Discipline: breeding; Keywords: breeding values, cow fitness, genetic improvement, heritability.
The aim of the paper by the authors cited below was to review the state of fertility of female dairy cattle in South Africa and to compare it with international efforts at improving fertility. Fertility in dairy cows is defined as the ability to conceive from first insemination soon after calving and to carry the calf full term to calving. Although it is one of the main profit drivers in the dairy enterprise, it is a complex trait that is influenced by the environment, genetics and their interaction, and therefore milk production, being the primary trait influencing profitability, has been the focal point of selection programmes. The low heritability of fertility traits is another factor that discouraged efforts to include fertility in genetic evaluations. Since most fertility traits are negatively correlated to milk production traits, there in general has been a decline in dairy cow fertility across breeds worldwide because of the intense selection for milk yield, milk components, and body conformation traits. Irrespective of the negatives mentioned, owing to its economic importance, female fertility has recently been included in the breeding objectives for dairy cattle in several countries.
International results show that the declining trend in fertility is being reversed by its inclusion in multi-trait selection indices, together with production and other functional traits. Fertility traits have reasonable additive genetic variation, which shows that improvements are possible through genetic selection, despite the low heritability estimates for individual traits. Several countries have constructed multi-trait selection indices to select for all traits of economic importance, including fertility. Also genomic selection provides a promising opportunity for accelerating genetic improvement of complex traits such as fertility and therefore several countries have implemented genomic selection and demonstrated its potential in accelerating the rate of genetic improvement and showed the cost benefits thereof. In South Africa, successful implementation of additional fertility traits in genetic improvement programmes will depend on whole-herd reporting and on cattle breeders optimising the use of technologies to improve the current state of female fertility.
Kgari, R.D., Muller, C.J.C., Dzama, K. & Makgahlela, M.L., 2020. Evaluation of female fertility in dairy cattle enterprises – A review. South African Journal of Animal Science 50, 819-829.