Dietary factors influencing milk fat

Milk fat is the easiest of the milk components to manipulate and altering either the ingredients in the diet or the physical form of the diet can induce marked changes in milk fat %. However, diet formulation is often a compromise as many factors leading to an increase in milk fat % can cause reductions in milk protein %. A summary of some of the major dietary factors influencing milk fat % is presented in Table 1.

Table 1      Dietary factors affecting milk fat %

Increase milk fat %

Decrease milk fat %

Increase fibre

Reduce fibre

Long fibre

Finely-chopped forages

Low grain / Low starch

High grain / High starch

Cracked or coarse-rolled grains

Ground cereals

Small, frequent concentrate feeding (e.g. TMR or
out-of-parlour feeders)

Large, infrequent concentrate feeds (e.g. twice per day in parlour)

High-C16 fat supplements (e.g. Mega-Fat 88 and
Mega-Fat Extra)

Rumen-active fat supplements, vegetable oil, fish oil, high-oil byproduct feeds (e.g. brewers grains)

In simple terms, high starch, low fibre rations generally induce low milk fat %, while adding rumen-active oils can lead to the production of particular trans fatty acids which are a major cause of milk fat depression.