Effect of Time of Artificial Insemination After Estrus Detection on Corriedale Sheep Pregnancy Rates

A total of 240 adult Corriedale ewes from the Magallanes Region of Chile, were synchronized with progestagens and randomly assigned to one of four groups, according to the time elapsed between estrus detection and artificial insemination (AI) with semen obtained from 2 Corriedale rams. The first three groups were inseminated at 3 and 6; 6 and 12; or 12 and 18 h after estrous detection; the fourth group received a single insemination 18 h after estrous detection. Semen was extracted and frozen in a solution of skimmed milk, glycerol and egg yolk, thawed and used, registering the depth of semen placement in the cervix and the quantity and nature of the cervical mucosa. Pregnancy was assessed by ultrasound 30 days after insemination. No significant statistical differences were detected among pregnancy rates, which were 22; 31; 22; and 21% for groups 1; 2; 3 and 4, respectively. Nor were there significant differences with one or two inseminations. Results showed that fertility did not differ when insemination was performed 3 to 18 h after estrous detection, and that double insemination is not necessary, as long as insemination coincides with the middle of the estrous period. Un total de 240 ovejas Corriedale fueron sincronizadas con progesterona y asignadas al azar a 4 grupos, según el tiempo transcurrido entre la detección de celo y la inseminación artificial (IA) con semen de carneros de la misma raza. Los primeros 3 grupos fueron inseminados luego de 3 y 6, 6 y 12; ó 12 y 18 h de detectado el celo; el cuarto grupo recibió una sola inseminación 18 h después de detectado el celo. El semen fue extraído y congelado en una solución de leche descremada, glicerol y yema de huevo, descongelado y usado, registrándose la profundidad de depositación del semen en el cérvix y la cantidad y naturaleza de la mucosa cervical. Treinta días después se determinó la preñez mediante ecografía. No se detectaron diferencias estadísticamente significativas entre los porcentajes de preñez, que fueron de 22; 31; 22; y 21%, para los grupos 1, 2, 3 y 4, respectivamente. Tampoco fueron significativas las diferencias en fertilidad con una o dos inseminaciones.