Abstract
Four protozoa-free steers were given diets consisting of a concentrate mixture of flaked maize plus tapioca with either chaffed untreated barley straw (US) or chaffed ammonia treated barley straw (AS). The diets were supplemented with urea (USU; ASU) or urea plus fishmeal (USF; ASF). The diets were calculated to be isoenergetic and given in amounts calculated to provide sufficient metabolisable energy (ME) to support a growth rate of 0.5 kg day −1 in a 4 × 4 Latin square arrangement. Both diets were also calculated to be isonitrogenous with respect to rumen degradable protein (RDP). Chromic oxide and polyethylene glycol were given as digesta flow markers and ribonucleic acid (RNA) and 35S were used as microbial markers. Flows (g per 24 h) at the abomasum of nitrogenous constituents and carbohydrate components were determined. Rumen pH was consistently lower and rumen ammonia concentrations were higher with urea plus fishmeal supplemented diets (USF, ASF) than with urea supplemented diets (USU, ASU). No significant differences were observed in either parameter between treated and untreated straws, however supplemented. Non-ammonia nitrogen flows at the abomasum were significantly higher with fishmeal supplemented diets than with urea supplemented diets but there were no significant differences relating to straw treatment. Microbial nitrogen flows at the abomasum were not significantly different between diets and averaged 37 g day −1. Efficiencies of microbial protein synthesis were not significantly different between diets and averaged 23 g N kg −1 apparently digested organic matter (ADOM), 18 g N kg −1, truly digested organic matter (TDOM) and 24 g N kg −1 total carbohydrate fermented. Total feed nitrogen degradabilities between the mouth and abomasum were 0.84, 0.69, 0.85 and 0.68 for diets USU, USF, ASU and ASF, respectively. Nitrogen degradability values of the basal straw plus concentrate components were 0.53 and 0.57 for diets US and AS, respectively. Degradability of fishmeal nitrogen was 0.43 and 0.38 for diets US and AS, respectively. Digestibility coefficients for the main structural sugars arabinose, xylose and cellulose-glucose were 0.60, 0.53 and 0.59, respectively, for diet USU. The corresponding values for diet ASU of 0.71, 0.62 and 0.66 were all significantly ( P < 0.05) higher. Fishmeal supplementation significantly enhanced ( P < 0.05) the digestibilities of the structural sugars with both types of straw.
Published Version
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