There may be the following reason for the fall of SNF and Lacto on the cows. Let me help you with certain facts so that you can able to understand that what exactly caused that. Milk composition is economically important to milk producers and processors and nutritionally important to consumers. It has been known for years that variations in milk composition occur; however, the composition of milk marketed nationally has been rather constant over the last 15 years, averaging 3.6 percent fat, 3.2 percent protein, and 4.7 percent lactose (Young et al., 1986). This is probably partly because of the prominence of the Holstein breed and the pricing of milk based on fat concentration. The introduction of milk pricing on a component basis and the perception by consumers that animal fats are unhealthy to have created new interest in how milk components can be altered to accommodate these emerging markets. The paper starts with a brief overview of the biosynthesis of milk components since changes in these reflect changes in the mammary gland synthesis or secretion of the component. Factors affecting milk composition such as breed, genetic variation within the breed, health, environment, management practices, and diet are then reviewed.