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Understanding the genetic basis of fertility and semen quality in bulls

10 July 2020
Type Media Article

In seasonal production systems, demand for semen from young genetically elite bulls often exceeds supply. As part of a large Science Foundation Ireland funded project researchers are examining the role of both early life nutrition and genetics in regulating sexual development and subsequent semen quality and fertility in young bulls.

In seasonal production systems, demand for semen from young genetically elite bulls often exceeds supply. However, compared with their mature contemporaries, both the quantity and quality of semen from young bulls is relatively poor, gradually improving in the months following onset of puberty. Thus, there is a requirement to expedite the onset of sexual maturation in young bulls in order to ensure the timely availability of consistently high quality semen. Sexual development in the bull is regulated by both genetics and nutritional status, particularly during early life.

As part of a large Science Foundation Ireland funded project we are examining the role of both early life nutrition and genetics in regulating sexual development and subsequent semen quality and fertility in young bulls. Key fertility traits including those related to sperm production capacity and quality are known to be heritable and thus hold potential for genetic selection. 

On-going research at Teagasc Grange is aimed at identifying key genes/genetic variants associated with early onset of sexual maturation and improved semen quality in young bulls.

In a large on-farm experiment, intensive reproductive measurements including scrotal characteristics and electronically measured sperm kinetics and morphology traits are being recorded on 1,000 Spring born early post-pubertal Holstein-Friesian bulls.

In addition, these young bulls are being genotyped and their DNA profile interrogated for single nucleotide polymorphisms (SNP), small changes in their DNA sequence of their gene, that are associated with improved semen availability and quality during the early post-pubertal period.

Preliminary results to-date show, as may be expected, large variation in semen quality characteristics amongst individual young bulls. Once semen sampling is complete on participating herds, a genome wide association study will be undertaken to determine genetic biomarkers associated with earlier sexual maturity and improved semen quality.

It is expected that the work will yield a panel of SNP, which, following appropriate validation, could be exploited within current genomic selection assisted breeding programs for beef and dairy cattle. This will facilitate earlier availability of semen and subsequent propagation of genetically superior animals, thus increasing genetic progress and shortening the generation interval for both beef and dairy cattle in Ireland.

This collaborative project, funded by Science Foundation Ireland (16/IA/4474), is led by Teagasc in partnership with University College Dublin, the University of Limerick and the Irish Cattle Breeding Federation.