By Oliver Charlton, BVSc MRCVS

For natural service herds, the bull is 50% of your herd fertility.

An infertile (or more commonly subfertile) bull can result in major losses in the production and profitability of the herd, especially with block calving herds.

Cows not getting in calf to a subfertile bull will be seen repeating three weeks later, causing at least a three- week delay in the calving block, plus time to source a new bull.Even if a bull has been working successfully the previous year, that doesn’t guarantee that he will work this year, (various injuries/infections can occur to reduce a bull’s fertility) so testing all breeding bulls prior to use is a good idea.

To classify as ‘fertile’ we expect a mature bull to be capable of a 60% pregnancy rate, meaning that in a group of 50 healthy and cycling cows at least 90% would be in calf after nine weeks.

A subfertile bull capable of e.g. 40% conception rate may go unnoticed, but will lead to a barren rate at nine weeks of 28% rather than 6%. Approximately a third of bulls we test fail the fertility exam for one reason or another.

This can be physical injury, age-related loss in semen quality, physical issues (corkscrew penis), infection, etc. Not all of these issues would mean they wouldn’t get any cows in calf; some may still get some cows in calf, but likely not as many as we’d expect, leading to more returns and drawn out calving windows.

These bulls are almost worse than the obviously infertile ones, as they can go unnoticed for longer and cause more long-term issues.

It is estimated that for both beef and dairy farms, keeping cows not in calf costs approximately £3-4 per cow per day, so ensuring a tight window and cows back in calf, is vital for profitability.

To test a bull we require:

l A secure crush (preferably with an opening side to allow access to collect the sample)

l Some power

l Some form of table to set up the microscope to evaluate the sample there and then.

We perform a brief clinical exam, then assess the testicles, before using a probe to obtain a semen sample. The sample is looked at immediately on farm, and if everything else is acceptable then a stained sample will be made to look at later or back at the office to assess morphology.

Knowledge is power, and ensuring the bull has a full “MOT” every year gives you the opportunity to counteract any brewing issues, long before you see cows returning.