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Myth-busting calf acidosis: 5 misconceptions and the truth behind them

Tom Earleywine for Progressive Dairy Published on 01 November 2021
Calf hutches

“We have way too many calves with acidosis.”

“Rumen pHs are low, must be acidosis.”



“I need to switch calf starters; this one is causing acidosis.”

Have any of these thoughts crossed your mind? If so, you’re not alone. But you might be missing the real question: Do your calves actually have acidosis?

There are true cases of calf acidosis, but not as many as one might think. Just because a calf has a low rumen pH doesn’t mean it has acidosis. In fact, a low rumen pH may be part of normal calf rumen development.

So when it comes to calf acidosis, what’s fact and what’s fiction? Here are five common myths about calf acidosis busted:

Myth 1: Every calf with a rumen pH below 5.5 has acidosis.
Truth: A rumen pH below 5.5 may be a normal part of rumen development.


Calves are born without a developed rumen. Starter helps develop the rumen, but it also causes fermentation and produces acid, resulting in a dip in rumen pH. A low rumen pH might be a necessary part of normal rumen development for young calves on starter feed.

The real problem lies in unexpected, drastic drops in rumen pH which last for a long time and cause damage to the rumen. Sudden spikes in starter intake can cause too much acid production all at once, resulting in acidosis.

The best way to identify true rumen acidosis is to monitor calves during times of stress and when approaching weaning or just starting the weaning process. Watch for calves that go off feed, scour or are generally less frisky.

Myth 2: Acidosis only happens at weaning.
Truth: Acidosis can occur at various times throughout a calf’s life, and it is especially dependent upon milk consumption. Even after weaning, acidosis can occur due to stressors or diet changes.

The rumen is still developing in young calves and isn’t ready to handle high-starch diets. Calves fed less milk or milk replacer early in life may have increased starter intake they aren’t ready for, resulting in acidosis. The rumen takes time to develop.

And if calves aren’t receiving enough milk or milk replacer nutrition pre-weaning, they start the weaning process hungry and quickly try to gobble up enough starter to meet energy requirements. But the starter prompts acid production, and the acid accumulates and causes problems.


Feeding higher levels of milk or milk replacer pre-weaning ensures calves receive the nutrition they need without overeating starter.

Myth 3: The type of starter fed can cause acidosis.
Truth: The starter formulation itself can play a role – but it’s minor in comparison to the amount of starter consumed. No matter which starter you feed, managing intake to avoid big dips in pH is the best tool to help prevent acidosis.

Things that can prompt sudden increases in feed intake include:

  • The introduction of starter too late (if you’re not offering free-choice) or introduction to a new type of starter feed.

  • Water quality or availability issues. For example, the water bucket freezes and starter consumption drops, then it thaws and calves eat a bunch of starter.

  • Weather changes causing shifts in eating patterns. For example, hot temperatures set in, causing calves to eat less, then the weather breaks and calves have a sudden uptick in consumption. Or cold weather comes suddenly and starter consumption spikes due to low milk or milk replacer feeding.

  • Disruptions to a calf’s normal routine, causing stress and disrupting the gut. Transportation, vaccination or even skipping a day’s bedding can cause gut dysfunction, which alters the microbiome and increases the odds for acidosis.

It’s nearly impossible to judge a starter’s impact on acidosis by the label. That said, a starter with a proper balance of starch, sugars and fibre can provide insurance against pH dips. You can also provide a starter with proven consistent consumption to minimize intake fluctuations.

Myth 4: Calves with acidosis may struggle for a day or two, but they’re fine after that.
Truth: The negative impacts of acidosis on rumen health and the microbiome are far-reaching. If rumen pH gets too low or drops too suddenly, calves will go off feed, which has a big impact on calf growth, especially when you’re weaning calves.

But the more critical issue is long-term impacts. Rumen acidosis could cause ruminal scarring which, in the long run, deters nutrient absorption and overall rumen health. Calves experiencing acidosis may also be predisposed to ulcers. The dysbiosis or upsetting of the gut microbiome can also have similar long-term impacts on the calf.

A calf with rumen acidosis may also have poor feed efficiency long-term, resulting in lower milk production as a cow or poor finishing performance in steers.

Myth 5: Calf acidosis always requires treatment.
Truth: Typically, calves with acidosis will go off feed. Since there’s no substrate to produce more acid, the rumen stabilizes on its own. The bigger question to ask, if a calf has acidosis, is not how to treat it – but how did they get it in the first place?

Then the next challenge is when the calf goes back on feed – intake goes up, and the calf is back at risk.

For calves off feed due to suspected acidosis, be conservative with starter as they come back to health and start eating again. If a calf didn’t consume any starter the day before, don’t go from zero to 60 and suddenly offer up 2 kilograms of feed. Instead, gradually reintroduce starter and closely monitor intake.

Work with your local calf specialist to evaluate your feeding program and find areas to adjust to help reduce the incidence of rumen acidosis. end mark

PHOTO: A low rumen pH doesn’t automatically equate to rumen acidosis in calves. Photo courtesy of Purina Animal Nutrition.

Tom Earleywine
  • Tom Earleywine

  • Director of Nutritional Services
  • Land O’Lakes Animal Milk Solutions
  • Email Tom Earleywine