A Cautionary Tale; An Outbreak of Drench Gun Injuries

Farm Vet David Charles discusses the dangers of drench gun injuries and you tips on how to prevent injuries from occurring

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This quarter, as well as the usual updates and seasonal discussion, I wanted to highlight an interesting case I dealt with last year, as it involves something that tends to impact large numbers when seen.

As with many cases, this one started with a phone call from a client who wanted to discuss an outbreak of sudden deaths in their flock, and a few lumps on some sheep….

The swellings were all seen around the jawline, sometimes bursting out a thick, creamy pus and sometimes just resolving themselves, or bursting into the mouth. The ewes that had died tended to have had smaller swellings that hadn’t burst. Being in the run up to tupping, handling of the ewes had been minimal except for a mineral drench a number of weeks ago and they were being flushed on good pasture.

We bled a number to check for the particularly nasty Caseous Lymphadenitis (CLA); a bacterial disease which causes infectious abscesses of the lymph nodes both internal (causing weight loss) and external (such as the ones at the corner of the ear and base of the jaw), if these burst outwards the pus is wildly infectious to the flock, and the farm staff. Isolation and antibiotics were also used to reduce the infection in the ewes with the external swellings. Thankfully, the test came back negative but we still needed an answer!

Being linked with the University of Nottingham Vet School (who now also have an APHA contract for post mortem examinations ), it was agreed that if any more sudden deaths with facial swellings occurred we would send one in for a full and detailed post mortem examination (opting to do this at the university rather than on farm due to the risks if it was CLA and opening a lesion out on farm).

A call from the client followed a few days later ‘I’ve lost another one’, so off the carcass went to the university, and what followed surprised us all! There was no pus found in the mouth and no internal abscesses, instead just inflamed and oedematous muscle and lymph node tissue. However, the rumen was full of blood (which had clotted by the time the carcass arrived for PME). (Figure 1)

Fig.1 F21-183 coaugulated blood admixed with ruminal content in the rumen

It is likely that the bacteria had been introduced during that mineral drenching earlier in the year, and had entrenched itself as an abscess slowly necrotising (killing) the neighbouring muscles and eroding away until all of a sudden it reached and eroded the wall of the carotid artery (Figure 2) causing mass internal bleeding, clotted blood in the rumen as seen on the post mortem exam and sudden deaths in the sheep due to shock from blood loss.

 

Fig.2 F21-183 left retropharingeal haemotoma and necrotising to gangrenous myositis

For those where the bacteria worked outwards rather than deeper into the body, this would explain the large facial abscess which had been observed to be bursting out with the thick pus that was part of the original phone call discussion.

Unfortunately drench gun injuries are still all too common; often seeing ‘waves’ with high numbers of ewes in the same flock being affected due to the tendency to treat groups of ewes at a time.  Not all present as sudden death, many flocks will suffer a number of sudden deaths alongside a higher number of swollen necks, jaws and ewes which struggle to eat, of which less than half would be expected to recover.

What can be done to reduce drench gun injuries?

Dave’s top 7 Steps:

  1. Use the correct size drench gun for your sheep – significant trauma occurs when sheep are drenched with cattle drench guns.
  2. Check the angle of the arm; any bending or impact on the gun may change the angle and increase the risk
  3. Is the person drenching the sheep trained and capable of doing so? Can training be given if not
  4. Restrain the animals properly – use a race +/- a headstand, or have two people to make it easier
  5. Maintain your drench gun! To ensure it’s delivering the dose it says (calibration) but also to ensure it’s not being worn and creating sharp spurs on the end
  6. Place the nozzle over the back of the tongue to introduce the dose into the back of the throat so it’s all swallowed
  7. Consider if the treatment is needed; many animals are drenched when there isn’t a need for worming or mineral supplementation, putting animals at risk for no medical benefit

(We can also see these with bolus application – sometimes even finding boluses lodged in the muscles of the neck on post mortem exam – so these key tips apply there too)

(photos provided by School of Veterinary Medicine and Science- University of Nottingham and the Animal and Plant Health Agency)

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