Genomic regulation of oestrous behaviour in dairy cows

Intensive selection for high milk yield in dairy cows has raised production levels substantially but at the cost of reduced fertility. This problem manifests itself in different ways, including reduced expression of oestrous behaviour. To identify the genes responsible for the regulation of oestrous behaviour, the Animal Breeding and Genomics Centre (ABGC) at Lelystad conducted an experiment with 28 primiparous Holstein Friesian cows. Gene expression in each brain area per cow was measured in a microarray experiment using 24K bovine oligonucleotide microarrays produced by the Bovine Oligonucleotide Microarray Consortium (BOMC), USA.

For each cow an average heat score value was calculated based on the oestrous signs observed during the oestrus of previous cycles. Tissue samples were collected from five different brain areas of 14 cows at the start of oestrus (day 0) and 14 cows at mid-cycle (day 12).

Our aim was to identify those genes that were associated with oestrous behaviour among genes expressed in the bovine anterior pituitary, either at the start of the oestrous cycle, at mid-cycle or regardless of the phase of the cycle. To do so, gene expression was modelled as a function of the average heat score values using a Bayesian hierarchical mixed model on data from day 0 cows alone, day 12 cows alone, and the combined data from day 0 and day 12 cows.

Genes whose expression patterns showed significant linear or non-linear relationships with average heat scores could be identified in all 3 analyses (177, 142, and 118 genes respectively). Gene ontology terms enriched among genes identified in data from day 0 cows revealed a number of clear processes associated with expression of oestrous behaviour. In contrast, the gene ontology terms enriched among genes identified in the other two analyses were general processes, not specifically linked to behaviour. The results of this study have been submitted for publication.

In future studies, similar analyses will be done on other brain areas already sampled in this experiment and the results integrated to get an overall view of the gene expression patterns in brain areas associated with heat scores. Studying these genes will help to improve our understanding of the genomic regulation of oestrous behaviour, ultimately leading to better management strategies and tools to improve or monitor reproductive performance in bovines. This study is financed by the EU.