Influence of yucca extract on ruminal metabolism in cows.

Two trials were conducted to determine the influence of yucca extract on ruminal digestion, fermentation, and ammonia patterns using ruminally and duodenally cannulated dairy cows. In Trial 1, urea at 0 or 1% of the diet and yucca extract at 0 or 4 g/d formed four dietary treatments in a 2 x 2 factorial arrangement. The experimental design was a 4 x 4 Latin square with 15-d periods. Duodenal digesta were sampled every 6 h during the last 4 d of each period to determine OM and ADF digestibilities and bacterial protein synthesis in the rumen using Cr2O3 and 15N markers. Ruminal digestibilities were (percentage): OM 46.3 vs 43.0%, and ADF 35.9 vs 41.4%, with or without Deodorase. Microbial protein entering the duodenum averaged 2.7 vs 3.1 kg/d for the respective treatments. Ruminal measurements were not affected by treatment (P > .10). In Trial 2, five cows were used in a 5 x 5 Latin square with 7-d periods. Treatments were 0, 2, 4, 6, and 8 g/d of yucca extract administered via ruminal cannulas. Ruminal fluid was sampled 0, 1, 2, 4, 7, 11, 16, and 22 h after feeding during the last 2 d of each period. Average ruminal NH3 N ranged from 31.4 to 35.4 mg/dL, pH 5.99 to 6.18, and total VFA from 120 to 129 mM, and all did not differ among treatments (P > .10). Yucca extract administered at 4 g/d did not significantly affect ruminal digestibilities of OM and ADF, and up to 8 g/d did not affect ruminal NH3, pH, or VFA.

Influence of microbial colonization of feed particles on determination of nitrogen degradability by in situ incubation.

Stable 15N isotope was used to determine the extent of microbial colonization of in situ incubation residues and the influence of colonization on estimates of ruminal degradability of feed N. In an in vitro trial, 15N:total N ratio remained unchanged after the soluble (by water, saline, or buffer solution) fraction of plant N was removed, suggesting that 15N was uniformly distributed in the soluble and insoluble N fractions. In three in situ trials, corn grain, corn husks, and alfalfa hay labeled with 15N as an internal marker were incubated in Dacron bags in the rumen of two lactating Holstein cows for 3, 6, 12, 24, 36, and 48 h. Enrichment of 15N in samples decreased with increased time of incubation for all feeds. At 48 h of incubation, 31, 71, and 65% of the residual N was microbial N for corn grain, corn husks, and alfalfa hay, respectively. Bacterial cell DM, as a percentage of residual DM, increased in a quartic manner, suggesting that microbial colonization depended on substrate availability. For 24, 36, and 48 h incubation, bacterial DM, as a percentage of total residue, averaged 10.0 +/- 1.0% for corn grain, 17.5 +/- 1.4% for corn husks, and 22.0 +/- .2% for alfalfa hay. Apparent degradability of N after 48 h of incubation was approximately 65% for corn grain and alfalfa hay and 19% for corn husks. When corrected for bacterial N, degradabilities of N in all feeds increased and the degradabilities for corn husks became similar to those for corn grain.(ABSTRACT TRUNCATED AT 250 WORDS)