How to minimise acidosis risk at turnout

Wet weather, which has delayed turnout of stock this year, combined with fodder shortages is likely to increase the risk of acidosis when cows are eventually turned out to grass.

The shorter transition period from silage to grazing could have a major effect on rumen function for several weeks.

One risk of this is sub-acute ruminal acidosis (Sara), seen whenever rumen pH falls below the optimum score of 6 for two to three hours.

In addition, stocks of silage, wholecrop, straw and fibrous feeds such as beet pulp are tight and consequently expensive this spring, meaning fibre supplements (which can reduce acid build-up) will be harder to provide.

See also: Four tips to get timing of first-cut silage right

Compounding the issue, the extra costs incurred by keeping stock housed for longer and the falling milk price mean farmers are under more pressure to push production from grazing.

This strategy runs the risk of leading to acidosis, according to independent nutritionist Hefin Richards.

Acidosis and its effect on milk solids

Charlotte Ward, KW Alternative Feeds nutritionist, says improving feed efficiency and fibre digestion by avoiding Sara needs to be a top priority to support milk fat synthesis.

“One of the biggest problems caused by Sara is low milk fat, and with many milk processors altering supply contracts to focus more heavily on milk solids, maintaining milk quality is going to be even more important than in the past,” says Ms Ward.

“For cows that get turned out, fresh grass is the cheapest feed available, and making the most of that value is the key to maximising income over feed costs during the grazing season.

“Even the best-quality swards grazed under good conditions will only realistically deliver maintenance plus 15-20 litres a cow, so it is essential none of this is lost to Sara,” she adds.

Fodder and straw shortages limit fibre availability

“Sara usually occurs as a result of cows consuming too much fermentable carbohydrate [sugar and starch] or too little digestible and physical fibre, or usually a combination of all of these factors,” explains Mr Richards of Rumenation Nutrition Consultancy.

“Historically it would be associated with silage or concentrate feeding and there was widespread denial that it could occur in grazing cows.

“A number of studies around the world have confirmed it can and often does occur in grazing cows as a result of high levels of sugar and low levels of effective fibre. This is exacerbated by high levels of protein, which increase the rate of passage through the rumen and further reduces rumination or cud chewing rates.”

Sara leads to sick cows, poor feed use and low butterfat percentages (see “What is Sara and what are the symptoms?”)

What is Sara and what are the symptoms?

The effects of Sara are seen whenever rumen pH drops below the optimum level of 6 for two to three hours or more. They include:

  • Substantial reduction in fibre-digesting microbe activity
  • Reduced digestion of fibre
  • Reduced grass use

Clinical symptoms include:

  • Undigested feed in the manure
  • Increased diarrhoea
  • Manure that is foamy in appearance
  • Reduction in eating times (in more severe cases), leading to:
    * Cows that are quick to lie down
    * Cycling between periods of good and poor intake

Source: KW nutrition

“Unless feeding a partial mixed ration alongside grazing, there is limited opportunity to include buffers and yeast unless a stable product is used and incorporated into compound feed,” says Mr Richards.

Therefore, it is important that farmers are aware of the increased threat and try to deploy preventative strategies to minimise the risk of acidosis in the herd (see “Top tips to prevent Sara”).

Top tips to prevent Sara

Hefin Richards shares his advice on preventative strategies for Sara with Farmers Weekly readers.

  • Gradually change diet when moving from winter diet to grazing – this allows time for the rumen microbes to adapt to the massive shift in substrate.
  • Buffer feed and give cows time to eat. Include fibrous forages in the ration to slow down the rate of passage of leafy grass – silage, chopped hay or straw, maize, wholecrop and nutritionally improved straw are effective at doing this.
  • Feed higher-digestible fibre concentrates such as sugar beet pulp and soya hulls, and limit starch levels. Focus on slowly degradable starch feeds such as sodawheat or maize grain rather than rolled or milled wheat.
  • Include rumen buffers to provide a direct antacid effect, and possibly live yeast or yeast cultures to stimulate the pH-sensitive fibre-digesting bacteria that are the first casualties of Sara.
  • Limit amounts of concentrate fed in single feeds and target intensive grazing at later lactation. Lower-yielding cows are deemed to be at lower risk.
  • Manage grazing so that cows not only consume the highly digestible leaf, but also a proportion of the more fibrous grass plant base.
  • Maximise lying times to promote rumination.
  • Other factors such as heat stress will further increase the risk because lying times and rumination rates will decline. A spell of weather with temperatures in the mid-20Cs and high humidity will push the thermal heat index into the risk/danger zone.