Phenotypic and genetic trends for peak yield, milk yield, and lactation persistency in the Murciano-Granadina breed

This study evaluated the genetic (TG) and phenotypic (TF) trends for the peak yield (PP), milk yield (RL), and lactation persistency (P) traits of the Murciano-Granadina (MG) goat lactation curve obtained from 80,872 lactations of 85,404 goats (historical records from 1990-2012). The biomodelling of lactation curves allowed us to estimate the PP, RL, and P traits using the Spline model in the "R" software. The genetic values (VGs) were obtained using the univariate animal model with repeated observations, employing the MTDFREML package. The TG and TF were estimated via the least-squares regression of the average of VGs and known yield information according to the year of birth. While calculating the TG and TF, linear regression coefficients (b) were obtained, where the b values for PP, RL, and P were +0.00071, +0.00698; +0.00114, +0.01117; and +0.00002, -0.00076, respectively. The TG and TF for the PP and RL behaved similarly following an upward trend line with increasing and decreasing intervals. The TG for P showed seasonal variations while the TF followed a downward trend with more consistent points in its trajectory; supporting the idea that high yields are detrimental to the P. These results inform the breeders about the behavior of these traits and provide the basis for the incorporation of the lactation persistency as a selection criteria in the genetic program of the MG breed.