PERIPHERAL CONCENTRATIONS OF A 60-KDA PREGNANCY SERUM-PROTEIN DURING GESTATION AND AFTER CALVING AND IN RELATIONSHIP TO EMBRYONIC MORTALITYIN CATTLE

In order to have a specific marker for studying pregnancy in cattle we examined the characteristics of a pregnancy serum protein produced by the placenta (PSP60). Its profile in peripheral blood was determined by radioimmunoassay in pregnant cows of 3 breeds after artificial inse mination (Al): Charolais (n = 24), Normande (n = 24) and Holstein (n = 26). From 27 d post-Al to the end of pregnancy the plasma PSP60 conce ntration increased, especially during the last 2 wk, to reach a peak a few d before calving, which was higher (P < 0.00 1) in the Charolais (1238 +/- 422 ng/ml) than in the other breeds (528 +/- 458 and 444 +/- 204 ng/ml). With an apparent half-life of almost-equal-to 8 d, this p rotein was still detectable in the maternal blood from 105, 85 and 87 d post-partum in the Charolais, Normande and Holstein breeds, respecti vely. Fertility results on 1 102 inseminations in the Charolais breed showed that the PSP60 concentration dropped then disappeared after emb ryonic mortality. Sequential assays of this protein between 28-90 d af ter Al are useful for studying the course of pregnancy, although they do not allow discrimination between early embryonic mortality and non- fertilization which together constitute 75% of pregnancy failures