Ruminants have four stomachs and the rumen is the main stomach. Good rumen health is vital. The normal rumen acts like a huge fermentation vat where millions of micro organisms, such as bacteria and protozoa break down and utilise dietary carbohydrates, dietary protein/ non protein nitrogen and dietary ﬁbre. There must be a correct balance between the sugars and starches in the diet and effective ﬁbre in the diet. Sugars and starches ( present in a higher proportion in concentrates and lush grass) are fermented rapidly by the rumen microﬂora resulting in acid production in the rumen.
Volatile fatty acids are absorbed from the rumen and used as energy precursors. So acid production is necessary in the cow. It is when the balance between acid production and the buffering capacity of the cow is upset that we see problems. In acute ruminal acidosis, lactic acid is mainly produced. The normal cow can buffer the decrease in rumen pH resulting from VFA production. She does this by doing what happy cows do – chewing the cud. A dairy cow can produce up to 1 kg of bicarbonate (base) in its saliva over 24 hours IF THERE IS SUFFICIENT LONG FIBRE AND EFFECTIVE FIBRE IN THE DIET.
A simple check test – go out and observe your cows at rest – what percentage are chewing their cud?
Ruminal acidosis is where there is excess acid produced in the rumen over and above the cowʼs capacity to buffer the acid.
Acute ruminal acidosis is seen following ʻgrain overloadʼ – massive amounts of rumen acid produced in a short time.
This is a veterinary emergency.
Signs are seen 12-36 hours after excess concentrates are consumed. Cows may be dull, ʻdrunkenʼ gait, ears drooping, saliva drooling. Cows quickly deteriorate leading to hypovolaemic shock – sunken eyes, increased heart rate, weakness, death. Acute ruminal acidosis can be diagnosed by history of access to excess fodder and clinical signs. Intensive treatment to try to buffer the acid that has been and continues to be produced in the rumen is necessary.
TRY TO ENSURE CATTLE DO NOT GAIN ACCESS TO EXCESS CONCENTRATES. GO OUT AND HAVE A LOOK AROUND THE FEED STORES AND SEE WHERE THE WEAKNESSES ARE. THIS VETERINARY EMERGENCY IS NOT THAT UNCOMMON.
SARA occurs most commonly in early lactation cows, grazing very lush grass and also getting plenty of concentrates in the parlour.
Subacute ruminal acidosis (SARA) is a more subtle herd problem, with individual cows showing more severe signs than the average in the herd.
Cows might have loose, watery faeces. They might look empty ( they graze less) . You might ﬁnd dropped cuds on the ground ( cud too acidic).
SARA is also associated with other herd health problems – increased prevalence of lameness and laminitis, increased risk of abomasal ulceration and liver abscessation.
How do I know if I have SARA in my herd?
SARA is associated with a drop in herd milk fats.
If > 10% of the milking cows have milk fat < 2.5% or milk fat < protein by more than 0.4%, then it can indicate that SARA is present.
Deﬁnitive diagnosis involves a procedure called rumenocentesis.
Treatment of SARA involves increasing ﬁbre content of diet decreasing fermentable carbohydrates adding rumen buffers to diet.