MICROBIOLOGICAL EVALUATION OF PROCESSED AND PRESERVED FEED
Dr.Sudhanya Nath1*,Dr.AdyaPrakash Rath2, Dr.Saurabh Karunamay3, Dr. Smita Patil4 and Dr.Diptanu Das5
1PhD Scholar, Department of Animal Nutrition, West Bengal University of Animal & Fishery Sciences, Kolkata, West Bengal – 700037, India
2PhD Scholar, Department of Veterinary Pathology, Guru AngadDev Veterinary and Animal Sciences University, Ludhiana, Punjab – 141001, India
3PhD Scholar, Department of Livestock Products Technology, West Bengal University of Animal & Fishery Sciences, Kolkata, West Bengal – 700037, India
4PhD Scholar, Department of Livestock Production Management, West Bengal University of Animal & Fishery Sciences, Kolkata, West Bengal – 700037, India
5PG Scholar, Department of Animal Nutrition, College of Veterinary Sciences and Animal Husbandry, Selesih, Aizawl, Mizoram – 796014
*Correspondence:sudhanyanath@yahoo.com
INTRODUCTION:
Animal feeds are blended or processed products of plant and animal origin whose principal purpose is to meet animal’s nutritional needs. A number of feed and feed ingredients are imported and feeds are often produced as processed finished or compound feeds.
In recent years, there has been a diversification in feed ingredients available and feeding practices. For example, there has been an increased use of compound feeds in the dairy industry, reflecting the rapid growth and intensification in that sector. In addition, there is a growing range of imported feed and feed ingredients from a variety of overseas sources, which poses an additional risk for the introduction of pathogens and contaminates into the food chain. There has been interest in further elucidating the relationship between pathogenic/spoilage bacterial contamination of animal feed and human foodborne illness.
A wide range of microbes occurs naturally on, or as contaminants of forages, cereal grains, oilseed by-products and compound feeds. Animal feeds may become contaminated with harmful bacteria such as Salmonella, Listeria and E. coli. In the case of the latter organism, faecal sources and slurry have been identified as the primary routes of contamination both in pastures and compound feeds. Cereal grains and oilseed by-products are regularly contaminated with fungi occurring as plant pathogens or developing during storage. Major adverse effects arise in farm animals due to the production of mycotoxins by certain species and strains of these fungi.
Beneficial effects of microbes in feed can result from the occurrence of the lactic acid bacteria during the fermentation of forages in the process of ensilage. These bacteria favour the production of lactic acid, which helps in reducing the pH to around 4.0, thus preserving the forage for winter-feeding to ruminants.
Animal feed, due to its composition, provides a favourable environment for the growth of microorganisms. Microorganisms found in the feedstuffs can be saprophytic, pathogenic, conditionally pathogenic and toxic. Their growth and proliferation in the feed depends on numerous factors, such as moisture, temperature, type of feed, aerobic and anaerobic conditions, chemical and physical properties of raw material, feed pH value, presence of feed supplements, storage periods and conditions as well as feed decomposition products.
Feed may be contaminated during processing, storage or transport. Some microorganisms introduced during storage, primarily moulds, can negatively affect feed quality including reducing dry matter and nutrients, causing musty or sour odours, and producing toxins. Mouldy raw materials are not appetizing and can considerably reduce feed consumption. Contaminated feed frequently causes zoonoses and for that reason, it is necessary to establish surveillance programs for microbiological feed hazards.
The importance of microbial quality of the feed is not being considered in animal feeding till they affect the life or performance of the host animal. These microbes not only affect the animals but also the human with respect to salmonellosis, scrapie, listeriosis. The contamination with fungus leads to not only change in colour, flavor and palatability, but also causes hepatic and kidney damages due to production of mycotoxins. These toxins also possess tumour causing properties. The presence of microbial population in silage is very much important for the preparation of good quality silages. However, this area of animal nutrition is rarely under studied except the mycotoxins. The importance of microbiological quality is gaining importance over the past two decades since the report of bovine spongiform encephalopathy in Europe.
The microbiology of animal feeds emerged as an important issue in the wake of the Salmonella, E. coli, Campylobacter and Bovine Spongiform Encephalopathy(BSE) crises in the EU and elsewhere and the foot and mouth epidemic of 2001-02 in United Kingdom.
FUNGAL CONTAMINATION OF CONCENTRATES AND FORAGES
Contamination may occur during processing and storage of harvested products and feed whenever environmental conditions are appropriate for spoilage fungi. Moisture content and ambient temperature are key factors affecting fungal colonization of and mycotoxin production in concentrates and compound feeds. The risks arise primarily from the ability of particular species and strains of fungi to produce harmful compounds known as mycotoxins.
Fungal contamination of animal feeds is a regular occurrence on a worldwide scale and detrimental effects have been observed in all classes of farm animals due to the production of mycotoxins by certain species and strains of moulds. There are few grounds for complacency as regards animal feed safety and vigilance should now be the watchword for all those involved in the livestock industry.
