Sub acute rumen acidosis

Published 18 May 12

Over the last couple of months there have been some articles in the press about Sub acute rumen acidosis (SARA) in grazing cows. Piers Badnell, DairyCo extension officer, looks at the facts and issues behind the condition.

"The articles have explained that good quality grass has high levels of rapidly fermentable carbohydrates, which lead to a build up of lactic acid," says Piers Badnell. "This causes the rumen pH to fall, leading to acidotic conditions. The low fibre levels mean cows cud less, which in turn reduces the buffering capacity of saliva. The results of this can mean less milk sold, more lameness, reduced fertility, extended calving intervals and higher vet bills.

"The articles state that this potential problem can be avoided by feeding various yeasts and protected starches and proteins etc,"he continues.

"The press articles quote a paper that was in the Veterinary Journal 176 (2008) 44-49 by Luke O'Grady, Michael L Doherty, Finbar J. Mulligan from the School of Agriculture, Food Science and Veterinary Medicine, University College Dublin, which is an excellent piece of peer reviewed work.

"But I think the results of this paper have been taken out of context and used to promote a product which may well not be necessary," Piers Badnell explains. "Cows grazing can potentially be susceptible to SARA, but the incidences are low and the paper certainly did not say whether feed additives would or would not help.

"Some of the points in the conclusions of the paper were that low and sub optimal rumen pH was only found in a sub population of grazing herds and it questions whether this has an effect on herd health.

"It also states that there are difficulties in interpreting the significance of rumen pH," he continues. "The pilot study found no statistical correlation with problems of animal health, however some studies showed an association between low rumen pH and lameness negative energy balance and infertility, note an association not direct cause and effect.

"The paper suggested that further studies are needed into;

  • the incidence of SARA in grazing cows
  • understand rumen pH variation at grass
  • the prevalence of SARA in grazing cows between herds and other stages of lactation as this study only focussed on peak dry matter intake period. The paper recommends more work to examine other stages of lactation in case this was a lactation stage effect or a grass effect.

"Another point to consider is that to feed various yeasts and protected starches and proteins you will need a buffer feed, which means more feed in the yard, more expense and less time grazing," Piers Badnell continues. "More feeding inside leads to a cow that is less proficient at grazing and thus added direct cost of production and there are also those hidden extra cost of yard work etc.

"So from this I conclude it is far less a risk and potential problem from SARA than alluded to in the articles. Part of the problem I think comes down to grazing ability and behaviour in the cow. If a cow has not been trained to graze and therefore chooses what she eats, does not graze hard and achieve good residuals, she will just graze the tips of the grass which are the "concentrate part of the plant," he says.

"They carry high fermentable carbohydrates and low levels of physical fibre. So the key is good grazing pressure and training cows to graze to a good residual which all cows can do if grazing is allocated properly. Taking away cow choice means she then grazes hard to a good residual and takes in more fibre from the stem. This means intakes are balances and it helps avoiding the possible effects of SARA as quoted in the article," Piers Badnell explains.

"In the paper there also appeared to be a clear herd effect.  Some herds had cows with SARA and some herds had no or very small number of cows with SARA. Also when comparing between cows with or without SARA signs there were no clear differences in terms of performance. There was no explanation or investigation as to if there was a difference in management of the herds and whether this had an influence. Also when comparing between cows with or without SARA signs there were no clear differences in terms of performance. But what this does signify is you can graze cows and not get SARA," he states.

"Graze properly and you reduce the chances of problems. Read the paper itself and look out for the symptoms in the cows. If you are grazing properly I think it is unlikely you will find them but if you do eliminate other possible causes and take action on fact rather than opinion," he concludes.