Sweeper bulls need some rest and rotation

It is possible to have too much of a good thing – and for a sweeper bull, that is being expected to serve more than 30 cows within a three-week period.

Even in a block-calving herd, bulls can get bored with lots of eligible females to serve. And in year-round calving herds, few will have an even calving spread, so at certain times, a sweeper bull may get overworked, says vet Rachel Risdon of Stock1st, Cornwall.

“It’s good to rotate them every three weeks to stimulate their interest and keep them active. People should think about how many cows a bull is expected to be covering and consider his peak workload.

Remember that if you are going to rely on a bull, make sure he is fully fertile. Have a back-up bull so that the first one can be rested and sent out keen again,” she says

“It’s also a good idea to rest a bull working on concrete to save his feet. He has more weight to carry and he won’t be keen if feeling footsore or lame,” she adds.

In large herds, or those where conception rates to AI have been particularly poor, more than one bull may be needed. For instance, in a 700-cow herd, when 70% of cows are in calf after AI, 210 cows need to be served by the sweeper bull over a year. This equates to four cows a week, but will be more when there are high returns to AI services, or a condensed calving.

As well as a good libido, a sweeper bull should have full working tackle. Having him checked physically by a vet before use will go a long way to avoiding delays in conception due to physical or semen abnormalities. In addition to feet, the vet check assesses scrotum size, swelling or scarring, plus damage or warts on the penis and semen quality. “Sperm production takes two weeks, so if a bull is off-colour, lame or with a high temperature, that’s going to affect his ability to get cows pregnant several months down the line.

“About 30-40% of bulls fail this breeding soundness examination, but are rarely completely infertile.”

Typically, a sweeper bull runs with the low yielders – cows that are pregnant, or remain empty after several inseminations – but this makes service dates uncertain. Even in an extended calving period, there is a defined start and finish, often to avoid calvings while silage making. Mrs Risdon finds many herds keep the sweeper bull in a pen by the collecting yard to help with heat detection and control service dates.

Another option is to use a chin ball harness to mark served cows, leading to more accurate calving dates and drying off dates, adds vet Paddy Gordon of Shepton Vet Group, Somerset. “When cows are at grass, heat detection rates tend to fall, as staff are busy with field work. You may record some serves, or none at all. A chin ball harness should increase your ability to record dates. This is important in managing cell counts and drying off dates to give cows long enough time to recover without losing milk yield,” he says.

• Check feet and fertility before use
• Rotate bulls regularly
• 30 cows to one bull

CASE STUDY

Nick Granger
Bude, Cornwall

Rotating two sweeper bulls every 3-4 days keeps them active and keen, says Nick Granger of Darracott Farm, Bude, Cornwall. He block calves 140 crossbreds over 10-12 weeks, starting in the second week of February.

Timing is crucial to block calving, so starting at the end of April, all eligible cows are inseminated with dairy semen to breed replacements. After 6-7 weeks, the Hereford and Angus sweeper bulls are turned in with the herd for 6-7 weeks. “By then we have a good picture of return rates, as we use tail paint. We monitor and record everything and we can get an idea of cow numbers to allocate bulls to. It’s no good having 50 cows and putting one bull in to do the job,” says Mr Granger.

Bulls are removed on time to ensure a cut-off point for calving. But Mr Granger stresses the importance of giving each bull a thorough health check. “There is no point having them if they are only doing half a job. It’s now our policy to test them every year, check their feet, testicles and sperm samples. The cost is minimal compared to still having cows empty at the end of the mating period.”