Expressing female fertility in the Walloon region of Belgium: how to do?

Since September 2007, the Walloon Region of Belgium has used a genetic evaluation system for pregnancy rate in Holsteins and has participated in 3 of the 5 MACE trait INTERBULL runs for female fertility. In order to define general way of female fertility expression, a principal component analysis was carried out on six published foreign female fertility indexes. Results of were used to compute a direct female fertility index with the INTERBULL international female fertility proofs available on the Walloon scale. An indirect female fertility index was also developed in order to increase reliability of young bulls. Approximate procedure based on selection index was used to combine both indexes in an overall index called combined female fertility index. This index was highly correlated with the direct female fertility index (.96) and the first principal component (.85), therefore it was considered as good expression of female fertility. Moreover, this allowed recovering 4,019 INTERBULL bulls with a publishable female fertility index.