Effects of hCG and GnRH injections on day 12 post-mating on the plasma progesterone concentration and litter size of Buchi sheep during the spring season

The present study was carried out to investigate the effects of different hormonal intramuscular (i/m) injections on plasma progesterone concentration on day 12 of pregnancy and the embryonic mortality resulting from reproductive performance of Buchi sheep bred at synchronized estrus during the spring season. Thirty 2-4 years old Buchi sheep, weighing 40-45 kg (Mean ± S.E.M) were selected. The daily feed/ration was seasonal fodder, tree looping and 250 g concentrate per sheep per day. Sheep were mated to ram at synchronized estrus via two i/m injections of 2 ml PGF2α analogue (Dalmazin) given 11 days apart. These sheep were divided into three treatment groups (10/per group) through random stratification by body weight. The animals were given either normal saline or 500 IU hCG or 2 ml GnRH on day 12 post-mating at synchronized estrus. Blood samples were collected from jugular venipuncture (3 ml) with a disposable syringe from 2-16 days after treatment. The plasma progesterone concentration was determined by ELISA. The overall mean progesterone concentrations were greater (P < 0.001) in the treated sheep than in the saline treated controls. GnRH or hCG treatment increased (P < 0.001) the mean plasma progesterone concentration. Compared with the control both treatment groups presented increased litter size and no embryonic mortality. In conclusion, the results of the present study demonstrated that treatment with hCG or GnRH may be luteotrophic and increase pregnancy rates and litter sizes in Buchi sheep.