Superovulation in ewes by a single injection of pFSH dissolved in polyvinylpyrrolidone (PVP): effects of PVP molecular weight, concentration and schedule of treatment

Abstract

Three experiments were carried out to evaluate induction in ewes of superovulation and embryo production by a single injection of a porcine pituitary extract (pFSH) dissolved in polyvinylpyrrolidone (PVP), investigating the effects of PVP molecular weight and its concentration (Experiment I), time and method of treatment (Experiments II and III). All ewes were synchronized for estrus by vaginal sponges impregnated with fluorogestone acetate (FGA; 30 mg, 9 days) plus PGF 2α (Cloprostenol, 50 μg, 48 h before sponge removal — s.r.), and superovulated by 250 IU pFSH. In Experiment I, 60 Gentile di Puglia ewes were subdivided into five experimental groups ( n=12): Group A, the control, received six decreasing intramuscular (i.m.) doses of pFSH, 12 h apart, beginning 48 h before s.r.; Groups B and C were given 48 h before s.r. a single i.m. injection of pFSH dissolved in PVP with MW=10,000, respectively, at concentrations of 15 and 30% w/v; Groups D and E received the same treatments as for B and C using PVP with MW=40,000. None of the pFSH–PVP treatments were effective in inducing superovulation. In Experiment II, 22 Leccese ewes were subdivided into two groups ( n=11): Group A, control received i.m. four decreasing doses of pFSH, beginning 24 h before s.r., 12 h apart; Group B was given a single i.m. injection of pFSH dissolved in PVP (MW=40,000 at 30% w/v), 24 h before s.r. The pFSH–PVP treatment provided an ovulation rate similar to the control and tended to enhance embryo yield (4.4 versus 2.4, P>0.05). In Experiment III, 60 Leccese ewes were subdivided into six treatment groups ( n=10). Groups A and D served as controls and received i.m. 12 h apart, six doses (from 48 h before s.r.) and four doses (from 24 h before s.r.) of pFSH, respectively. Groups B and C were treated by a single injection of pFSH in PVP (MW=10,000; 30% w/v) 48 h before s.r., respectively by i.m. or subcutaneous (s.c.) administration. Groups E and F received the same treatments as for B and C 24 h before s.r. Intramuscular pFSH–PVP administration 24 h before s.r. provided an ovulation rate (8.1), mean numbers of ova recovered (5.6) and fertilized (4.2) comparable to the six or four dose treatments and significantly higher ( P<0.01) compared to the pFSH–PVP treatment carried out i.m. 48 h before s.r. These results show that a single injection of pFSH dissolved in PVP at 30% w/v, performed i.m. 24 h before s.r., is able to induce a superovulatory response comparable to that following multiple injection treatment, regardless of PVP molecular weight.