Handling Deep Frozen Semen
Date Posted: 9th March 2023
Brian Kennedy MVB, DBR, MRCVS, FrAgs Company Veterinarian, AI Services (NI) Ltd
It is no coincidence that bull semen is packaged in long thin plastic straws. Certainly, the design facilitates a substantial amount of information be recorded to avoid confusion over sire identity.
However, the main reason why the straw was selected as a preferred way of semen storage is to maximise the surface area with respect to the volume of the extended ejaculate.
When bull semen is both frozen and thawed water crystals form and reform throughout the length of the dose. During this process sperm are damaged and often killed.
The principles of physics confirm that where a medium is frozen in a controlled, speedy and uniform fashion, the detrimental impact of crystal formation can be kept to a minimum. In a similar fashion, crystal formation occurs during the thawing process. Again the objective is to reduce damage.
To this end thin walled, slender plastic straws are ideal in controlling the uniform rate at which semen is frozen and thawed.
Even when observing best technique with respect of processing, freezing and thawing conventional semen, about 40% of the viable, progressive sperm are destroyed. Where straws are thawed using less than optimal protocols the percentage of sperm destroyed will increase.
Some farmers for example have been known to thaw semen in cold water, placing doses under armpits, in mouths or simply holding in air. None of these will kill all of the sperm but are certain to reduce the number that survive. Less viable sperm can only have a negative impact on subsequent fertility.
