Intestinal flow of microbial protein and rumen undegradable protein in cattle fed corn distillers grains and solubles, with emphasis during lactation

Metabolizable protein (MP) is the true protein absorbed by the intestine, supplied by rumen undegradable protein (RUP) and microbial crude protein (MCP). This research was focused on evaluating the effect of dried distillers grains with solubles (DDGS) on the nature and supply of MP, with emphasis during lactation.;Experiment 1 evaluated the use of DNA markers and the effects of fermentation time and DDGS on rumen microbial growth in vitro. Treatments were 1) CONTROL, 0% DDGS; 2) 20% DDGS replacing corn; 3) 20% DDGS replacing soybean meal and 4) 20% DDGS replacing corn and soybean meal. Results indicate that microbial growth reached peak at 32 h. In addition, DDGS improves or maintains rumen microbial growth.;Experiment 2 determined the RUP of DDGS and its effect on duodenal flow of MCP. Three steers fitted with ruminal and duodenal cannulae were used in a 3 treatment, 6 period cross-over design. Diets were 1) CONTROL, 0% DDGS; 2) 10% DDGS and 3) 20% DDGS. The value of DDGS RUP as a percent of CP was determined to be 63.0 +/- 0.64%. Results indicate that DDGS is a good source of RUP, but contrasting our expectations tended to decrease duodenal MCP flow.;Experiment 3 evaluated the effect of increasing levels of reduced-fat DDGS (RFDG) on lactation and duodenal microbial N flow. Sixteen Holstein cows, 4 of which fitted with ruminal and duodenal cannulae were used in a 4x4 Latin square design. Treatments were 1) CONTROL, a diet containing 0% RFDG; 2) 10% RFDG 3) 20% RFDG; and 4) 30% RFDG. Milk yield was not affected; percent of milk protein tended to increase; but percent of milk fat was not affected by treatment. In addition, duodenal microbial N flow was not affected. Overall, rations of dairy cattle can include up to 30% RFDG without negatively affecting lactation performance and rumen microbial growth.