Toxigenic fungi of concentrates and forages
| Fungi | Occurrence | Mycotoxins
|
| Aspergillusflavus; A.parasiticus
|
Peanut meal,
cottonseed cake, palm kernel cake, maize,compound feeds |
Aflatoxins
|
| A. flavus | Oilseed meals, compound
Feeds |
Cyclopiazonic acid
|
| A. ochraceus; Penicilliumviridicatum; P. cyclopium | Barley and wheat grains | Ochratoxin A
|
| P. citrinum; P. expansum | Cereal grains | Citrinin
|
| P. citreo-viride | Cereal grains | Citreoviridin
|
| Fusariumculmorum; F.graminearum
|
Cereal grains | Deoxynivalenol
|
| F. sporotrichioides; F.poae | Cereal grains | T-2 toxin
|
| F. sporotrichioides; F.graminearum; F.poae | Cereal grains | Diacetoxyscirpenol
|
| F. culmorum; F. graminearum;
F. sporotrichioides |
Cereal grains | Zearalenone
|
| F. moniliforme | Maize kernels | Fumonisins;moniliformin;
fusaric acid |
The Aspergillusgenus dominates all other fungi in respect of mycotoxin production in cereals and oilseeds. Some researchers observed that Aspergilluswas the most significant genus in dairy and other feeds in the tropics. Three species are responsible for virtually all mycotoxin production by this genus: Aspergillusflavus, Aspergillusparasiticusand Aspergillusochraceus. A. flavus, and A. parasiticussynthesise the aflatoxins, while A. ochraceus produces the ochratoxins.
The aflatoxins include aflatoxin B1, B2, G1 and G2 (AFB1, AFB2, AFG1 and AFG2, respectively). In addition, aflatoxin M1 (AFM1) may well occur in the milk of dairy cows consuming AFB1-contaminated feeds. The aflatoxigenicAspergilliare generally regarded as storage fungi, proliferating under conditions of relatively high moisture / humidity and temperature.
Salmonella species
Many species of Salmonella have been implicated in diseases of farm animals. Of these, S.typhimuriumis universally distributed while S. enteriditishas emerged as a regular pathogen ofpoultry and contaminant of eggs and chicken meat. Animal feeds are thought to be an importantsource of these bacteria. Meat and bone meal and fish meal are frequently contaminated with Salmonella. Intensive pasture utilisation provides an additional source through contamination offaeces from infected animals. Furthermore, the practice of spreading cattle slurry on to pasturesin conventional and organic farms is another potentially significant source of infection.
Escherichia coli
It is widely recognised that cattle feeds contain E. coli through contamination with faeces. There is particular concern over the occurrence of E. coli O157 since this form has been definitively linked with specific outbreaks of illness in humans.
The application of slurry on to pastures means that there is potential for the transfer of faecalE.colito grazing animals, a practice that has caused some disquiet among those concerned withfood safety. It was suggested that attention should focus on the replication of E. coli in moist feeds and duration of storage in feed bunks.
Foot and mouth disease:
Foot and mouth disease has been a major problem in the UK during 2001-02, with devastating effects on the livestock industry. The disease is spread by inhalation and by ingestion of contaminated materials. The outbreak in the UK has been tentatively attributed to the feeding of catering waste to pigs. While this association may never be confirmed, it is clear that in the intensive rearing of animals due recognition should be given to the need to correctly process animal feeds. However, in the EU, the feeding of catering waste containing meat products is banned under a recent directive.
Bovine Spongiform Encephalopathy(BSE)
The prion proteins of processed animal proteins have recently emerged as important feed contaminants implicated in the development of BSE in cattle. Prion proteins are normal animal tissue components with the capacity to transform into agents causing fatal neurological syndromes in a wide range of species. The initial onset of BSE was attributed to the feeding of cattle with meat-and-bone meal prepared from carcasses of scrapie-infected sheep. The latter disease is also caused by prion proteins as is the human equivalent, new variant Creutzfeldt-Jakob Disease (vCJD). The incidence of vCJD in humans has been linked with the consumption of BSE-contaminated beef. It is this association that has led to extensive and stringent legislation in the European Union concerning the use of specified animal products in livestock feeding.
SILAGE MICROBIOLOGY
The process of silage making plays an important role in feeding of green forages during post-monsoon seasons throughout the continents. Successful preservation of high-moisture forage and other crops depends upon the controlling the activities of microbes, particularly bacteria. Conditions favouring optimal preservation include the rapid imposition and subsequent maintenance of anaerobic conditions at all stages in the process of ensilage. Under these conditions, lactic acid bacteria proliferate, using endogenous plant sugars to produce sufficient quantities of the lactic acid to depress pH to around 4, the optimum value for successful preservation. Wet forages are difficult to preserve in this way and often provide ideal conditions for the growth of undesirable bacteria such as the Clostridia.
