Modelling the effect of high, constant temperature on food intake in young growing pigs

Performance in pigs is greatly reduced during periods of heat stress through a reduction in voluntary food intake (VFI). However, little information is available as to what extent growth in piglets is affected by high temperature. The objective of this study was therefore to quantify the change in VFI as affected by environmental temperature. Piglets, initially 15.5 (s.e. 1.9) kg body weight (BW), were individually housed and exposed over a period of 17 days to either 19, 21, 23, 25, 27, 29, 31, 33, or 35 degreesC. Animals had ad libitum access to a starter diet and water. VFI was measured daily whereas BW was determined twice weekly. Over the 17 days, daily VFI and BW gain were proportionately 0.48 and 0.51 lower at 35 degreesC than at 29 degreesC. Due to the reduced VFI at high temperatures, the average BW during the experiment was greater at low temperatures than at high temperatures. Consequently, part of the difference in VFI is directly due eo temperature and part may he explained by cascading, indirect effects (i.e. the increased BW). To account for this, VFI was expressed as a power function of BW (VFI = aBW(b)). It was assumed that environmental temperature affected the scalar (a) through a quadratic or a 'plateau-linear decline' function of temperature. The VFI appeared relatively constant between 19 and 25 degreesC (0.096 (kg/day)/(kg BW0.83)) and decreased thereafter. Between 25 and 35 degreesC, VFI decreased on average by proportionately 0.28 in a 20-kg pig.