Signs of SARA: optimising milk production from grass

David Jackson BVetMed MRCVS

SARA (sub-acute ruminal acidosis) is a constant challenge in dairy cattle. This is especially true in the grazing season. Acidosis upsets the delicate rumen microflora, reducing nutritional value obtained from the presented ration and in turn reducing milk production and milk quality.

In the dairy industry, we are getting very good at observing behaviour of housed cattle to give us clues about how happy our cows are and how we can make them more productive. Rumen-fill scoring, condition scoring, observing lying behaviour and faecal scoring are all very easy to do during housing but are often not prioritised with grazed cattle.

The ideal dairy diet would involve 12 identical meals per day, evenly spaced over a 24 hour period. Therefore, in theory, grazing better supports this. Access to grass is less restricted than with presented feeds, so cows are free to eat whenever they want.

However, grazing presents its own challenges:

Heat stress, even in the mildest of summers will reduce feed intakes.

There is often a lot of walking involved in the life of a grazing cow, reducing the time she is able to eat.

Water availability can be poor at grass, and cattle may not know where troughs are if grazing rotates regularly.

Grass varies from day to day, hour to hour, in our variable climate. This is not only due to growth and depletion. The percentage of dry matter will change drastically with rainfall, meaning cows will effectively have lower DMI’s on wet days.

Essentially there are a lot of unknowns compared with presented rations. We may know how much cake each animal eats in the parlour, but grass intakes +/- buffer feeding make rationing quite a guessing game. So much variability in diet day to day is a recipe for SARA.

So, let’s concentrate on what we do know. SARA is caused by variable feed composition and variable feed and water intakes. Therefore we can:

Monitor rumen fill (short term) and condition scores (long term) to assess the issue, and check whether intakes are sufficient.

Monitor herd butterfat’s, a dip in these is a big warning sign of SARA.

Monitor faeces for signs of SARA – Are there cows with dirty back ends indicating loose faeces? Do faeces contain undigested feed or fibres? Are there mucin casts in the faeces indicating gut damage?

Monitor cattle on the move and see if there is anything you can do to improve cow flow to and from grass and increase time available for feeding – Bottlenecks on tracks may be slowing cow flow, have a look to see if tracks are well maintained. Check if there are any obvious areas where cattle are slow. Any areas of standing water may indicate tracks need repair.

Monitor for signs of heat stress – Make sure there is enough shade for cattle, if cattle are seeking shade this may be a sign of heat stress.

Monitor drinking – Are troughs constantly crowded? Do cows know where troughs are?

Once we start to read the signals better, we can act on them. If your cows suffer heat stress, try to bring them in and buffer feed them during the hotter hours of the day to maintain feed intakes. If you are buffer feeding already, analyse your silage, and make sure it is consistent. Variable buffer silage on top of variable grass is a double challenge for the cow; does your buffer need a buffer? If grass quality drops, try not to use increased cake to compensate. Look for something to offset the missing fibre such as brewers grains. Also, check that you have enough water troughs and make sure they are easy enough for your cows to find and access. You will also need to ensure the troughs are refilling efficiently.

Essentially, the grazing season is a challenging time for feeding. The diet will change constantly and the rumen microflora will struggle to keep up. Make sure you watch your cows for signs of SARA, look out for risk factors and keep their grazing season as consistent as possible.

Your Molecare Farm Vets, Feed Solutions and Moletech teams can all offer advice and solutions for dealing with the challenges of grazing (and making the most of the benefits). Speak to your local representative today for farm-specific advice.