Cow signals, not pH, key to acidosis management, says consultant

Growing uncertainty over pH guidelines means dairy farmers should focus on feed quality and cow signals to control sub-acute ruminal acidosis (Sara), according to a leading researcher.

Ian Lean, managing director of dairy and beef research and consultancy company Scibus, warned ruminal pH measures are a “poor predictor” in diagnosing acidosis as they are far too simplistic and instead told farmers to focus on managing risky feeds.

Dr Lean added that stockmanship and dung checking should be a first port of call in flagging up problems at cow or herd level.

7 questions on sub-acute ruminal acidiosis

  • Is manure loose?
  • Is manure bubbly?
  • Does manure smell like fermented grain?
  • Have milk fat components dropped?
  • Is there a lameness problem such as laminitis?
  • Are starch and sugar levels too high?
  • Could I feed more fibre?

Addressing delegates at the Total Dairy Seminar at Tortworth Court Hotel, Gloucestershire, last week (1 and 2 June), Dr Lean called for a different approach in diagnosing Sara as he said practice was inconsistent with current biology.

See also: Tips on managing acidosis in grazing cows

Furthermore, he said developing research showed that volatile fatty acids (VFAs) were a more sensitive and specific test.

However, laboratory tests for propionate and valerate levels are confined to a select number of laboratories worldwide, he told Farmers Weekly.

“We’ve identified that propionate and valerate contents of rumen fluid produce a better test than pH levels for rumen acidosis,” said Dr Lean. “In the coming years we don’t doubt that there will be other tests that the industry can use.”

He outlined the range of Sara risk factors, stressing that it was not just a condition brought on by feeding grain.

Abrupt changes in feeding such as moving onto lush grass or clovers were flagged as risk factors, as were feeding wheat and maize silages.

He told the conference that faecal consistency, decreasing butterfat levels and a rise in lameness cases should prompt farms to assess whether starch and sugar are too high and if fibre intake should be increased.

Why not pH?

Outlining the shortcomings of pH as an acidosis marker, said Ian Lean, managing director of dairy and beef research and consultancy company Scibus.

Scibus’s Ian Lean explained rumen levels varied from cow to cow, across the day and within different places in the rumen, making it a “poor predictor” of acidosis.

There is no right or wrong place for veterinarians to take a rumen sample because the rumen is not homogenous, explained Dr Lean.

He added: “You can have animals running around with very low pHs that appear normal. What we’ve found is there is extreme variation in performance and the rumen contents of cattle that means you will certainly have cows that are acidotic if the diet is challenging.

“A cow could be at 5.2 or 5.4 and be performing very well, but of course the risk of her performing poorly improves the lower the pH drops.

“We did a large scale study finding cows running around absolutely fine with a pH of 4.5.

“The whole of the definition should not be based around pH but pH does have some use.”

He added that a range of approaches on minimum and maximum pH level and variation in sampling from fistulated cows and stomach tubing had shown just how unreliable and varied pH can be.  

“The best test will be to grab a rumen sample and the best way these days is with a stomach tube. If you do that you have a non-invasive test to give you rumen fluid to check if pH is high or low which can then confirm clinical observations.”

Above all, he stressed farms should never assume they are not running an acidosis risk simply because they are feeding an alternative grain to wheat.

Generally, barleys, maizes and triticales are less risky than wheat but Dr Lean warned that some have been found to be of even greater risk.