Variations in the rate of milk secretion in milking intervals of 2–24 hours

Summary The rates of secretion of milk, fat and solids-not-fat have been measured over milking intervals of 2–24 h in a series of experiments using thirty cows at various stages of lactation. To ensure that the results were not biased by a carryover of residual milk and fat the residual milk was removed after intravenous injections of ‘Pitocin’. The biases that can be caused by previous interval effects and lactation trends were eliminated by the balanced Latin square design used. Milk and solids-not-fat secretion appeared to be linear with duration of milking interval up to 16 h, but with longer intervals there was, in some experiments, a decline in the rate of secretion. There was considerable variation between cows in the decline in secretion rate with increasing milking interval and part of this variation was associated with differences in milk yield. In all experiments fat secretion appeared to be almost linear with time over a 24 h period. After milking intervals of 20 and 24 h the rate of secretion of milk and solids-not-fat, but not of fat, was depressed for at least 16 h.