The response of growing pigs to amino acids as influenced by environmentaltemperature - 1. Threonine

Two similar experiments (1 and 2) were conducted to measure the effects of a range of dietary threonine concentrations and environmental temperatures on the performance of pigs grown from 13 to 25 kg live weight. In both expe riments 48 Large White X Landrace entire male pigs were assigned at 13 kg t o one of six dietary threonine treatments (8.9 (T1), 7.6 (T2), 6.2 (T3), 4. 9 (T4), 3.6 (T5) g/kg and T5 + supplemented threonine (T6)) and one of four temperature treatments (18, 22, 26 and 30 degrees C). Animals were given a d libitum access to food until 25 kg live weight. There were significant in teractions (P < 0.05) between temperature and threonine content on the rate of growth (ADG) with the highest gains on T1 and at 22 degrees C. Similarl y the response in food intake (FI) to dietary threonine pins significantly (P < 0.01) modified by the ambient temperature. An increase in the supply o f threonine in the diet resulted in significant increases (P < 0.001) in th e gain per unit of food (FCE). A similar response to temperature occurred w ith the highest FCE recorded at 26 degrees C and the lowest at 18 degrees C . There was a 0.20 proportional reduction in body protein content at 25 kg live weight in pigs given T5 compared with those given T1 and similarly, ex cluding T6 because threonine may nor have been the most limiting amino acid , the fat content was 1.37 higher for pigs on T5 versus T1, which had the l owest fat content. Similar trends occurred in protein and lipid growth rate s with maximum protein deposition recorded on T1 (86 (s.e. 3.5) g/day) and maximum lipid deposition on T5 (108 (s.e. 5.8)g/day), over all temperatures . The response in total heat loss was similar to that observed in FI with t he effect of decreasing threonine content being dependent on the environmen tal temperature. Linens regression of daily empty body threonine accretion on daily digestible threonine intake showed an average efficiency of threon ine utilization for pigs between 12 kg and 25 kg live weight of 0.59 (s.e. 0.03). There were no differences in efficiency between temperatures. In con clusion, decreasing the threonine concentration below the requirement of th e animal resulted in a significant decrease in ADG, reduced FCE and fatter animals. Pigs given a diet deficient in threonine will attempt to maintain threonine intake as the concentration declines by increasing food intake bu t this compensation is dependent on the environmental temperature. Pigs are able to compensate better for a deficiency in threonine at 18 degrees C an d 22 degrees C than at higher temperatures due to the animals being able to dissipate more heat at the lower temperatures.