Effects of supplementation with rumen-protected methionine on milk performance, plasma biochemical indices and amino acid concentration in dairy goats subject to heat stress

Abstract

Th is study examined the eff ects of four levels of rumen-protected methionine (RPM) on the milk performance of dairy goats subjected to severe heat stress (temperature humidity index >90). Seventy-five Guanzhong dairy goats (52.6±4.9 kg) with the same farrowing period and lactation day (120±10 d) were randomly divided into five groups of 15 head and fed a 13.55% crude protein diet supplemented with 0, 1.5, 3, 4.5 or 6 g/d RPM in the concentrate. Th e trial included nine days adaptation time and 30 days of sampling and analysis. Th e addition of RPM did not change feed intake but 1.5 g/d RPM significantly increased milk protein content, the ratio of milk to feed, and the economic returns. No significant changes in milk fat or urea-nitrogen concentrations or somatic cell count were observed. Plasma ureanitrogen was significantly lowered in the 1.5 g/d RPM group. RPM supplementation increased plasma methionine concentration and total amino acid concentration in a dose-dependent manner. Th e highest dose of RPM (6 g/d) enhanced plasma immunoglobulin G concentration. It is demonstrated that supplementation with an appropriate dose of RPM to dairy goats fed a relatively low protein diet and subject to heat stress can increase milk protein production and improve economic returns.

Keywords

• rumen protected methionine
• milk composition
• plasma urea-nitrogen
• free amino acids
• immunoglobulin g
• dairy goats