Today we were joined by six students from the Royal Veterinary College (London). We also had a change in species from pigs (yesterday) to sheep and cattle. The ultimate process is relatively the same for sheep as it is for pigs. For cattle, a captive bolt is used pre-exsanguination. Also, with sheep and cattle, the hides are an important sale opportunity as well as a contamination risk. Therefore, unlike pigs which were dehaired, cattle and sheep are skinned and the hides are sold externally.
The cattle are fairly violent and it can be very dangerous work. The regulations surrounding the cattle and sheep are fairly strict. Of significant concern are the zoonoses of TB and BSE. TB vaccinations are a requirement for the British students upon entering vet school, similar to how we require rabies vaccinations. Today’s carcasses were mildly rewarding. We had evidence of liver flukes in one of the sheep carcasses. One interesting case was evidence of Cystercercus tenuicollis which is a tapeworm that typically is found in the intestines of the definitive host (canid species). However, in sheep, it causes visceral cystericercosis. Essentially, the tapeworm gets lost. In our case, the tapeworm had found its way to the liver and in an attempt to escape the liver where it could not survive, the tapeworm had formed a serpentine path through a section of the liver. Our other interesting case was tapeworm that had caused cysts in the lungs. We also learned about TB in ruminants. Although TB does cause nodules in the lungs (respiratory cases account for the vast majority of cases), the nodules are very small and difficult to see even though the OV is still required to feel the lungs. The ultimate key to diagnosing TB in a carcass is the lymph nodes that drain the lungs. In a TB positive case (even one that tested negative), the lymph nodes will be significantly enlarged. Also, when they are incised, they will have a grainy, sandy feel during the cutting process. Finally, in cattle, the heads are carefully inspected. The masseter muscles are incised in order to incise the parietal lymph nodes. The retropharyngeal lymph nodes and submandibular lymph nodes are also checked. An interesting point that I learned is that the eyes must be intact in the carcass because if they have been punctured and the animal had TB or some other serious zoonotic disease, then the entire carcass is now contaminated and therefore must be condemned.
We had a thoroughly explanation involving the captive bolt guns. The abattoir here uses a penetrating captive bolt gun which means that the bolt penetrates roughly seven centimeters into the skull (on this model). The other broad category of captive bolt guns is non-penetrating which means a broad-based, mushroom-shaped projectile percusses against the skull. Both categories function in essentially the same way to cause a concussive force from which the animal is thoroughly stunned and not likely to recover. However, if an animal were to recover from the stun (wake up), it would be more likely to occur with use of the non-penetrating captive bolt gun. After the explanation which involved the components of the captive bolt gun and how to care for it and put it back together, each of us were able to fire it into the heads of already slaughtered animals. We finished off the day with a nice pub meal involving one of the best chicken burgers that I have ever had!