Genetic correlation among linear type traits and productive traits in Girolando cattle

Linear conformation traits are important indicators of structural soundness and functional ability in dairy cows, whereas productive traits, especially milk yield, are central to dairy profitability. Understanding the genetic relationships among these traits and the effectiveness of selection indices is essential for breeding programs aiming to improve productivity and longevity simultaneously. Genetic parameters were estimated using bi-trait models for linear conformation traits (body conformation, dairy form, rump, feet and legs, and udder traits), milk yield, and longevity. Direct and correlated responses to selection were evaluated using 2 approaches: (1) pre-established indices from the Girolando breeding program and (2) optimized indices derived from genetic parameters estimated in this study. Heritability estimates ranged from 0.01 to 0.33 for linear traits and from 0.04 to 0.13 for productive traits. Genetic correlations among linear traits varied from -0.73 to 0.97, whereas correlations between linear and productive traits ranged from -0.50 to 0.69. Udder-related traits showed the strongest associations with longevity, with Fore Udder Attachment (FUA) consistently emerging as the most informative indicator. Selection indices generally outperformed direct selection for productive and longevity traits, particularly for traits emphasizing dairy strength and the mammary system. Among pre-established indices, the Mammary System index provided the best balance between milk yield and longevity. Optimized indices showed superior performance, and a reduced index focused on key traits yielded responses that were similarly correlated with greater parsimony. Overall, data-driven and biologically informed indices improved both productivity and functional longevity in Girolando breeding programs.