Bull Sperm Morphology is affected by breed, age, season and region, with the greatest effect being breed.

Categories: Blog, Research

Four years and 11,387 bulls later, QSML has published a study on the effect that breed, age, season and region have on bovine sperm.

Published in the prestigious journal Theriogenology, the title of the work is “Bovine sperm defects are affected by breed, age, season and region.” The epidemiological study is based on data from 500 herds in Australia and near Pacific Islands during the annual bull breeding soundness examination (BBSE) performed by QSML clients over a four year period.

This is the first study to comprehensively collect data from this wide geographical area and compare sperm morphology profiles among the Bos indicus and Bos taurus breeds. The research will allow veterinarians and producers to see what percent of a specific breed are likely to fail on their first morphology test at their annual BBSE.

Taking into account the impact of age, season, region, and breed, there were differences between breeds in both percent morphologically normal sperm and in some individual categories of sperm abnormalities.

Results for Breeds

Significantly more Brahman, Charbray, Droughtmaster, Santa Gertrudis, Belmont Red, Brangus failed the morphology test, whilst significantly less Friesian bulls failed the morphology test.

Whilst Bos indicus and Bos indicus cross breeds have a higher fail rate,we note that a wide variation exists between herds. Herds which had selected for morphology over time have significantly improved pass rates compared to their peers.

Region vs Breed

What was of interest in this study was our ability to take out the effect of region.

It is often put forward that Bos indicus and Bos indicus cross bulls fare less well due to their increased numbers in less favoured areas but this study shows that regardless of area some breeds perform more poorly than others.

Region and Season

When we considered the effect of climatic region we were surprised that bulls in the North East of Australia, where there is a high proportion of Bos indicus content bulls (95%), high temperatures, and greater levels of parasite burden such as ticks, had the highest pass rate compared to other areas of Australia (except the south; below 24ºC average daily maximum isotherm).

There was also some effect of season upon specific abnormalities. It was interesting to see that levels of vacuoles (an abnormality frequently observed in Bos indicus cross bulls) were increased in summer compared to other seasons. We have previously noted in our other studies that this abnormality is often observed following stress in Bos indicus cross bulls. Summer temperatures may therefore be sufficient to cause such stress in these bulls and others.

What does this mean for producers?

The biggest take home for producers may be to appreciate the levels of fail rates for bulls. In some breeds this was as high as 38-50% of bulls.

We know that sperm morphology is the trait most strongly correlated with calf output so, considering this high fail rate, omitting to test bulls for this trait does not make economic sense.

The findings of this study will act as a guide for veterinary practitioners and cattle breeders in the proportion of bulls that can be expected to pass the PNS test, by breed, age and region, based on a robust data set.
You can read the full paper here.

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