Longitudinal Genetic Analyses of Functional Traits in Dairy Cows Using Daily Random Regression Methodology

This study estimated heritabilities of daily observations on milk yield, milking speed, dry matter intake and live weight as well as genetic correlations among them over time using the random regression methodology. Data were from dairy cattle stationed in an experimental research farm over the past 10 years. All traits were recorded daily using automated machines. Estimated heritabilities were high, as expected from experimental farm datasets, and varied from 0.45 to 0.94 ( 2 h =0.71) for MY, 0.29 to 0.80 ( 2 h =0.55) for MS, 0.42 to 0.71 ( 2 h =0.57) for LW and, 0.23 to 0.92 ( 2 h =0.65) for DMI. Estimated genetic correlations varied from 0.16 to 0.64 between MY and MS, -0.47 to 0.29 between MY and DMI, -0.36 to 0.36 between MY and LW, -0.15 to 0.02 between MS and DMI, -0.42 to 0.03 between MS and LW and -0.89 to 0.29 between DMI and LW. Genetic correlations for MY, MS, DMI and LW at calving to middle of the lactation monotonly decreased to 0.40, 0.36, 0.14 and 0.36 and at the end of the lactation decreased to -0.06, 0.23, -0.07 and 0.09 respectively. Results could be useful when constructing selection indices for more than one trait, with an emphasis on timedependent genetic selection.