Archivos de Zootecnia
versión impresa ISSN 0004-0592
We evaluated pregnancy by timed artificial insemination (TAI) with ram semen chilled at 5oC during 12 or 24 h and insemination doses of 150 or 300 millions spermatozoa. Two hundred adult Merino sheep were randomly divided in 4 groups of 40 animals each, according to a factorial arrangement (2x2) plus a control group. During the breeding season, estrus were synchronized with intravaginal sponges impregnated with 60 mg of medroxyprogesterone acetate inserted for 14 days and administration of 200 UI PMSG at sponge removal. Twelve and 24 h before insemination, semen from adult Merino rams was collected, and after the ejaculates were diluted and chilled. Semen was diluted with the Ovipro extender (Minitüb®, Alemania) using a dilution rate of 1:2 (semen/extender). Control group was inseminated with fresh semen without diluent and an insemination dose of 100 millions spermatozoa. For every group, cervical TAI was performed 54-56 hours after progestational treatment. Preserved semen during 12 hours obtained 25% and 38% pregnancy with an insemination dose of 150 and 300 millions spermatozoa. Semen preserved for 24 hours caused 3% and 19% pregnancy with an insemination dose of 150 and 300 millions spermatozoa respectively. Control group showed a pregnancy of 59%, which evidenced that flock fertility was not affected by nutritional status or management. TAI with ram chilled semen during 12 h, with an insemination dose of 300 millions spermatozoa, was found to provide an acceptable fertility (38%), considering the benefit of carryng semen for long distances and the low operative cost for its implementation.
Palabras clave : Semen concentration.