Factors Affecting Efficiency of Ruminal Bacterial Growth and Site of Nutrient Digestion in Cattle

151 p.Thesis (Ph.D.)--University of Illinois at Urbana-Champaign, 1987.Three experiments with factorial designs were performed using multiple-cannulated steers to study dietary factors affecting efficiency of ruminal bacterial growth (E) and site of nutrient digestion.In the first experiment, greater surface area of ground hay, with no change in ruminal dilution rate (D), allowed greater amounts of organic matter (OM) and neutral detergent fiber (NDF) to be digested in the rumen than when chopped hay was fed. Apparent ruminal escape of nitrogen (N) and amino acids was lower for steers fed dry corn gluten feed (DCGF) than for those fed dry distillers grains (DDG). Ruminal NDF digestibilities were lower for steers fed at 90% (high intake (HI)) than at 60% (low intake (LI)) of ad libitum. Fluid and particulate D were positively correlated to E.In the second experiment, fluid D was greater when steers were fed at HI than at LI, probably resulting in faster passage of small particles and lower ruminal digestibilities of OM and NDF. Apparent ruminal N escape was not affected by intake but was lower for DCFG vs DDG. When steers were fed at HI vs LI, E was greater, probably due to faster D decreasing the proportion of maintenance: total energy expenditure by bacteria.In experiment three, rates of $\sp $N turnover in ammonia, non-ammonia-N (NAN) and fluid- and particulate-associated bacteria (FAB and PAB) were not affected by intake but were all faster when steers were infused intra-ruminally with urea at 1.2% (high urea (HU)) than at.4% (low urea (LU)) of the diet. Steers fed at HI vs LI has faster fluid and particulate D and decreased apparent ruminal and total-tract digestibilities of OM and NDF. Using $\sp $N resulted in higher duodenal flows of bacterial N and higher E than did using purines. Intake level did not affect E, perhaps because intra-ruminal N recycling was greater for HI vs LI. It was estimated that bacterial and protozoal N comprised 39 and 27% of duodenal NAN, respectively. Microbial $\sp $N was less digestible in the small intestine than was escaped dietary N.U of I OnlyRestricted to the U of I community idenfinitely during batch ingest of legacy ETD