Effects of a source of ruminally degradable protein and monensin on starch digestion in steers fed a high-grain diet

• Main Author: Cerrillo Soto, Maria Andrea
• Format: Dissertation
• Language: English
• Published: ProQuest Dissertations & Theses 01-01-1998
• Subjects: Anatomy & physiology; Animal sciences; Animals; Livestock; Physiology
• ISBN: 059194975X; 9780591949759

A digestion trial was conducted to evaluate a source of readily degradable protein and the polyether ionophore monesin on the accumulation of peptides and starch digestion in steers fed a high concentrate diet. Four dietary treatments: (1) urea supplement (urea), (2) soybean meal supplement (SBM), (3) urea plus monensin (urea +), and (4) soybean meal plus monensin (SBM +) were compared in a Latin Square 4 x 4 experimental design using four crossbred steers (BW = 280 $\pm$ 34 kg). Feeding SBM (P $<$.001) or monensin (P $<$.05) increased the concentration of peptides in ruminal fluid. Feed consumption was not affected by source of supplemental N or monensin (P $>$.05). Monensin decreased apparent organic matter digestion in the rumen (P $<$.10). Ruminal digestibilities of NDF, ADF and starch were not affected by supplemental N or monensin (P $>$ 10). Ruminal starch digestion, however, tended to be decreased by monensin (P =.18). Total tract digestibilities of OM, NDF, ADF and starch were not affected by source of supplemental N or monensin (P $>$.10). Supplemental SBM increased the flow of undegraded feed-N (P $<$.10). Monensin did not affect the flow of undegraded feed N (P $>$.10). Microbial efficiency calculated as g bac N/kg OM digested in the rumen was not affected by treatments although a numerical increase (P =.15) was observed with monensin. Microbial efficiency calculated as 9 bac N/kg starch digested in the rumen was improved when steers were fed SBM (P $<$.10) whereas there was no effect from feeding monensin. No significant effects of monensin on the molar proportions of ruminal acetate were observed (P $>$.10). Monensin increased the molar proportions of ruminal propionate when steers were fed urea supplemented diets but not when fed SBM supplemented diets (protein by monensin interaction, P $<$.001). Neither source of dietary N nor monensin influenced ruminal NH$\sb3$-N concentrations. Results are interpreted to indicate that accumulation of peptides in rumen fluid did not increase starch digestion. This study found no evidence to support in vitro studies that have shown that non-structural carbohydrate fermenting bacteria benefit from peptides present in the medium.