Relationships Between Reproduction Traits, Age and Body Weight at Calving, and Days Dry in First Lactation Ayrshires and Holsteins

¹ Dairy Herd Analysis Service, Macdonald College of McGill University, 21,111 Lakeshore Road, Ste. Anne de Bellevue, PQ, Canada H9X 1C0 and Centre for Genetic Improvement of Livestock, Department of Animal and Poultry Science, University of Guelph, Guelph, ON, Canada N1G 2W1

Individual cow test day records collected between December 1979 and June 1986 were used to calculate measures of reproductive performance, age and weight at calving, and days dry for 7824 Ayrshire and 79,755 Holstein cows in first lactation. Separate analyses by breed were carried out according to a multiple-trail mixed model. Sixty-two Ayrshire and 369 Holstein sires were treated as random in the analyses. Ayrshires were, on average, older and lighter at calving than Holsteins, but the breeds differed little in reproduction measures and days dry. Heritabilities of fertility traits, days to first breeding, days open, and services per conception were all less than .015 in the multi-trait analyses. With the exception of body weight, heritability estimates for the other traits were less than .05. Phenotypic correlations between traits were almost identical for the two breeds, and genetic correlations tended to be similar. Exceptions involved the traits days to first breeding and services per conception, but heritabilities of these traits were close to zero (<.008) in Ayrshires. Fertility traits were positively correlated genetically. Genetic correlations between days open and both age and body weight at calving were small. The genetic correlation between age and weight at calving was –.90 and –.68 in Ayrshires and Holsteins, respectively. Genetic correlations between days dry and all traits except body weight were moderate and positive.

Key Words: reproduction • calving age • body weight

Submitted on April 26, 1989
Accepted on September 18, 1989