High pasture fats can reduce butterfat test

Butterfat depression does not always mean the diet is low in fibre. When pasture is young and highly fertilised with nitrogen much of its energy is in the form of oils and fats. These unsaturated fats can interfere with the udder's ability to synthesise butterfat, resulting in severe fat depression. Unfortunately the common nutritional solutions such as providing more fibre have limited effect on correcting this sort of butterfat depression. Even restricting pasture may not be effective, as only small amounts of unsaturated oil are needed to affect butterfat test.

In the situation where low butterfat is the result of high oil content of pasture, follow all the steps normally taken to remedy a low fat test, as they may help to reduce the severity of the depression. Providing sufficient long fibre in the diet is particularly important as fibre is fermented mainly to acetate in the rumen. Acetate is the main building block required for the formation of butterfat. The physical act of chewing the fibre also helps buffer the rumen with saliva, producing an environment more suitable for acetate producing bacteria. If rumen pH needs to be lifted further, adding magnesium oxide to the pellets is often the best choice, as the conditions that cause the high oil levels in pasture also have a negative effect on magnesium absorption.

It is important not to over react by feeding excessive amounts of poor quality hay or cutting back on pellets, as this will generally result in reduced milk production. In the shorter term, fat percentage may lift as the same quantity of fat is diluted over fewer litres, but the total quantity of fat is no higher and total protein production will also be reduced. In most cases the tests will begin to climb again as pasture growth rate increases and the plant produces more of its energy as sugars and less as oil.

The graphs below show how the sugar and fat levels in pasture vary in relation to the protein content. In general as protein level increases the sugar level decreases and the fat level increases.

Andre Nel