Fagopyrum sagittatum (buckwheat), furocoumarin in Ammi majus (bishop’s weed), Cymopterus spp. (spring parsley, wild carrot, various clovers, alfalfa and brassicas) and perloline in Lolium perenne (perennial ryegrass). Ingestion of these plants in active growth can cause primary photosensitisation.
Secondary or hepatogenous photosensitisation occurs when liver cells are damaged, for example, in hepatitis or biliary duct obstruction. Phylloerythrin, an end product of chlorophyll metabolism normally excreted in the bile, is then liberated into the bloodstream and accumulates in the tissues to cause photosensitisation. Plants respon- sible for hepatotoxic damage and secondary photosensi- tisation include bog asphodel (Narthecium ossifragum), Lupin spp. (Lupinus), Lantana spp. (Lantana) and panic grass spp. (Panicum). Various fungi can be responsible, for example, Pithomyces chartarum, which contains sporidesmin, is found in perennial ryegrass (L. perenne) and is the cause of facial eczema in New Zealand sheep (big head or geeldikop in South Africa). Certain chemicals such as phenothiazine, carbon tetrachloride and corti- costeroids may also induce photosensitisation.
The lesions of photosensitisation are confined to the white
, unpigmented, less hairy and woolly areas of the skin which become reddened and oedematous. Commonly affected parts are the face and ears, but teats, vulva and perineum may also be involved. Skin necrosis and gangrene often ensue. General signs of weakness, fever, anaemia, posterior paralysis and nervous symp- toms with death are not uncommon.
The condition must be distinguished from ‘big head’ in sheep caused by Cl. oedematiens (Cl. novyi).
When bony structures are affected with pigmentation, consideration should be given to boning-out with release of the unaffected muscular tissue for food. In local affec- tions, the affected part only need be rejected.
Lipofuscin (‘wear-and-tear pigment’, pigment of brown atrophy, lipochrome, haemofuscin)
Causes of tumoursever, is the loss of body fat and an alteration in its consist- ency. The locations that normally carry adipose tissue
– mesentery, omentum, perirenal fat, mediastinum, sub- cutaneous fat and inter- and intramuscular fat – are shrunken, and the remaining fat has an abnormal appearance, being oedematous and jelly-like in consist- ency and of a sickly yellowish colour. The loss of inter- muscular fat gives a loose, flabby appearance to the muscles which may be pale in colour if accompanied by anaemia. There is also an increase in muscle connective tissue associated with atrophy of the actual muscles.
Chemical analysis of the meat reveals an increase in water content compared with the normal and a decrease of protein, fat and inorganic salts. In extremely emaciated ani- mals, the water content is about 80% and protein about 19%, giving a ratio of water to protein of over 4 to 1. In lean but healthy animals, the percentage of water is rarely above 76.5% and the protein content about 22%, making the water–protein ratio less than 4 to 1. The ratio between water and protein may be of value in distinguishing between car- cases that are very thin and those that are emaciated.
The lymph nodes, especially in young emaciated ani- mals, are enlarged and oedematous. The marrow of long bones is red, watery and poor in fat content, the fat in some cases being replaced by wet, slimy material (serous atrophy of fat).
An emaciated carcase does not set in the normal manner and has a moist appearance on its surface and in the body cavities. Changes in the consistency of the fat are best seen around the base of the heart, in the medi- astinum, in the kidney region or between the spinous processes of the vertebrae.
Judgement is based on the degree of loss of condition, efficiency of setting, presence of concurrent disease and results of laboratory examinations.
Both conditions, especially where unassociated with concurrent disease, are among the most difficult to assess on meat inspection. This is particularly the case in regions where conditional approval for manufacturing purposes and/or heat treatment is not authorised. Regard has to be given to the extent of emaciation, presence/ absence of oedema and concurrent disease.
In borderline cases, it is advisable to detain the carcase for 12 hours. If after this time there is considerable dry- ing of the body cavities with absence of serous infiltra- tion of muscles combined with negative laboratory tests, the carcase may receive a more favourable judgement.
Emaciation and oedema frequently coexist and are suggestive of pathological emaciation.
The Codex Alimentarius Commission Alinorm 93/16A Recommended Final Judgement for ‘General chronic conditions such as anaemia, cachexia, emacia- tion, loathsome appearance, degeneration of organs’ is total condemnation.
