Low Fat Milk From May Grass Down to Fatty Acids Not pH

IRELAND – Low milk fat caused by spring grazing is often down to fatty acids and not falling rumen pH, Irish farmers have been advised.
calendar icon 11 May 2015
clock icon 2 minute read

Fatty acids, specifically conjugated linoleic acid, are derived from the rumen metabolising grass which lower milk fat content, advise nutritionists at Ireland's Agriculture and Food Development Authority (TEAGASC). 

Cows indoors commonly have low milk fat content due to high starch and insufficient fibre intake causing rumen acidosis and lower milk fat levels. 

According to Teagasc, low milk fat is cause for concern indoors, but in grazing cattle is a problem that can resolve itself. This is if dry matter and neutral detergent fibres intake targets are met.

They say the change to fat content is made in the udder and not the rumen. 

“It is a false assumption that rumen pH must be lower if milk fat is low,” says Teagasc's dairy team.

“Indeed, studies have shown rumen pH to be similar for herds at 3.90 per cent fat and 3.45 per cent milk fat – differences were due to lipid content, not fibre in the diet.

“The change to milk fat production occurs within the udder itself, not in the rumen,” says Teagasc in its May newsletter.

“High quality second rotation grass increases the effect, and with cows also at peak yield the drop in milk fat can be quite noticeable."

Meanwhile, cows can often continue to milk well, eat well, but there are ways to address the fat components.

How to Address Low Fat in Milk

  • High intakes (17+kg DM) of quality grass, preferably on 24-hour allocations
  • Post-grazing residuals of 4.0-4.5cm;
  • Maintaining pre-grazing covers >1,200kg DM;
  • Ensuring minimum NDF requirement (33-35 per cent of DM) is met where grass is in deficit
  • Feeding slower degradability concentrate ingredients (maize preferred to wheat, hulls/beet pulp instead of citrus).

Applying the above points has been shown to address low fat content in a fortnight to three weeks, adds Teagasc. Rumen conditions can adapt or grass composition can alter with the cow typically remaining healthy throughout.


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