The placental growth factor (PGF)--a positional and functional candidate gene influencing calving ease and stillbirth in German dairy cattle.

The bovine placental growth factor-encoding gene (PGF) was analysed as a positional and functional candidate gene for the maternal effect on stillbirth and calving ease in first parity. Prominent levels of PGF expression have been reported for the whole human placenta and umbilical vein endothelial cells. Modulation of angiogenesis, vessel remodelling and vascular permeability during implantation and placentation suggest an influence on trophoblast function during pregnancy. Changes of expression or protein function may therefore be crucial to pregnancy and parturition. By comparative sequencing of bulls with extreme approximate daughter yield deviations for calving traits, we identified 37 SNPs and two insertions/deletions within the PGF gene. Seventeen of the identified polymorphisms were genotyped in 368 selected bulls and tested for association with approximate daughter yield deviations for calving traits. In a single marker analysis, all SNPs were significantly associated with maternal stillbirth and calving ease first parity. The allele substitutions of the significant SNPs explain 8% to 14% and 8% to 15% of the additive genetic variance for maternal stillbirth and maternal calving ease first parity, respectively. There is no evidence that any of the polymorphisms identified within this study could be the causal mutation underlying the QTL, which is likely to be a regulatory mutation. In summary, we report polymorphisms in the bovine PGF gene significantly associated with the maternal effect on stillbirth and calving ease in animals under selection. These results should be confirmed and extended in further studies to identify the causal mutation underlying the QTL analysed.