 21°C are presented in Table 5.1. As the values of CO2
production and O2 comsumption in series H, K and J were obtained with cor-rections for metabolic body weights and number of hens, no statistical compari-son was carried out between the series but only the magnitude of the means was inspected. The mean gas exchange was lowest in series G with in average 35 1 CO2 and 39 1 O2. The highest mean values were measured in series K with 43 1 CO2 and 47 1 O2 for both temperatures. The RQ values (CO2/O2) were 0.90, 0.86 and 0.92 in series G, H and K at both temperatures. In series J, RQ was 0.99 which may be caused by the O2-analysator giving too low values (cf. Table 2.4) in this series.
Table 5.1 Gas exchange. Mean values of carbondioxide production (CO2) and oxygen consumption (O2) from 26 to 47 weeks of age
Tabel 5.1 Luftstofskifte. Middelværdier for kuldioxydproduktion (CO2) og iltoptagelse (O2) i alderen fra 26 til 47 uger
Series Temp.
Balances
No.
°C n
G 21 81
17 27
H 21 24
17 32
K 21 24
17 8
J 21
8 CO2 Litres 35.2 40.8 38.9 43.0 43.5 41.5 39.6 SEM 0.41 0.44 0.49 0.26 0.37 0.30 0.64 O2 Litres 39.3 47.1 45.6 47.1 46.9 42.1 39.7 SEM 0.47 0.44 0.52 0.31 0.35 0.33 0.60
The differences caused by the temperatures were only 1.5 1 of CO2 and O2 in series H and there were no differences between 17°C and 21°C in series K and J. Comparing the hens with different origins and allocated to the same housing (series H and K) the differences were small, about 3 1CO2 and 1 102. Greater differences in gas exchange were noted between housing systems in which the hens kept singly (series G) had about 6 1 lower CO2 and 7 1 lower O2 than the groups in the battery cages (series H and K). The hens kept freely (series J) had 2 1 lower CO2 and 6 1 lower O2 than in series H and K.
The equations of CO2 production and O2 consumption were estimated for series H and K at each temperature with gas exchange regressed on the W,kg° 75
and ME as in series G. The functions of gas exchange in series J were not calcu-lated as the determinations were uncertain. The performed multiple
regres-sions gave the possibility to test the effect of the temperature and origin and to inspect the influence of housing on gas exchange. Statistical analyses between the regressions at 17°C and 21°C, separately in series H and K showed no signifi-cant (P > 0.05) differences in gas exchange for the two temperatures. Con-sequently the regressions on the pooled observations (17°C + 21°C) in series H were compared with series K as in both series the hens were in the same housing and the gas exchange of each group (3 hens) was calculated in the same way (cf.
Chapter 2.3.3). The regressions for the two origins of White Leghorns (series H vs. K) were not significant (P > 0.05). Finally the total regressions of gas ex-change were calculated for all measurements in series H + K. The results are tabulated below together with the values for series G, and the equations for each housing system are inspected.
Model: CO2 or O2,l = bx x W,kg0 7 5 + b2 x ME,kJ
W,kg075 ME,kJ
bj se b2 se RSD CV,%
CO2 production, litres
G ( n = 81) 17.3 1.61 0.0094 0.0020 2.51 7.15 H + K ( n = 1 0 7 ) 18.0 0.92 0.0120 0.0010 1.33 3.20 O2 consumption, litres
G ( n = 81) 22.7 1.80 0.0063 0.0023 2.82 7.17 H + K (n = 107) 24.1 1.12 0.0072 0.0012 1.62 3.48
All regressions of gas exchange showed satisfactory residual standard devia-tions (RSD) in the rangae 1.3-2.8 corresponding to the relative RSD (CV) be-tween 3.2-7.2%. Due to the different method of calculation the gas exchange in each housing system, no statistical analyses were carried out between the re-gressions but in order to compare the influence of the housing systems an at-tempt was made to preedict the gas exchange in each housing by means of the obtained regression equations. By assuming daily food intake of 100 g i.e. about 1130 kJ ME and live weight of 1.8 kg i.e. 1.55 W,kg075 the following values of CO2 production and O2 consumption were obtained:
Series Housing CO2,1 O2,l G 1 hen/cage 37 42 H + K 3 hens/cage 41 46
The results indicated that the groups of hens in the battery cages (series H, K) would have had about 11% higher CO2 production and 8% higher O2 con-sumption than the single hens (series G) under the given ascon-sumptions.
