Involvement of major histocompatibility complex class I compatibility between dam and calf in the aetiology of bovine retained placenta

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Abstract
Summary. The possibility was examined that in cattle compatibility of major histocompatibility complex (MHC) products between dam and calf might negatively influence the placental maturation and expulsion, and therefore increase the risk of retained placenta in healthy, normally calving cattle. Fifteen combinations of a single dam and two offspring were selected; the placenta of the first offspring was normally expelled (control) and the placenta of the second one was retained (case). The MHC class I and class II antigens of the animals were typed by immunoprecipitation and by one‐dimensional isoelectric focusing (1D‐IEF). Compatibility or incompatibility of class I or class II antigens was established by comparison of the IEF banding patterns of dam and calves. Analysis revealed that MHC class I compatibility between dam and calf increased the risk of retained placenta. In this study, the effect of class II compatibility was not significant, nor was the effect of the interaction of class I and class II. In a subsequent, additional sample the experimental design was extended: induction of tolerance against non‐inherited maternal antigens (NIMA) might be implicated in the occurrence of the disorder within the group of class I incompatible cases. In three out of the five class I incompatible retained placenta cases, the banding pattern of the incompatible haplotype of the calf was identical to that of the haplotype of the granddam that was not inherited by the dam (NIMA). Notably, within the nine class I incompatible controls, there were none in which the offspring shared a paternal class I type with the granddam. This might suggest a toleranceinducing effect of NIMA in cattle in relation to retained placenta. The results for the nine cases and 11 controls analysed in this second set confirmed the results of the first set: again there appeared to be an increased risk of retained placenta due to class I compatibility (direct or through NIMA). We suggest that retention of the placenta is, at least in part, the result of the lack of alloreactive mechanisms.