Maintaining fertility of ram sperm for improved artificial insemination success

Take Home Message: Ovine sperm can be kept mobile and fertile for several days when semen is maintained at 4°C without dilution.

Collecting semen before an animal's death is not always possible and being able to preserve post-mortem semen from animals of high genetic value or endangered species is of great benefit.

Traditionally semen is stored at either 5oC to 15oC, or frozen and kept in liquid nitrogen, however the fertility of liquid stored sperm declines by 20-40% a day so most insemination is performed on the day of collection.

The short time frame puts constraints on the transport of semen between collection centres and farms and improving in vitro (in test tube) sperm storage for artificial insemination is a significant challenge for sheep.

In other mammals the epididymal medium (the fluid in which the sperm are stored within the animal) has been demonstrated to be the best sperm environment to maintain sperm viability over several days and weeks.

Now a study has been carried out to evaluate the motility and in vivo (within the live animal) fertility of ram epididymal spermatozoa following the storage of semen for up to 4 days at 4°C undiluted in epididymal fluid.

The study published in the journal Animal, was undertaken with two sheep breeds (Ile de France and Corriedale).

Researchers in Uruguay and France reported that if the spermatozoa (the mature, mobile male sex cell) were collected immediately after epididymal sampling rather than 24 hours after castration or animal death, then the percentage decrease of motile sperm during storage was lower.

They also found that sperm motility over three days in storage was better when kept in this epididymal fluid compared with skimmed milk (a conventional dilution solution used for this purpose).

After chilled storage, the fertility of the stored sperm and the subsequent artificial insemination ranged from 55% to 24% following 24 to 96 hours of sperm storage respectively.

Scientist Dr Daniel Fernandez Abella concluded that the findings showed that fertile spermatozoa can be preserved for several days when the epididymal spermatozoa are stored at 4°C without any dilution.

Researchers remain mystified as to the exact epididymal conditions that enable the sperm to survive and remain mobile for so long.

However, this study demonstrated that artificial insemination in sheep can be improved by chilling the sperm at 4oC and maintaining them in their natural fluid without dilution.

Fertility of undiluted ram epididymal spermatozoa stored for
several days at 4°C, D. Fernández Abella, M. Da Costa, Y. Guérin and J. L. Dacheux
Animal (2015), 9:2, 313–319

By Joanne Stocks, University of Nottingham