BREED AND NUTRITIONAL EFFECTS AND INTERACTIONS ON ENERGY-INTAKE, PRODUCTION AND EFFICIENCY OF NUTRIENT UTILIZATION IN YOUNG BULLS, HEIFERS AND LACTATING COWS

Red Danish (RD), Danish Friesian (DF), Danish Red and White (RW) and Danish Jersey (DJ) heifers had ad libitum access to total mixed rations designed to promote low (L), medium (M) or high (H) growth rate from 6 weeks of age to approximately the time of puberty. Heifers then were managed uniformly through 250 days of their first lactation. Paternal half-brothers of the heifers were tested from 6 weeks to 11 months of age on a high concentrate or on a roughage diet. For prepubertal feed intake, growth and efficiency of feed utilization of heifers, breed and rearing intensity effects were important, but breed x rearing intensity interactions were non-significant or inconsistent. Breed and rearing intensity effects were important but their interaction was not for precalving weight gain, calving weight, milk yield, and feed intake and efficiency during lactation. Females of the larger breeds ate more, grew more rapidly, were heavier and produced more energy corrected milk than Danish Jerseys; but breeds did not differ for efficiency of nutrient utilization during lactation or for post-partum weight change patterns. Increased prepubertal daily gains induced by higher-energy diets were associated with lower subsequent milk yield and reduced energy intake during lactation. The RD, DF and RW bulls ate more and grew more rapidly than DJ bulls. Daily energy intake and gain were higher for concentrate-fed than for roughage-fed bulls. Breed and dietary energy level did not interact significantly for these traits. In conclusion, there was little evidence that Danish dairy and dual-purpose cattle breeds differed in the sensitivity of their subsequent milk yield to excessive rates of gain during the rearing period or in response of young bulls to high concentrate versus roughage diets.