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

Gene action and heterosis in seven lifetime traits of Holstein-Friesian x Sahiwal crosses was studied by fitting genetic additive-dominance and Dickerson, Sheridan models. The additive-dominance model is found adequate for all the traits except 'average milk yield per day of total productive life'. The heterosis measured from mid-parent varied from 15% in 'total life' to 108% in 'milk yield from all available lactations'. Heterosis measured from superior parent ranged from 6% in 'total milk yield of first three lactations' to 75% in 'milk yield from all available lactations'. The larger heterosis observed in some of the lifetime traits is attributed as the direct consequence of longer productive life in F₁S compared to parental breeds. On the basis of the predicted performance of some of the nonavailable grades like 2/3 exotic, creation of synthetics is mooted.