So what are the components of milk? There are three main categories:
- Other solids.
When a cow’s rumen digests fiber, it produces fatty acids. Some of these fatty acids are processed in the udder and released into the milk, accounting for about half of the fat naturally found in milk. The other half of the fat enters the milk from the bloodstream, often coming from the cow’s liver or backfat, or directly from fats absorbed in the diet.
Because fiber is important to producing milk fat, cows generally have higher levels of fat in their milk when fed diets high in natural forages of good quality. Cows are sometimes fed low-fiber, high-energy diets to increase total milk production. Needless to say, this extra production comes at the expense of the fat component.
Fat content is generally expressed as a percentage. This is important because a high-producing cow like a Holstein may yield more pounds of fat per lactation than a Jersey. However, a gallon of Holstein milk contains a higher percentage of water than a gallon of Jersey milk does. Total milk yield and percentage of components are usually inversely related.
Protein makes its way into milk thanks to the action of rumen microbes that start the process of breaking proteins down into amino acids. Mammary glands later reconstruct the amino acids back into proteins with the aid of glucose. Also, small amounts of albumin and immunoglobulin proteins enter milk directly through the bloodstream.
It is interesting to note that the chemical makeup of the protein component can vary from cow to cow. Casein is the main type of protein found in cow’s milk, but it can come in two forms, known as A1 and A2. The latter type is considered easier for humans to digest.
A deficiency of dietary protein will indeed reduce the amount of protein in a cow’s milk. However, once the cow’s protein needs are met, feeding additional protein will not further increase amount of protein in the milk. Beyond this point, protein content is strongly influenced by genetics.
Like fat, the protein content of a cow’s milk is expressed as a percentage.
Many times, when milk components are under discussion, fat and protein are the main solids of interest. However, there are many other solids that make milk:
- Lactose: A type of sugar; the carbohydrate component of milk.
- Minerals: Including calcium, magnesium, phosphorus, potassium, and selenium.
- Vitamins: Particularly vitamins A and B complex.
Why Components Matter
- Components indicate cow health. A healthy, well-fed cow with minimal stress will have plenty of fat, protein, and other nutrients to spare for her milk. On the other hand, a cow suffering from mastitis or from rumen acidosis will show a considerable drop in fat and protein components.
- Components are important for human nutrition. Two glasses of milk from two different cows are vastly different. A glass of milk from a cow bred and fed for high total milk production is mostly water. A glass of milk from a cow bred and fed with an eye to components contains more of the proteins, vitamins, and minerals necessary for good health. Even the fats are beneficial to humans, as they are important for building cells.
- Components offer value-added opportunities. Fat and protein are necessary for making butter, cream, and cheese, among other dairy products.
- Components give rich flavor and texture to dairy products. Milk fat and other solids are what make ice cream creamy. In fact, one of the factors that separates gourmet ice cream from just plain old ice cream is a higher percentage of fat.