MANY Bos indicus and Bos indicus cross breeds in Australia have a higher morphology test fail rate than Bos taurus breeds - regardless of region, research published this month has shown.
The findings from the first comprehensive study to look at the effects that breed, age, season and region have on bovine sperm morphology in Australia are published in the prestigious journal Theriogenology.
Morphology testing of bull sperm is a critical part of the bull breeding soundness examination (BBSE) as it is the measure most strongly correlated with calf output.
Bulls with low percent normal sperm get fewer cows in calf and importantly, it takes longer for the cows to become pregnant.
Conducted by Dr Viv Perry, from the Queensland Sperm Morphology Laboratory, the epidemiological study is based on data from 500 herds over a four year period sent to the laboratory from Australian and nearby Pacific Island clinics during the annual BBSE.
The research will allow veterinarians and producers to see what per cent of a specific breed are likely to fail on their first morphology test at their annual BBSE.
Dr Perry said the biggest take-home message for producers was to appreciate the levels of fail rates for bulls.
In some breeds, the percentage of bulls failing the test was as high as 38 to 50 per cent, whereas in other breeds only 10-20pc of bulls failed the test.
Considering these findings on the high percentage of bulls which fail the morphology test, not testing bulls for this trait, or buying from a stud that does not complete morphology testing, does not make economic sense, Dr Perry said.
"What we hope this research says to stud producers starting out on morphology testing and finding many bulls have failed is not to be put off selecting on morphology," she said.
"When vets get results back and see 40pc have failed, the producer typically thinks it's unusual but this study shows it is not, if you haven't done any selection for morphology.
"Understand we've had studs involved in selecting for good morphology results over 10 to 20 years and they have significantly improved the numbers of bulls passing."
Previous work by Dr Perry also indicated morphology testing should be conducted annually because results can be affected by environment such as following high grain feeding and by age, for example during the peripubertal period.
Dr Perry said this was the first scientifically-based study that showed a significant difference between the range of breeds present in Australia in sperm morphology.
Taking into account the impact of age, season, region, and breed, there were differences between breeds in both the percentage of morphologically normal sperm and, in some individual categories, of sperm abnormality.
Significantly more Brahman, Charbray, Droughtmaster, Santa Gertrudis, Belmont Red, Brangus failed the morphology test when compared to the reference.
"What was of interest is that in this study we were able to take out the effect of region as we had a considerable number of Bos indicus cross breeds particularly in the north, north east and inland," Dr Perry said.
"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 in the morphology test.
"When we considered the effects 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, high temperatures, and greater levels of parasite burden such as ticks, had the highest pass rate compared to other areas of Australia."
There was some effect of season upon specific abnormalities but not overall, Dr Perry said. 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," Dr Perry said.
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