Sara - Not Just A Winter Problem

5 Apr 2017


Maintaining butterfat levels during the grazing season is one of the main challenges facing milk producers. Spring calvers are particularly affected, but even later lactating cows will typically produce milk with lower butterfat content when grazing.

The high sugar, low fibre content of modern ryegrass swards now typically persists right through until late summer, resulting in an excess of quickly available energy whenever cows are grazing. Furthermore the risk of subacute ruminal acidosis (SARA) rises as cows are fed more rapidly fermented concentrate. The risk is higher if there’s insufficient digestible and structural fibre in the ration, both of which are essential to maintaining optimum conditions in the rumen.

Rumen fermentation efficiency
Below pH5.8 fibre digestion within the rumen starts to become impaired, below pH5.5 cows are considered to be suffering from SARA. This means reduced nutrient supply to the cow, lower feed intakes, falling milk and butterfat production and an increase in the incidence of health problems, such as laminitis.

An investigation in Austria monitored daily rumen pH fluctuations in cows fed either grass only, or grass supplemented with 3kg of concentrate twice daily during milking. The cows receiving concentrate showed significantly lower average rumen pH and minimum rumen pH, plus 347 minutes each day below pH5.8 and 101 minutes below pH5.5.
Unless properly balanced in the rumen, these factors combine to create conditions in the rumen that are detrimental to fibre digestion and butterfat. As a result, milk fat levels often drop rapidly as soon as cows are turned out to grass and stay low for most of the summer

Therefore it is important to monitor cows for signs of SARA throughout the grazing season. Undigested grains and fibre in the manure – coupled with decreased butterfat levels – are indicative of poor fibre digestion due to increased rumen acidity  whilst mucin tags will also be visible in the manure in extremely acidotic conditions.”
Producers should aim to balance energy release in the rumen and limit the dramatic rumen pH drop associated with high intakes of grazed grass and starchy concentrates.

By balancing energy release in the rumen and providing a stable pH, producers can optimise fibre breakdown by minimising the time spent below pH 5.8. This will help to maximise production of the volatile fatty acids (VFA) acetate and butyrate, both of which are important precursors for milk fat production.

Even farms supplementing grazing with compound in the parlour can switch to a feed based on digestible fibre energy, rather than starch energy. Feeding concentrates ‘little and often’ will further help maintain a stable rumen pH needed for good fibre fermentation, as will addition of a slow release rumen conditioner, like Acid Buf and a live yeast like Vistacell. In a recent trial using cows receiving a 65:35 forage to concentrate diet were fed both Vistacell and Acid Buf increasing both butterfat production by 12% and fat- corrected milk yield by 5%.