Abomasal Bloat in Calves

Abomasal bloat in calves can occur between 4 to 14 days of age and up to 21 days of age and it has been on the increase in recent years. Calves are monogastric animals up to the first 3 weeks of life and the only stomach compartment that is functioning at this time is the abomasum, this is where all the milk or milk replacer is digested. The abomasum is an acidic environment important in creating the milk clot before it passes to the small intestine for the absorption of nutrients. This condition can present itself as a sudden attack with symptoms of abdominal distension, bloat, colic with calves kicking the abdomen, grinding of teeth, salivation, slosh in the abdomen calves can also have diarrhea. Death can be the outcome for 50% to 60% of affected calves. Calves will die from shock or compromised respiration due to the enlarged stomach.


The primary cause is excess fermentation of whole milk, milk replacer or high energy oral electrolyte solution that can cause overgrowth of the bacteria Clostridium perfringens type A. These bacteria are part of the normal gut flora but its proliferation can produce a build-up of gas and β-toxins, resulting in distension of the abdomen and bloating this slows down abomasal emptying. Abomasal emptying is influenced by the following, volume, osmolality the caloric content as well as the pH of the abomasal and duodenal pH (Sen et al,2006).

The volume of the milk/milk replacer fed alters the rate of abomasal emptying that ensures nutrients arrive at the small intestine at a constant rate stabilising the blood glucose levels. The abomasal emptying rate for an entire meal has been shown to be 40% slower when feeding a high volume per feed (4litres) compared to a low volume per feed (2litres), (McPherson et al, 2016).

Following volume osmolality is important in the emptying of the abomasum. Whole milk has total solids reading of around 12.5% which gives it an osmolality of 300mOsm/L, this is optimal for the digestion and absorption of nutrients. Increasing the solids concentration adding more powder is likely to delay abomasal emptying until enough water is secreted into the intestinal tract to dilute the concentration down to 300mOsm/l this will take time. The objective is to keep the osmolality to less than 500-600mOsm/l. Liquids with an osmolality greater than 600mOsm/L should never be fed without water available (McGuirk 2003). Ingredients in electrolytes such as sugar and sodium are highly osmotic.

Mixing rate, is key in determining the osmolality so use a weighing scales, but when mixed to the correct concentration other on-farm factors can subsequently increase osmolality. These factors are,

  • Calf Health (dehydrated calves)
  • Use of soft water (high sodium content) to mix the milk replacer.
  • Low water intake
  • Addition of water-soluble antimicrobials and rehydration fluids to the milk replacer (these can be hypertonic and raise the osmolality)
  • Bacteria count in the colostrum, milk feeding equipment and water particularly where water is from the farm well.
  • Stress, during the first 2 weeks.


Abomasal bloat happens so quickly that no clinical signs are seen, it’s a multifactorial issue involving both management and nutritional factors. When an incidence occurs assess the potential risk factors and make changes.

  • Colostrum management remember the 5C’s (quantity, quality-IgG, cleanliness, comfort, consistency)
  • Milk replacers will be mixed at between 12% to 15% total solids targeting to keep the osmolality at less than 500-600mOsm/L. The total solids content can be estimated by using a Brix refractometer, a correction factor will need to be applied for the optical and digital refractometer. A correction factor of 1.1% for the optical and 1.5% for the digital should be added to the Brix reading (a Brix reading of 12 would indicate 13.1%- 13.5%). These readings are specific to the milk replacer being used (Floren et al,2016). This can also be done with whole milk.
  • Acclimatise the calf to large volumes and stick with this being consistent in the quantity and the time delivered in the day. Feed a max of 3 litres/feed and reduce to 2 litres/feed in bloat situations.
  • Have clean water available. Check your well’s bacterial count ,75 boreholes tested in Ireland in 2011 were positive for thermotolerant coliforms (Bacci and Chapman,2011).
  • Avoid use of soft water when mixing milk replacer.
  • Monitor feeding temperature, ideally 38ᵒC to 39ᵒ
  • Ensure feeding equipment is clean and feeding nipples are not damaged.
  • Calves with diarrhea it’s absolutely necessary to replace the water lost and this should be done with electrolytes mixed with the water.
  • Don’t add electrolytes to the milk replacer.
  • Check the osmolality of the electrolyte.
  • Feeding groups 12-15 calves a maximum of 20.
  • Introduce concentrate from day 3 and keep it fresh and dry.

Following the guidelines and keeping abomasal emptying in mind, calves can have a greater GI health and lower incidences of abomasal bloat.

In addition to consistent feeding and good practices, a healthy calf starts with a healthy cow. Good dry cow management for the cow and in-calf heifer to ensure quality colostrum and low stress environment pre-calving is important. Vaccinating the dry cow with Rotovac Corona and Bovivac S can help manage the bacterial side of the disease.