Breed variations in the shape of the lactation curve of cattle and their implications for efficiency

ABSTRACT Mean daily milk yield, fat percentage and protein percentage were recorded monthly, from August 1978 to July 1979. for 579 303 British Friesian, 6 608 Shorthorn, 27 374 Ayrshire, 19 529 Jersey, and 19 760 Guernsey cattle and classified by breed, parity and stage of lactation. Parameters of the function y(n) = anb ecn were estimated for each breed/parity group for yield, fat percentage and yield, protein percentage and yield, and energy (MJ) output as milk (b and c describe the shape of the curve, a is a scalar, n the week of lactation and e the base of natural logarithms). In the mature cows of each breed (parity 4 or more), the shape constants (b, c) for milk, fat and protein production in kg respectively were: Generally, cows of all five breeds which calved in the winter produced about 4% more milk, fat and protein than average, and those that calved in the summer produced about 4% less. After allowing for that, and removing the effect of the calving pattern, a seasonal variation in production occurred to produce a peak in June 1979 nearly 12% above average for liquid milk, in July 1979 about 4% for fat and in June 1979 about 12% for protein production (not percentage). Trough month was January 1979 for all three characters: —8%; —4% and — 9% respectively. A consideration of the theory of metabolizable energy suggested that the peak of energy output which occurred about week 4 of lactation in all breeds and parities, expressed as a fraction of the live weight of the animal, had a critical bearing on the need to mobilize body reserves.