We’re often asked here at QSML whether crush side testing of bull sperm alone is sufficient. So this week we thought we would address those questions so that you can make an informed decision about the process.
What is Crush Side Testing of sperm?
As part of the Bull Breeding Soundness Examination (BBSE), semen is collected from the bull following physical examination. This is usually done using an electroejaculator. As the seminal fluid goes from clear to cloudy, a sample is collected by the veterinarian. Immediately following this collection a drop of semen is assessed under a crush side field microscope on a warmed microscope slide with a coverslip. A 10x microscope objective is often used first to assess wave motion and concentration followed by a 20x or 40x objective to assess sperm motility. This is always done using a warm stage (at 37C) so that no cold shock affects the sperm.
What does crush side testing look for?
The crush side test checks whether the sperm are progressively forwardly motile – that is; can they swim and are they swimming rapidly forward at >2 body lengths per second. It also checks for adequate concentration. If the sample is too dilute or the sperm are insufficiently motile, or swimming backwards, a second sample is often collected.
The crush side test, therefore, aims to ensure a representative sperm sample is collected and that the sperm are alive and swimming. The motility of the sperm is scored as a percentage. If >30% of the sperm are actively progressively motile then the bull will pass the motility section of the BBSE.
What does off-site, central laboratory testing do?
At the same time as the drop of semen is placed onto the microscope slide for motility scoring a drop is also placed into a small vial containing a preservative. This small vial is taken back to the veterinary clinic and posted off to an independent laboratory for the assessment of sperm morphology. Sperm morphology is also scored as a percentage figure and is often confused with the sperm motility percentage but the two are quite different and often not related. For example, a recent bull had 70% motile sperm but only <50% normal sperm. 41% of the sperm had a diadem defect (picture attached).
Sperm morphology is assessed on the killed preserved sperm and examines the integrity of the sperm head and tail. A score of 70% is required to pass the morphology section of the BBSE.
What are the benefits of off-site, central laboratory testing?
The examination of sperm morphology is essential to the BBSE as it is the test most strongly correlated with bull fertility and calf output. A crush side motility test will tell you the percent of the sperm that are swimming but it will not tell you if those sperm are able to penetrate the egg or form a viable embryo. The morphology test checks for known sperm abnormalities that have been established to cause reduced conception rates.
The report from the sperm morphology laboratory is sent back to the veterinarian within one week of being received at the laboratory. This allows the veterinarian to send out to the producer the best prognosis for his bulls following the BBSE.
How to arrange morphology testing that includes both crush side and off-site laboratory testing?
Contact your local cattle veterinarian requesting BBSE of your bulls prior to mating or sale that includes sperm morphology testing from a recognised laboratory: Preferably one that participates in ongoing standardisation by exchange of test samples. Most cattle veterinarians will include off-site independent laboratory morphology testing as part of their recommended BBSE but it is always wise to specifically ask for this test to be included.