5.3 Discussion
Respiratory studies on the domestic fowl are few and generally carried out with fasting hens, kept isolated in the respiration chambers and measured in re-latively short experiments as reviewed by Misson (1974) and Boshouwers &
Nicaise (1981). Under practical conditions laying hens are rarely fasted or kept on low feeding level and therefore it is of greater interest to obtain values for gas exchange from hens fed ad libitum, kept in conditions close to practical farming and measured over a longer period of laying as it was done in the pre-sent investigation. The gas exchange in the prepre-sent experiment was either mea-sured in hens kept singly (series G) or in groups permanently placed in the re-spiration chambers in the battery cages with 3 hens/cage or kept freely with 6 hens/chamber. In all series CO2 production was lower at the beginning of the laying period than in the later periods and the curves of CO2 production (Fig.
5.1 and 5.2) were parallel to the curves of food intake (cf. Fig. 3.1 and 3.2) thereby indicating a close relationship between CO2 production and food in-take during laying period.
The CO2 production and O2 consumption are close related to metabolism of the animal, and the levels of CO2 and O2 are directly dependent on animal size including body mass and surface. It is generally agreed that the power of live weight to which gas exchange is related is between 0.6-1.0 as reviewed by Blax-ter (1972). It has been agreed at a conference on energy metabolism in 1964, Kleiber (1965), that for the sake of simplicity in calculations and for between species and interspecies comparisons the power of weight to which metabolism is proportional should be 3/4 and the metabolic body weight may be defined as W,kg°75. The linear relation between gas exchange and metabolic body weight can be obtained as long as there is a relatively big variation in live weight, for example for growing chickens, Chwalibog et al. (1978), however, in laying hens the variation might be too small to give any reasonable function of gas ex-change, Geers et al. (1982), and in order to predict gas exchange other variables should be included. In the present experiment an attempt has been made to pre-dict gas exchange by means of multiple regressions of CO2 and O2 in relation to W,kg075, metabolizable energy and egg production. As it was mentioned be-fore the curves of CO2 production were similar to the curves of food intake and thereby to ME, furthermore it was assumed that gas exchange is dependent on egg production, hence non laying hens have lower heat production than layers, Waring & Brown (1965), Tasaki & Sasa (1970) and O'Neill & Jackson (1974).
The multiple regressions were performed on the individual measurements in series G where the data of gas exchange were not divided between hens (cf.
Chapter 2.3.3). The calculations showed that egg production could be excluded from the equations as its regression coefficients were not significantly different from zero and the following predictions of gas exchange were obtained:
CO2,1 = 17.3 x W,kg075 + 0.0094 x ME,kJ, O2,l = 22.7 x W,kg075 + 0.063 x ME,kJ.
The gas exchange was lowest for single hens (series G) and it was highest for the groups in the battery cages (Table 5.1). The valus of RQ were between 0.86-0.92 for series G, H and K being in accordance with the results obtained in experiments with poultry fed ad libitum or near ad. libitum, Shannon &
Brown (1969) for cockerels, Lundy etal. (1978) for laying hens, Johnson & Far-rell (1982) for broiler breeders and Thorbek & Chwalibog (1984) for chickens.
Considering that gas exchange can be satisfactory predicted from metabolic body weight and metabolizable energy as it was demonstrated for individual measurements in series G, the same regression model was applied in the other series. The regression equations were not significantly different between the applied temperatures and the origins indicating that independent on the origin the decrease in temperature from 21°C to 17°C did not cause an increase in the gas exchange and thereby no changes in heat production should be expected.
However, the functions of gas exchange demonstrated that CO2 production and O2 consumption in the hens kept in groups (series H+K) was higher than for single hens (series G) when assuming an equal live weight and food intake.
Since it is difficult to accept that differences in gas exchange were caused by dif-ferent metabolic processes for hens in the two housing systems, the result may be explained by differences in the locomotor activity (MacLeod et al. 1982). It has been previously discussed (cf. Chapter 3.3.2) that the hens kept in groups caused by the social facilitation by eating had a higher activity which can be the exclusive reason for the higher level of gas exchange indicating an extra energy expenditure and heat production. The fact may be considered both in nutri-tional cost and in design of environmental control system in poultry houses.