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CONTRIBUTOR(S): Toby Mottram, Keith Cutler,

Rumen bolus administration

Rumen bolus administration

Rumen bolus administration allows the continuous slow release or pulse release delivery of minerals, anthelmintics and other pharmaceuticals.

Bolus location; stainless steel and plastic bolling guns ©Toby Mottram


As a result of gravity and muscular peristaltic movements, weighty items that make their way into the rumen tend to be retained in the reticulum. An example would be wires, ingested by cattle. These are swallowed and move into the reticulum. Once in this location, providing they do not penetrate the wall of the gut (resulting a very sick animal), they may remain in situ for the life of the animal.

The Latin name of reticulo-rumen is a clue to its function. Reticulo means “net”. The reticulum is part of the rumen which sits at the lowest point of the abdomen inside the rib cage, behind the brisket.

The ability of the reticulorumen to retain weighty items in this way has been exploited by bolus manufacturers to allow the continuous slow release or pulse release delivery of minerals, anthelmintics and other pharmaceuticals. Following administration, these boluses sit in the reticulum during and after their period of activity.

More recently telemetry boluses which monitor, for example, temperature, rumen pH and the rate of rumen contraction have also been developed to provide information that may be useful in diagnosing issues in cow feed management.

How are boluses administered?

Boluses are administered by mouth in a simple procedure using a bolusing (or bolling/balling) gun. Some guns can administer two boluses concurrently when this is required.

It is important that correct procedures are used to ensure the safety of the animal, the equipment and the operator. The most important point here is the risk to the animal. Risk of choking: if bolus is ejected from the bolusing gun into the trachea then the animal will be at risk of immediate suffocation. Risk of esophageal damage.

Different boluses will fit into different guns. It is important to use the correct gun for the correct bolus.

Do not undertake this procedure unless you are confident that you have been adequately trained to do so. Poor technique can result in injury to the cow and the operator. Seek advice from you veterinarian if you have any doubts as to your ability to place rumen boluses. The process of handling cattle can potentially lead to harm to the animal or handlers therefore, it is essential that appropriate health, safety and welfare measures are taken in the entire process.


Ensure that the bolusing gun is hygienically clean. Restrain the animal in a crush, securing the head in a locking yoke. Consider placing clean rubberized matting on the floor below the animal’s head to minimize contamination or damage to the bolus if spat-out.

Some farmers have taken to writing the animal’s identification number on the bolus to be administered, in indelible ink. This is so that should the animal cough up the bolus and the bolus then be found in the cattle yards, it may be possible to clean and reinsert the bolus into the correct animal. Telemetry boluses are pre-marked with an identifying number and this must be linked to the cow identity.


Load the bolusing gun with the bolus, weighted end facing towards the animal. Insert the bolusing gun gently into the front of the mouth (not at either side).  The front of mouth approach is preferred for the following reasons:

  • Lower risk of bolusing failure: a cause of bolus deployment failure is damage to the bolusing gun. One common issue faced is where a “side of mouth” approach is performed incorrectly and the bolus aperture is bitten and damaged by the molars. This is not common, however it is a risk both to equipment and to the bolus being inserted. This risk is reduced considerably by the “front of mouth” approach.
  • Familiarity: diagrammatic instructions supplied with many types of bolus device clearly show a preferred front of the mouth approach. Additionally, the same method is demonstrated in the AHDB Parasite Control Guide (see below).
  • A “side of mouth” approach: carries a small risk of damage to the side of the tongue and to the opposite internal cheek.
  • Reduced risk of injuring the animal: bolus guns are designed at a specific length and with a specific shape, based upon the gun being used from the front of the mouth. For example, when the gun is inserted fully from the front, the curve of the gun shaft has passed over the natural curve formed by the tongue and when released, the bolus should deploy accurately into the oesophagus. Inserting the gun from the side risks forcing the gun too-far down the animals oesophagus.

Slowly and with gentle, firm pressure, push the bolusing gun over the tongue. You will know when the gun is in position, as you will encounter a slight resistance followed by the animal starting to swallow. Ensure the bolusing gun is not inserted too far down the throat. Fully depress the plunger or trigger to eject the bolus. Gently remove the bolusing gun fully from the mouth.

What should I look out for post-administration?

Observe the animal for a short time to ensure that the bolus has been swallowed. Many animals will demonstrate a ‘flehmen’ type response after successfully swallowing the bolus being administered. Clean the bolusing gun between animals.

If you have any concerns that the animal has been harmed during the procedure then contact your veterinarian for advice.

Signs of problems may include blood on the bolusing gun or in the animal’s mouth, animal not eating, animal choking, animal drooling excessively, animal showing signs of discomfort.


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