Estimation of Genetic Parameters for Lactation Persistency and Productive Maturity in the Italian Brown Swiss Breed

Abstract

Modern dairy cattle breeding increasingly emphasizes functional efficiency and lifetime productivity to enhance herd sustainability. The Italian Brown Swiss breed, characterized by relatively flat lactation curves, represents a suitable population for selection on lactation persistency and productive maturity. This study aimed to estimate genetic parameters for protein yield (kg) across four lactation phases using a multi-trait repeatability animal model. Traits were defined as early (0–150 days) and late (150–300 days) production in first and subsequent lactations. After stringent data editing procedures, approximately 500,000 test-day derived records were included in the analysis. Heritability estimates ranged from 0.11 to 0.25 across phases, in agreement with values commonly reported for protein yield in Brown Swiss populations. Genetic correlations between phases were high (0.75–0.88), indicating substantial shared genetic background across lactation stages and parities. Correlations with the official protein index were above 0.90, supporting the consistency of the proposed model with the current evaluation system. Model validation, based on residual diagnostics and sire ranking comparisons, confirmed its ability to discriminate animals according to differences in lactation curve shape. Based on these results, synthetic indices for persistency and productive maturity are under evaluation to provide new selection tools aimed at reducing metabolic stress and improving lifetime efficiency.