The data on 305-day milk yield and age at calving in F, H. Friesian X Sahiwal crossbred cows for 1977 to 1990 were utilized for this study .. The average 305-day milk yield for 1057 normal lactation records was 2622.71 litres and the average age at different calvings was 66.62 months. The maximum milk production (2993.84 litres) was achieved at the calving age of 117 months; the milk production then began to decline at a comparatively slow rate. The quadratic equation developed was: Y, = 1568.33 + 24.422 m, - 0.1046 mj2
