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This 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. The 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 urea-nitrogen 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. The 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. [ABSTRACT FROM AUTHOR]

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