Factors that can influence Milk Butterfat levels at Grass

Dairy Cow & Calf

As cows begin to calve and are looking at being turned out to grass, milk quality, particularly butterfat can be hard to maintain. Low butterfat levels can be seen in quite a number of herds once turnout occurs thus leading to financially damaging penalties.

This article examines the factors, which can influence butterfat levels.

Cow Affects

Season and Stage of Lactation Effects/Breeding

  1. The typical seasonal trend in the content of milk fat with autumn calving cows is a peak in late summer and a trough in winter and early spring. Traditionally milk fat takes a ‘dip’ and milk protein rises when cows go out to grass. Over the past few years this ‘dip’ in milk fat has been more severe and prolonged in quite a number of herds.
  2. Milk composition also changes with the stage of lactation. As yield increases over the first few months of lactation the compositional quality decreases, this is known as ‘the dilution affect’
  3. Part of the seasonal trend in milk fat is due to this, when the majority of the herd is in early to mid lactation the fat content of milk is expected to be lower than normal
  4. Over the past number of year’s cow genetic merit has increased, leading to increased yields which can reduce butterfat because of this dilution affect, but maybe more importantly bull selection was mainly focused on litres of milk and protein % with fat % viewed with less importance or even ignored completely.

Dietary influences

Many dietary factors have been identified as influencing milk butterfat levels and fairly large responses both increases and decreases, can be obtained. This is in contrast to milk protein, which offers less opportunity to be manipulated.

Fibre content of the diet

  1. The fibre content of the diet has a major influence on milk fat, with high-fibre diets promoting high butterfat’s via the production of acetic acid in the cow’s rumen, whereas it is widely accepted that high cereal/starch diets will produce higher levels of propionic acid, which can promote milk protein. There is a definite relationship between diet composition, rumen activity/function and milk composition. Length and structure of the fibre in the diet is vitally important in maintaining butterfat levels, this determines how much the cow ‘cud’s’ or ‘ruminates’ which in turn determines the amount of saliva a cow produces. This can have major effects on maintaining a stable rumen pH, which will ensure adequate fibre digestion and lead to good butterfat levels
  2. Grass swards, especially those which are heavily fertilized in order to maintain sward productivity, are often low in structural fibre and high in soluble sugars, which again can lead to low butterfat levels and in some cases, sub clinical rumen acidosis. A diet low in fibre can be associated with cows being very ‘loose’ in the dung as commonly seen on lush spring grazing although low dry matters and high levels of soluble protein will also affect this
  3. With poor grazing conditions farmers tend to feed more meal and this can further depress butterfat level by reducing the forage to concentrate ratio of the diet.

Level and type of concentrate

  1. Trial work carried out at Hillsborough has shown that cows fed concentrates containing large quantities of cereals produce milk with lower butterfat concentration
  2. The inclusion of high digestible fibre based ingredients such as citrus pulp, beet pulp and soya hulls in the concentrate can help improve milk butterfat
  3. At low levels of concentrate feeding (up to 3.0kg/day), the type of concentrate fed, whether cereal based vs. pulp/fibre based, has been shown to have little effect on butterfat levels. Above these feed levels the effect is more pronounced with high digestible fibre diets generally promoting higher butterfats
  4. The use of most fat supplements can have variable results. Generally, moderate levels of standard commercial fat products can increase milk fat by a small amount or not at all, whereas smaller amounts of free oil/unsaturated fats (soya oil, fish oil etc.) can cause milk butterfat concentration to fall, due partly to their negative effect on fibre digestion in the stomach these oils have also been seen to have negative effects on milk protein. Milk butterfat contains a high level of saturated fat or C16:0 fatty acids (palmitic acid). The use of supplemental dietary fats which contain high levels of palmitic acid has been shown to increase butterfat above normal levels or indeed improve situations where low butterfats exist in a lot of cases.

Ways of increasing Butterfat levels

If yields are holding and milk protein levels are normal, then low butterfats are generally caused by inadequate long fibre in the diet and/or possible sub clinical rumen acidosis caused by high soluble sugar levels found in the grass itself. Some ways to increase butterfat levels are:

  1. Inclusion of a rumen buffer yeast product in the ration
  2. A small amount of good quality hay, roughly chopped straw (>4cm), or some un-chopped round bales may help to rectify the problem
  3. The use of a buffer feed at milking time can also give good results, whole crop wheat, maize silage or just a mix of clamp silage and chopped straw being examples. However, this can lead to possible yield reductions unless the buffer feed is of reasonably good quality, as good quality grass may be replaced by poorer quality buffer feed resulting in high grass substitution rates and overall reductions in dietary energy supply
  4. Grass availability and stocking density must also be considered. With poor or restricted grazing, buffer feeding will generally give better results
  5. The use of saturated fat products containing high levels of C16:0 fatty acids can be very effective in most situations. ‘Butterboost’ from Trouw Nutrition is one such product. Fed at up to 350grms/cow/day it has been shown to effectively increase milk butterfat without having any of the negative effects described above.

As mentioned before, it must be noted that during the past 5-10 years bulls have been selected for yield and protein production and generally butterfat production has been ignored. This influence may now be coming to the fore!

As yields increase along with increased meal feeding in most herds, the problem of low milk butterfat may become more pronounced as genetic merit increases.

Please contact your local Quinns rep for the best advice on your feed needs.