Nutritional Factors Affecting the Solids-Not-Fat Content of Milk

Abstract

The nutri t ion of the cow has a marked effect on milk composition. Considerably more research has dealt with feeding factors affecting milk fat than solids-not-fat (SNF). However, several very good reviews have summarized known effects of diet on the SNF content of milk (7, 12, 20, 23, 42, 43, 55, 60). Dietary energy. As early as 1941, Ridett et al. (53) observed a decrease in milk SNF of cows fed about 50% of the recommended energy level. In 1944, Rowland (61) reported field observations that SNF decreased in the winter and increased when cows were put on spring grazing. In a subsequent study, Rowland (62) noted that a lower SNF (8.34 vs. 8.68%) resulted from feeding energy at 75% of Woodmau's standards, compared to 100%. It is now widely recognized that restriction of energy to less than the recommended standard causes a marked reduction in milk SNF (12, 20, 23, 54, 60). Smaller increases have resulted from raising the energy intake well above sta, dard (6, 8, 14, 15, 17-19, 31, 32, 34-36, 50. 57). For example, I-lolmes et al. (32) fed four leveis of concentrate (0, 0.9, 1.8, 2.7 kg/gal milk) and noted an increase in SNF frora 8.3% on the lowest level of feeding to 8.6% on the highest. When Huber and Boman (36) fed four levels of grain to cows on pasture (0, 0.14, 0.29, and 0.57 ke,'/kg milk), the SNF content for the respective levels averaged 8.51, 8.64, 8.86, and 9.08%. In many areas, it has been a general observation that cows placed on lush pasture in the spring undergo an increase in the SNF content of their milk (22, 31, 55, 61, 62, 66). Studies by Rook et al. (59) demonstrated that this was due to an increase in the plane of nutrition. They showed that cows which had received 75% of the Woodman Standard for energy during a winter-feeding period increased 0.33% in SNF when placed on lush pasture in the spring; whereas, a group receiving 130% of standard underwent a 0.12% decrease in SNF when they commenced to graze. Similar results we,'e observed by Castle and Watson (19) and Waite et al. (66). Increases noted in mill< SNF at hi~'h energy intakes have generally occurred in the protein