FEED EFFICIENCY OF DAIRY COWS DURING FIRST LACTATION

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Abstract
Feed efficiency was examined from approximately 3200 records of feed intake, milk yield, weight and weight change during the second eight weeks of first lactation on Holstein (H line), Ayrshire based (A line) and crossbred (C line) cattle. Herd, year-season and age at first calving with either genetic line or original breed source additive, heterotic and maternal effects were included in models. Heterotic and maternal effects on milk yield, TDN consumption and feed efficiency were generally unimportant when initial weight, weight change and milk yield or TDN covariates were considered. Line (A, H and C) and breed source additive effects within line were generally significant (P < 0.05). Efficiency was highly correlated phenotypically (0.64) with milk yield but only mildly correlated with measures of feed intake (0.13, 0.38). The negative correlation of efficiency with initial weight (−0.13) and weight change during the trial (−0.15) indicated that the larger animals or animals which gained more weight use a higher proportion of feed energy for maintenance requirements and growth than lighter animals. The strong correlations (0.63, 0.81) between milk yield and consumption arose in part from feeding concentrates according to milk production and made appropriate analyses difficult. Adjusted for covariates, Canadian (CH) and American (USH) Holsteins were the highest producers followed by Norwegian Red (NR), Agriculture Canada Holsteins (ACH), Ayrshires and Brown Swiss. North American Ayrshires (NAA) consumed the least TDN, adjusted for covariates, with Holsteins intermediate and Brown Swiss highest. In general, Ayrshires were more efficient than Holsteins. Feed efficiencies of NAA, Finnish Ayrshire and NR were superior to those of ACH with other genetic groups intermediate. Key words: Genetic, feed efficiency, lactation, cattle

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