What Drives Fat Percentage in Milk? Errr What All?

A high component price means it’s more important than ever for dairy producers to make sure their cows are producing as much fat as possible.

Low fat % is not just due to nutrition and breed. While genetics and nutrition are critical for improvement in fat tests, and though most farmers breed for the fat test, many have the major influence, one cannot ignore the other factors influencing fat %.

Milking procedure

Longer intervals between milking result in lower fat % than shorter intervals.

Inefficient milking or milking machines. The last milk drawn from the udder is considerably higher in fat than the first drawn milk, and, the higher the milk yield, the higher the quality of residual milk. If milking procedures, or faulty machinery, are incorrect, then there will be a depression in the fat. Keeping cows stress-free is critical for drawing the last milk.

Bulk tank

Over/under agitating of milk.

Taking samples after using a plunger is advised to get the correct fat reading.


A well mixed ration that doesnt allow herd to sort what it eats adds to fat %.

Health and body fat of cows affect fat % especially at calving and early lactation. Good pre calving practice is important. Body condition score of 3.5 is a good pre calving benchmark to have.

Buffers must be included in high grain containing concentrates to stabilize rumen pH.

Noteworthy that excessive available fats interfere with digestion of fibre resulting in lowered fat%.

Particle size of roughage as well as concentrates also affects fat %. The smaller the particle size, the faster the consumption and less chewing time which produces less saliva resulting in a lowered rumen pH.

Roughage to concentrate ratio should be at 60:40. Below this could also drive fat % down. Quality and quantity of fibre need to be monitored while maintaining the ratio. If the fibre is ineffective, the result will be lowered fat %.

Rations too high in grain should be fed strategically – a benchmark could be 3.5kg grain per feeding.

Animal factors

Apart from the obvious of breed and genetic selection within the breed, other factors such as age, stage of lactation and pregnancy status play a role.

Older cows have a lowered fat %. Age of herd is therefore important.

Days in milk influence fat %. First third of lactation fat % is lower, second third sees a stable fat % and last third has an increase in fat %. If calving to match roughage growth, this is an important factor as weighted heavy calving will influence fat %.

Open cows in late lactation tend to have lowered fat %.

Disease or infection to the mammary system (mastitis and high somatic) will result in a lowered fat %. Such milk should anyhow be disposed off and not sold.

High yielding herds have a lowered fat % than low yielding herds.


Higher temperatures (+21 C) may see a reduction in fat %.

Seasonal changes in the growth of roughage. Spring and beginning summer flushes of pasture generally see a lowering of fat %.

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