Abomasal bloat in calves: what causes it and how to reduce the risk

Abomasal bloat in calves: what causes it and how to reduce the risk

Bloat is an over-expansion of the abomasum soon after milk feeding. It is due to gas (produced by the normal fermentation of feed) building up and being unable to escape.

  • Abomasal bloat is typically seen in calves five to 10 days old.

The exact cause of abomasal bloat in calves is unknown, but certain things must happen to produce the condition:

  • An excess of fermentable carbohydrate in the abomasum (from milk, milk replacer or electrolyte solution)

  • A fermentative enzyme (produced by bacteria, many of which are present in the calf stomach all the time)

  • Something that has slowed the rate of abomasal emptying. The pre-weaned calf must have milk to grow and develop, but anything that slows down the rate at which milk empties from the abomasum will give the bacteria present more time to ferment this essential feed.

It’s hard to identify the specific reason for abomasal bloat but understanding the main risk factors for the condition, correctly and consistently mixing a proven milk replacer and always following best rearing practice will help.

Practical tips to help reduce the risk of abomasal bloat

Always feed a minimum of 2L of high quality (> 22% brix) maternal colostrum within 2 hours of birth and a further 2L within 12 hours. If high quality maternal colostrum is not available use a high quality, high IgG colostrum replacer like Launchpad 18.

To guarantee the calf gets a minimum 100g IgG for immunity, feed 2L Launchpad colostrum within 2 hours of birth. Feed a further 2L quality maternal colostrum within 12 hours.

Ensure equipment and teats are in good condition and scrupulously clean.

Use a Brix refractometer on a regular basis to make sure a consistent product is being fed to the calves. Bloat risk can increase where the total solids concentration is greater than 15% as this can affect the rate of abomasal emptying.

If you’re just feeding whole milk every day and not putting anything in it, you may have major issues. However, if you are fortifying milk or using a milk replacer, you should check this on a regular basis.

If feeding once a day and using a more concentrated milk replacer solution, be sure to follow manufacturer’s recommendations.

Tip: Take a Brix reading from milk fed to the first calf, the middle calf and the last calf. A big variation between these readings will indicate a mixing error.

Calves should have a daily routine. Feeding at the same time each day reduces stress.

  • Milk feeds should be limited to 3L per feed (reduce to 2L per feed for bloat cases).
  • Always mix the milk replacer according to manufacturer guidelines and mix it at a consistent concentration.
  • For higher osmolality products, you should feed a lower volume. How concentrated the milk is influences how long the milk sits in the stomach.
  • Where you have a high risk of bloat, consider more regular, smaller feeds per day - calves fed ad lib or even three times per day can do better than calves fed once or twice daily.

Make sure the milk or milk replacer offered to the calves is consistently 38-39ºC. Variations in milk temperature will alter the rate of abomasal emptying and stop the closure of the oesophageal groove.

A lower water intake will increase the osmolality of the milk and slow the abomasal emptying rate.

  • Offer fresh, clean ad lib water to calves at all times from the first day of life.
  • If there are more than 20 calves in a mob, provide two water points.


Water from a bore, well or surface water source may contain a high microbial content which can cause bloat.

An abrupt diet change can slow abomasal emptying rate and lead to excessive gas.

Whilst it can be difficult to identify the specific cause of bloat in your calves, implementing an easy to follow routine and keeping your processes consistent will help to reduce risk. Plus, choosing a specialist, low osmolality, high quality calf milk replacer means one less thing to worry about in the dynamic rearing environment.

Choose Sprayfo milk replacers for optimising calf growth

AgriVantage offers a choice of high energy or whey Sprayfo calf milk replacers, each one offering different benefits for calf growth and development, whilst reducing the risk of bloat.

Sprayfo Delta CMR

Sprayfo Delta Energised Calf Milk

Our premium curding calf milk replacer for optimised growth.

Sprayfo Blue CMR

Sprayfo Blue Premium Calf Milk Replacer

Our premium whey calf milk replacer for enhanced rumen development