Cows at grass

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There are a number of ways of manipulating milk solid levels through feeding, although the cost-effectiveness of ration adjustments always needs to be assessed against the specific milk contract. The two main sources of energy in a dairy cow ration are the fibre components and the sugars and starch.  Generally, fibre stimulates milk fat and sugars and starch stimulate milk protein.

Milk fat

Improving milk fat levels comes from ensuring a stable rumen environment for the celluolytic microbes in the rumen.  High fibre diets promote milk fat percentages.  This can be achieved by adjusting the forage to concentrate proportions of the ration.  Very short chopped forage (less than 0.7 cm), over processed TMR forages and young spring pasture can all reduce milk fat levels.

Offering more frequent concentrate meals will create a more stable pH level in the rumen, thus promoting milk fat levels.  The inclusion of fats can effect rumen function and therefore milk fat production.  However, this may be avoided by the inclusion of a proportion of protected fats in the diet.  Fats are protected from rumen degradation either by conversion into a rumen insoluble soap or naturally by virtue of a high melting point which makes them relatively inert in the rumen. The form of protection must, of course, ensure they are available for breakdown and absorption lower down the digestive tract.

The fatty acids making up protected fats can be a relatively pure source of 16 carbon chain molecules and C16 fatty acids can be directly converted into milk fat to boost milk fat percentages.

Milk fat percentages can be increased by:

  • Increasing the forage to concentrate ratio.
  • Feeding high fibre forages.
  • Providing sufficient long fibre.
  • Feeding high digestible fibre concentrates.
  • Feeding concentrates little and often to stabilise rumen pH.
  • Avoiding too high levels of oil by-products like distillers and brewers grains.
  • Avoiding whole oil seeds like full fat soya and whole rape seed.
  • Feeding small amounts of a protected fat.
What to do Response Comments
Increase energy 0.06% for 10 MJ of ME Use starch sources, not fat to increase milk protein. Fodder beet can be very effective.
Different forage sources, e.g. maize silage 0.1 to 0.15% Increased intake and therefore energy effect.
Starchy concentrate 0.1% Starch at over 30% in concentrate, but NDF over 35% of total diet.
Protected amino acids .1 to 0.2% Last option, when rest of diet is spot on
Caustic wheat 0.1 to 0.2% Increased starch intake
Rolled maize 0.1 to 0.2% By pass starch source
High DUP in dry period 0.2 to 0.3 % Overall ration should be less than 16%

Milk protein

Changes in the concentration of milk protein can be brought about by dietary manipulations but compared with those possible in fat concentration, the scope is far smaller.

Increased amounts of concentrate in the diet are associated with elevations in milk protein.  The effect of increasing energy intake from forage is also likely to increase milk protein.  The effect of increasing energy intake from forage is also likely to increase milk protein.

Increased starch intakes generally increase milk protein.  When starch is included in the diet, it generally replaces energy from grass silage and so increasing the energy available for rumen microbes (FME).  Increasing FME will lead to increased microbial protein which in turn increases protein supply to the small intestine and amino acids in the blood stream.  A small but variable amount of dietary starch escapes degradation by the rumen microbes and passes into the small intestine (by-pass starch).  The small intestine has a higher energy demand.  With a low starch diet there is little glucose in the small intestine and amino acids are deaminated and used as an energy source.  By pass starch is thought to supply glucose to the small intestine and therefore spares the use of amino acids in the intestinal wall, thus increasing the supply of amino acids to the blood.  Milk protein requires certain amino acids, so supply of those amino acids is likely to limit milk protein.  Therefore, large, but often variable responses can be expected from feeding protected amino acids, such as methionine and lysine.  However, supplementation with protected amino acids will only work if the overall crude protein, ERDP and DUP of the ration are adequate.

Partly substituting grass silage with other forages can lead to a milk protein response.  Also, feeding molasses may encourage increased forage intake and thus energy consumption.  However, this will likely result in increased intake, so increasing energy intake and milk yield.

Feeding a small amount of high protein feed containing a high proportion of DUP has been shown to increase milk protein production.  Increasing the bypass fraction of the protein component is thought to be due to elevations in dry matter and energy intakes.  However, this is likely only to be the case where protein is limiting.

Fat cows with body condition score greater than 3.5, have lower intakes and therefore lower energy consumption, which leads to them producing milk with lower protein content.  Therefore, it is important to get the cows in the correct condition before the lactation begins.  Feeding a small amount (2kg) of high DUP concentrate in the dry period has been shown to increase milk protein in the subsequent lactation.  There may also be a milk yield response with this feeding regime, which may produce a dilution effect on milk protein.

In summary, milk protein percentages can best be increased by:

  • Increasing the energy density of the ration.
  • Feeding high ME silages with good intake potential.
  • Feeding mixed forages.
  • Increasing the degradable starch content of the ration with ingredients like rolled wheat.
  • Increasing the by-pass starch content of the ration with ingredients like rolled maize.
  • Increasing the protein of the ration if the diet is short of protein overall.
  • Feeding protected methionine or lysine.
  • Avoiding added fat (even protected fat).
  • Calving cows in optimum condition.
What to do Comments
Increase fibre content of ration Physical form is also important to provide scratch in the rumen
frequent meals Effective if high levels of concentrates are fed in the parlour
Protected fats Keep overall fat levels to 6% maximum with 4% in rumen degradable form.
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