The cows go out and butterfats plummet. It's a picture repeated across the country every year. But is it worth doing anything to maintain butterfats, and if so what? David Woodcock, Technical Business Manager with Optivite considers the options.

As ever at this time of year, thoughts turn to what should be done, if anything, to boost butterfat levels at grazing. Nationally we usually see a 0.4% fall in butterfat levels. In some herds the decline can be as much as 1%.

There is no doubt that butterfat is increasingly becoming a problem area for those in the EU responsible for managing the overall milk market. Globally butterfat prices continue to fall on the commodity markets.

However many UK milk contracts still include both bonuses and deductions dependent on butterfat levels. Dairy farmers looking to maximise returns from their contract must keep a close eye on butterfats.

The first stage in deciding whether it would make sense to try and maintain fats at grass is to understand the terms of your milk contract. If the contract will reward high butterfats or penalise low levels, then it is worth considering what the options are to maintain or increase levels. If there is no milk price advantage, then don't incur extra costs chasing something you won't get paid for.

If it makes sense to take nutritional action to influence butterfats, the next stage is to look at what has happened historically on your farm. What are fat levels at turnout and by how much do they usually fall? What are fat percentages now and how do they compare to previous years? It may be that fat levels are higher than usual now and even if you experience a typical grazing depression you will still exceed the deduction threshold.

Once you understand the extent of the possible problem it is time to consider what action can be taken.

There are two crucial points that must be remembered. The first is that approximately half of a cow's milk fat production comes from her being able to convert the end products of rumen fermentation into milk fat. The remainder of the butterfat produced comes from fats fed in the diet, or from the mobilisation of body reserves.

The second vital point to remember is that feeding dietary supplements will have little effect if the basic rumen fermentation is incorrect. Therefore the starting point to achieve higher fats at turnout is the rumen.

To achieve high levels of fat production, the diet needs to encourage a fermentation, which results in high levels of acetic, and butyric acid, which are the precursors for milk fat. This in turns requires a diet high in structural fibre and low in sugars. This is exactly the reverse of what we find in spring grazing.

The other problem is that the fermentation encouraged by high grass intakes can lead to an acidic rumen, which can further inhibit fibre digestion. If you want to increase grazing butterfats the first stage must be to ensure an adequate supply of structural fibre to help control rumen pH and increase the supply of butterfat precursors.

Check the fibre levels in all supplementary feeds and consider changing to a HDF concentrate or feeding beet pulp. The other option is to hold cows back on a winter ration for part of the day. Bear in mind that any significant supplementary feeding will reduce grazing intakes and you may need to tighten stocking rates.

The other way to boost fat production is to increase the supply of fat fed in the diet but care needs to be taken to feed the right sort of fat because different fats have different effects in the cow. Some can create an oil slick in the rumen, which reduces fibre digestion and dry matter intakes.

Fats based on calcium soaps are shown to be effective in raising milk yield but not fat percent. The best fats for improving milk fat contain a high proportion of palmitic acid (C16 fats), which is readily utilised by the cow and efficiently diverted to the udder.

In the right circumstances it will pay to feed for increased fats at grazing but make sure you will be paid for the effort.

If you have done your sums, then consider the following products, and to help you we have put a comparison table at the end to show typical costs per day of feeding various fats.