Bull semen evaluation: avoiding artefacts

When assessing bull fertility, careful consideration must be given to the entire bull breeding soundness examination (BBSE) process. The purpose of this article is to share some advice on semen handling and evaluation techniques, to reduce the chance of artefacts occurring and increase trust in interpretation of results.

All measures should be taken to ensure that the sample we see down the microscope is a representative ‘biopsy’ of what would be ejaculated during natural service. However, with each handling process and exposure to the environment the semen cells can become damaged and further removed from this.

Cold shock is challenging to overcome but preparation and suitable equipment can help avoid premature death and artificially low motility of the cells. A small incubator, a slide warming bench and a heated microscope stage are worth the investment. The laboratory equipment should be set up before the bull examination to allow the kit to reach the optimal temperature of approximately 37°C (as per the manufacturer's instructions) (Appell et al, 1977). Slides, coverslips, pipette tips, collection tubes, collection sheaths, phosphate buffer solution (PBS) and nigrosin-eosin (NE) stain can be heated quickly on the warming bench and should be maintained at temperature in the incubator. Access to electricity should be checked (before arrival) to ensure the set-up is as close to the crush as possible, to reduce the time between collection and semen examination. The collection tube should remain close to body temperature during and after the collection too. Keep the pre-warmed tube in a pocket while carrying out the clinical examination, in hand during collection and in the incubator during evaluation. On really cold days insulating the tube with cotton wool can help.