What Drives Butterfat Percentage

Low butterfat % is often seen as a two dimensional problem, that of nutrition and milk testing. Whilst nutrition may have the major influence from month to month or season to season, one cannot ignore the other factors influencing butterfat %.

Whilst the legal limit for butterfat % is 3.3%, butterfat is considered to be low when the milk protein: butterfat ratio is greater than 1: 1. Once it is established there is a butterfat % problem, all areas, as discussed below, need to be investigated.

Milking procedure

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

Inefficient milking or milking machines. The last milk drawn from the udder is considerably higher in BF 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 butterfat.

Cows under stress during milking due to poor milking procedure, poor stockmanship or faulty milking machines.

Bulk tank

Theft by skimming off the top of the tank.

Over/under agitating of milk.

Taking of milk samples, equipment and method.


The old saying “thin cows make thin milk” applies at calving and early lactation. Make sure of good pre calving practice.

Buffers must be included in high grain containing concentrates, especially when “slug” feeding. This to stabilize rumen pH.

Excessive available fats interfere with digestion of fibre resulting in lowered BF%.

Particle size of roughage as well as concentrates will effect BF%. 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 drive BF% down.

Ratio of roughage to concentrate alone is not the only factor to consider as effectiveness, quality and quantity of fibre need to be addressed. If the fibre is ineffective, the result will be lowered BF%.

Rations too high in grain should be fed strategically, no more that 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 BF%. Age of herd is therefore important.

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

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

Disease or infection to the mammary system (mastitis and high somatic) will result in a lowered BF%.

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


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

Seasonal changes in the growth of roughage. Spring and beginning summer flushes of pasture generally see a lowering of BF%. This situation may be worsened by the tendency to weight calving during the flush growth in pasture.

Date published: 2004-03-01

Jane Holiday