Artificial Insemination in Sheep
The optimal time for insemination with nonfrozen semen is 12–18 hr after the onset of estrus. When estrus has been synchronized or induced using progestagens and gonadotropins and/or ram effect, most ewes are in estrus within 36–48 hr and ovulate at ~60 hr. Insemination should be done 48–58 hr after pessary removal for cervical insemination, or 48–60 hr for intrauterine insemination with frozen-thawed semen, with highest conception at ~53–54 hr.
Extended fresh or chilled semen can be placed into the vagina or cervix, and extended fresh, chilled, or frozen-thawed semen can be placed into the uterus. Frozen-thawed semen reconstituted with fresh seminal plasma can be placed into the cervix with conception rates >50%.
An artificial insemination pipette with a 1–2 mL syringe attached is placed deep into the vagina. This method is quick and involves minimal restraint of the ewe. For cervical insemination, the ewe is restrained to limit movement and to present the hindquarters at a convenient height for easy access to the vagina. After cleaning the vulvar region, the cervix is located with the aid of a speculum and suitable illumination, and the insemination made as deeply as possible into the cervical canal. A long, thin inseminating tube with attached syringe or a semiautomatic inseminating device can be used. The relatively long, tortuous, and firm-walled cervical canal of the ewe usually precludes penetration by the tube for >1 cm. In old, multiparous ewes with cervical tissue distortion, the difficulty increases, and the semen is deposited into the posterior folds of the cervix. In periparturient ewes, the cervix may be fully penetrated. In maiden ewes, in which insertion of the speculum and dilation of the vagina can cause injury, the semen should be deposited in the anterior vagina.
Food and water should be withheld from the ewe for ~12 hr. Ewes should be sedated with 1.5–2 mg xylazine, IM, and placed in cradles that restrain and invert them, first in dorsal recumbency for preparation of the abdomen. Local anesthetic may be injected SC at two sites (~4 cm on each side of the ventral midline and ~6 cm anterior to the udder). The cradle is then raised at the posterior end so that the ewe is tilted at ~45° with the lateral abdomen presented to the operator. The anesthetized sites allow for entrance of two trocars and cannulae; carbon dioxide is insufflated through the first cannula to distend the abdomen. The laparoscope is inserted through the near cannula, the uterine horns are visualized, and a glass or plastic inseminating pipette or sheathed inseminating gun is inserted through the second cannula. Semen is deposited into the lumen of the uterus. Conception rates are similar if semen is deposited into one or both horns of the uterus.