Influence of short- and long-term administration of Melengestrol acetate on estrus activity and reproductive performance of nulliparous Barki ewes

In Egypt, research focusing on estrous synchronization in small ruminants based on Melengestrol acetate (MGA) supplementation, particularly in nulliparous ewes, is still lacking. The present work aimed to evaluate effect of long-term and short-term administration of melengestrol acetate (MGA) treatments on estrus synchronization and reproductive performance of nulliparous Barki Ewes. This study was performed in Siwa Oasis Research Station (Tegzerty Experimental Farm for animal production), belonged to Desert Research Center, Egypt. Forty five nulliparous Barki ewes with age ranging from 15.5 to 16.5 months, and 38 ± 0.23 kg average live body weight were assigned to one of three groups: (1) control (C, n = 15); (2) long-term treatment with MGA (n = 15, 0.22 mg/ewe/d for 14 days) and (3) short-term treatment with MGA (n = 15, 0.22 mg/ewe/d for 7 days). At the end of MGA treatment (14 or 7 d) all treated ewes were injected by 600 IU PMSG intramuscularly. The results showed that, ewes treated with MGA exhibited highest (P<0.05) estrus response rate (100%) in short term-MGA, followed by long term-MGA (93.33%), whereas the lowest was observed in control group (80%). Conception rates after natural mating were 85.71% and 93.33% for long term and short term MGA treated ewes, respectively. However, it recorded 100% in the control group. Fertility rate was significantly the highest (P<0.05) in short term-MGA (93.33%) than other groups (73.33%). There were no significant differences (p>0.05) in terms of lambing rate and prolificacy among the control and treated ewes. In the meantime, mean values of serum estradiol 17-β were lower (P≤0.01) in long-term treated ewes compared to those of short-term treated ones (27.20±1.78, 32.67±1.27pg/ml), respectively, while the lowest (P<0.05) level was recorded in the control ewes (13.01±1.31 pg/ml). Furthermore, overall mean values of serum progesterone in the control group (1.32 ± 0.09 ng/ml) was higher (P<0.05) than those of long- and short-term MGA treated groups (1.01 ± 0.13, 0.92 ± 0.11, ng/ml), respectively. It is concluded that reproductive efficiency of nulliparous Barki ewes could be improved by short-term supplementation with MGA.