Dietary Arginine:Lysine Ratio and Methionine Activity at Elevated Environmental Temperatures

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Abstract
There has been much controversy concerning the relative efficacies of equimolar quantities of DL-methionine (DLM) and 2-hydroxy-4-(methylthio) butanoic acid (HMB). Inspection of published literature suggests that the dietary Arginine:Lysine (Arg:Lys) ratio could be involved, especially during heat stress. In Experiment 1, conducted at 32°C, increasing supplemental HMB from 0.16 to .32% in a diet with an Arg:Lys ratio of 1.36 produced a significant increase in body weight gain (BWG) from 21 to 38 days. However, increasing DLM in an equimolar manner did not. Feed intake (FI) was better for the HMB birds. In Experiment 2, where diets with an Arg:Lys ratio of 1.03, 1.20, or 1.34 were fed at 32°C, birds fed HMB gave significantly improved BWG and FCR at a higher FI between 42 and 48 days compared to birds fed DLM. The FI of birds fed DLM decreased more rapidly than the FI birds fed HMB as dietary Arg:Lys ration increased. Therefore, a knowledge of Arg:Lys ratio appears to be required to optimize the methionine activity source.