Heat stress (HS) reduces voluntary feed intake in pigs and indispensable amino acids (AA) supply. Providing high levels of crude protein (CP) may correct the situation but would further increase overall load of body heat. Using free AA may offer a better approach without affecting heat load in HS pigs. Two 21-d experiments were conducted. First, the Exp. 1 used 30 pigs (31.1 ± 1.2 kg BW) to determine the performance depression under ambient temperature HS (room temperature varied 24.5 to 42.6°C). Pigs were allotted to 3 treatments as: 1) thermo neutral (22 ± 2ºC) pigs fed a 22% CP control diet (TN-C); 2) HS pigs fed the control diet (HS-C); 3) HS pigs fed a 14% CP and supplemented with AA diet (HS-AA). Compared to TN-C pigs, the HS pigs lowered ADG and Lys utilization efficiency, and consumed 20 and 25% less Lys and Thr, respectively. In Exp. 2, 25 pigs (33.6 ± 0.65 kg BW) were used to evaluate the effect of supplementing AA either as protein-bound or free AA on the performance and carcass traits under HS (room temperature varied 27.7 to 37.7°C). Treatments were: 1) control wheat-SBM-free Lys, Thr and Met diet (CON); 2) additional 30% more CP than CON (HSxP); and 3) additional free AA to contain at least 25% extra AA than the recommended level (HSxAA). The dietary treatment had no effect on daily feed and NE intake. However, Lys, Thr, and Met intake was greater in pigs fed the HSxP or HSxAA diets than in pigs fed the CON diet. The average daily gain (ADG) was unaffected by the diet, but G:F tended to be higher and the Lys utilization efficiency (ADG, g/g Lys intake) tended to be lower in HSxP pigs than in CON pigs. The HSxAA pigs had higher ADG and tended to have greater weight of hot carcass and leg muscle than the CON pigs. The weight and daily weight gain of loin muscle was higher in the HSxAA than in the HSxP pigs. Kidney weight and serum urea in HSxP pigs were higher than in CON and HSxAA pigs, but spleen weight was higher in HSxAA pigs than in CON and HSxP pigs.
In conclusion, results confirm that HS reduces voluntary feed intake, and that higher AA levels as free or protein-bound do not worsen HS effects. Furthermore, using free AA supply ameliorate the reduced growth performance of HS pigs rather than the use of protein-bound AA.
Morales, A., Chávez, M., Vásquez, N., Htoo, J. K., Buenabad, L., Espinoza, S., and Cervantes, M. (2018). Increased dietary protein or free amino acids supply for heat stress pigs: effect on performance and carcass traits. Journal of animal science, 96(4), 1419-1429. https://doi.org/10.1093/jas/sky044