Estimation of genetic trends for lactation traits in Saanen × Beetal crossbred goats under sub-tropical conditions

Abstract

This study presents genetic trend analysis to evaluate the efficacy of a multi-decadal selective breeding program in a Saanen × Beetal crossbred dairy goat flock, reared under subtropical conditions at the ICAR-NDRI livestock farm. A dataset comprising 699 first-lactation phenotypic records for 150-day milk yield (150DMY), total milk yield (TMY), peak yield (PY), and days-in-milk (DIM) was utilized, with progeny originating from 109 sires and 444 dams over a 48-year period (1973–2021). The analytical framework involved fitting a mixed model to estimate variance components and derive estimated breeding values (EBVs) for all animals. The genetic trends for each trait were quantified through the regression of these EBVs on the birth year of the individuals. The analysis revealed consistent positive phenotypic progress, with mean annual increases of 67.42 g for 150DMY, 138.72 g for TMY, 0.04 days for DIM, and 0.24 g for PY. Critically, the regression of EBVs over time demonstrated significant and positive genetic trends for the primary milk yield traits, providing definitive evidence that the observed phenotypic improvements are underpinned by genetic gain. This confirmed that the systematic selection practices implemented within the flock have successfully harnessed additive genetic variance, leading to a sustained and heritable enhancement of milk production performance