The effect of inbreeding on components of dairy cattle fertility as calculated from non-return data, using a multiphasic logistic function

This pilot study demonstrates the use of multiphasic analysis of non-return data to study effects of inbreeding on conception rate, calving rate and calving rate given conception when only non-return data is available. The results indicate that inbreeding of the cow mainly affects late embryonic mortality while inbreeding of the embryo mainly affects foetal mortality. However, interpretation of the results is difficult since inbreeding of the cows is confounded with inbreeding of the embryos. It is concluded that application of multiphasic analysis, as used in this study, is only feasible when extreme large numbers of first insemination are available per bull. Only then will it be possible to include effects of inbreeding of the cow and inbreeding of the embryo simultaneously in order to disentangle effects of inbreeding of cows and embryos.