Fixed time protocol for frozen AI

A fixed time insemination protocol described by researchers from Brazil could encourage a greater use of frozen semen in equine reproduction.

One of the reasons frozen semen is not more widely used for breeding mares is the need for insemination to occur close to the time of ovulation. This necessitates repeated ultrasound examinations when the mare is in season, making the technique time consuming and labour intensive.

For artificial insemination with frozen semen to become more widespread, a simplified routine is needed that is less labour intensive, but does not sacrifice fertility.

Bruno Ribeiro Avanzi and colleagues at the Department of Animal Reproduction and Veterinary Radiology, Universidade Estadual Paulista at Botucatu, used a fixed time insemination protocol to achieve conception rates comparable with those using a more traditional approach.

Semen from two stallions was used in the study. One stallion (A), a Westphalen, was of good fertility, the other, (B) a Mangalarga Marchador, was of poor fertility.

The semen was collected, processed and frozen using a standard method.

Twenty nine mares were enrolled in the study. The oestrus cycle was monitored by rectal palpation and ultrasound scanning. Once a pre-ovulatory follicle of at least 35mm diameter was present, each mare received an injection of the gonadotrophin releasing hormone deslorelin acetate.

Growth of the follicle was monitored every six hours, starting eighteen hours after the deslorelin. Half of the mares were inseminated when ovulation had been detected, the others were inseminated 40 hours after the administration of deslorelin regardless of whether ovulation had occurred or not.

All mares were inseminated into the tip of the uterine horn adjacent to the follicle.

For frozen semen from the fertile stallion, the researchers reported pregnancy rates of 46.7% (7/15) when bred 6 hours after ovulation, and 66.6% (10/15) for inseminations performed 40h after ovulation induction.

The less fertile stallion achieved pregnancy rates of 35.7% (5/14) when bred 6 hours after ovulation and 21.4% (3/14) for inseminations performed 40h after induction of ovulation.

The researchers conclude that insemination at a fixed time after ovulation induction is efficient. “The present data supports the feasibility of equine frozen semen as a technology to be widely used and spread since it reduces mare management and costs.”

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