UNILATERAL STIMULATION OF BOVINE OVARIES BY LOCAL INJECTION OF PREGNANT MARE'S SERUM GONADOTROPHIN
K. J. BETTERIDGE
Treatment with PMSG is still the most widely used method of inducing superovulation in cattle. A major problem, however, is the great variation in response of individual animals to identical treatments (Foote & Onuma, 1970; Mariana, Maul\l=e'\on,Beno\l=i^\t & Chupin, 1970). This variation may, in part, be due to differences in the absorption of injected PMSG and its subsequent distribution to the ovary. In rabbits, intraovarian rather than systemic injection is said to be a more sensitive test
... or PMSG in the Friedman pregnancy test (Chicchini & Chiacchiarini, 1963) and intrafollicular injection of LH also induces ovulation (Jones & Nalbandov, 1972) . This report describes an investigation of the possibility that local injection of PMSG into bovine ovaries might produce more consistent superovulatory responses than do systemic injections. As outlined in Table 1 , thirteen heifers of mixed breeding were used in fifteen experiments. Two heifers were used a second time (Exps 9 and 11) 54 and 90 days, respectively, after excision of the treated ovary at the completion of Exps 1 and 6. Oestrous cycles were recorded by daily observation ofbehaviour in the absence of a bull. Ovaries were injected with various doses of PMSG (Gestyl, Organon) at laparotomy on Day 16 of the cycle (day of oestrus = Day 0) in all but two cases (Exps 3 and 5) which were treated on Day 17. Laparotomy was carried out under general anaesthesia (halothane in N20/02) and injections were given either to the ovary containing (ipsilateral to) the CL or to the contralateral ovary. Four routes of injection were used : intrastromal (i.s.), sub-cortical (s.cort), intra-arterial (i.a.) and intrafollicular (i.f.). Injections by the first three routes were made with a 25or 26-gauge needle, the required dose of PMSG being dissolved in 1-0 ml of 0-9% NaCl. For the first three routes, doses were injected: (1) 1-5 cm into the ovarian stroma (i.s.), (2) just below the surface at two sites (s.cort.), or (3) into the convoluted ovarian artery about 5 cm from the hilus (La.). For i.f. admini¬ stration (Exps 14 and 15), a microsyringe and 27-gauge needle were used to inject each of five follicles (5 mm in diameter) in each treated ovary with 20 i.u.