Soybean oil and crude protein levels for growing pigs kept under heat stress conditions

This study was conducted to evaluate the effect of different levels of soybean oil (SO) and crude protein (CP) on performance and physiological and hormonal parameters of pigs in high-temperature environment. Eighty-four growing pigs with initial weight of 36.9±3.0 kg were assigned to treatments in 2×3 factorial arrangement of dietary treatments plus 1 [two levels of CP, 18% and 15.5%, and three levels of SO, 1.5%, 3.0%, and 4.5% with all pigs kept at room temperature of 32 °C, and an additional treatment (control) with 18% CP and 1.5% SO with pigs kept at 22 °C], in a randomized block design with the block being the initial weight. In animals maintained in the high-temperature environment, there was no interaction between CP and SO levels in any of the variables evaluated. The addition of SO improved (P<0.05) the average daily gain (ADG) and feed:gain (F:G), but did not affect the average daily feed intake (ADFI). The reduction of CP resulted (P<0.05) in lower ADFI. Compared to animals kept at the comfort temperature, a high-temperature environment decreased the F:G (P<0.01) of animals fed diets with 18% CP and 1.5% SO. However, increasing the SO level resulted in similar values of F:G. For animals kept in a high-temperature environment, CP can be reduced in diets supplemented with amino acids only in diets with high SO levels. The high-temperature affected (P<0.01) body temperature and respiratory rate, but was not sufficient to change the levels of T3 and T4. It is concluded that SO levels should be increased in diets for animals kept in high-temperature environment, and the CP levels can be reduced only under these conditions, since supplemented with amino acids.