Genetic analysis of udder traits in Manchega ewes

Abstract

Five udder traits, udder depth (UD), udder attachment (UA), teat placement (TP), teat size (TS) and udder shape (US), have been studied in Manchega ewes. The raw data scale, ranging from 1 to 9, was transformed by the Snell method into a new scale from 0 to 100, to achieve more normalised data. Snell transformation was not effective in some cases, UA and US traits, as was demonstrated by a χ 2 test. But for UD, TP and TS transformed data had χ 2 values lower than those obtained with raw data, showing the goodness of this method in obtaining more linear data in these cases. Snell transformation did not affect variance component estimation. Heritabilities of UD (0.19) and TP (0.20) indicate genetic variability of these traits, which could be exploited in breeding programs to improve machine milk ability. High genetic correlations found between US–TP (0.81) and US–UA (0.94) indicate that this general and more subjective trait is highly conditioned by TP and UA perception, but not for UD (−0.03) and TS (−0.03), and thus, does not reflect the global udder conformation. The genetic correlation found between UD and 120 days milk yield, 0.64, indicates that selection for milk yield could lead to excessive depth udders, and therefore, that this trait might be considered in selection programs of dairy ewes, to avoid damage of udder conformation.