Feeding and Management Effects on Herd Differences in Milk Yield

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Abstract
Feeding and management data in 741 Illinois [USA] Holstein Dairy Herd Improvement herds were obtained by questionnaires. Feeding and management practices were associated with each other. Confounding of housing system with feeding system, of amount of grain fed in 1st lactation with that in 2nd lactation, and of roughage feeding system with grain feeding system was almost complete. Twenty factors plus interactions of amount of grain fed to lactating cows with sources of summer and winter roughage were studied. The factors affecting milk yield of herds were: source of summer roughage for lactating cows; interaction of source of summer roughage with grain fed to lactating cows yielding 11-23 kg milk/day; amount of grain fed to heifers between 12-18 mo. of age and during 2 mo. before calving; and ideal weight for breeding heifers. Herds accounted for 37% of total variance of milk yield. Herd variance of milk yield was reduced by 24% by considering the 20 factors plus interactions with 102 degrees of freedom. Factors and interactions significant at .10 or .05 with 40 degrees of freedom reduced the herd variance by 12%. Other feeding and management practices may explain the large portion of herd variance in milk yield that remains unaccounted for.