Dietary arginine : lysine ratio and methionine activity at elevated environmental temperatures

There has been much controversy concerning the relative efficacies of equim olar quantities of DL-methionine (DLM) and 2-hydroxy-4-(methylthio) butanoi c acid (HMB). Inspection of published literature suggests that the dietary arginine:lysine (Arg:Lys) ratio could be involved, especially during heat s tress. In Experiment 1, conducted at 32 degrees C, increasing supplemental HMB from 0.16 to 0.32% in a diet with an Arg:Lys ratio of 1.36 produced a s ignificant increase in body weight gain (BWG) from 21 to 38 days. However, increasing DLM in a equimolar manner did not. Feed intake (FI) was better f or the HMB birds. In Experiment 2, where diets with an Arg:Lys ratio of 1.0 3, 1.20, or 1.34 were fed at 32 degrees C, birds fed HMB gave significantly improved BWG and FCR at a higher FI between 42 and 48 days compared to bir ds fed DLM. The FI of birds fed DLM decreased more rapidly than the FI of b irds fed HMB as dietary Arg:Lys ratio increased. Therefore, a knowledge of Arg:Lys ratio appears to be required to optimize the methionine activity so urce.