Rumen health seminar: Understanding acidosis

Key points

With the average 300-cow dairy herd recording up to 4500 cases every lactation, ruminal acidosis remains the most prevalent disease affecting dairy cows in Australia.

Speaking at the Lallemand Animal Nutrition Rumen Health Seminar, Professor Ian Lean, says that many studies find about 10% of cows are affected at any one time and the case duration is two days.

“That equates to 1500 cases per 100 cows each 300-day lactation,” he says.

Dr Lean says despite the plethora of terms used to describe acidosis; they simply represent a spectrum of severity.

“Everybody loves to categorise things,” he says.

“We’ve got lactic acidosis, ruminal acidosis, acute vs. sub-acute acidosis, clinical vs. subclinical acidosis and hindgut acidosis.

“Then we’ve got the sequalae of acidosis, such as liver abscess and laminitis, which are their own separate disorders but have acidosis as their cause.”

“Are these definitions really useful?

“The answer is ‘yes’ because understanding the root causes aid in treatment and management.

“It does matter what you call it, what we are really looking at is a continuum of severity.”

Professor Lean defines ruminal acidosis as being a ‘complex of conditions related to the rapid increase or change of rapidly-fermented carbohydrates when there is insufficient physically effective fibre, leading to an accumulation of organic acids that reduce microbial protein yield, fibre digestion and dry matter intake.’

“Rumen pH is only one factor that causes pathology and measuring rumen pH – whether it’s less than 5.0, less than 6.0 or an average of 5.6 for three days – is far too simplistic to describe acidosis,” he says.

“Rumen pH varies from cow to cow, feed, substrate, hour-to-hour, day-to-day and even within the rumen itself.

“Acidosis severity is ultimately based on the animal’s ability to safely sequester hydrogen, i.e. the amount and speed of hydrogen creation and distribution. The hydrogen comes from the process of digesting feeds. Sugars and starch are digested more rapidly than forages and release hydrogen more readily.

“So how should we be assessing rumen function and acidosis risk, which is effectively a measure of hydrogen, if rumen pH is not the best measure?

“Go and listen to what your cows are telling you.

“Look at their rumen fill, the percentage of your cows that are ruminating or any sudden changes in their body condition score.

“Look for the evidence of grain, bubbles or smell in their faeces. Is there scouring? What is the incidence of lameness?

“Is the feed fully pushed up in the feed pad? Has there been sorting? What’s the chop length? Do all the cows have equal access to feed?

“Look at your milk production history, particularly the milk fat: protein ratio – is it below 1:1?”

Professor Lean says the best way to manage acidosis is to create and maintain a stable and healthy rumen environment.

“And that’s a rumen that has been adapted to consistently receive a well-balanced ration with adequate protein, physically effective fibre, carbohydrates, fat, vitamins and minerals with fast, medium, and slow-fermenting components suitable for the physiological stage of the animal,” he says.

“Determine feed value of all feed components and adjust the ration accordingly.

“Include rumen modifiers and buffers at the correct dose rate and ensure all ingredients are correctly processed.

“Adapt cattle to new feeds, avoid rapid feed changes and supply a transition ration for 21 days before calving.

“Feed at regular intervals rather than ‘slug’ feeding and ensure all cows, particularly heifers, have equal access to feed.”

One of Professor Lean’s colleagues, Dr Helen Golder, who has a strong record of investigating acidosis has explored genetic markers for susceptibility or resilience to acidosis. Her work is the first to link the genetics of the cow to the bugs in the rumen and rumen function.

Dr Golder found evidence of interaction between the rumen environment (particularly rumen phyla, sugar and CP), milk production and genetics.

In one of her studies conducted in Australia, the USA and Canada, 26% of cows were classified as being at high risk of acidosis based on their rumen phyla, rumen fermentation and production data.

A further 27% were classified as being at medium risk and 47% as low risk.

“We have found genetic markers for rumen environment, but as yet, not for acidosis susceptibility,” she says.

“The key finding of this part of my research is that more is required, particularly a larger sample size. However, she is confident that further work will identify means to produce a better adapted cow.”