Pedigree analysis and inbreeding effects on calving traits in large dairy herds in Germany

A pedigree analysis was carried out for a subset of the German Holstein population with respect to the effective number of founders and the ancestors with the highest effect on 2 defined reference populations. Reference population 1 contained animals born between 1998 and 2002 (n = 19,537), and reference population 2 included animals born between 2003 and 2007 (n = 19,060). The pedigree file included 73,946 animals in total. The effective number of founders was 111.3 and 92.8 in reference populations 1 and 2, respectively. In reference population 1, 52.22% of the gene pool could be explained by 10 ancestors. In reference population 2, the 10 ancestors with the greatest effect contributed 57.22% of the gene pool. The effect of inbreeding on birth weight, calving ease, and stillbirth was also analyzed in this study. Two models were used to estimate the effect of inbreeding. One model fitted inbreeding as a regression on the inbreeding coefficient of the dam, whereas the other model fitted inbreeding as a regression on the inbreeding coefficient of the calf. Phenotypic data for this study were collected on 3 large commercial milk farms. Data recording took place from February 1998 to December 2008 and 36,623 calving events were recorded; 8.19% of the calves died at or within 48 h after calving. All calves were weighed after birth and the average birth weight was 43 kg for calves born alive and 42 kg for stillborn calves. Calving ease was recorded on a scale between 1 and 4. The distribution of scores was 69.81, 21.02, 8.96, and 0.22%, ranked 1 (without assistance or assistance by 1 person), 2 (assistance by 2 or more persons or mechanical assistance), 3 (veterinary assistance), and 4 (operation), respectively, on the calving-ease scale. Twins were excluded from all analyses. Dam inbreeding had no significant effect on the traits of this study. The inbreeding coefficient of the calf had no significant effect on birth weight and calving ease but showed a significant effect on stillbirth: the risk of stillbirth was found to increase by 0.22% per 1% increase of the inbreeding coefficient of the calf.