26 - Are Subjectively Scored Linear Type Traits Suitable Predictors of Genetic Merit for Feed Intake in Grazing Holstein-friesian Dairy Cows?

Measuring dry matter intake (DMI) in grazing dairy cows using currently available techniques is invasive, time consuming, and expensive. An alternative to directly measuring DMI for use in genetic evaluations is to identify a set of readily available data sources that can be used in a multi-trait genetic evaluation with DMI. The objectives of the present study were to estimate the genetic correlations between readily available body-related linear type trait information and DMI in grazing, lactating Irish dairy cows and to estimate the partial genetic correlations between linear traits and DMI, after adjusting for differences in genetic merit for body weight. After edits, a total of 8,055 test-day records of DMI, body weight, and milk yield from 1,331 multiparous dairy cows were available, as were chest width, body depth, and stature scores for 47,141 first lactation dairy cows. In addition to considering the routinely recorded linear type traits individually, novel traits were defined as the product of two or three linear type traits as an approximation of rumen volume. The genetic variance of DMI, body weight, milk yield, and linear type traits were estimated using univariate animal linear mixed models. Sire linear mixed models were used to calculate genetic and phenotypic covariances. All linear type traits were moderately heritable (0.27 to 0.49) and genetically correlated (0.29 to 0.63) with DMI. The genetic correlations between the individual linear type traits and DMI, when the latter was adjusted for differences in the genetic merit for body weight, varied from 0.00 to 0.39. If the (partial) genetic correlations were validated with genetic evaluations, routinely available linear type trait records and live weight data could facilitate the selection of DMI in dairy cows, removing the need to capture large amounts of cost prohibitive feed intake phenotypes.