7 September 2001

Pay attention to bull fertility

By Hannah Velten

LESS than 1% of bulls are examined by a vet for breeding soundness prior to sale or use, according to a Royal Veterinary College study, despite research showing that three in 10 bulls are sub-fertile, infertile or sterile.

This is worrying, says Mike McGowan, professor of farm animal medicine and surgery at the college. He believes there is scant recognition of the importance of bull fertility.

"Cow fertility is given great emphasis, yet a sub-fertile or infertile bull has a greater effect on herd reproductive performance than an individual sub-fertile or infertile cow. He could be responsible for impregnating 20-70 females/season."

At breed-sponsored sales, bulls are usually visually and physically examined for breeding soundness. But Prof McGowan says about 20% of physically normal bulls either have poor semen quality or are incapable of mating because of low libido, penile deviations or musculoskelatal abnormalities.

Producers should also ask about feeding of the bull prior to sale. "Bulls fed high energy diets to maximise growth rates during the six months before sale could develop foot lameness, have poor quality sperm or digestive tract disorders.

"Buying a bull must be akin to buying a second-hand car – you wouldnt just look at it, but also give it a test drive."

He urges dairy and beef producers who use natural mating to adopt breeding soundness examinations as part of the herds routine management. "Bulls must be able to graze and maintain body condition at pasture, locate oestrus females, repeatedly mount and serve females and produce high quality semen."

Using a sub-fertile or infertile bull brings financial consequences and delays genetic progress, says Prof McGowan. "Seasonal calving dairy herds need a compact calving period of 2-3 months to optimise efficiency and economic returns. Using AI in the first cycle is likely to result in conception rates of 50-55%, so the rest are mated naturally."

When a bull with reduced fertility is relied upon, the calving period is drawn out leading to lost milk production/day, late calvers failing to conceive and increased culling, he explains.

In beef suckler herds, lower numbers of animals conceiving extends the calving period resulting in calves of different ages, making routine management and nutrition complicated. "Other consequences will be fewer calves weaned and lighter carcass weights, because on any given day calves born 21 days later will be about 21kg lighter."

A bull is also a package of genetics which must be effectively delivered into the herd for genetic progress. "Choose the bull first and then test to see whether he will be able to deliver that genetic package," says Prof McGowan.

He believes producers may be coping with a sub-fertile bull by running a greater number of bulls with the herd to compensate. "But this means greater costs/calf weaned. By testing bulls for breeding soundness, fewer and better bulls can be used. Instead of buying two bulls with reasonable beef values, one bull with a superior BV can be bought."

Herds running a single mating sire are at the greatest risk of buying a duff bull, so producers must consider a vet examination of his physical condition, semen quality and serving ability.

Multi-bull mating poses less of a risk of using a sub-fertile or infertile bull, but examinations are still essential, he believes. However, there are some aspects of bull management which will prolong their working life and fertility.

Vaccination or testing for diseases which may cause death, fever, body condition loss and infertility is crucial, says Prof McGowan. "Bulls also need to acclimatise to new surroundings before they are expected to work.

"Bulls should only be run with others of the same age to prevent domination by an older, possibly less fertile bull and reduce bull breakdown caused by fighting."

Over-fat bulls should be avoided because they may have lower libido and poorer quality semen. They must be fit, not fat with condition scores no greater than three before working. However, when working, bull condition must be monitored and maintained at 2.5, with regular checks on foot condition.

Rotation of bulls to maintain libido is also crucial when relying on natural mating. A fit, mature bull at two years old should be able to serve 70 females, but older bulls may need a reduced workload. &#42

BULLINFERTILITY

&#8226 Adopt clinical examinations.

&#8226 Finances and genetic progress suffer.

&#8226 Bull management crucial.

Vet examination of bulls to prove breeding soundness is vital for a herds genetic progress, cost-efficiency and ease of management, according to Mike McGowan.