Superovulatory response of Chios sheep to PMSG during spring and autumn

Abstract

To study the superovulatory response of Chios sheep to pregnant mares' serum gonadotrophin (PMSG), two experiments were carried out; one in spring and one in autumn. Four doses of PMSG (1500 IU, Group 1; 1000 IU, Group 2; 750 IU, Group 3; 500 IU, Group 4; controls, Group 5) were tested on 46 ewes. Oestrus was synchronised by means of MAP intravaginal sponges and PMSG was injected i.m. at the time of sponge withdrawal. When in oestrus, ewes were naturally mated. On Day 7 after sponge removal, mid-ventral laparotomy was performed and the uterine horns and/or oviducts were flushed with 20–40 ml Dulbecco's phosphate-buffered saline supplemented with 15% foetal bovine serum (FBS). The embryos were examined under a dissecting microscope and were evaluated according to morphological criteria. The interval from sponge removal to the onset of oestrus was significantly (P < 0.001) shorter in autumn than in spring in all groups. No significant differences regarding superovulatory response, collection and fertilisation rate or numbers of ova and embryos collected were found between spring and autumn. The clinical signs of oestrus started earlier (P < 0.001) in all PMSG treated animals than in the controls, both in spring and in autumn. The highest ovulation rate was recorded in Group 2 (5.9 ± 1.0), followed by Groups 1 (5.0±0.9), 3 (3.9±0.5), 4 (26±0.4) and 5 (1.3±0.1). The increase observed in total ovarian response (corpora lutea + large anovulated follicles) parallelled the increase of PMSG dose (10.7 ± 1.6, 7.7 ± 0.9, 4.5 ± 0.6, 3.4 ± 0.5 and 1.8 ± 0.2 for Groups 1, 2, 3, 4 and 5, respectively). The highest mean number of ova was collected from Group 3 (3.4±0.5), followed by Groups 2 (2.6 ± 0.4), 4 (2.2 ± 0.3), 1 (1.6 ± 0.5) and 5 (1.1 ± 0.1). The higher doses of PMSG (1500 and 1000 IU) significantly increased the mean number of anovulated follicles and significantly decreased recovery rate. Mean number of high viability embryos collected per ewe treated (0.9 ± 0.6, 1.5 ± 0.4, 2.2 ± 0.5, 1.5 ± 0.4, 0.9 ± 0.1 for Groups 1, 2, 3, 4 and 5, respectively) was not improved by PMSG dose. It is concluded that Chios sheep can be superovulated in autumn and in spring with similar results. Clinical signs of oestrus are initiated earlier in autumn than in spring. PMSG treatment shortens the interval from sponge removal to the onset of oestrus. Although PMSG does not seem to be the most suitable hormone for the induction of superovulation in Chios sheep, a dose of 750–1000 IU PMSG gives satisfactory results; higher doses are associated with side effects in a significant number of animals (many anovulated follicles, low recovery rate).