Rumen acidosis

What is rumen acidosis?

In rumen acidosis the rumen is too acidic. The rumen microbes ferment carbohydrates into acids. Normally these are absorbed through the rumen wall and buffered by saliva. If the cow gets more rapidly digestible starch or sugar than the rumen can handle, the acids are produced faster than they are removed. The pH drops.

The normal pH in the rumen is roughly between 6.0 and 6.8. There are two forms:

• Subacute ruminal acidosis (SARA): the pH stays below about 5.8 for several hours a day. The cow does not look ill, but performs less well. This form is common in dairy herds.
• Acute rumen acidosis: the pH drops below about 5.0, usually after a large amount of grain in one go. This is an emergency for the vet.

Causes

• A lot of rapidly degradable starch, such as wheat or barley, or a lot of sugar
• too little physically effective fibre, for example very finely chopped silage
• sorting: cows pick the concentrate out of the ration and leave the straw
• large concentrate portions in one go instead of several small ones
• increasing concentrate too quickly after calving
• heat stress, because the cow ruminates less and loses buffer through panting

How do you recognise subacute rumen acidosis?

Individual cows rarely show clear symptoms. Typical signs show at herd level:

• fluctuating feed intake, with cows eating well one day and poorly the next
• loose, frothy or yellowish manure, sometimes with undigested grains or fibres
• fewer cows ruminating in the lying area
• low milk fat content and a fat-to-protein ratio below 1.0 in milk recording
• later on, more claw problems such as sole ulcers and laminitis

The acid damages the rumen wall. Bacteria and toxins then pass into the blood more easily, which can encourage inflammation in the body and liver abscesses.

Prevention through the ration

The best protection is a ration that suits a ruminant. A guideline is at least 16 to 18 percent crude fibre in the dry matter, with enough structure. Mix the TMR so that cows cannot sort it. Straw is best cut to 2 to 4 cm. A mix that is too dry makes sorting easier.

Feed concentrate in small portions spread over the day and build it up over two to three weeks after calving. Pay attention to the starch source: grain maize is broken down more slowly than wheat. Buffers such as sodium bicarbonate can supplement the ration, but they do not replace structure.

Checks in the barn

Regularly count how many of the lying cows are ruminating. It should be at least half. Assess the manure and check the milk fat content and fat-to-protein ratio in your milk recording. Cows with neck collar or ear sensors give you rumination time per day. If it drops in a group, it is worth looking at the ration.

If cows look clearly ill, stop eating or have diarrhoea, call your vet. You can read more about the rumen and heat stress in Heat stress in dairy cattle.

Effects on claws and fertility

The effects of rumen acidosis often only show weeks later. Inflammatory substances from the damaged rumen wall disturb the blood supply to the corium in the claw. Horn quality gets worse, and bleeding in the sole and defects in the white line appear. Biotin production in the rumen also falls.

Frequently asked questions

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