Calving interval (CI) is a fertility trait that can be used in selection programmes to minimize the negative effects that selection for production have on fertility. CI can be derived from milk recording data, therefore this fertility trait can easily…
Variance components and breeding values of production traits and somatic cell score of South African Guernsey, Ayrshire, Holstein and Jersey breeds have been estimated using a multi-lactation repeatability test-day model, including tests of the first three lactations as repeated measures…
A comparison of breeding values and genetic trends of production traits from two models is made. One set of breeding values and trends was estimated by the September/October 2003 South African National Genetic Evaluation, using a Lactation Model (LM). The…
Procedures have been developed for calculation of a Persistency Index for South African dairy breeds. This index is based on the Canadian Persistency Index, which is simple and easy to understand. Data used in this study were test-day records of…
Estimated breeding values and genetic trends were obtained in Ayrshire cattle by using DFREML procedures for 9 050 first lactation records calving down from 1977 to 1992. Environmental trends were calculated as the difference between the phenotypic and genetic values.…
For the estimation of additive and error variances and resulting heritability estimates 9 050 first and 5 541 second lactation records were used. Analyses were conducted using DFREML procedures. The heritabilities for first (and second) lactation for milk, fat and…
