A selection project produced control cows from continuous matings with breed average bulls for predicted transmitting ability for milk (PTA-milk) in 1964 and select cows from matings to four of the highest PTA- milk bulls each year since 1964. Blood samples were collected in 1992 when milk yield difference of select and control line cows exceeded 3,800 kg of milk/305- day lactation. Genomic DNA from control (n = 49) and select in = 101) cows was analyzed for the presence of variants associated with amino acid position 127 (leucine, AluI[+]; valine, AluI[-]) of bovine somatotropin (bST). Amplification of a 428 base pair fragment of the bST gene from individual cows, subsequent restriction enzyme (AluI) digestion, and separation of resulting fragments indicated three genotypes AluI(+/+), AluI(+/-), and AluI(-/-) in 110, 39, and 1 animal(s), respectively. Gene frequencies of leucine127 and valine127 alleles were similar for control (0.867, 0.133) and select (0.861, 0.139) animals. United States Department of Agriculture-PTA values were compared between the two genotypes, AluI(+/+) and AluI(+/-). Estimated breeding value for milk (EBV- milk) and average yield deviation for milk (AYD-milk) were not associated with genotype for control animals. However, presence of the valine allele was correlated with decreased EBV milk (P = 0.03) and AYD-milk (P = 0.16) in select animals and accounted for a decrease of approximately 170 kg of EBV- milk and 240 kg of AYD milk.
Bibliographical noteFunding Information:
Published as paper No. 22,279 of the scientific journal series of the Minnesota Agricultural Experiment Station on research conducted under project No. 16-045 supported by the College of Agriculture. The authors thank the Dairy Research Initiative Program of the Department of Animal Science and College of Veterinary Medicine for financial support. We also thank Dr. Charles Young for initiating the dairy cow breeding project in 1964 and the dairy staff at the University of Minnesota, Southern Experiment Station for care of the animals used in this study. * Address all correspondence to: B.A. Crooker, 130 Haecker Hall, Department of Animal Science, University of Minnesota, 1364 Eckles Ave., St. Paul, MN 55108, Tel. 612-625-3185, Fax 612-625-1283, E-mail crook001 @maroon.tc.umn.edu.