The derivation and calculation of daughter yield deviation (DYD) using an animal model was reported by VanRaden and Wiggans (1991). DYD, which is a measure of unregressed daughter performance, has become very important in dairy cattle research. It was initially the variable of choice for international evaluations by Interbull but due to the inability of several countries to calculate DYD, de-regressed proofs were used (Sigurdsson and Banos, 1995). In a recent study, Madsen et al (2001) demonstrated that when connections among countries are few, the use of de-regressed proofs for low to moderately heritable traits resulted in a downward bias in genetic parameters estimated using AI-REML. However, the use of DYDs gave estimates similar to the true values. Moreover, DYDs are commonly used in dairy cattle studies aimed at detecting quantitative trait loci based on the grand-daughter design (Weller, 2001). The recent trend in dairy cattle genetic evaluations is towards application of random regression models (RRM) using test day (TD) records. The calculation of DYDs using a RRM have not been reported. VanRaden and Wiggans (1991) also gave simplified equations that explained animal evaluations in terms of contributions from various sources of information. Similar equations have not been presented for a RRM to date. This paper outlines the calculation of DYDs and cow yield deviations when using a RRM. Equations similar to those derived by VanRaden and Wiggans (1991) are presented for RRM. Calculations are illustrated with evaluations for somatic cell count (SCC) using a RRM.

R. A Mrode, G. JT Swanson

Proceedings of the World Congress on Genetics Applied to Livestock Production, Volume 2002. Session 1, , 1.04, 2002
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