Rumen pH and NH3-N concentration of sheep fed temperate pastures supplemented with sorghum grain

Abstract

The aim of this study was to evaluate the effect of sorghum grain supplementation on ruminal pH and NH3-N concentration of wethers consuming a fresh temperate pasture (Lotus corniculatus) in metabolism cages. Sixteen Corriedale x Milchschaf wethers were fed temperate pastures ad libitum and were non-supplemented or supplemented with ground sorghum grain at 5, 10 or 15 g/kg of their body weight (BW). Rumen fluid samples were collected at 0, 1, 2, 3, 4, 5 and 6 h after supplementation through permanent tubes inserted in the rumen. Ruminal pH was measured immediately and NH3-N concentration was determined by direct distillation. Mean daily pH values for non-supplemented wethers and supplemented with 5, 10 and 15 g/kg of their BW were 6.45, 6.14, 6.09 and 5.43, respectively. Significant differences in pH were found between the 15 g/kg supplemented group and non-supplemented, 5 and 10 g/kg supplemented groups, while a trend was found between non-supplemented and 10 g/kg supplemented group. After 0 h, all mean pH values for the non-supplemented group were above 6.15, while values for the 10 and 15 g/kg supplemented groups were below 6.2 and 6.0, respectively. No differences in NH3-N concentration among groups (mean = 37.15 mg/100 mL), between time or interaction between time and treatment were found. There was a correlation between pH and NH3-N when all measurements were considered. Ground sorghum grain supplementation significantly reduced rumen pH when 15 g/kg of BW was provided to wethers fed temperate pastures, but it did not affect NH3-N concentration.