Trial of the Scandinavian AI method under British sheep farming conditions

The results indicate that vaginal deposition of frozen-thawed semen can achieve conception rates in the sheep of 50%, which suggests it may be a viable alternative to laparoscopic intrauterine deposition of frozen-thawed semen. The advantages of vaginal AI over laparoscopic intrauterine AI are that it would be cheaper, could potentially be performed by farmers themselves, and does not require an invasive procedure or chemical restraint of the sheep. As such it may increase the use of artificial insemination within the British sheep industry and so allows the importation of superior genetic merit germplasm into a flock without the need to purchase a ram. This reduces the risk of disease introduction and also is significantly less expensive than the purchase of a high-quality ram. It also allows small flocks to survive without the need to buy in a new ram every two years (a necessity otherwise in order to avoid father-daughter matings).

 

The study findings also indicate that transabdominal ultrasound can be used to estimate foetal age, which may have a role to play in the investigation of poor flock fertility in terms of providing estimates of the timing of events which may have affected conception rates

Cervical and vaginal insemination of ewes with frozen-thawed semen is widely practiced in Norway and Sweden and reported conception rates are encouraging, 64-75 % and 63-71% respectively. This is in contrast to the situation in the UK where AI of sheep is almost universally performed by laparoscopy under anaesthesia. This is due to widely reported far better conception rates to intrauterine insemination compared to cervico-vaginal insemination.

 

The laparoscopic method currently used in the UK raises some concerns as regards the ethics of subjecting healthy animals to a surgical procedure which is not to their benefit, plus the increased cost incurred by the laparoscopy (and synchronisation and anaesthesia that make laparoscopic AI possible) reduces the uptake of AI among sheep farmers.

40 randomly selected breeding ewes from the university flock will be isolated in a paddock on their own during October. A vasectomised ram (“teaser”) will be introduced for 3 days and then removed. 14 days after initial teaser introduction the teaser will be re-introduced with keel paint applied. Ewes identified as being in oestrus by the teaser will be removed from the paddock to a separate pen twice daily. Higher conception rates to natural rather than synchronised oestrus are reported. 

Oestrous ewes will be artificially inseminated 12-24 hours after initial identification.

One of the flock’s own Texel rams will have semen collected and tubes of frozen semen with 200x106 spermatozoa per dose produced by a commercial sheep breeding/AI company. Higher sperm doses result in greater conception rates but doses of 200 x 106 spermatozoa are standard for Scandinavian cervico-vaginal AI. The use of a Texel semen for AI with a Suffolk ram as sweeper should enable easy assignment of paternity to subsequent lambs.