Complementary Milk and Its Relationship to Lactation

Since Ott and Scott (18) reported that the injection of the posterior pituitary extract into the vein of the goat rapidly and greatly increased the secretion of milk, many workers (8,19,26) have experimented with the posterior pituitary extract and verified the results with different animals.The active factor of the extract was later found by Ely and Petersen (5) to be oxytocin.Gaines (6) found that the injection of pituitary extract into goats milked "dry" never failed to yield more milk.Since then other workers have found similar conditions in cows and human subjects (1,2,12,13,17,24,27).Knodt and Petersen (1~) postulated that the amount of both nlilk and milk fat produced may be dependent upon the completeness of the evacuation of the gland at each milking and that the failure of the cow to completely let down her milk may account for the rapid decline in milk production with the advance in lactation.Donker et al. (3), using identical twin cows, showed that the milk let-down was a factor related to persistency, thus bearing' out the theory set forth by Knodt and Petersen.