Gene action and heterosis in lifetime traits of Friesian x Sahiwal crosses

Gene action and heterosis in seven lifetime traits of Holstein-Friesian x S ahiwal crosses was studied by fitting genetic additive-dominance and Dicker son, Sheridan models. The additive-dominance model is found adequate for al l the traits except 'average milk yield per day of total productive life'. The heterosis measured from mid-parent vaned from 15% in 'total life' to 10 8% in 'milk yield from all available lactations'. Heterosis measured from s uperior parent ranged from 6% in 'total milk yield of first three lactation s' to 75% in 'milk yield from all available lactations'. The larger heteros is observed in some of the lifetime traits is attributed as the direct cons equence of longer productive life in F(1)s compared to parental breeds. On the basis of the predicted performance of some of the nonavailable grades l ike 2/3 exotic, creation of synthetics is moored.