The Use of Synthetic Analogues of Prostaglandins for Inducing Luteolysis in Mares

Abstract

SUMMARYThe potency, toxicity and clinical value of two synthetic analogues of Prostaglandin F 2-(ICI-7()939 and ICI-8ioo8) for inducing luteolysis in mares is discussed. Measurement of peripheral plasma progestagen levels in over 4 oo Thoroughbred mares has demonstrated that abnormal persistence of luteal function (prolonged dioestrus) is the major cause of the failure of nonpregnant mares to exhibit regular oestrous cycles during the breeding season.

Control of the oestrous cycle of the mare

“…Even during the breeding season the interval between the PG and hCG injections may need to be modified. An interval of 6 days which was effective in May was too long in July and resulted in ovulations before the hCG injection in a large number of mares (Palmer, 1976a (Allen & Cooper, 1975;Nelson, 1976), progesterone (Loy & Swann, 1966), hCG (Loy & Hughes, 1966) or combined treatments (Holtan et al, 1977;Palmer, Saint-Quentin &Thimonier, 1976) have never been shown to decrease fertility significantly in experimental or in farm animals. However, comparison between inseminating once after synchronization and multiple insemination of treated or control animals (Holtan et al, 1977) (Palmer, 1977b …”

“…Whether persistence of the corpus luteum in non-pregnant mares is due to a lack of PG dis¬ charge at the normal time or to an increased secretion of luteotrophic factors is unknown. However, the persistent corpus luteum remains sensitive to exogenous PG treatments (Allen & Cooper, 1975). In recent years, PG injections have become widely used for the treatment of mares with a persistent CL (Allen & Cooper, 1975) or for stud management (Palmer, 1976b).…”

“…However, the persistent corpus luteum remains sensitive to exogenous PG treatments (Allen & Cooper, 1975). In recent years, PG injections have become widely used for the treatment of mares with a persistent CL (Allen & Cooper, 1975) or for stud management (Palmer, 1976b). Prostaglandin F-2a, in spite of mild side effects (Miller, Lauderdale & Geng, 1976), can be used for this purpose.…”

“…After the foal heat the mare has regular cycles. However, some mares may not continue to cycle because of a persistent corpus luteum (Allen & Cooper, 1975 (Palmer & Jousset, 1975a Ginther (1974) but not by Stabenfeldt et al (1972).…”

“…In almost all animals treated at an appropriate time of the luteal phase, oestrus will begin 2-5 days later. During induced oestrus, hormonal levels and fertility (Allen & Cooper, 1975 ;Nelson, 1976) injection of 1500-3000 i.u. hCG will induce ovulation about 24-48 h later (Loy & Hughes, 1966;Sullivan, Parker & Larson, 1973) when mares are treated on the 2nd day of oestrus.…”