Article written by Josephine Child, BvetMed CertAVP PGcertVPS MRCVS and Helen Rogers MA, VetMB, MRCVS, DBR
In 2025, 28% of bulls tested at Friars Moor Livestock Health failed their Bull Breeding Soundness Examination (BBSE). This means that we identified a cohort of subfertile bulls, ahead of them being used in or purchased for suckler or dairy herds. By removing these subfertile bulls, we reduce the chances of a poor conception rate and subsequent high empty rate for block calving systems, as well as a protracted calving period.
Buying a bull sounds like a relatively straightforward process, but the reality is very different! Matching up your health status, genetic and EBV requirements with actual bull availability is a real headache. We need to ensure that the BBSE is rigorous and correctly identifies subfertile bulls. The benefits of carrying out a BBSE are undeniable, but as bull purchasing can be challenging, the procedure needs to be carried out well in advance of the start of breeding season to ensure there is an opportunity to retest and replace a subfertile bull. As bull semen production takes 61 days, we recommend carrying out the procedure at least two months prior to use.
The effect of a lame bull on heifer pregnancy rate
The length of the sperm production cycle is slightly shorter in rams (49-61 days); however, a target of testing your rams two months prior to the start of the service period is equally sensible.
The procedure for both rams and bulls involves a physical examination of all areas required to serve a cow/ewe, the eyes, musculoskeletal system, heart and lungs, as well as scrotum, penis, prepuce and internal sex glands. In addition, a probe, inserted into the rectum, is used to stimulate the ejaculatory nerves and a semen sample is collected. This is immediately analysed and the general (gross) and progressive (forward) motility assessed, alongside the morphology. There are specific targets to meet for each of these factors to allow the male to pass his exam.
If you have a team of bulls or rams, all breeding males should be tested regardless of how well they have performed in previous years. Don’t be lulled into a false sense of security just because you have calves and lambs on the ground this year. Illness, fever or injury will have an effect on sperm viability, and we are not always aware of these occurring in rams or bulls.
A large estate in Wiltshire runs 850 mule x ewes with a mixture of Romney, Suffolk and Texel rams. They have been working with us to semen test all the rams in this flock prior to the mating season for the last 4 years. On average, we find 30% of these rams are subfertile. The shepherd for this flock is really pleased with the results; he says it allows him to place less fertile tups with 2 more fertile ones in a group mating setting and gives him the confidence to single-sire mate elite groups of ewes. It has also led to a tighter lambing period, with reduced returns in second and third cycles. Over this time, the lambing percentage has increased across the flock by around 5%, and the barren rate for 2026 is just over 1%.
It has been an interesting exercise to see how different rams perform in subsequent breeding seasons, especially first-time breeding rams and older rams towards the end of their working lives.
Most of our BBSE exams are now carried out in our foot trimming crushes, which provides a great opportunity to also check and trim the feet of the bull. A proportion of subfertile bulls are identified as soon as we pick up their feet, establishing that they are not viable to last the service period. Lameness is one of the most common causes of subfertility in breeding bulls and rams.
What do we do when we identify a subfertile bull?
Depending on the findings, we may recommend culling and replacing the bull ASAP. Alternatively, we may book in a retest and assess whether any improvement has occurred since the previous test. This is only possible if there is sufficient time left before the start of the service period.
One ram this year was found to be producing double-tailed sperm. This ram passed a physical examination with no problem in terms of physical health and size of testicles; however, examination of a semen sample revealed a high percentage of sperm with this abnormality.
Should you wish to explore fertility testing services with your own flock or herd, contact your vet to discuss the options available.
