Duodenal Bacterial and Nonbacterial Protein Supply in Steers Fed Forage and Grain Diets

Abstract

Four beef steers (avg wt 300 kg) fitted with duodenal re-entrant cannulae were used to study the effect of dietary concentrate to forage ratio on bacterial and nonbacterial N flow in the duodenum. According to a change-over design, the steers were designated to receive an all forage (83% alfalfa hay and 17% wheat straw) and an 80% sorghum grain diet. Lignin (ADL) and chromium oxide (Cr2O3) ratio techniques were compared with automated total collection (ATC) of digesta for quantitating duodenal protein flow and efficiency of bacterial N yield in the rumen. Estimates of bacterial protein synthesis and ruminal escape of feed protein based on Cr2O3 and lignin tended to be higher by 8 to 16% than those obtained by ATC. Efficiency of ruminal bacterial protein yield estimated by these two markers tended to be greater than that based on ATC (16 vs 12 g of bacterial protein/100 g ruminal true digestion of dry matter corrected for bacterial cell synthesis). Efficiency values did not differ between diets. Crude protein flow into the duodenum was about 33% greater (P less than .01) for the grain than the forage diet, although protein intake was about 10% less on the grain diet. Duodenal bacterial protein, rather than feed protein escaping ruminal degradation, accounted for most of this difference. Average duodenal flow of N, expressed as g/Mcal metabolizable energy (ME) intake, was 11.9 for the forage diet and 10.3 for the grain diet.(ABSTRACT TRUNCATED AT 250 WORDS)

Steam-processed corn and sorghum grain flaked at different densities alter ruminal, small intestinal, and total tract digestibility of starch by steers.

“…These numerical increases agree with data summarized by Theurer et al (1996Theurer et al ( , 1999a that showed a 10% average increase in MN flow by beef cattle fed diets greater in ruminally degradable starch and by dairy cows fed SFS compared to DRS diets. Our mean values for MN flow for SFS vs DRS (87 vs 80 g/d; Table 3) are similar to those reported by Spicer et al (1986;81 g/d) for DRS, somewhat lower than those reported by Rahnema et al (1987; 100 and 90 g/d for SFS and DRS, respectively), and substantially higher than those reported (∼ 53 g/d) by Wanderley et al (1987) for SFS and Streeter et al (1990) for DRS. Microbial N as a percentage of total N in duodenal digesta was 46 and 50% for DR and SF diets, respectively.…”

Rumen fermentation, microbial protein synthesis, and nutrient flow to the omasum in cattle offered corn silage, grass silage, or whole-crop wheat1

“…This suggests recycling of N either across the rumen wall or through salivary secretion (Siddons et al, 1985a). These findings are consistent with results for high-grain diets (Wanderley et al, 1987;Al-Dehneh et al, 1997). Al-Dehneh et al (1997) reported that endogenous urea accounted for 0.191 and 0.074 of N in duodenal digesta for lactating cows fed high-grain and high-forage diets, respectively.…”

Predicting the metabolizable energy intake of ruminants using digestibility, ruminal methane production and fermentation data

“…While there have been few studies on the contributions of mammalian digestion and fermentation to whole tract digestion (Ørskov et al 1968), assessments of variance in the proportions of the diet disappearing from the forestomachs relative to the intestines (small and large) abound. Results of these studies are summarized in Table 3, but more exhaustive reviews focusing on starch and protein digestion have been prepared by Merchen et al (1997) and Wanderley et al (1987). Importantly, the CV across studies is of the order of 0·10 (Table 3), indicating that an assumption of a constant partitioning between forestomach and intestinal digestion is inappropriate in seeking to develop accurate estimates of MEI for individual animals.…”