Reproductive response of ewes synchronized with different lengths of MGA treatments in intrauterine insemination program

A total of 415 fat tailed ewes were randomly assigned to two groups to assess the effect of duration of melengestrol acetate (MGA) (9 versus 12d) administration on reproductive parameters associated with laparoscopic artificial insemination. At the end of MGA treatment, ewes in each group were subdivided and inseminated with one of two different insemination doses (10×10⁷ or 20×10⁷ sperm per 0.5ml insemination dose) of fresh diluted semen. Inseminations were carried out 11-18h after first detected estrus. Ewes were screened for their return to oestrus from 10 to 21 days post AI and inseminated at their returned oestrus. Pregnancy diagnosis was done from approximately 55 days after insemination in both synchronized and return estrus. For short (9-day) and long (12-day) term MGA treated groups, estrus rates were 62% versus 89% (P<0.0001), respectively. Ewes (n=115) that returned to estrus were inseminated (7-11h after estrus detection) with fresh diluted semen at different doses (20×10⁷ or 40×10⁷ or 60×10⁷ sperm per 0.5ml insemination dose). Pregnancy rates were 41% and 44% for short term and long term MGA treated ewes, respectively. Pregnancy rate of ewes which returned to oestrus was 53.4%. There was a significant (P<0.05) increase in pregnancy rates (38-52% for 11-16h; 63% for 17-18h) when insemination was held at 17-18h after first detected estrus following MGA treatments. Pregnancy rates were found to be similar in ewes inseminated with 10×10⁷ (36%) or 20×10⁷ (47%) motile spermatozoa at first AI, and 20×10⁷ (44%) or 40×10⁷ (59%) or 60×10⁷(48%) at second AI.It was concluded that short term MGA treated ewes were recorded with lower estrus rates but was similar to pregnancy rates with long term MGA treatment. Acceptable pregnancy rates were achieved in MGA induced estrus when insemination is conducted at 17-18h after estrus onset and with 20×10⁷ sperm per insemination dose.