Acidosis in dairy cows
Like ketosis, acidosis in ruminants is a metabolic disorder. It is generally caused by poor feed management and exists in several forms that are more or less easy to detect.
Description
This pathology initially manifests as a drop in pH in the rumen (paunch), thus an acidification of this organ and then of the blood in the most severe cases.
Too energy-rich feeding is the main cause of acidosis, for example when animals ingest too large an amount of feeds rich in rapidly fermentable sugars (such as starch). These sugars are massively fermented by the bacteria of the rumen, through a process that generates Volatile Fatty Acids (VFAs) whose immediate impact is to lower the pH.
At this stage, the cow's salivation becomes insufficient to neutralize the effects of the accumulation of lactic acid.
By way of illustration :
- Hay and most dry forages are feeds rich in fiber and cellulose : fermentation will be slow and the acidogenic potential low.
- Concentrates or cereals such as corn are rich in energy and fermentable sugars : their fermentation is rapid and causes acidification of the rumen.
The different forms of acidosis
Acute acidosis
Acute acidosis is the most severe form of this pathology. It usually results from an accident : distribution problem, animals had abnormal access to the concentrate silo, etc.
Animals ingest a large amount of concentrates which causes a sudden acidification of the rumen (a pH drop from 7 to 5.5 for example). This reaction disrupts the bacterial flora of the rumen : predominance of amylolytic flora at the expense of cellulolytic flora.
When too many Volatile Fatty Acids have been produced, acidosis becomes systemic and compromises the animal's health in the short term.
The following external symptoms are then visible :
- The animal is prostrate (lying down).
- It is cold and not ruminating.
- It has elimination diarrhea.
- Its mucous membranes are red.
- It shows signs of dehydration and bloating.
If these symptoms occur after a feeding incident, it is urgent to contact a veterinarian as the animal is in danger of death.
The treatments generally administered in emergency are oral sodium bicarbonate to raise the pH.
Subacute acidosis
Also called latent, subclinical, or ruminal instability acidosis, SARA (Subacute Ruminal Acidosis) refers to more common and less visible symptoms. A too abrupt transition in the ration, or an unbalanced formulation with a relative excess of energy can cause it.
The consequences are numerous and may vary from one animal to another. Indeed, they can take the form of one or more symptoms listed below, however these are not always attributable to subclinical acidosis. They are therefore not reliable indicators to determine the presence of the pathology :
- A decrease (or variation) in appetite leading to decreased production
- A drop in fat content (6 points or more) and a low fat-protein difference (less than 3 points)
- Poor digestion, observable with soft or variable consistency dung (presence of grains)
- Increased blood flow in the hooves which can create/amplify lameness (laminitis), or abnormal growth of the horn which becomes brittle
- Loss of body condition, dull coat
The diagnosis of subacute acidosis will be made by the convergence of two or three visible signs.
Chronic acidosis and preventive measures
This term characterizes more the persistence of this pathology than its intensity. Indeed, a subclinical acidosis phenomenon can last several weeks if the ration is poorly balanced, the distribution method inappropriate, or if animals tend to sort too much the feed given to them (this is sometimes the case in small ruminants).
Under these circumstances, the ruminal pH is constantly too low and can lead to a total replacement of the cellulolytic bacterial flora by an amylolytic flora, and more generally to the appearance of the symptoms mentioned above.
For the farmer, the main economic consequences are then the weakening of the animal's immune system and the decrease in its production performance (milk yield, productivity, etc.).
To durably prevent the onset of acidosis, there is a series of measures to implement :
- Regularly provide feed containing fiber that stimulates salivation through rumination and chewing. Indeed, cow saliva naturally contains bicarbonate which helps raise ruminal pH.
- Avoid excess fermentable carbohydrates : < 30% DM of starch + sugars in the ration, and spread their distribution : especially avoid giving them when cows have an empty stomach.
- Progressive transitions between different rations over two to three weeks.
- In critical periods, such as during a stock shortage, sodium bicarbonate is recommended in the ration at 250 to 300 g/dairy cow/day.
Summary
Acidosis in dairy cows is a complex pathology for farmers to understand. Its acute forms are rare but require urgent reaction, and its subclinical and/or chronic forms are much more difficult to detect because they are hard to distinguish from other disorders.
Further reading
Visit the website of EILYPS, a consulting and expertise company in livestock :
https://breeder-connect.com/article/acidose-comment-la-prevenir
Appendices
Sources
- EILYPS : HOW TO PREVENT ACIDOSIS IN YOUR COWS? accessed in February 2022.
- Finistère Farmers Development Committee : Technical sheet - Managing acidosis risks in winter rations 2013.
