[Progesterone and estrogen concentrations in the peripheral blood of heifers in relation to the course of calving].

Concentrations of progesterone (P), free (E1) and conjugated (E1S) oestrone and free (E2) and conjugated (E2S) oestradiol-17 beta were determined in plasma samples from twenty-five heifers of three different breeds (Holstein, Meuse-Rhine-Yssel, Dutch Friesian). The blood of the animals was sampled once weekly from the jugular vein during the period from the 29th to the 9th day before parturition. Findings in five heifers were not included in analysis because of malpresentation of the calf. Nine of the remaining twenty heifers had difficulties in calving and nine others, partially the same animals, gave birth to dead calves. The total period of sampling was divided into three periods of seven days and, within each period, the direct relationship between hormone levels and ease of calving was examined. For this purpose hormone concentrations were corrected within each period, for a number of days prepartum, breed, sex of calf, birth weight, length of gestation and season of calving, when these were significant. Only the effect of birth weight of male calves on P, the effect of season on E2S and that of days on E1 and E2 in period 3 (15-9 days before parturition) were significant. As a rule, there were only small, non-significant differences in corrected hormone concentrations between heifers with and those without dystocia. A comparison of average concentrations between heifers which gave birth to a stillborn calf and heifers giving birth to a living calf showed similar results. Measurements on the calves suggested that dystocia was more likely to be caused by an oversized calf than it was by abnormalities in hormone levels in these cases.