This only applies to the 350 to 550 mm zones. A generation ago, most cows were of the traditional British breeds, weighed 750 to 950 lb. and weaned a 305 lb. calf. Crossbreeding programs with mostly continental European breeds have increased cow size to an average of 1,200 to 1,300 lb. The range in cow weights extends from 1,000 to 1,600 lb. These larger cows require more energy for maintenance and for greater milk production.
Calves are bigger too.
The genetic changes that boost cow size also yield a larger-framed calf. This calf size combined with a general shift towards earlier calving, clearly suggests the modern calf requires more nutrition than the standard calf. The bottom line is that bigger cows and heavier calves graze more grass, so adjustments need to be made when matching livestock needs with available forage. In Table 2, the energy requirements of the 1,000 lb. AU with standard milking ability and an average calf are compared with those of a large 1,500 lb. cow and her calf. A 1,500 lb. cow will require 33 per cent more energy.