The effect of the different dietary linoleate levels ranging from 0.04 to 9.5 energy% on energy metabolism was measured in balance and respiration trials during the growth period as described in Chapter III, and the requirement for linoleic acid is derived from these results.
The intake of gross energy (GE) and its digestibility (DE) was described in Chapter III and V, respectively. So, it remains to describe the metabolizability (ME/GE) and the utilization of metabolizable energy (ME) for total energy re-tention (RE), the proportions of energy retained in protein (RPE) and fat (RFE), and heat production (HE). Furthermore, the efficiency of utilization of ME for growth (ME) and the partial efficiencies of protein (kp) and fat (kf) re-tention were calculated.
Part of the results concerning energy metabolism in young pigs (15-50 kg live weight) was presented at the 8th Symposium on Energy Metabolism (Christen-sen et al, 1980).
7.1 Principles of measurements, calculations and statistical evaluations 7.1.1 Measurements and calculations
The standard procedures employed at the Department of Animal Physiology were used both for the measurements and the calculations. The factors used for calculations of the energy balances from the carbon and nitrogen balances and the gas exchange measurements in the respiration chambers were those prop-osed by Brouwer (1965). A detailed description of the calculations is given by Thorbek (1975) and Thorbek et al. (1984). The following is a short summary of the measurements performed in the present studies.
Figure 7.1 summarizes the fate of the dietary energy (GE) in the organism.
Metabolizable energy (ME) is the difference between GE and the loss of energy in faeces (FE), urine (UE) and methane (CH4E), i.e.
(7a) ME = GE - (FE + UE + CH4E)
The metabolizability is expressed as ME in percent of GE (ME/GE,%).
The methane production was not measured in all pigs because of technical problems. However, as will be seen in the following, methane production was low in the growth period in question (15-100 kg live weight) and therefore may be totally neglected.
GE Gross energy = Energy intake
> FE Energy in faeces DE Digestible energy
— > UE Energy in urine
— > CH4E Energy in methane Metabolizable energy
— > HE Heat energy RE Retained energy
Figure 7.1. The individual components of an energy balance (RE = GE - (FE + UE + CH4E + HE)
De individuelle komponenter i en energibalance (RE = GE - (FE + UE + CH4E + HE)
Part of ME is retained (RE) and part is dissipated as heat (HE), i.e.
(7b) ME = RE + HE
RE was calculated from the nitrogen and carbon balances, and so was the amount of energy retained in protein (RPE) and fat (RFE), anticipating that all retained carbon in N-free material was deposited as fat. Thus
(7c) RE,kJ = 149.1 x g deposited N + 51.9 x g deposited C in N-free material (7d) RE = RPE + RFE
The total heat production or heat energy (HE) was then calculated as the dif-ference between ME and RE called HE(CN), i.e.
(7e) HE(CN) = ME - RE
HE(CN) is shown in section 7.2 for the individual series of esperiments.
The total heat production (HE) was also calculated from the measurements of the gas exchange (volumes of oxygen consumption and carbon dioxide
pro-duction), the methane production and the nitrogen excretion in the urine (UN).
The HE is termed HE(RQ), where RQ refers to the respiratory quotient (litres CO2/litres 02), and according to Brouwer (1965) was calculated as follows:
(7f) HE(RQ),kJ = 16.18 x litres 02 + 5.02 x litres CO2-2.17 x litres CH4 - 5.99 x g UN
HE(RQ) is only shown for the total material (see section 7.3) in comparison with HE(CN) which was also calculated for the total material. In order to calcu-late the efficiency of utilization of metabolizable energy (RE/MEg), ME which comprises metabolizable energy for maintenance (MEm) and growth (MEg), has to be split up into its components:
(7g) ME = MEm + MEg
This can only be done if MEm is measured per se or knowledge about the value has been obtained in previous experiments. MEm was not measured in the present experiments, but the value obtained in fasting experiments with pigs (Thorbek and Henckel, 1976) have been adopted. According to the latter au-thors MEm,kJ = 4060 + 210 x LW,kg°75. The efficiency of utilization of energy for growth was evaluated for the total material, and the results are presented in section 7.5. From the following equation:
(7h) MEg = bx x RPE + b2 x RFE
the partial efficiencies of protein and fat retention were calculated, kp being 1 /b | and kf l/b2.
