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Febrile carcasses in pig slaughterhouses

The concept of "febrile carcass" (a.k.a. fevered carcass, in spanish carnes febriles) is frequently used in the inspection of carcasses in the slaughterhouse to  describe carcassses that show extensive alterations in coloration and texture.

In the texts of hygiene and meat inspection febrile carcasses are described with the following characteristics, without specifying differences between species (Meat hygiene and inspection, B. Moreno García 2003):

• Paleness (appearance of cooked meat) and loss of brightness of the muscular surface.
• Evident congestion of the vessels of connective tissue and fat (which contrasts with the paleness of the muscle).
• Presence of serosanguinolent exudate on the connective tissue, mainly accumulated in lowermost parts.
• Abnormal smell of the canal (it is appreciated especially at the evisceration stage).
• Flaccid carcass due to lack of rigor mortis.
• Haemorrhagic or edematous lymph nodes.

The interpretation is that these animals have been slaughtered during an acute phase of disease, involving a feverish process. Often, however, it is unknown whether the animal in question had any type of ante-mortem signs.From pig slaughterhouses doubts have raised regarding the classification of pig carcasses under this concept.

In pig, the causes that can alter the appearance of the canal are multiple and one should take into account, apart from the alterations that can be observed at the muscular and connective tissue level, the alterations of the skin, since the carcasses arrive at the post-mortem inspection with this organ. Even though the use of the generic term "febrile caracasses" can be useful when it comes to justifying the condemnation of a caracass, this concept does not have a specific pathological correlate.

That said, from SESC, what we suggest is to try to clarify criteria to identify some of the pathological and/or physiological entities that can be observed in the slaughterhouse and that cause changes in the appearance of the caracass, to be used, if applicable, as criteria to justify a condemnation within the concepts of general illness or pathophysiological alterations, reasons for condemnation described in Chapter V, Section II, Annex I of EC Regulation 854/2004.

The idea would be to avoid the use of this nonspecific terminology and try to use descriptive diagnostic terms as specific as possible. And, with the support of SESC, try to arrive, when possible, to a more accurate, even etiologic, diagnosis.

Alterations of the quality of the carcass unrelated to lesional changes:

Response to stress: pigs respond in a peculiar manner to stress during handling. Deficient management or overexcitation can cause hyperemia and also the emergence of bleeding/blood resorption to lymph nodes as well as erythematous lesions on the skin and subcutaneous tissue, which must be distinguished from septicemia or viremic lesions.

The quality and appearance of meat in the hours after slaughter can also vary depending on environmental or handling factors and the response to the stress of the animal. Two main alterations of the quality of meat are defined:

• Dark, firm and dry meats, known as DFD meats, formerly known as "tired meats": for proper conversion of the muscle into meat it is vital that there is glycogen in sufficient quantity and that it, as a result of rigor mortis, is slowly consumed as the animal's carcass cools down. This use, which will occur in the absence of oxygen (the animal is dead and therefore does not breathe), will result in the production of lactic acid, which will activate the enzymatic protheolysis of the muscle, the loss of water ( known as exudate of the muscle) and the loss of pigmentation (for that reason the liquid that undercooked meat leaks is red and many people mistakes it for blood). Consequently, a piece of meat is softer (protein degradation), clearer (loss of pigments and changes in the refraction of light) and juicy (it is exuding water) than the origal muscle, but the conversion process into meat takes around 20 hours pigs and vacuum days, so it is very important to stress that no one foresees DFD meat a few minutes after slaughter. DFD meat is just a muscle that is still muscle because there was not enough muscle glycogen at the time of sacrifice. So what causes DFD meat? Well, everything that depletes the animal's glycogen before its sacrifice, beginning with very long fasting, endless transports and eternal waiting time for slaughter. From here, if the time of these three factors is reduced, it will depend on the intensity with which these animals live. That is to say, for example, if the waiting times are short but they spend this time fighting among themselves instead of resting, the risk of DFD increases. Finally, it is important to remember that the meat, due to the lowering of the pH because of lactic acid it is hygienically safer than muscle (it is a more hostile environment for many of the pathogenic microorganisms), so DFD meat (with a higher pH) implies shorter life times of these products.
  

