GENOTYPE BY ENVIRONMENT INTERACTION IN SOUTH AFRICAN HOLSTEIN CATTLE IN REPRODUCTION AND PRODUCTION TRAITS

Genotype by environment interaction in dairy cattle is a contentious issue that is usually ignored in genetic evaluations. It can, however, play a significant role in the accuracy of breeding values in different environments with a negative impact on genetic response. In South Africa we have two main production environments. The majority of cows in milk recording are kept under a total mixed ration (TMR) system, and there are also a significant number of herds on pasture-based systems. Currently, many bulls are used in both systems without consideration of a possible change of rank between systems, if a genotype by environment interaction happens to occur. The purpose of the study was therefore to investigate a possible genotype by environment interaction in first calf South African Holstein cows for both production and reproduction traits.

Data from 100 975 cows on TMR and 22 083 cows on pasture were included in the study. The cows were the progeny of 4 391 sires and 84 935 dams produced over a period of 11 generations. Traits analysed were milk production (corrected to a 305-day equivalent) and age at first calving. Both were recorded over a period of 30 years from 1980 to 2010. Production or age at first calving in each environment (TMR vs. pasture) was treated as a separate trait and analysed through model development.

The genetic correlation for milk production measured in the two different environments was 0.90 and that of age at first calving 0.28. The heritability estimate for milk production was 0.23 on average for the TMR system and 0.32 for the pasture-based system, whereas the estimates for age at first calving were 0.063 and 0.055 respectively, illustrating the comparatively high heritability of production traits normally recorded and the low heritability of reproduction traits. However, the rather large-scale effect in the heritability (0.23 to 0.32) of milk production from TMR to pasture-based system, as well as the correlation of less than one for milk production between the two environments, suggests a possibility of a genotype by environment interaction. For age at first calving, the low genetic correlation (0.28) between the two environments is real and indicates that genotype by environment interaction should be taken into account when sires are selected. This implies that farmers should rather use bulls that were selected from production systems they themselves employ.

Reference:

F.W.C. Neser, J.B. van Wyk& V. Ducrocq, 2014. A preliminary investigation into genotype x environment interaction in South African Holstein cattle for reproduction and production traits. S. Afri. J. Anim. Sci., 44 (Issue 5, Suppl. 1) , S75-S79.