Acidosis

Acidosis is a metabolic disease that occurs when rumen pH levels fall below normal.

It usually occurs when cows are not properly transitioned onto high sugar/starch feeds (commonly brassicas or fodder beet) or when large quantities of high sugar/starch feeds are included in the diet.

Acidosis is most common between day 7 and 14 of fodder beet transition.

Acidosis symptoms

Cows with mild clinical acidosis will exhibit scouring, will be off their feed and hanging back from the rest of the herd.

In more severe cases the disease may progress to include metabolic acidosis, depression, dehydration, bloating and milk fever like symptoms. Severe acidosis may result in cows going down, coma and death within 8-10 hours.

Subclinical acidosis

In lactating animals, sub-clinical acidosis is usually of greater economic importance than the clinical disease and can often affect a significant proportion of the herd.

The implications of sub-clinical acidosis on non-lactating cow performance are less well researched but one area it will impact will be body condition score gain.

Cows with clinical acidosis will go off their feed and with sub-clinical acidosis digestion of nutrients will be reduced so fewer nutrients will be available for body condition score gain.

Detecting sub-clinical acidosis in non-lactating cows is challenging as the best diagnostics appear to be VFA, lactic acid and ammonia concentrations, and rumen pH, none of which are easy to measure.

How does acidosis occur?

The rumen in the cow is a huge fermentation vat. It's where rumen microbes ferment feed for further digestion, or for direct use by the cow for things like milk production.

The microbes operate in a fine balance around optimal pH, with the rumen operating best at a pH between 6 and 7.

This pH balance is maintained by buffering agents in the saliva, produced by chewing the cud, and by absorption in the body of weak acids (mainly volatile fatty acids), essential for milk fat production.

When an animal ingests feed that is rich in fermentable carbohydrates or sugars they are not accustomed to, this can upset the pH balance.

• Readily fermentable carbohydrates have a lower fibre content, which results in less cud chewing so less saliva is produced.
• The high sugar content promotes the growth of lactic acid forming bacteria. Lactic acid is a stronger acid than volatile fatty acids that are produced during normal digestion processes and so, in turn, the pH drops.

At low rumen pH the microbes that digest fibre are less efficient and changes to rumen function result. In extreme situations the rumen stops working altogether.

Acidosis is also known to damage the rumen papillae (small finger like projections in the rumen through which nutrients are absorbed) further reducing the ability of the animal to absorb nutrients.