Influence of wet vs. dry by-product ingredients and addition of branched-chain volatile fatty acids and valerate to dairy diets. 3. Kinetics of rumen ingesta turnover, whole tract digestibility, and some plasma hormone concentrations.

Abstract

Four cows with rumen cannulae were fed twice daily on totally mixed diets containing equal amounts of hay crop silage and maize silage plus a mixture of maize gluten feed, beet pulp and brewers' grains. Diets contained wet ensiled (WET) or dry (DRY) byproduct ingredients without (MINUS) or with (PLUS) a supplement (ISOPLUSReg.) containing the branched-chain volatile fatty acids (isoacids) isobutyrate, 2-methyl butyrate, and 3-methyl butyrate, as well as valerate. Measurements were made from weeks 12 to 28 of lactation to determine effects of treatments on whole tract digestibility, kinetics of rumen ingesta turnover, and plasma concentrations of insulin and somatotropin. Whole tract apparent digestibility of organic (OM) and most OM components was higher with WET diets. Estimated true digestion of dietary nitrogen and OM were also higher (P<0.05) with WET diets but differences were small. Whole tract digestibility of OM components was not influenced by supplementation with ISOPLUS. Rumen bacterial OM pool was larger (P<0.05) and rumen bacterial N pool was larger (P<0.10) with DRY diets but this did not increase the rate of rumen digestion of neutral detergent fibre. Rumen pool sizes of N and OM components, rate of rumen digestion, passage of neutral detergent fibre and plasma concentrations of insulin and somatotropin were unaffected by the addition of ISOPLUS or diet form. (Abstract retrieved from CAB Abstracts by CABI’s permission)