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

Gene action and heterosis in seven lifetime traits of Holstein‐Friesian × 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.