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.

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