During the last years increasing attention has been paid to ventilation in piggeries and to the influence of climatic factors in the piggery on the growth of fattening pigs. It was necessary to accumulate more information on the heat and water vapour production of pigs in order to enable the construction of piggeries with climatic conditions for optimal production. For that reason an investigation into the influence of different temperatures on the heat production of growing pigs was started. The animals were kept singly with two pigs each in a metabolism cage or in groups of 4-5 pigs in one chamber. The experiments were performed in two new climatic chambers of the department of Animal Physiology of the Agricultural University at Wageningen. These chambers were constructed for respiration trials. These investigations were performed in a close cooperation between this Department and the Department of Animal Husbandry. In order to obtain data on the energy metabolism of pigs which could be compared as much as possible with conditions in husbandry practice, the animals stayed inside the respiration-climatic chamber during their whole fattening period from about 20 to 100 kg.
To investigate the temperature influence the following scheme was designed. After arrival the pigs were allowed to become accustomed to the chamber at 23-24 °C during a period of about 5-6 days and then a measurement of gaseous exchange was performed during a period of two days. After this period the temperature was lowered (usually 2-3°C) and a new period of gaseous exchange determination followed after an adjustment period of 2-3 hours. The 2-3 hours were found to be adequate for the animals to produce the heat required under the new established temperature. The temperature was lowered again after the end of the two-day period and gaseous measurement started after 2-3 hours. This procedure was repeated until the temperature was about 8 °C, and after the period of declining temperatures the same trials were performed with temperatures changing in a reverse direction, up to 18-19°C because in the meantime the animals had grown and had a lower limit of the thermoneutrality traject and therefore required a relatively lower temperature. The whole sequence was repeated until the animals weighed 80-100 kg. By following this experimental scheme a cyclical change in environmental temperature was achieved to avoid possible adaptation to cold conditions. In the literature these adaptations to cold conditions have been described. The cyclical change is more or less in accordance with the temperature fluctuations within 24 hours in practice. The animals were fed according to the normal feeding standards in usual use in The Netherlands (CENTRAAL
The singly housed animals were kept in metabolism cages of which two were placed together in one respiration chamber, whereas the group of 4-5 animals was housed in a pen built inside the chamber. Both housing systems had a wooden floor.
To obtain information on the energy balances the digestibility and metabolisability of the feed was determined 3 or 4 times with the single housed animals at 18-20 °C during periods of one week each in the course of the fattening period. The results of these determinations were applied to the other periods with single housed pigs and also to the experiments with groups of animals. The pigs in the groups were of the same weight and received the same amount of the same feed. The determination of metabolisable energy with groups of pigs was, of course, hardly possible and because of this reason the results obtained with the single housed animals were used.
Analysis of the errors made in the determination showed that this procedure of reducing the number of metabolisability determinations only slightly increases the inaccuracy of the results of balance trials provided that dry matter of the same feed was determined for every ration the animals received. Therefore during each part of the fattening period (20-50 kg and 50-90 kg) the feed was the same.
Since in the literature many balance experiments with grown-up pigs (FINGERLING, NEHRING) and growing pigs housed singly (LUND, BREIREM, LUDVIGSEN and THORBEK) are recorded it was decided also to use these data in the computations on the relation between heat production, feed-intake and metabolic weight in the zone of the thermoneutrality with such equations as
H = (1-a) ME + ak 1
H/Wp = (1-a) ME/W p
+ ak 1
+ bW (2)
In these equations:
H = heat production in kcal/animal. day;
ME = metabolisable energy intake in kcal/animal. day;
W = body weight in kg;
a, b, p and k 1
represents the maintenance heat production and is calculated from ak 1
The computations with the equation (see Chapter 6) showed that the best value of p in these trials could be found between 0.50 and 0.70 for pigs above 50 kg and between 0.80 and 0.90 for animals below 50 kg. The differences in goodness of fit (R 2
) with p = 3/4, however, were very small.
