Sperm morphology explained
A plain-English guide for bull owners and breeders. If you're booking a bull breeding soundness exam, ask your vet to include morphology from a UQSMSP certified laboratory.
What is a sperm morphology test?
A small drop of semen is added to a vial of formal saline crush side and sent to the laboratory. There it is examined under a high-powered microscope that shows the head and tail of each sperm in detail.
Why does it matter?
Sperm morphology is the trait most strongly linked to calf output. Even if sperm can swim to the egg, no calf will result if the sperm head is defective. The sample is essentially a biopsy of what has happened in the reproductive tract, giving insight into how well the testis and epididymis are working.
How are results reported?
As the percentage of sperm that look normal, plus seven categories of abnormality. A bull needs 70% normal sperm to pass the morphology section of the BBSE.
Why are there seven categories of abnormality?
The categories are those in the current Australian Cattle Veterinarians system (McAuliffe, Johnston, Perry 2010), developed by Dr Viv Perry. They help with the prognosis, because bulls recover from some categories faster than others (Fordyce et al., 2006).
What if a bull gets a poor result?
Retest. Usually after 10 weeks, to allow a full cycle of sperm production and passage through the tract. Your vet may retest sooner if the abnormalities recorded suggest it.
How is the semen collected?
By manual palpation, electroejaculation or artificial vagina, as part of the vet’s bull breeding soundness exam.
Is a crush side test enough on its own?
No. The crush side test checks the sperm are alive and swimming. It doesn’t tell you whether they can fertilise an egg. A bull can have 70% motile sperm and fewer than 50% normal sperm.
Read more: is crush side testing enough?