Whether you are a beef farmer or a dairy farmer, block calving or all-year-round, it is important to carry out bull breeding soundness evaluations to test for bull fertility.
Unless the bull has an obvious physical ailment that is stopping it from being able to serve cows it is impossible to determine its fertility just by looking at it. Being fertile the previous year does not guarantee that the bull will be fertile the following year.
Vet Laura Gibson, from Westpoint Farm Vets, says studies have consistently shown that between 20 to 25 per cent of bulls that undergo routine breeding soundness tests are found to be sub-fertile or infertile.
She says: “Infertility is rare but sub-fertility is far more common. These bulls have the ability to serve and impregnate cows, but they are unable to achieve a conception rate that would be expected of a fertile bull.
“These sub-fertile bulls are often hard to discover without a bull breeding soundness evaluation (BBSE), particularly if the farm runs more than one bull, as the others will continue to serve the cows and effectively ‘cover up’ the sub-fertile bull’s shortcomings.”
She adds that poor fertility figures, poor conception rates or a spread-out block calving pattern are all possible outcomes of using a sub-fertile bull.
“These sub-fertile bulls will typically achieve a 40 per cent conception rate, whereas a fertile bull will achieve at least 60 per cent when running with an appropriate number of healthy cycling females.”
She says on a herd of 100 cows a sub-fertile bull would give you a 13 per cent barren rate after 12 weeks, whereas a fertile bull should leave you with only 2 per cent empty cows (see graph). The calving pattern is also more spread out.
Ms Gibson adds: “A target of more than 65 per cent of cows calving in the first three weeks of the start of calving is achieved in herds with good fertility in cows and bulls, with a target of a barren rate of less than 5 per cent.”
She says if these issues are being picked up retrospectively the damage has already been done and it is therefore important to have bulls tested at least two months before you intend to use in block calving systems.
Ms Gibson adds that in all-year-round calving herds the sub-fertile bull is particularly difficult to spot.
“There will be more cows returning to heat, leading to an extended calving interval and reduced milk production.
"Without having the bull tested it can be easy to wrongly consider the cows to be the problem rather than the bull. A routine BBSE is therefore recommended at least once a year to ensure this issue does not go unseen.”
Ms Gibson explains that a bull breeding soundness evaluation (BBSE) can only be carried out by someone who holds a veterinary licence.
She says the test looks at the motility (ability to swim) of the sperm produced by the bull and the morphology (shape) of the sperm.
She adds: “The vet will then also do a physical assessment of the bull and look at his confirmation, checking things such as the angle of his back legs, the alignment of his feet and his penis in order to ensure that he will be able to function normally when trying to serve cows.
“If the bull passes on all these criteria he is deemed sound, and the only thing left to check is his libido and ability to serve.
"This can be done by the farmer and both can be checked at the same time. Libido is his drive to want to serve cows, if he shows more interest in food than in the cows that can sometimes be a problem.
"His ability to serve is simply being able to mount a cow and effectively achieve penetration. If you watch him and see him serving cows effectively, he can be considered to have a good libido and able to serve. Therefore if you observe this, and he is deemed sound on BBSE, he can be considered a fertile bull.”