Effect of Some Environmental Factors on the Milk Fat and Solids-not-fat Content of Cow's Milk

Two-day composite samples of milk were collected monthly from 243 Holstein and 276 Jersey cows for the first 305 days of lactation. The milk samples were analyzed for percentage of milk fat and SNF. The effects of lactation number, calendar year, stage of lactation, and month of year were determined. Age, stage of lactation, and month of year appeared to be major sources of variation in milk fat and SNF percentage. The percentage of milk fat and SNF tended to decrease as lactation number increased. Both breeds reached a low in percentage of milk fat and SNF 60-90 days after parturition, and both increased thereafter until the end of lactation. The two breeds also decreased in percentage of these two milk constituents with age.