Influence of high ambient temperatures on performance of multiparous lactating sows

Multiparous Large White sows (n = 63) were used to investigate the effects of five ambient temperatures (18, 22, 25, 27, and 29 degrees C) and two die tary protein contents on their lactation performance. At each temperature t reatment, ambient temperature was maintained constant over the 21-d lactati on period. Dietary protein content was either 14 or 17% with essential amin o acids levels calculated not to be limiting. The animals had ad libitum ac cess to feed between the seventh and the 19th day of lactation. Diet compos ition did not influence lactation performance. Over the 21-d lactation, fee d intake decreased from 5.67 to 3.08 kg/d between 18 and 29 degrees C. Betw een d 7 and 19, the corresponding values were 7.16 and 3.48 kg/d, respectiv ely. This decrease was curvilinear; an equation to predict voluntary feed i ntake (VFI) from temperature (T, degrees C) and body weight (BW, kg) is pro posed: VFI = -49,052 + 1,213 T - 31.5 T-2 + 330 Bm - .61 BW2 (residual stan dard deviation: 1,018). Skin temperature increased regularly with increased ambient temperature (34.6 to 37.4 degrees C between 18 and 29 degrees C), whereas udder temperature reached a plateau at 25 degrees C (38.3 degrees C ). The gradient of temperature between skin and rectum was minimal (2 degre es C) at 27 degrees C and remained constant at 29 degrees C. This constancy coincides with the marked reduction of feed intake. The respiratory rate i ncreased from 26 to 124 breaths/min between 18 and 29 degrees C, and this i ndicates that the evaporative critical temperature was below 22 degrees C, The BW loss increased from 23 to 35 kg between 18 and 29 degrees C, but its estimated chemical composition remained constant. Pig growth rate was almo st constant between 18 and 25 degrees C (241 g/d) and was reduced above 25 degrees C (212 and 189 g/d at 27 and 29 degrees C, respectively). In conclu sion, temperatures above 25 degrees C seem to be critical for lactating sow s in order to maintain their performance.