THE IMMUNOLOGICAL MEASUREMENT OF PREGNANT MARE SERUM GONADOTROPHIN

Abstract

SUMMARY A quantitative haemagglutination—inhibition assay was used to measure pregnant mare serum gonadotrophin (PMSG) concentration in six Welsh Mountain pony mares and ten thoroughbred mares during early pregnancy. In both groups of animals PMSG was first detected in the serum between 35 and 41 days of gestation, the limit of sensitivity of the assay being 0·6 i.u. PMSG/ml. The levels rose sharply to reach a maximum at 55–60 days of gestation in the ponies and 60–65 days in the thoroughbreds. The highest concentrations recorded in both groups were 100–112 i.u. PMSG/ml., although one animal never produced more than 11 i.u./ml. The highest concentrations were found in the primiparous ponies. The rate of decline of the PMSG concentrations was not as great as the initial rate of increase, and in all animals PMSG had virtually disappeared from the serum by 120–130 days of gestation. The haemagglutination-inhibition assay was evaluated as a pregnancy diagnosis test; 183 sera from 58 mares of various breeds between 41 and 87 days of gestation all gave a positive result, whereas 47 sera from non-pregnant mares, geldings and stallions gave uniformly negative results. An additional 64 sera from 23 mares between 88 and 110 days of gestation gave 62 positives, the two negative reactions being in a pony mare that showed exceptionally low concentrations of PMSG throughout pregnancy.