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The international bull fertility conference lasted four days and incorporated both practical and non-practical sessions. These sessions covered everything from male reproductive physiology to bull production, selection and evaluation. We explore two of the key points taken from the Tuesday of the conference.
One in four bulls questionable for breeding soundness
Al Barth from the University of Saskatchewan, Canada, presented stark figures on the number of bulls failing bull breeding soundness evaluations. He said that it has been commonly reported that one in five breeding bulls are deemed infertile based on physical inspection and semen analysis.
He said that when serving capacity is added into the evaluation, the situation gets worse, with one in four bulls then failing the evaluation, with research in a Canadian research station returning a result of 72.2% being deemed satisfactory, 12% questionable and 15.8% unsatisfactory.
Al said that a rising difficulty in assessing the breeding soundness of young bulls is a switch in North America to bulls being presented for sale at 12 to 13 months of age over the traditional approach of bulls being presented at 18 to 24 months of age.
He said that, in general, about two thirds of bulls will mature at 14 months of age, with some taking longer and, likewise, some reaching a level of maturity at a younger age.
This, he says, makes it much harder to achieve an accurate semen analysis at 12 to 13 months of age, with sperm morphology poor at the onset of puberty.
He said that it is remarkable how quick bulls with poor sperm morphology can produce good semen, with a 100-day window greatly increasing semen quality.
Where the semen quality of young bulls is questionable at a young age, Al says there is a great temptation to use a decision deferred evaluation for semen quality.
He highlighted that this is a very risky method, with a 10-year study carried out in a Canadian research station showing that just 35% of bulls on average that had questionable semen quality subsequently were deemed satisfactory.
Another element that Al believes would benefit bull soundness evaluations is an independent team of veterinarians that are sufficiently trained, while he says there is also a need for well-equipped laboratories that are specialised in semen testing.
Thermoregulation of testes and semen quality
John Kastelic from the Department of Production Animal Health, University of Calgary, Canada, gave a presentation titled testicular vascular cone development and its association with scrotal thermoregulation, semen quality and sperm production in bulls.
The talk gave some important insights into the negative effect that increased testicular temperature has on semen quality.
The damage is proportional to the degree and duration of warming, with higher than normal temperatures leading to an increase in mortality of spermatocytes, reduction in motility and an increase in abnormal sperm.
John said that it will take six weeks for sperm to return to normal following damage caused by excessive testicular temperature and even when sperm gets back to normal, there may be higher levels of early embryonic death.
There are a number of factors that will influence testicular temperature, with illness being one of the greatest factors. Outside of this, factors such as the location of testes will have an influence on thermoregulation.
A bull’s testes are 2°C to 6°C lower than body temperature. When body temperature is higher, scrotal muscles regulate temperature by increasing or reducing the length at which testes are located from the body.
For this reason, John says bulls with a small scrotum and testes located very high up will find it much harder to regulate testes temperature. Other issues include overfeeding and excessive feeding of bulls, with a resultant higher level of scrotal fat impairing an animal’s ability to regulate temperature.
The overfeeding of young bulls was one of the key topics on the third day of the conference. It focused on the effect the pushing of young bulls to be sold for breeding at a young age was having on both the bull’s short-term fertility and long-term survival in the herd. Next week, Shane Murphy looks at this topic in a bit more detail.
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