PSXI-21 Effects of different levels and protein sources on ruminal fermentation of feedlot Nellore steers fed high-concentrate diets

Abstract

The goal of this study was to evaluate the effects of different levels (10 and 13% crude protein) and protein source on ruminal fermentation of feedlot Nellore steers fed high-concentrate diets. The protein sources tested were urea, dried distillers grains (DDG) and corn gluten meal. The DDG and gluten were used as RUP sources. We used 6 cannulated Nellore steers, rumen, duodenum, and ileum arranged in 6×6 Latin square designed in factorial (2 nitrogen levels and 3 protein sources) balanced for residues. The pH was measured immediately after rumen fluid sampling at 0, 2, 4, 6, 8 and 10h after feeding. The NH3-N concentrations were determined with micro-Kjeldahl apparatus. The concentration of volatile fatty acids (VFA) was assessed by gas chromatography. Data were evaluated using the MIXED procedure of SAS, with repeated measures over time. There was no interaction between sampling time and treatments for NH3-N and pH (P > 0.05). Animals fed diets containing Urea had a higher concentration of NH3-N (20.6 mg/dL) than animals supplemented with Gluten (16.2 mg/dL) or DDG (12.7 mg / dL). There was an increase in the NH3-N concentration (P = 0.049) with the increase of the protein level 10 to 13% CP with 14.7 and 18.3 mg/dL, respectively. The ruminal pH was affected by the dietary protein level (P = 0.016), in which animals fed a level of 10% CP had a higher pH (6.80) compared to the level of 13% CP (6.43). Total and individual VFA concentration was not affected by protein levels and sources (P > 0.05). The reduction of N level and the use of RUP did not adversely affect the ruminal fermentation. Although significant differences were observed for pH, they were small and adequate for microbial protein synthesis in the rumen.