Heterosis in the lactation curves of Girolando cows with emphasis on variations of the individual curves

Abstract

Linear and nonlinear models were used to evaluate the effect of heterosis on the components of the lactation curves of different crossbred groups of cows from Girolando cattle. Data consisted of 233,587 test-day milk yield records from 33,995 primiparous cows from 1998 and 2014. The Wood’s linear model (WDlin), Wood’s nonlinear model (WDnlin), Wilmink’s model (WL) and Ali and Schaeffer’s model (ASH) were used to estimate individual peak milk yield (PY), day of peak milk yield (PT), 305-day milk yield (TMY), different persistency measures and parameters of lactation curves. The quality of fit of models was different for the genetic groups. The WL model was used to the estimation of heterosis because of the best fit of lactation curve. The heterosis effect was significant (P < .001) for TMY, PY and for the ‘a’ parameter of WL model (initial production). For TMY and PY, crossbred cows presented 14.64% and 20.60% larger yields than the average of the parental breeds, respectively. The heterosis effect from crossbreeding presents more benefits for the components of initial stage of milk yield and milk yield at the peak and with a lesser extent with the two final stages (persistency).

Keywords

• crossbreeding
• dairy cattle
• daily milk yield
• lactation model