Depending upon the extent of the condition the fol- lowing conclusions may be drawn:
1 Approved as fit for human consumption, with distri- bution restricted to limited areas
2 Meat showing minor deviations from normal but fit for human consumption
3 Conditionally approved for human consumption after heat treatment, if economically justified
Total condemnation is always warranted if the condi- tion is caused by chronic infection and laboratory exam- ination has established presence of infection, recent use of antimicrobial substances or drug residues.
Contamination with faeces is one of the greatest hazards to public health encountered in meat inspection. This is most commonly due to presentation of heavily soiled and/ or wet animals to hurried or poor ‘bunging’ technique and full stomachs and intestines rupturing on removal. Food business operators could greatly reduce this risk by the introduction of mechanical bungers such as the Jarvis or Jupiter systems for cattle and pigs, by tying or bagging the ‘bung’ in cattle and sheep or by applying ligatures, clips or elastrator rings or ‘rodding’ the oesophagus.
Contamination of the carcase with purulent material, bile or faeces should always be removed by trimming.
Found in pigs, A. suum is a large roundworm the migrat- ing larvae of which cause typical white spots on the liver rendering in aesthetically unfit. The largest nematode of the pig is up to 40 cm long. Its life cycle is direct.
Eggs are passed in the faeces of pigs and are very resistant to temperature extremes. The egg is viable for more than 4 years in the environment. After ingestion, the egg hatches in the small intestine, and the larva pen- etrates the intestinal mucosa and travels to the liver and then via the circulation to the lungs and onto the small intestine via the bronchi, trachea and pharynx.
An effect of the migrating larvae on the lungs is ‘milk spot’ or ‘white spot’ which appears as cloudy whitish spots of up to 1.0 cm in diameter on the surface of the liver and results from a fibrous repair of inflammation reactions to the passage of larvae in the livers of previ- ously sensitised pigs.
Echinococcus granulosus: Hydatidosis and hydatid cyst
This is a small tapeworm of the dog with intermediate hosts which include domestic and wild ruminants, man and primates, pigs and lagomorphs. Eggs are passed in the faeces of the dog. After ingestion by the intermediate host, for example, sheep, the ova hatch and the oncospheres penetrate the gut wall and travel to the liver (70%) or lungs (25%) and occasionally to other organs and tissues (5%). Transmission to humans is not via consumption of infested bovine organs but rather through the handling of infected dogs or contaminated soil, water or food (Fig. 9.21).
Figure 9.21 Life cycle of Echinococcus multilocularis (Courtesy of Pro A.T. Trees).
In the liver and lungs, the hydrated cyst is 7–20 cm in diameter but in the abdominal cavity where unrestricted growth is possible they may be much larger and may con- tain several litres of fluid. Brood capsules may be formed. In animals, the majority of infections are only evident at the abattoir, in contrast to man where the hydatid, in its pulmonary or hepatic site, is often of pathogenic signifi- cance. Control is based on the regular treatment of dogs and
prevention of them eating material containing hydatids.
Taenia hydatigena (known as Cysticercus tenuicollis in larval stage)
This is the largest of the intestinal dog tapeworms with the cysticerci found in the abdominal cavity and liver in inter- mediate hosts (sheep, cattle, deer, pig, horse), the mature Cysticercus tenuicollis being about 5–8 cm in diameter when they emerge as ‘bladder worms’ on the peritoneum. Dogs and cats are infected by consuming the cysticercus in the tissues of the intermediate host. If untreated, these may sur- vive for several months up to a year or more. The interme- diate host is infected through the ingestion of tapeworm eggs in infected faeces on pasture. The ova hatch in the intestine, and the oncospheres, infective to sheep, cattle and pigs, are carried via the blood to the liver in which they migrate for about 4 weeks before they emerge on the surface and attach onto the peritoneum. These appear in the liver as serpentine haemorrhagic tracts especially near the thin edge. At first, these tracts are dark red in colour but soon become brown or green and finally whitish due to fibrosis.
Taenia ovis (previously known as
Taenia ovisis is a tapeworm of the dog which measures 1–2 cm and forms its cystic stage in sheep. Cysticerci, 3–9.5 cm in size, are found in the skeletal muscles, par- ticularly the heart, diaphragm and masseter muscles 3 months after ingestion (Fig. 9.22).
Figure 9.22 C. ovis in a lamb, courtesy of Ian Robinson, RMHI.