7.1.2 Statistical evaluation of results
The whole material was treated statistically by means of regression analyses (Henckel, 1973) at A/S Regnecentralen, Copenhagen. In some cases analyses of variance or covariance have been carried out at NEUCC, Lyngby, by means of ANOVA or GLM procedures as described by Freund and Littell (1981).
Specific attention was paid to the heat production. A regression analysis of HE(RQ) in relation to metabolic live weight (kg075) including the total material until 50 kg live weight (N = 179) within linoleate levels x »sex« showed that statistically significant differences existed between linoleate levels (F = 2.13* *).
Thus the total material could not be pooled. From this material it appeared that statistical significant differences in HE(RQ)/LW° 75 might exist between bar-rows and sows. Therefore, regression analyses were performed using all the data from all the series (C-D-E-G-H) representing both barrows (N = 112) and sows (N = 110) to test the effect of »sex« on RN/LW°-75-LWL5°, HE(RQ)/
LW° 75 and RE(CN)/MEg. These analyses showed that statistically significant effects of »sex« existed with respect to nitrogen retention (F = 15.7*) and heat
production (F = 5.16*), but not with respect to the efficiency of utilization of energy for growth. Then, the material was divided into barrows and sows and the effect of linoleate levels tested by means of regression analyses with respect to CO2/LW° 75,02/LW°75, HE(RQ)/LW°75, HE(CN)/LW°75' RE(CN)/MEg and MEg = bi x RPE + b2 x RFE.
Although statistically significant differences occurred between linoleate levels within »sex« a critical examination of the results did not show any sys-tematical effects of the different linoleate levels except in Series B, where the two groups were not fed iso-energetically. So, for all other series, the results concerning energy metabolism and gas exchange from the different groups were pooled within »sex«, and mean values and their standard errors (SEM) were calculated for each series of experiments. These results are shown in Sec-tion 7.2 and 7.3.
In order to be able to compare the results obtained in the present experi-ments with previous experiexperi-ments carried out at the department or described in the literature, the total material was pooled within »sex« and the above-men-tioned criteria were calculated. The results from these calculations are de-scribed in Section 7.4 and 7.6.
7.2 Energy intake, energy loss and energy retention in the individual series of experiments
Series B comprised 4 barrows receiving 0.4 energy% linoleate (Group 1) and 4 barrows receiving 9.5 energy % linoleate (Group 2) from 25 to 100 kg live weight. However, the two groups were not fed iso-energetically. As shown in Table 7.2.1 Group 2 received on an average 11.4% more GE than Group 1 dur-ing the growth period. The loss of energy in faeces (FE), urine (UE) and methane (CH4E) is shown in Table 7.2.2 both in absolute values and in percent of GE, and the results from the statistical evaluation are shown in Table 7.2.3.
As can be seen from these tables there was no statistical significant (P>0.05) difference between the two linoleate levels in loss of energy in faeces and urine.
FE/GE was about 5% during the whole growth period, whereas UE/GE in-creased significantly (P<0.001) from 1.9% at 28 kg live weight to 3.0% at 100 kg live weight. The methane production was significantly (P<0.001) greater in Group 1 than in Group 2, the energy loss being 0.6 and 0.3% of GE, respec-tively, at 28 kg live weight icreasing to 1.1 and 0.9% of GE, respecrespec-tively, at 90 kg live weight. This difference in methane production is shown graphically in Figure 7.2.
