difference in feeding between seasons. Normally, milk contains about 3.3 g/100 g protein, which comprises mainly casein and whey proteins. Lactose is the major carbohydrate in milk. Other carbohydrates, including oligosaccharides, glucose, and galactose, are present in trace amounts. Although the lactose concentration decreases progressively during lactation, the variation in lactose content of milk is much smaller than that of the other two macronutrients. This is mainly due to the important role of lactose in the osmotic pressure of milk. The osmotic pressure of milk is identical to that of blood, and is therefore very constant (Paques & Lindner, 2019). The minerals in milk include, amongst others, calcium, phosphorus, magnesium, potassium, selenium, and zinc. Although they are present at low concentrations, many minerals have important functions in the body, e.g. regarding bone formation and enzyme activities. Table 1.1. General composition of milk from lowland breeds *. Component Average content (g/100 g) Range (g/100 g) Water 87.1 * Adapted from Walstra, Wouters, & Geurts (2005).