Fasciola hepatica: Liver fluke
Adult fluke in the bile duct lay eggs into the bile which travel to the intestine. Eggs that are passed in the faeces develop and hatch, releasing motile ciliated miracidia, and if certain conditions are correct will find their way to an intermediate host, for example a snail of the genus Lymnaea, most commonly L. truncatula. In infected snails, development proceeds through the sporocyst and radial stages to the final stage in the intermediate host, the cercaria. These are shed from the snail as a motile form and attach themselves to grass blades and encyst there to form the infective metacercariae. It takes a minimum of 6–7 weeks up to several months for development from miracidium to metacercariae. These metacercariae when ingested by the final host excyst in the small intestine, migrate through the gut wall, cross the peritoneum and penetrate the liver cap- sule. The young flukes tunnel through the liver paren- chyma for 6–8 weeks, enter the small bile ducts and then the larger ducts and sometimes the gall bladder and reach sexual maturity. The pre-patent period is 10–12 weeks. The minimum period for completion of life cycle is 17–18 weeks. Fasciola hepatica can survive in untreated sheep for years. In cattle, it is usually less than 1 year.
Damage to the liver in wet seasons in the United Kingdom can be extensive and render the liver aestheti- cally unsuitable for food (Fig. 9.23).
Paramphistomiasis, rumen fluke, has become a common finding adhering to the wall of the rumen of cattle and sheep, as an incidental finding at post-mortem, in the United Kingdom in recent years (see Fig. 9.24). The life cycle is similar to Fasciola, in that snails act as an inter- mediate host with miracidium, sporocyst, rediae and cercariae stages.
There are large numbers of Sarcocystis species. The life cycle has the sexual reproductive stage occurring in the predator or scavenger host which come infected by con- suming meat containing infected sarcocysts. These are shed as sporocysts or sporulated oocysts in the faeces after about 1 week. The intermediate host (prey) is infected by ingestion of sporocysts in contaminated food and water. These are released in the intestine, penetrate the blood and lymphatic systems and after several generations encyst within the muscle, heart, liver, lung and neuronal tissues. In muscle, the cysts lie within and between indi- vidual muscle fibres and have a characteristic cigar shape (4.5 × 0.35 µm). Grossly, infected tissue generally has a greenish, eosinophilic myositis appearance. The final host
Figure 9.23 Lesions of F. hepatica, liver fluke.
becomes infected by ingestion of mature sarcocysts, usu- ally by eating contaminated meat of the intermediate host. Humans may also serve as intermediate hosts and suf- fer myositis and vasculitis, but this tissue phase is rare, and the source of such human infection has never been determined. Human intestinal illness, with clinical signs of nausea, abdominal pain, and diarrhoea that lasts up to 48 hours, as followed ingestion of sarcocysts of S. suihom- inis in uncooked pork and S. hominis in uncooked beef. The extent of human illness from ingestion of infected meat has not been documented, although the meat from infected animals will be condemned on aesthetic grounds.
Courses of action
The decisions made at post-mortem inspection vary in different parts of the world depending mainly on local disease incidence, local economy and the presence or absence of facilities for the heat treatment of meat condi- tionally approved for human consumption. The main decisions in most countries, however, are as follows:
Figure 9.24 Paramphistomiasis, bovine rumen fluke.
1 Approved for human consumption 2 Totally condemned
3 Partially condemned
The category of conditionally approved for human con- sumption is utilised in some countries: carcase meat which is hygienically unsatisfactory or which in some way may be hazardous for human and animal food is treated, for example, by heating or freezing under official supervision, in such a manner that makes it safe for human consumption.
In certain regions, meat classed as inferior meat, namely, safe hygienically but of a lower standard, may be sold as raw meat without undergoing any treatment. Such meat must be labelled so as to indicate that it is of inferior quality and sold under close supervision by the controlling authority. It includes meat of abnormal col- our, odour or taste, with slight oedema or poorly bled and, like the following category, is found in those coun- tries where there is a scarcity of protein.
Lastly, meat may be approved for human consumption, with distribution restricted to limited areas. This category also occurs in those countries where meat is at a pre- mium and includes meat from animals in an area under quarantine because of an outbreak of contagious animal disease. In this case, there must be no risk to public health, and the meat must be restricted in sale to the affected area to avoid the possible spread of disease. The category would also include meat from animals vacci- nated in a restricted area.
It is the duty of the official control staff to arrange for the health marking of the carcases when passed and to ensure the proper disposal of unfit material. It remains important in Europe that checks to ensure the efficient and hygienic removal of the SRM associated with BSE from the carcase and viscera and their correct animal by- product categorisation, marking and disposal.