The computations of the literature trials also suggested that p may be lower than 3/4 in mature animals and 3/4 or higher in growing animals of 20-100 kg. In general R 2
from equation (1) was between 0.77 and 0.99 in the results of these trials and between 0.85 and 0.99 in results of trials from the literature. It was concluded that p = 3/4 can be used without much hazard to express metabolic weight, especially when small weight ranges are concerned. Further the computations show a significant influence of age which in some of the literature trials had been taken as the variable instead of weight. No influence of weight (except in one case) in the present material for 20-50 kg or 50-90 kg was found. From those literature data which had a varying amount of ME/W 3/4
(NEHRING) 1-a was found to be 0.30 and this value was also used in the other trials from the literature in which a much smaller variation in feeding level was present. The by this method computed maintenance requirement (= maintenance heat production computed from ak 1
/a) was between 60 and 92 kcal, ME/W 3/4
for animals above 100 kg and between 100-110 kcal ME/W 3/4
for animals between 20 and 90 kg. From the results obtained with formula (2) without the term bW 1-a was found also to be about 0.30 in the trials with the highest variation in feeding level (ME/W 3/4
When again 1-a was assumed to be 0.30 the computed maintenance requirement was slightly higher than in the literature trials. This value however was the same in trials with single pigs and in those with groups of animals. Although there were consistent differences in these values between the various pairs of singly housed animals and also between the various groups of animals, the average for animals of 20-50 kg was about 122 kcal ME/W 3/4
and for animals of 50-90 kg about 116 kcal ME/W 3/4
Most of the presented experiments, however, were carried out at temperatures below the thermoneutral zone. Hypothetically a linear relationship between critical temperature of an animal and the weight and feedintake could be expected. Moreover the increase of heat production below the critical temperatures was assumed to be linear with the deviation from the critical temperature. To compute this relation the following regression equations were used:
= (1-a) ME/W p
+ bW + e(Tcr-T) + fΔt + ak 1
= bW + e(Tcr - T) + fΔt + ak 1
+ 160 (4)
Tcr = k 2
- cW - d ME/W p
(for formula (3))
Tcr = k 2
- cW (for formula (4))
in which H, W and ME represent heat production per day in kcal, body weight in kg and metabolisable energy in kcal respectively; Tcr = critical temperature in °C, T = temperature in °C and t is temperature difference in °C between the actual temperature in the chamber and the temperature in the chamber during the preceding two days. k 1
, k 2
,b, d, a, c, e and f are coefficients. The value 160 refers to the heat production within the zone of thermoneutrality at the highest feeding level (about 250-270 kcal ME/W 3/4
In the experiments belonging to this kind of temperature trial the feeding level was kept as constant as possible. Therefore the results obtained with equation (3) and (4) were compared. Regression equations according to (3) and (4) were computed from data obtained with each pair and each group of animals, when using different values of k2 and c in Tcr for formula (4). It was found that in animals below 50 kg the lowest residual standard deviations were obtained with k 2
= 21 and c = 0. 1. This indicated that the critical temperature at a constant feeding level i.e. a level giving a thermoneutral heat production of 160 kcal/W 3/4
, could be computed with 21 -0.1 W for animals housed singly. With groups of pigs 20-0.1 W fitted as well as 21-0.1 W. Therefore the critical temperature in groups may be equal or only slightly less than in single animals.
In pigs from 50-90 kg also the values 20 and 21 for k 2
were found to give the best results with groups and singly housed pigs and c could be considered to be somewhat higher than 0.1 i.e. 0.15.
So probably the decrease in Tcr with decreasing body weight is somewhat faster in the animals above 50 kg. No significant influence of weight in equation (4) was found. Further the value of e in (3) and (4) refers to the effect of temperature below the critical level on heat production an effect which differed considerably between pigs housed singly or in groups. Between the different pairs of single pigs and groups significant different values of e were also obtained. As an average the single housed animals produced about 3.5-5 kcal H/W 3/4
extra per °C below the critical whereas in groups this effect was 0.8-1 kcal H/W 3/4
. This means that groups of pigs, kept in this way, saved about 70 - 80 % of the extra heat required below the critical temperature compared with the single housed animals merely by huddling.
From computations with equation (3) and (4) it was found that the direction of temperature change had in some cases a significant influence. Especially in pigs kept in groups the heat production increased with decreasing temperatures. Animals kept in groups produced below the critical temperature often more heat at the same temperature when they had been kept during the preceding two day period at a higher temperature than when they had been kept that preceding two- day period at a lower temperature. Perhaps this resulted from the fact that the animals were somewhat more restless due to looking for a better place in the huddled group.
The energy gain of the single animals measured with animals weighing 20-50 kg and at different temperatures was distinguished as fat and protein. The low temperatures hardly affected the protein deposition of single animals of 20-50 kg but considerably reduced their fat deposition. The animals obviously mobilised body reserves to meet the required heat production while they still gained protein.
In the discussion it has been pointed out that the amount of feed required to meet the extra heat necessary at low temperatures should be determined with animals kept in groups. Determination of critical temperature, however, can be made with singly-housed animals. Furthermore investigations will be necessary to study the influence of temperature on heat production of groups of pigs under different housing systems e.g. floors. The influence of temperature on the composition of body weight gain in groups of pigs has also to be investigated further.