The effect of different oestrus-induction protocols to the hormonal changes and pregnancy rates in ewes out of the breeding season

Background: There are several different hormonal methods influencing the ovine breeding season. Objectives: In our experiment we induced the cycle of ewes outside of the breeding season, using different sex-hormones (GnRH, eCG, and long-term progesterone treatment). We examined the effect of the treatments to the blood progesterone and estradiol 4* levels, and to the pregnancy rate and lambing rate. We also examined the possible fertility of the second oestrus after the induction. Materials and methods: We included 44 Hungarian merino ewes in our experiment in a Hungarian sheep farm. Group 1 (n = 13) was the control, where the animals received long-term progesterone treatment (14 days) in the form of Chronogest CR vaginal sponge (MSD Animal Health). Group 2 (n = 15) was treated with a GnRH injection (0.01 mg buserelin/animal, Receptal, MSD Animal Health) 2 days after the sponge removal. Group 3 (n = 16) got an eCG injection (500 IU/animal, Folligon, MSD Animal Health) at the time of sponge removal. All groups were inseminated twice via hand mating, two days after sponge removal. We collected blood samples at 4 different time points (day 0, day 14, day of the first mating, and at early pregnancy stage). We examined the blood progesterone and estradiol 4* levels at each time point. Results and discussion: The blood progesterone levels were significantly higher only at the 4th time point (see Table). In terms of estradiol 4* levels, the groups differ significantly at the 3rd time point. Group 3 has elevated estradiol 4* levels (p = 0.0048). This implies that eCG was successful in enhancing follicular growth. After the first oestrus, the proportion of pregnant ewes were the highest in Group 3 (not significant). 36.36% of all ewes got pregnant after the first oestrus cycle, and an additional 32.14% of the remaining animals at the following oestrus cycle (56.81% in total). Based on these numbers, the second oestrus, after the induced one, is fertile and can be used to increase the lambing rate.