Responses of broilers at moderate or high temperatures to dietary arginine: lysine ratio and source of supplemental methionine activity

Recent studies have shown that the relative feed intake (FI) and bodyweight gain (BWG) responses of chronically heat-stressed broilers to equimolar additions Of DL-methionine (DLM) or 2-hydroxy-4-(methylthio) butanoic acid (HMB; Alimet) can be altered by changing the arginine: lysine (arg: lys) ratio of the diet. However, no information is available concerning responses of broilers during acute heat stress. Broilers were exposed to either 22degreesC or 30degreesC during 3 consecutive 5-day experimental periods between 28 and 43 days of age. Responses to equimolar additions of the 2 sources of supplemental methionine activity were similar during exposure to 22degreesC at 28 33 days and 38-43 days of age. However, between 33 and 38 days of age, when the temperature was 30degreesC, increasing the dietary arg: lys ratio from 1.04 to 1.35 significantly improved the FI and BWG of broilers fed HMB, but not DLM. At an arg:lys ratio of 1.35, the BWG of broilers fed HMB was significantly greater than that of broilers fed DLM. Therefore, under acute heat stress conditions the choice of a supplemental source of methionine activity should be dependent upon the dietary arg: lys ratio.