The total loss of energy in faeces, urine and methane for the growth period in question amounted to 9.1% of GE for Group 1 and 8.2% of GE for Group 2 and this difference was statistically significant (P<0.05). Thus, as an average for the whole growth period Group 2 received 7.3% more ME daily than Group
and energy retained in protein (RPE) and fat (RFE) in barrows fed 0.4 (Group 1) or 9.5 (Group 2) energy % linoleate during 7 balance periods
Tabel 7.2.1 Serie B. Energiomsætning. Middelværdier for bruttoenergi (GE), omsættelig energi (ME), varmeenergi (HE), aflejret energi (RE) samt energi aflejreti protein (RPE) ogfedt (RFE) hos galtefodret med 0,4 (Hold 1) eller9,5 (Hold2) energi% linoleat gennem 7 balanceperioder
Period
Table 7.2.3 Series B. Results of two way unbalanced analysis of variance on measure-ments of energy metabolism. F-values and mean square of error (MSE) Tabel 7.2.3 Serie B. Resultater fra tosidet ubalanceret variansanalyse på målinger af
ener-giomsætningen. F-værdier og residualmiddelkvadratsum (MSE) Source of variation
Degrees of freedom
FE/GE % UE/GE % CH4E/GE % ME/GE %
Period 6 3.07 ns 36.5***
16.0***
1.02 ns
Group 1
1.91ns 0.26 ns 36.6***
4.26*
Interaction 6 1.44 ns 0.62 ns 0.69 ns 1.08 ns
MSE 36 0.50 0.039 0.022 0.65
1. In both cases the metabolizability (ME/GE) was quite high being 90.0% for Group 1 and 91.8% for Group 2.
Because of different live weights between the groups in the balance periods, analyses of covariance adjusting for live weight (LW°75) were performed to test ME, HE(CN), RE, RPE and RFE between the two groups. The results showed that statistically significant differences existed between groups with respect to the intake of ME (F = 67.5***), retained energy (F = 17.1***) and the amount of energy retained in protein (F = 7.77**) and fat (F = 29.3* * *), but not with re-spect to heat production (F = 0.87).
The mean values of retained energy (RE) determined on the basis of the nit-rogen and carbon balances increased during the growth period from 6362 to 22420 kJ/day for Group 1 and from 7716 to 23649 kJ/day for Group 2. As shown in Table 7.2.1 RE/ME was 40.1 and 43.3% for Group 1 and 2, respectively, at 28-29 kg live weight increasing to 57.0 and 54.1%, respectively, at 91-100 kg live weight. Generally, more energy was retained in Group 2 than in Group 1, and conversely, generally more energy was lost as heat (HE) in Group 1 than in Group 2. The total loss of energy in faeces, urine, methane and heat amounted to an avaerage of 53.1% of GE for Group 1 and 51.4% of GE for Group 2.
The most marked difference between the two groups is found in the propor-tions of retained energy in protein (RPE/RE) and fat (RFE/RE) as evidenced in Table 7.2.1. During the whole growth period the pigs of Group 2 deposited about 8% units more of the retained energy in fat than did the pigs of Group 1.
Figure 7.3 shows the difference in fat retention (g/day) between the two groups during the growth period in question.
Series C was carried out with two groups of pigs (two barrows and two sows per group) fed iso-energetically without (Group 1) or with (Group 2) 2% beef tallow. Group 1 received 0.04 energy% linoleate and Group 2 0.2 energy%
linoleate from 30 to 50 kg live weight. Two of the pigs had digestive troubles in Period IV and were not subjected to balance and respiration trials. The results
gy % linoleate during 7 balance periods
Tabel 7.2.2 Serie B. Middelværdier for energitab i faeces (FE), urin (UE) ogmethan (CH4E) hos galte fodret med 0,4 (Holdl) eller 9,5 (Hold2) energi%
linoleat gennem 7 balanceperioder
Period
0>
E
300-1 2001
O) c LU