Avoiding acidosis

Healthy and productive cattle have a ruminal pH of 6.5 to 7. If the ruminal pH changes too much (gets too low or too high), cattle begin to experience symptoms that impact health and reduce performance. 

Symptoms to watch for:

• Depression/lethargy 
• Off-feed
• Elevated heart rate
• Diarrhea
• Poor body condition
• Reduced growth/weight loss
• Elevated temperature
• Bloat
• Reduced rumen contractions
• Liver abscesses (at slaughter or post-mortem)

How?

Cattle have a specific balance of microbes living in their rumen. These microbes help cattle to break down food and absorb nutrients. At any time, cattle have both ‘good’ and ‘bad’ microbes in the rumen. When ruminal conditions are ideal (at the right pH), the ‘good’ microbes thrive, and so do the cattle. However, when ruminal conditions change, the ‘good’ microbes become less effective or die, leaving room for the ‘bad’ microbes to grow.

When the pH of the rumen falls, ‘bad’ acid-producing microbes become more active, which makes the pH fall further, making the rumen more acidic, in a harmful cycle. 

If the rumen becomes too acidic (pH falls below 5.5), the rumen can stop moving. This reduces appetite as well as production—cattle that don’t eat and digest can’t grow. When the rumen becomes very acidic, acid is absorbed out of the rumen and into the blood stream. This form of acidosis, metabolic acidosis, can cause shock and death.

Why does the rumen become acidic?

The rumen becomes more basic (pH increases) when cattle are deprived of feed. This change can harm ‘good’ rumen microbes. Some of these ‘good’ microbes are essential to helping cattle cope if the rumen becomes too acidic. So, if the rumen becomes basic and good microbes are harmed, once the rumen returns to normal, the ‘bad’ microbes can take over, creating a more acidic rumen. These shifts in pH are undesirable.

For example, an animal that was transported for several hours went without feed, and the rumen became more basic (pH increased). This harmed ‘good’ rumen microbes. When the animal gets off the trailer, it consumes a large meal of concentrates. This can cause the rumen to become more acidic, falling below the ideal range. Now the animal has an acidic (low pH) rumen and the microbes that would have helped them bring the pH back to normal were harmed when the animal was off feed. In this way, cycles of feed deprivation followed by overeating greatly increase the risk of acidosis. 

Any other situation that causes cattle to eat large meals of concentrates, such as competition for bunk space, can also increase the risk of acidosis. 

Like most metabolic disease, for every animal you identify, there are several more who are experiencing the disease but not showing symptoms. 
Keep an eye on the manure of your herd. Any changes should be quickly addressed.

Controlling rumen pH

When cattle are fed high-grain diets without access to fibre the rumen can also become more acidic. Long fibre in the diet can reduce the risk of acidosis. Fibre needs to be chewed and ruminated more than concentrates. This chewing and ruminating creates saliva, which is swallowed and ends up in the rumen. Saliva makes the pH of the rumen less acidic (this is called buffering).

Feed that is easier to digest, such as cracked corn, requires less chewing, leading to less saliva buffering, and a more acidic rumen. 

Including long fibre in the diet provides other benefits, such as encouraging rumen development and rumination, and reducing abnormal behaviour. Reducing the risk of acidosis is another reason to consider providing long forage to veal cattle.