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Genetic Change in Minnesota Holstein Herds^{1 ,2,}

Department of Animal Science, University of Minnesota, St. Paul 55108

ABSTRACT

First-lactation records of 52,894 Holstein cows in 713 Minnesota herds on Dairy Herd Improvement for 7 yr or more were analyzed to estimate genetic trends in herd averages and to identify breeding practices that enhance herd improvement. Mean predicted difference milk among herds was –3 kg and mean cow selection differential +118 kg. Annual trends in milk yield as measured by mature equivalent, predicted difference, and selection differential were 117, 20, and 1 kg. Genetic change in herds was estimated by the negative of two times the pooled intrasire regression of daughter contemporary deviation on time. The mean for genetic trend was 60 ± 30 kg milk. Production averages and production trends for herds were influenced positively by predicted difference and selection differential, predicted difference being the more important of the two. Because of large sampling variances, little of the variation in estimates of genetic change in herds was accounted for. There was a tendency for estimates of genetic change to vary inversely with average predicted difference and directly with the trend in predicted difference.

¹ Scientific Journal Series Paper No. 9083, Minnesota Agricultural Experiment Station, St. Paul.

² A contribution to regional project NC-2.

³ West Central Experiment Station, University of Minnesota, Morris 56267.