Residual Milk from Oxytocin Injections Throughout the Lactation

The changes in residual milk during the first 10 mo. of lactation have been studied in ten cows of the Jersey and Holstein-Friesian breeds. The amount of residual milk obtained by injecting 10 I. U. of oxytocin intravenously varied roughly as the normal milk yield within breeds. The differences in residual milk yield between breeds were not significant. The fat test of the residual milk varied inversely as the fat test of the normal milk throughout the lactation within breeds, but Jerseys had higher fat tests than Holstein-Friesians. The results of these experiments are interpreted to indicate a progressive decrease in amount of active secretory tissue in the udder from the peak to the end of lactation, with a marked decrease during the last 2 mo.