OPTIMAL GENETIC-IMPROVEMENT FOR THE HIGH PRODUCING HERD

Genetic merit for milk production is increasing over 150 kg of milk/yr in the Holstein cow population. Nationwide decreases in payments for fat differential since 1987 have not been counter-balanced by similar increases in payments for protein differential, resulting in a steady increase in the value of carrier. Protein yield should be emphasized r ather than specific casein or whey fractions of protein because nation al recording, evaluation, and payment structures are not in place. Gen etic merit of bulls for markers may differ across families, making sel ection for marker traits of limited value in current breeding schemes. Conformation traits that appear to have the highest correlation with measures of herd life are udder depth, fore udder attachment, and teat placement. Selection for health traits is difficult because of limite d genetic information. National evaluations for SCC are being develope d, but average difference between extreme bulls is only slightly more than one linear SCC. Managers of high producing herds should continue with primary selection emphasis on production traits. The greatest cha llenge to dairy producers is to develop management systems, particular ly in nutrition, that allow maximal expression of genetic potential.