Relation of Natural Copper in Milk to Incidence of Spontaneous Oxidized Flavor

Milk as it is produced by the cow contains a low but variable concentration of copper (natural copper).Results are presented that show a relatively high concentration (ca.0.2 p.p.m.) of natural copper in early lactation milk, and a level of about 0.02-0.04p.p.m, for most cows during the remainder of a lactation period.These results are similar to others reported recently.No difference was observed between pasture and dry feed in the natural copper concentration in the resulting milk.When cows on dry feed were drenched with large (10-g.)doses of copper sulfate, there was an increase in the natural copper content of their milk and in the incidence and intensity of spontaneous oxidized flavor.For cows on an alfalfa hay-grain concentrate ration, and not in early lactation, a highly significant correlation was observed between the concentration of natural copper in milk and the incidence and intensity of spontaneous oxidized flavor.It is concluded that the copper present in milk as it comes from the cow is an important catalyst of oxidized flavor.Copper is an effective catalyst of oxidized flavor in milk, but it has not been established whether the small amount normally in milk (natural copper) is important to development of the defect.The principal purpose of this study was to investigate the relation of natural copper concentration to the incidence of spontaneous oxidized flavor in milk produced by cows on alfalfa hay-grain concentrate ration.Values reported for the natural copper content of milk are variable, with early workers obtaining higher results.The differences appear to be attributable to improvements in analytical technics (1) and to reduee:l contamination of samples.Koppejan and Mulder (6) and Menger and Mulde, r (8) indicated the variations that may be expected in milk samples taken from individual cows at different stages of lactation.Natural copper in milk is high (as high as 0.2 p.p.m.) during the first days of a lactation period, and gradually declines to normal levels (0.02-0.04 p.p.m.) (luring the first 2 me.The natural copper content of milk generally is not considered to be influenced by the cow's feed or copper intake (4, 8).However, Davis (2) stated that the copper content of milk can be almost doubled b.y a large increase in a cow's copper intake. EXPERIMENTAL PROCEI)UREExperimental cows.The cows used in this study were a group of 20 Holsteins maintained contimmusly (except for a week on pasture) on a dry ration con-