Gas exchange and heat production in growing pigs fed different feed compounds
6.2 Gas exchange and heat production in relation to metabolic live weight The figures for mean live weight in the 8 experimental periods given in Table
36 have been transformed to metabolic live weight (kgP-75) and plotted against the mean values for gas exchange and heat production in Figures 27 and 28.
This transformation of live weight clearly indicates a pronounced linear relation between gas exchange and heat production respectively to the meta-bolic live weight. By means of the 367 individual measurements indicated in the main tables, regressions of gas exchange and heat production (RQ) on meta-bolic live weight (kg0-75) according to model 1, with intercept have been calcul-ated and the regression equations for CCh-production, Ch-consumption and heat production (RQ) are given in the first part of Table 38.
For reasons of comparison similar equations based on the work of Nielsen (1970) have been computed and added to the table. The data consists, as mentioned in the foregoing section, of the measurements of gas exchange in 80 pigs in 6 periods of different type of feeding ( n = 480). The data has been grouped by Nielsen and is given as the mean of 4 pigs, thereby reducing the number of observations for this calculation to 120. From the work of Verstegen (1971) 109 observations concerning heat production in pair of pigs kept above the critical temperature have been used to compute the regression on meta-bolic live weight and the equation is also shown in Table 38.
I
1000
900
800
g. 700
o
* 600
O
500
400
300
• Coproduction ø Q - - consumption
10 15 20 Metabolic live weight
25 kg 0.75
Figure 27.
Gas exchange in relation to metabolic live weight (kgO75).
Respiratorisk stofskifte i relation til metabolisk legemsvægt (kg0-75).
Comparing the equations estimated from the results of Nielsen with the present investigation it is found that the standard deviations of the regression coefficient are of the same magnitude in the two investigations. A somewhat higher S.D. of the residuals are found in the present investigation compared with the trials of Niels en, which may by explained by the fact that it was sought to have a rather large genetic variation between the animals in our experiments in order to facilitate a general application, as discussed in chapter 3. Further-more the data of Nielsen consist, as mentioned, of mean values.
The curves obtained for heat production from the two trials are demonstrated in Figure 28. As discussed in the previous section the heat production in the trials of Nielsen, was somewhat higher for the heavier pigs, caused by an intake of protein being above the requirement for maximum protein retention. Never-theless the curves are very similar, and the difference in heat production at 25 kg live weight ( 11.2 kg met. live weight) was found to be 2% lower in the trials of Nielsen and 3% higher at 85 kg (28.0 kg met. live weight) than in the present investigation.
kcal
5000
4000 .2
tJ 3000
ï
h.
r. 2000 1000
Present invest.
Nielsen (1970) Verstegen (1971)
10 15 20 Metabolic live weight
25 kg
Figure 28.
Heat production (RQ) in relation to metabolic live weight (kg0-75).
Varmeproduktion (RQ) i relation til metabolisk legemsvægt (kg0-75).
Considering the many different types of feed compounds in question in the two trials it may be concluded that the equations given in Table 38 based on metabolic live weight would give reliable results for calculating the expected
Table 38. CCh-production, Ch-consumption and heat production (RQ) in relation to meta-bolic live weight (kg0-75) in growing pigs from 20-90 kg
Tabel 38. COi-produktion, Oi-forbrug og varmeproduktion (RQ) i relation til metabolisk legemsvægt (kg0-75) hos voksende svin fra 20-90 kg
Present investigation. Series C-D-E-F. (n = 367)
CCh-production, litres = ( 76 + 34.2 kg0-75) ± 36 s Ch-consumption, litres = (180 + 25.3 kg0-75) ± 41 si =i
= 7, sb = 0.35 sb = 0.40 Heat production (RQ), kcal = (786 + 138 kg0-75) ± 194 s, = 36, sb = 1.87 Nielsen (1970). (n = 120)
CO2-production, litres Ch-consumption, litres Heat production (RQ), kcal Verstegen (1971). (n = 109)
Heat production (RQ), kcal
( 40 + 35.3 kg0-75) ± 25 (140 + 28.5 kg0-75) ± 24 (607 + 150 kg0-75) ± 114
s, = 8, sb = 0.40 s, = 7, sb = 0.38 s, = 36, sb = 1.84
= ( -6 + 162 kg0-75) ± 351 s, = 101, sh = 5.25
protein, securing maximum protein gain. Thereby the errors which would occur by calculating heat production proportionally to live weight, as discussed in the previous section, could be avoided.
The regression equation (Table 38) and curve (Fig. 28) for heat production based on observations made by Verstegen (1971) with pair of pigs kept above the critical temperature differ rather much from the results obtained with the respiration plant in Copenhagen. The intercept is not significant, the slope of the curve is much steeper and the standard deviation of the residuals is greater than in the trials from Copenhagen. At 25 kg live weight the heat production calculated according to the equation based on measurements of Verst egen was about 22% below the values obtained from the present investigation, while at 85 kg the difference was only about 2%. The rather low heat production in the first period of growth is probably connected with the protein norm applied, as the intake of ME is of the same magnitude as in the Danish investigations. Some nitrogen balances were determined by Verstegen indicating that the nitrogen intake for the lighter pigs was too low to secure maximum protein gain. In the weight group from 25-30 kg, seven pairs of pigs, had a mean nitrogen retention of 11.3 g daily, corresponding to 70 g protein. Based on the same live weight and intake of energy, a low protein norm will reduce the heat production, as demonstrated from the results of Verstegen.
In a recent paper, Fuller & Boyne (1972) have presented their results concer-ning the heat production in 18 pigs divided into 9 groups at different temperatu-res and levels of feeding, determined by means of a closed-circuit chamber. The mean values for the heat production of two pigs kept at 23°C and with a daily intake of 116 g food/kg073, corresponding to the conditions in the present investigation, have been used for comparison. The figures for heat production given for live weight groups from 25-85 kg have been plotted against metabolic live weight. A linear function could be demonstrated, and a graphical estimate of the regression gave HP (RQ) — 500 + 140 kg075, corresponding rather well with the equation derived from the trials of Nielsen and from the present investigation.
Close, Mount & Start (1971) have measured by direct calorimetry the heat losses in pigs from 30-40 kg live weight, housed in groups of 5 animals kept at different temperatures and levels of feed. Comparing their results from pigs kept at 20°C with the present investigation it was found that the heat loss was somewhat lower in groups of pigs, than in pigs kept singly. With approximately the same intake of energy and protein the difference was about 300 kcal at a live weight of 30 kg decreasing to 200 kcal at 40 kg. The heat loss was thereby 10 to 6% lower for group of pigs compared with our results with singly kept pigs.
6.3 Heat production calculated according to the RQ- or CN-method