INFLUENCE OF DEGRADABILITY OF SUPPLEMENTAL PROTEIN AND TIME POSTPARTUM IN EARLY LACTATION DAIRY-COWS .1. RUMEN FERMENTATION AND MILK-PRODUCTION

Eight ruminally cannulated lactating dairy cows were fed high or low concentrate totally mixed diets in two blocks of four cows. The forage source was a low quality (9.1% crude protein, 61% ND fibre) whole crop oat silage. Degradability of supplemental protein was varied within each block by substituting corn gluten meal, a slowly fermented protein, for canola meal, a rapidly fermented protein. Measurements were made in early lactation (Weeks 4-13 inclusive) to determine the effects of degradability of supplemental protein and time post-partum on feed intake, rumen fermentation, and milk production. Numerically higher dry matter intake for cows fed high vs. low concentrate diets failed to reach statistical significance and there was no effect of either degradability of supplemental protein or time post-partum. As expected, cows fed high concentrate diets had lower rumen pH and higher concentrations of most volatile fatty acids (VFAs). However, differences caused by dietary protein type or time post-partum were small within each concentrate level. Milk yield was higher for cows fed high concentrate diets; milk fat proportion was lower and milk lactose proportion higher. However, differences in milk yield and composition due to dietary protein type and time post-partum were small within each concentrate level. There were few significant interactions between concentrate level and protein type or time post-partum. Results demonstrate how little can be done to increase the intake of low quality forage by modifying the degradability characteristics of supplemental dietary protein.