Estimates of genetic parameters for lactation shape parameters with multivariate statistical technique in brown Swiss cattle

This study was conducted to estimate heritabilities of milk yield traits (305-d milk yield, persistency, and peak time & lactation curve shape parameters as per Wood model) and two latent variables from Factor Analysis on the basis of 10 test day (TD) milk yield records. Data on pedigree and 504 production records of 272 Brown Swiss cattle were analyzed to estimate genetic parameters with univariate and bivariate animal models. Factor analysis was fitted to 10 TD milk yield records (assumed as independent measures) in order to define lactation curve shapes and two latent variables (FC1 & FC2) were derived from Factor analysis. Kaiser-Meyer Olkin (KMO) measure of sampling adequacy (0.93) and Bartlett's test of Spherity (P less than 0.001) were used to determine whether the available data were appropriate for factor analysis. Results suggested that application of factor analysis was an accurate decision to analyze the data. Of the 10 TD milk yield records, first five TD milk records reflected the first part of lactation, FC1, on ascending in milk yield until peak, whereas 6th to 10th TD milk records represented lactation persistency, the second part of lactation, FC2, on descending in milk yield after peak. Heritabilities of 305-d milk yield, a, b, c (lactation shape parameters on Wood model) persistency, peak yield, peak time, FC1 and FC2 were 0.25, 0.14, 0.18, 0.15, 0.29, 0.23, 0.42, 0.13 and 0.15, respectively. Genetic correlations of 305-d milk yield with FC1 and FC2 were 0.66 and unity, respectively. The genetic association of persistency of lactation with peak yield time (0.95) and FC2 (0.23) was observed. Medium to high genetic correlations of FC1 with b parameter (0.33) and peak yield (0.48) were observed in the present study. High genetic correlations among different traits under the study suggested that the scores of two latent (FC1 & FC2) variables, defining lactation curve shape, could be us ed reliably for genetic improvement in milk yield and peak yield through selection.