Progesterone concentration and lambing rate of Karakul ewes treated with prostaglandin and GnRH combined with the ram effect during breeding and non-breeding seasons

The combination of ram effect with two injections of PGF_2α 10-days apart and the same protocol plus an additional injection of GnRH prior to the first injection of PGF_2α were examined in Karakul ewes during breeding and non-breeding seasons, respectively. Plasma progesterone (P₄) concentrations (to detect the presence of active corpus luteum), twin lambing, litter size and synchronization of lambing were evaluated. In each study 70 ewes (2-4 years old) were divided to a treatment (n = 40) and a control (n = 30) group. During the breeding season, on days -10 and 0 before ram release, the treatment group was injected intramuscularly with PGF_2α (D-Cloprostenol; 0.15 mg). During the non-breeding season, on day -15 before ram release the treatment group was injected with GnRH (buserelin; 4.2 μg) intramuscularly followed by two injections of PGF_2α on days -10 and 0. In both studies, the rams were released into the ewe flock after the second prostaglandin injection (day 0). Blood samples of ewes were collected on days -10, 0, 20 and 70 of the study in breeding season and on days -15, -10, 0, 20 and 70 during non-breeding season. The treatment group had higher P₄ concentrations compared to the control ewes on day 0 in the breeding season (5.80 ± 0.61 vs. 5.0 ± 0.93 ng/mL) and day -10 in the non-breeding season (3.50 ± 0.33 vs. 2.70 ± 0.35 ng/mL) though the differences were not significant (P > 0.05). Based on plasma P₄ concentrations (>1 ng/mL) on day 70, in the breeding season all control ewes (100%) and 91.9% of the treatment ewes were detected to have active corpus luteum (P = 0.09). An almost inverse result (90% vs. 97.5%; P = 0.2) was detected in the non-breeding season. The lambing rate was higher (P = 0.03) in the treatment group compared to the control ewes during the non-breeding season (90% vs. 70%), but tended to be lower (P = 0.07) in the breeding season (73% vs. 90%). Twin lambing rate was higher in the treatment group compared to the control ewes in the breeding (40.7% vs. 0.0%; P < 0.05) and non-breeding (22.2% vs. 0.0%; P < 0.05) seasons. The litter size of the control and treated ewes were 1.0 ± 0.0 vs. 1.40 ± 0.10 in the breeding and 1.0 ± 0.0 vs. 1.22 ± 0.10 in the non-breeding season (P < 0.05). No effect was observed regard to synchronization of the treated ewes. In the breeding season two injections of PGF_2α ten days apart combined with ram effect, may lower the lambing rate, but may enhance twin pregnancies and litter size in Karakul ewes. In the non-breeding season, however, the GnRH-PGF_2α treatment plus ram effect may enhance the lambing rate, twin pregnancies and litter size.