Discipline: management; Keywords: age at first calving, lifetime efficiency, productive life, selection, genetic parameters.
Longevity in dairy cows is an important trait affecting the genetic progress, lifetime (birth to cull) performance and lifetime efficiency. An early age at first calving increases productive life (total number of days in milk) while also reducing rearing costs, and financial sustainability of a dairy herd. However, calving problems may increase when age at first calving is too early. For this reason most farmers rear heifers to reach first calving at an older age although not necessarily at a higher live weight. This increases the overall rearing costs because of a longer feeding period. High growth rates and longer feeding period may result in over-conditioned heifers which could result in dystocia. Age at first calving is therefore a benchmark that should be properly managed to increase economic returns. Limited research has been conducted in South Africa on the effect of age at first calving on lifetime performance. In a study by the authors cited below, preliminary estimates of the productive life, lifetime, productive lifetime efficiency, and lifetime efficiency for Holstein cows in South Africa as affected by age at first calving were calculated.
Lifetime production records of 509 715 cows born between 1989 and 2008 which had calved down at least once, were included in the study. Cows calving down earlier than 18 months and later than 48 months of age were removed from the data set. For each cow, the total milk, fat and protein yield, days in milk (productive life) and lifetime of cows were determined. From this, the productive lifetime efficiency and lifetime efficiency of milk yield for each cow were estimated.
The results showed that whereas lifetime increased with a later age at first calving, productive life decreased especially after 29 months of age. An earlier age at first calving resulted in higher lifetime production. Milk production lifetime efficiency and lifetime efficiency increased to 25 months of age after which both traits decreased. Genetic parameters should be estimated for age at first calving, lifetime, productive life, lifetime production, productive lifetime efficiency and lifetime efficiency measures to determine their relative emphasis in selection. Further analyses using alternative statistical methods, which include pedigree or genotype information, may offer additional parameters for selection in a breeding programme with these objectives.
C.J.C. Muller, H.L. de Waal & M.M. Scholtz, 2018 (?). PRELIMINARY ESTIMATES OF PRODUCTIVE LIFETIME AND LIFETIME EFFICIENCY IN HOLSTEIN COWS AS AFFECTED BY AGE AT FIRST CALVING. Proc. Assoc. Advmt. Anim. Breed. Genet. 22, 497-500