Some physical aspects of digestion of forages by steers : and binding of ytterbium and hafnium as digesta particle markers

Abstract

Ingestive and ruminative chewing, meal and dorsal rumen contractions were measured in yearling beef steers offered foraged diets based on either Coastal bermudagrass [Cynodon dactylon (L.) Pers] or sorghum X sudan [Sorghum bicolor (L.) Moensch] hays. Diets were supplemented with soybean meal [Glycine max] and/or 3% ammonia. Responses were collected and analyzed by computer programs. Chewing attributes were collected and analyzed as either eating chews or ruminating chews. Criteria for ruminating chews were set forth as 10 to 80 chews at a frequency of >1 chew/2 s, with an intercycle time of 4 to 10 s. Eating chews were the total number of jaw movements-rumination chews. Contraction of the dorsal rumen were measured as deviations in pressure from a baseline established between a balloon located in the dorsal sac of the rumen and external atmospheric pressure. A second series of experiments were conducted to test the binding of ytterbium and hafnium to forage particles and resistance to displacement by protons at a low pH as might be observed in portions of the gastrointestinal tract. Low levels of binding and resistance to proton displacement were observed for ytterbium. In contrast, binding and resistance of hafnium was higher and resistance to proton displacement was greater than observed for ytterbium. Results of these experiments indicate that hafnium is an excellent candidate as a digest particle marker. Ytterbium, on the other hand, may have limited possibilities.