Effect of high ambient temperature on protein and lipid deposition and energy utilization in growing pigs

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AbstractThe effects of high ambient temperature (T) on protein (PD) and lipid deposition (LD) and energy utilization were studied on 36 Piétrain ✕ (Landrace ✕ Large White) barrows according to a factorial design including two temperatures (23ºC for thermoneutrality and 30ºC for the high temperature) and four feeding levels. One feeding level corresponded to the voluntary food intake (VFI) at each temperature. Expressed as proportion of VFI at 23ºC, the actual feeding levels were 1·00, 0·90, 0·80, 0·70 at 23ºC and 0·80, 0·73, 0·68 and 0·62 at 30ºC. Animals were offered a wheat, maize and soya-bean meal based diet containing 187 g crude protein per kg and 0·95 g ileal standardized digestible lysine per MJ of net energy. Pigs were housed individually and had free access to water. The experiment started at 24 kg live weight and animals were slaughtered at 65 kg live weight and their body composition was measured. Slaughter of nine control pigs at the beginning of the experiment allowed calculation of the composition of gain (nutrients and energy) according to the comparative slaughter technique. Reduction of metabolizable energy (ME) intake resulted in a reduced live-weight gain at each T: the maximum gain was 1052 g/ day in pigs offered food ad libitum at 23ºC and the minimum (760 g/day) at the lowest intake at 30ºC. Visceral organ mass was lower at 30ºC than at 23ºC but was not affected by feeding level within T. Growth responses were described as polynomial or broken-line functions of ME intake (linear-plateau for PD). Both the slope and the plateau were influenced by T. At 30ºC, PDmax (143 g/day) was reached at 22·8 MJ ME per day, while at 23ºC PDmax (165 g/day) was reached at 28·4 MJ ME per day. In both cases, PDmax was reached at 0·88 of VFI at this temperature. Also the marginal response of PD to ME intake before the breakpoint was affected by T (5·9 and 4·5 g PD per MJ ME at 23ºC and 30ºC, respectively). At identical high ME intake (e.g. 0·80 of VFI at 23ºC), PD was greater at 23ºC than at 30ºC. In contrast, severe food restriction reduced PD at thermoneutrality more than an identical food restriction obtained at high ambient T. The results indicate that heat stress has a direct negative effect on PD and affects the partitioning of energy gain between protein and fat deposition.