The effects of alfalfa hay fiber and vitamin B₁₂ levels in body fluids on milk fat production in high-producing dairy cows Public Deposited

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  • The research presented in this thesis was designed to evaluate the effects of feeding alfalfa hays from the Klamath Basin of Oregon in practical dairy rations on milk fat production in high-producing Holstein cows. Thirty-two second lactation or older animals estimated to be capable of producing at least 70 lbs of milk daily were utilized in a 4 X 4 latin square experiment with eight replications. Four rations based upon four different lots of hay, ranging from 15.2 to 22.0% crude protein (CP), from 29.9 to 35.1% acid detergent fiber (ADF) and from 109 to 132 in Relative Feed Value, were fed during four periods, each lasting about 28 days. Rations were formulated to be comparable in caloric and nitrogen content, and all consisted (as a percent of ration dry matter) of 50% concentrate, 30% chopped alfalfa and 20% corn silage, fed as a mixed, complete ration. A digestibility study was also carried out involving four steers fed the four alfalfa hays only. The digestibility trial showed that there were no significant differences among the four alfalfa hays in feed intake, % digestible dry matter, % digestible ADF and % digestible CP. In the production trial, no differences were seen in feed intake or persistency, and body weight changes were significantly different only for periods. Both daily 4% fat-corrected milk (FCM) and milk fat percentage were observed to have highly significant differences for all sources of variation except treatments. Treatment means for rations 1 through 4 for 4% FCM were 48.88, 48.02, 48.38 and 48.24 lbs, respectively, and those for percent milk fat were 3.13, 3.12, 3.05 and 3.01, respectively. Differences in other sources of variation for these two measurements were attributed to variation among cows and stage of lactation effects. Important changes were noted in the relative proportions of volatile fatty acids in the rumen. While there were no significant changes in rumen acetate concentration, highly significant differences in propionate content were seen for all sources of variation. Treatment means for rations 1 to 4 were 18.14, 17.56, 19.44 and 23.03 pmoles /ml of rumen fluid. This response was reflected also in highly significant differences in ruminal acetate:propionate (A:P) ratios. Means here for rations 1 through It were 2.82, 3.00, 2.36 and 2.23, respectively. Correlation coefficients were determined for A:P ratios and several hay and ration characteristics, and only that with hay % NDF was significant. It was concluded that changes in rumen fermentation typical of milk fat depression occurred which were not severe enough to actually reduce butterfat levels. The literature indicates that there may be a relationship between milk fat synthesis and tissue vitamin B₁₂ status, i.e., that B₁₂- deficient animals will secrete milk with reduced fat percentage. In this experiment, serum vitamin B₁₂ levels did not respond significantly to treatments, nor did fat percentage, the correlation between them was very low, and there was no indication of vitamin B₁₂ deficiency among experimental animals. Our results, therefore, are interpreted as not being in conflict with the hypothesized relationship.
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