Test-day models for South African dairy cattle for participation in international evaluations

Abstract

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 and fitting the permanent environmental effect across lactations. Multitrait evaluations were done for the production traits (milk, butterfat and protein) and single trait evaluations for somatic cell score. Heritability estimates were comparable with yield and somatic cell score estimates obtained by test-day models from other countries (17-24% for milk yield; 10-13% for butterfat yield; 14-19% for protein yield and 6-8% for somatic cell score). Proofs of qualifying sires were sent to the International Bull Evaluation Service (INTERBULL) for participation in the March 2005 test runs. Genetic correlations between South Africa and other participating countries, estimated by INTERBULL, compared well with those amongst the other participating countries. Trend validation tests were successful using this methodology for all traits and breeds except for somatic cell score of the Guernsey breed, due to insufficient data for this trait. South Africa can now participate in routine INTERBULL evaluations to obtain Multiple Across Country Evaluation (MACE) breeding values, using this methodology.

Environmental factors influencing milk urea nitrogen in South African Holstein cattle

“…In Table 1 descriptive statistics for the original data set are presented. Age restrictions at calving, definition of seasons, yield limits and MUN concentration ranges were in accordance with data editing as performed in the South African Best Linear Unbiased Predictions (BLUP) analyses (Mostert et al, 2006). To ensure reasonable calving down ages in specific lactations, restrictions on age at calving were imposed, i.e.…”

“…To ensure reasonable calving down ages in specific lactations, restrictions on age at calving were imposed, i.e. between 20 and 42, 30 and 54, and 40 and 66 months for the first, second, and third lactation, respectively (Mostert et al, 2006). Seasons of calving were defined as summer (October -March) and winter (April -September).…”

Genetic analysis of somatic cell score and udder type traits in South African Holstein cows

“…These trends may be a correlated response to intense selection for increased milk yield, which has remarkably increased genetic merit for milk yield in the past two decades Mostert et al, 2006b). Intense selection for milk yield causes an unfavourable response in udder health (Castillo-Juarez et al, 2002;Hansen et al, 2002;Koivula et al, 2005).…”

An analysis of the genetic relationship between udder health and udder conformation traits in South African Jersey cows

“…In South Africa, selection in Jersey cattle has been mostly on milk yield, which has resulted in a considerable increase in genetic merit for milk production, over the past two decades 2006b). Selection on milk production has been observed to have an adverse effect on udder health (Castillo-Juarez et al, 2002;Hansen et al, 2002;Koivula et al, 2005).…”