Feed intake and milk production from three rates of concentrate for cows bred to differ in size

Two groups of Holstein cows sired by bulls that had been selected partly for transmitting ability for size averaged 525 and 570 kg weight after second calving. Cows were fed 1.0 kg concentrate to 5.0, 3.0, or 1.5 kg milk above 9.1 kg per day and forage to appetite during first and second lactations (248 lactations). Generally equal quantities of alfalfa haylage and corn silage were fed each day in weighed amounts to exceed consumption. At times haylage constituted the only forage fed. Results of feeding low (2.2 kg), medium (3.8 kg), or high (6.9 kg) concentrate dry matter daily per cow were: concentrate as a percent of total dry matter consumed, 12.2, 20.2, and 37.1%; dry matter intake from forage, 15.6, 14.5, and 11.6 kg/day; dry matter intake as percent of body weight, 3.25, 3.32, and 3.33; crude fiber as percent of dry matter consumed, 25.2, 23.6, and 20.5; crude protein as percent of dry matter consumed, 15.7, 15.4, and 15.1; total digestible nutrients consumed per day, 10.8, 11.4, and 12.2 kg; milk produced as milk/day, 18.7, 19.9, and 21.3 kg; fat-corrected milk/day, 18.6, 20.0, and 20.7 kg; fat-corrected milk as percent of body weight, 3.44, 3.68, and 3.78; and fat-corrected milk as gram per weight kg .75, 166, 178, and 183; fat content of milk, 4.00, 4.11, and 3.92%; protein content of milk, 3.49, 3.58, and 3.61%; gross efficiency of milk production, .591, .579, and .595 kg total digestible nutrients/kg fat-corrected milk; and net efficiency, .304, .308, and .332 kg total digestible nutrients/kg fat-corrected milk. Cow size, parity, and period of lactation affected most variables. These latter effects are illustrated in graphs or tables.