  Examples of DFD and PSE meat comapred to a normal one. Source: FAO.

• Pale, soft and exudative meats, known as PSE meats: in this case, what has happened is that at the moment of the animal's slaughter the muscle already had a large amount of lactic acid. At this time point the carcasss is still very hot, therefore the enzymatic reactions in the muscle are also accelerated. Proteolysis is more intense (the muscle softens mor than usual), it exudates (the muscle loses more water than usual) and it loses color (the flesh becomes pale). In order for these changes to happen, the animal must have undergone a situation of intense muscular exercise just before the sacrifice, and this includes not having rested well enough after the effort that an animal undergoes during the transportation to the slaughterhouse. However, there are obvious differences between animals and genetic lines. In general, all those animals used to exercise will be less likely to suffer from these problems, because the muscles are better irrigated and it is more difficult to get them to work in anaerobiosis. On the contrary, those genetics that are more muscular, will be much more likely to suffer these problems, especially if they had little activity during the period of fattening. It should be remembered that this is a problem of the muscle conversion process into meat, so that no signs of it will be seen until after the first 20 hours post slaughter. One way to predict the problem is to measure the PH shortly after the sacrifice (45 minutes-1 hour). If the pH is below 5.8, it is very likely that it will end up being a PSE meat.

These alterations could come into the definition of febrile caracass, especially PSE meats, although they correspond to healthy animals without any pathology. But rarely they will be observed in a whole carcass since they are alterations that do not appear until after many hours after the sacrifice (> 20h), moment in which the carcass usually has already been cut. If these alterations are identified, it is advisable not to use the term of febrile meats.

Impacts on the handling of the channels on the slaughter line:

A lack of bleeding prior to scalding or an incomplete bleeding could give images of intense congestion (both  of the skin and viscera), especially in the lower parts of the carcasss. In these cases, the lymph nodes should look normal. It is necessary to contemplate the possibility that an animal enters stunned, but not dead into the scalding tank, this would cause a peripheral hyperemic reaction to the extreme heat. In this last case, it can be checked to see if there is scalding liquid inside the airways.

Changes in the quality of the channel related to pathological changes:

Then there are pathological conditions that cause congestion, edema or hemorrhages of the carcass, lesions that would explain its classification as febrile carcasses.

In an post published earlier in thig blog, we discussed the reasons that could lead to a pig carcass to present a reddish color.

Diseases that cause inflammatory lesions that, at the level of the skin, result in the presence of erythematous and / or haemorrhagic lesions.

In this category we can find: erysipelas, porcine dermatitis and nephropathy syndrome, actinic dermatitis, contact dermatitis, allergies, exudative epidermitis, insect bites, mange, dermatophytosis, african swine fever, classical swine fever ... Each one may have more or less identifiable patterns and location and, if there are haemorrhages in the dermis, blood resorption to lymph nodes can also be observed.

One speaks of viremia or septicemia when it comes to generalized viral or bacterial ethiology, respectively. Among the agents that can cause septicemia in the pig are: Actinobacillus suis, Erisipelothrix rhusiopathiae, Streptococcus spp., Listeria monocytogenes ... In these cases it is usually accompanied by changes in the lymph nodes, usually increased in size.

In a previous post the different causes of lymphadenopathy in pig carcasses were reviewed.

Causes that cause hemorrhagic diathesis (a tendency to bleed) in the animal: Anticoagulant poisoning (warfarines, for example, rodent poisoning), thrombocytopenia , vitamin K deficiency, copper toxicity, zinc, etc.  These conditions were also reviewed in a post on hemorrhagic diathesis in porcine carcasses.

Traumatisms: as a result of fights, scratches or strokes during the transport of animals can present with muscular bruising and wounds, haemorrhages or erosions on the skin.

A cardiopathy, that implies insufficient venous return could predispose an animal to the dermal congestion. One should think about this cause when the problem occurs in isolated animals.

Dr. Antoni Dalmau of the Animal Welfare program in IRTA has participated in this post.