Utilisation of post-mortem data
As virtually all food animals end up in the slaughter- house, whether prime livestock or end-of-production cull animals, for example, cull cows and sows, it is with- out doubt the critical and most efficient point of produc- tion at which to carry out surveillance for animal disease.
This disease data has the potential to be used for:
1 Reduction of losses due to disease and injury through feedback to livestock producers and private veteri- nary practitioners
2 Demonstration of trends and variations in animal disease incidence due to husbandry methods, season, geographical location, etc.
3 Tracing of affected herds as part of national disease control programmes
4 Extent, cost and reasons for condemnations due to disease and injury
5 Measurement, benchmarking and improvement of animal welfare on farm – fighting and tail biting in pigs
6 Use of information regarding animal housing and hus- bandry, including breeding data, to improve standards on the farm, including those of animal hygiene
7 Demonstration of certain subclinical conditions
8 Forecasting of disease outbreaks in conjunction with meteorological data
9 Enhancement of the clinical competence of the prac- tising veterinary surgeon regarding data on client’s slaughtered stock, especially casualty animals
10 Provision for research investigations
11 Quality control check on inspection standards
The slaughter establishment has therefore an impor- tant role to play in epidemiology and preventive vet- erinary medicine, not only in relation to post-mortem findings but also following examination of the live ani- mal prior to slaughter. Harley et al. (2012) reviewed the uses that the data could be put to in improving ani- mal welfare, highlighting the financial loss to the producer.
With the exception of a few countries, the potential of post-mortem data is regrettably not being fully exploited. Among the reasons for this deficiency are lack of coordi- nation between those in charge of meat inspection and primary production, the practical difficulties in slaugh- ter line recording (e.g. fast rail speeds, inadequate inspec- tor manning levels) and traditional livestock marketing systems, through intermediaries and markets.
Many variations of systems are in existence. Those countries which possess cooperative livestock/meat systems, for example, the Netherlands and Denmark, are better placed to organise an efficient recording and feed- back of information to producers.
Inherent in any scheme for the utilisation of abattoir data is the need for precise diagnoses, standard nomen- clature for the diseases encountered and recognised forms of presentation of the disease data. There is no point in referring back vague or inaccurate information to livestock producers. Equally important is efficient identification of live animals as well as of their carcases and offal, which must be correlated. The system in the abattoir must include full details of the carcase and spe- cies, disease condition, part of carcase affected, weight of meat and offal condemned and, if necessary, be supple- mented by the results of laboratory examinations. The disease conditions to be recorded should be of a type that is readily identified, of economic importance in the ani- mal health and/or public health sphere and easily con- trollable. There is a key role for the private veterinarian in the interpretation of data on farm and implementation of controls and preventative herd health programmes.
Previous barriers to implementation of post-mortem feedback systems have largely been eliminated by web- based electronic communications. Post-mortem data recorded on the slaughter floor onto a specifically pro- duced web site with controlled access can be instantane- ously downloaded by the farmer via smartphone technology. Such as a system developed in Northern Ireland has added post-mortem data from pig slaughter- houses to information already available for the grades of pigs, delivered through an app to the producers’ phone with analysis as a weekly download.
While the EFSA opinions question the efficacy of post-mortem inspection for public health purposes, they emphasise the significance of the process for animal health purposes and particularly its use on farm.
Control of hygienic production
While the responsibility to produce safe food lies with the operator, meat inspection has a critical role to play in inspection and verification of hygienic production sys- tems and particularly the absence of visible contamina- tion of the meat. In addition, it is important that all inspections must be carried out with due regard for hygiene. It is essential that the official inspectors set and achieve the highest standards of hygienic dress, appear- ance and operations if they are to have any hope of enforcing high standards within the plant. Operational hygiene has been dealt with in Chapter 8.
Before the day’s slaughter commences, the inspector must verify that the premises, equipment and facilities are hygienic and in good working order and that meat operatives are properly clothed and adequate in number. Slaughter should not be allowed to commence until a satisfactory situation obtains. This pre-slaughter check
may take the form of a visual and microbiological verifi- cation of the meat plant’s own monitoring system. The preferred system is one where the operatives themselves are responsible for ensuring that the premises are hygienic, the meat inspection team merely verifying their checks.
The prevention of contamination must remain the aim, rather than post-production contamination reduc- tion by means of water, organic acids, other bactericides or irradiation. Washing has been demonstrated (Ellerbroek et al., 1993) to have no effect in reducing pathogen levels on the surface of the carcase and can, in fact, have a detrimental outcome by spreading the con- tamination over the surface of the carcase to less con- taminated areas and increasing the available water remaining on the carcase. Suitably controlled, organic acids, irradiation, etc. may be useful tools in helping to ensure a safe product; they must not be allowed to mask poor manufacturing practice.
