21 May 2023

The factors affecting bull fertility

David Kenny, Teagasc Animal & Grassland Research and Innovation Centre, Grange, Co. Meath, reports on some of the factors affecting the fertility of bulls.

Irish statistics suggest that the main reasons for the culling of natural service breeding bulls in beef herds were: injury (23.2%); locomotory issues (21.9%); and, infertility per se (7.2%). Infertility is undoubtedly underestimated given that many sterile bulls are now being identified at an earlier stage following the recent adoption of bull breeding soundness evaluations (BBSEs).

Subfertility is estimated to affect 20-25% of bulls. It may be caused directly by low libido, sperm defects, or indirectly by physical factors affecting bull mobility or mating ability.

Recent Teagasc research has shown that while high-concentrate diets from birth right through to 17 months old had no discernible effect on any aspect of sperm production, quality, or fertility measured, research into long-term effects on bull longevity is warranted. The potential acute and chronic effects of such acidotic diets on the incidence of inflammatory conditions like laminitis and ultimately on lifetime hoof and joint health need to be established and will be the focus of a new Teagasc-led project commencing later this year.

In a separate study Teagasc, together with University College Dublin (UCD) and the University of Limerick (UL), have conducted research into various aspects of bull fertility as part of a large Science Foundation Ireland (SFI)-funded project. The work investigated optimising the rearing management of young bulls, relating differences in the DNA profile of young bulls with age at sexual development and sperm quality, as well as the biochemical differences in the sperm of mature bulls ranked as either high or low fertility.

The results of the project have yielded much new information on the main factors affecting the fertility of bulls, as well as identifying some key biomarkers for the early identification of better fertility and the culling of sub-fertile animals. Such information will be harnessed within the national genomically-assisted cattle breeding programmes for the long-term improvement of bull fertility in Ireland.

This article first appeared in the May Teagasc Advisory Beef newseltter.