The Effect of Post-Mating Progesterone Supplement on Pregnancy and Lambing Rates of Ewes Bred Out-of-season

Abstract

Abstract:The objective of this experiment was to determine whether post-mating progesterone (P 4 ) supplement improves pregnancy and lambing rates in ewes bred during the seasonal anestrous period. In June, 39 synchronized to estrus Awassi ewes were allowed with four harnessed fertile rams immediately following CIDR-G device removal (day 0 and 0 hour). Five days following ram introduction, ewes were randomly assigned to four groups to be treated post-mating with intramuscular injections of 20 mg P 4 supplement once daily from day 5 to day 9 (P 4 -D5-9), days 10 to 14 (P 4 -D10-14), days 5 to 14 (P 4 -D5-14) or did not receive P 4 supplement (control). Blood samples were collected from all ewes for P 4 analysis. Progesterone concentrations prior to CIDR-G insertion were basal and no differences in P 4 concentrations were found on days -12, -10 and between days 0 and 5 among groups. Progesterone concentrations between days 5 and 15 differed (p<0.001) significantly due to treatment effect. Maximum P 4 concentrations were reached on day 9 in group P 4 -D5-9 and between days 11 and 15 in groups P 4 -D10-14, P 4 -D5-14, and control. Pregnancy was diagnosed based on day 19 P 4 levels and day 30 ultrasonic examination in 5/10, 6/10, 5/10, and 5/9 ewes in groups P 4 -D5-9, P 4 -D10-14, P 4 -D5-14 and control, respectively. Pregnancy loss was detected by ultrasonography on day 45 in 3/6 and 3/5 ewes in P 4 -D10-14, P 4 -D5-14 groups only. Overall pregnancy (53.8%) and lambing (41%) rates were similar among groups and were not influenced by P 4 supplement. In conclusion, P 4 supplement administered intramuscularly between days 5 and 14 post-mating is not effective in improving pregnancy, embryonic survival and lambing rates in Awassi ewes pretreated out-of-season. Pregnancy loss which occurred only in P 4 -D10-14 and P 4 -D5-14 groups maybe attributed to factors including the sharp decrease in P 4 concentrations on day 15 and stress experienced during the period of maternal recognition of pregnancy process.