Breed differences in ruminal digestibility of forages in dairy cows receiving high concentrate diets

[摘要] ENGLISH ABSTRACT:Statistical analysis was conducted on data from two Elsenburg herds, containing 105 Jerseyand 232 Holstein cows. The data was examined for external factors which may affect milkyield and milk composition. The data consisted of 337 first lactation records, taken over a 20year time period. Breed of cow had an effect on milk yield, butterfat and protein production,as did the year in which the cows were born and the age of the heifer at first calving. Therewas a significant interaction between the breed and year of birth. There are other externalfactors, which are difficult to quantify, which may have an effect on production. In thefollowing trials, eight ruminally cannulated dairy cows (four Jerseys and four Holsteins) wereused to determine the effect of breed on forage digestibility in the rumen. All cows received ahigh concentrate mixed ration, with supplementary wheat straw. An in situ rumendegradability trial was conducted with three different forages, viz. lucerne, wheat straw andNaOH-treated wheat straw. The bags were incubated in the rumen for time intervals of 2,4,8, 12, 16,20,24, 36,48, 72 and 96 hours and samples were analysed for dry matter (DM) andneutral-detergent fibre (NDF). Higher rumen degradability values (P<0.01) ofDM and NDFwere observed in Jerseys for all three forages. Differences were more apparent for wheatstraw and treated wheat straw than for lucerne. The rate of passage of digesta from the rumenwas measured in both breeds by a chromium mordanted wheat straw marker. The Holsteinsmanifested a higher rate of passage (P<0.05) than the Jerseys, while daily feed intakes werealso higher (P

[发布机构] Stellenbosch University