In the experience of the author, carcase meat which looks clean and smells clean, in general, has low micro- biological counts. Meat microbiology is a tool that must be used intelligently to improve hygiene systems or stand- ards within an establishment rather than to determine if meat is ‘safe’ or to compare the safety of meat between establishments or countries. There are just too many vari- ables to permit simplistic rules for interpretation of results. These include differences between sampling and laboratory techniques, transport media and time, sample and culture; the variation in pathogenicity of different bacteriological strains; the retrospective nature of the results and the effect of storage conditions on the final bacterial count. This view was endorsed by Engel et al. (1997), who carried out a scrutiny of the effectiveness of the microbiological criteria imposed by the Dutch meat inspection regulations in place at that time.
Despite this, microbiological sampling is a useful tool especially if used with a food safety management system (FSMS) designed to prevent contamination of the meat with potential hazards and can be used to set HEIs lead- ing to a final FSO at consumer level. Within meat inspec- tion, the FSMS usually incorporates the principles of hazard analysis and critical control points (HACCP).
Hazard analysis and critical control points (HACCp)
HACCP is a system which identifies, evaluates and controls hazards which are significant for food safety. As the specific detail of HACCP as applied in different countries varies, this definition and all those quoted are those to be found in documentation issued by Codex Alimentarius, in particular Recommended International
Code of Practice, General Principles of Food Hygiene, as revised.
It builds upon the good manufacturing practice, described in Chapter 8, and through a process of logical steps identifies the risks to food safety and identifies points in the production process where the application of controls will eliminate or reduce that risk to accepta- ble levels – the critical control points (CCPs).
International acceptance of the approach was first underlined during the Uruguay Round of the General Agreement on Tariffs and Trade (GATT) 1994, when the inclusion of the Codex Alimentarius Commission’s recommendations on the application of HACCP was specifically identified as the baseline for consumer pro- tection under the Agreement on the Application of Sanitary and Phytosanitary Measures.
implementation of an HACCp system
Many books and manuals are available which describe how to implement an HACCP system within a food processing setting. The information included here is merely intended to provide a brief overview. The con- cept is no longer new, and over the years, understand- ing of its effective use has developed and practical deployment improved. It is now widely accepted that the concept works best if the principles are applied flex- ibly to meet the identified targets FSO but then imple- mented rigidly – to do what the HACCP plan says you are going to do.
The first step in preparation is to construct a process flow diagram of the process to be controlled, including step by step the introduction of all raw materials and each part of the process. This must be detailed and the accuracy validated repeatedly against what is happening on the factory floor (Fig. 9.25).
All HACCP systems comprise the following sequen- tial steps:
1 Hazard analysis.
The first step in applying the HACCP system to a food manufacturing operation is to identify and quantify the microbiological, physical and chemical hazards and risks within the operation. The following defini- tions are important:
a. Hazard is a biological, chemical or physical agent in, or condition of, food with the potential to cause an adverse health effect.
b. Severity is the seriousness (magnitude) of the hazard.
c. Risk is an estimate of the likely occurrence of a hazard. The analysis requires the specialist knowledge of a multidisciplinary team and should include food microbiologists, engineers, veterinarians, cleaning experts and so on. A step-by-step investigation of the
Production Transporting Holding
(Cattle, sheep, goats, horses)
Figure 9.25 Flow diagram for fresh meat production and processing. ○ indicates a site of minor contamination. ● indicates a site of major contamination; CCP1, effective CCP; CCP2, not absolute (International Commission on Microbiological Safety of Foods (ICMSF)).
process is carried out, from the specification required for the raw material through the manufacturing pro- cess to the distribution chain.
Epidemiological investigation of historical episodes of premature spoilage or food poisoning in which the product was implicated can provide valuable informa- tion about potential hazards. All of the data emerging from this analysis should be collated into a flow chart and all of the hazards identified and evaluated with regard to their severity and likely frequency of occurrence.
2 Determination of the CCPs.
The classical definition of a CCP is a step at which control can be applied and is essential to prevent or eliminate a food safety hazard or reduce it to an acceptable level.
The proper identification of CCPs can make the difference between an effective HACCP programme and one that, by the identification of too many points in the system which must be considered as critical, becomes ineffective. A decision tree is often used as a useful tool to determine if a particular control is in effect a real CCP. However, informed professional judgement is key.