Genotype by environment interaction (G×E) is one of the issues the dairy farming industry faces due to the globalization of using artificial insemination with genetically superior bulls to improve the performance of their herds. This includes distribution of genetic material to multiple environments within countries and between countries. The major concern is that animal rank may change across the environments which mean that the best animals in one environment are not the best in another environment. In this thesis, the genetic variation and G×E effect on fertility traits was investigated in Nordic cattle. Two types of fertility traits were studied: 

·         Automatically recorded fertility traits based on the physical activity measuring devices and,

·         Traditional fertility traits based on the AI recording.

The study includes activity measuring such as “interval for calving to first high activity (CFHA)”, “duration of high activity as an indicator of oestrus duration (DHA)” and “strength of high activity as an indicator of oestrus strength (SHA)”. The activity measuring was based on cows in commercial herds and these were compared to the traditional goal of “interval between calving and first insemination (CFI)”.

Selection criteria for reproductive performance may be improved

It was demonstrated that CFHA displays a higher heritability estimate than CFI, and that there is a very strong genetic correlation between the two traits. Consequently, the selection criteria for fertility may be improved by including “time from calving to first high activity”, because it reflects the ability of the cow to return to reproductive cycling and heat after calving.

The PhD study also focused on seasonality of estrus activity traits with respect to the month of calving. It was found that the CFHA period was shorter during the summer calving season compared to the winter, spring or fall seasons. Further, there was a genetic correlation between CFHA and “energy-corrected milk yield 70 days after calving (ECM 70)” wasn’t constant over the production environment. This correlation decreased as production environments increased, and this means that the adverse genetic correlation between fertility and milk yield is weakest in the best production environments. The effect of geographical location in Scandinavia was of minor importance.

The obtained results are useful for improving genetic evaluations of Holstein cow fertility using data from a wide range of geographic locations and seasons.

The PhD study is accomplished at Center for Quantitative Genetics and Genomics, Department of Molecular Biology and Genetics, Aarhus University and Department of Animal Breeding and Genetics, Swedish University of Agricultural Sciences, Uppsala, Sweden.

Download the complete PhD thesis here.

Further information:

Ahmed Ismael, Department of Molecular Biology and Genetics, Aarhus University
E-mail: ahmed.ismael@mbg.au.dk