During ensilage either one of the two types of fermentation (homo- and hetero-fermentation) takes place and ultimately determine the silage quality. Among these two fermentation types, the homo-fermentative is more desirable as maximum acidity could be obtained which inhibits the growth of aerobic organisms, mould and yeast and protect the silage form spoilage. The maintenance of anaerobic environment during silage making not only favours the growth of lactic acid bacteria but also the growth of obligate anaerobe clostridial organisms. The lactic acid bacteria (LAB) are of two types. The homofermentative species include Lactobacillus plantarum, Pediococcuspentosaceus and Enterococcus faecalis. The heterofermentative species comprise Lactobacillus brevis and Leuconostocmesenteroides. The homofermentative group are more efficient in converting forage sugars into lactic acid .
Two groups of Clostridia are also recognised. The saccharolytic group includes Clostridium butyricumand C. tyrobutyricum. These species ferment residual sugars as well as lactic acid to butyric acid, causing a rise in pH. The proteolytic group includes C. bifermentansand C. sporogenes. These bacteria ferment amino acids to amines and ammonia generation which causes ammonia odour as well as increase in the pH toward alkaline side (>5). This raise in pH accompanied with high moisture facilitates the growth of fungus which changes the smell, taste and colour which in turn affect the acceptability by the animals. The production of butyric acid as a result of clostridial fermentation caused reduced feed intake in ruminants.
The Enterobacteria include Escherichia coli andErwiniaherbicola and are also considered to be undesirable in that they compete with LAB for plant sugars fermenting them to acetic acid, ethanol, CO2 and H2. They are also capable of catabolising amino acids to NH3.
Listeria monocytogenesis widely distributed in nature and also occurs in silage, particularly big bale silage. The increased incidence of listeriosis in sheep and cattle has been partly linked with the introduction of big bale silage. The relatively low density and limited fermentation characteristics of big bale silage and susceptibility of the bags to damage all favour the growth of L. monocytogenes. This organism is of particular significance because of it potential to contaminate animal products destined for human consumption.
Fungi occur in silages as yeasts and moulds. The yeasts include species of Candida, Saccharomyces and Torulopsis. The moulds associated with silages include various species of Aspergillus, Penicilliumand Fusarium. The occurrence of these fungi is of particular concern due to their potential to produce harmful mycotoxins.
Wilting the crop before ensiling is a common method of restricting fermentation, allowing the growth of LAB but inhibiting the activities of undesirable organisms such as Clostridia and Enterobacteria.
Microbiology of ensilage
| Organisms | Conditions required | Major products/effects
|
| Lactic acid bacteria (LAB) | Anaerobic; wilting of crop is desirable; crop should be chopped for rapid establishment of LAB.
|
Homofermentative pathway: lactic acid and some acetic acid.
Heterofermentative pathway: lactic acid, ethanol, mannitol, acetic acid and CO2. |
| Clostridia | Anaerobic; wet forage | Saccharolytic species: butyric acid, CO2 and H2.
Proteolytic species: butyric acid, acetic acid, amines, CO2 and NH3.
|
| Enterobacteria | Anaerobic; optimum pH 7.0; active in early stages of fermentation.
|
Acetic acid, ethanol, CO2 H2 and NH3.
|
| Listeria | Aerobic; pH above 5.5; growth possible at low temperatures and in high-dry matter silages
|
Listeriosis, especially in sheep. |
| Fungi | Aerobic; active on surface layers of silage.
|
Spores and mycotoxins.
|
MICROBIAL ASSESSMENT :
The assessment of microbial contamination in animal feeds needs to be rapid, sensitive and representation of diverse population.
The approaches includecollection of samples, isolation of microorganisms bythe complete enumeration by total plate count (both aerobic and anaerobic organisms), identification of bacterial and fungal isolates;bacterial isolates were identified based on their gram staining and biochemical characteristics (indole test, sugar fermentation, methyl red test, voges- proskauer test, catalase test, coagulase test, citrate test etc.), fungal isolates were identified based on their morphological characteristics on SDA(Sabouraud Dextrose Agar) and Lactophenol cotton blue stain identification.Thin layer chromatography (TLC) quantifiesmycotoxins formed and indirectly measure the extent of fungal contamination during the post-harvest and storage periods.
These conventional procedures are less sensitive and time consuming; hence, the modern techniques of polymerized chain reaction could be used in assessment of feed microbial quality. This test will be rapid, more sensitive and also representation of diverse microbial contamination in the feed.
CONCLUSION:
Microbiological safety and cleanness of animal feeds is essential not only due to the sanitary conditions of animals, but also because of indirect impact on health of consumers. Therefore, it is important that the producers of animal feeds, having in mind health consequences in animals and humans who consume food products of animal origin, provide the highest possible microbiological cleanness of their products. An essential role is also played by the farmers, who are producers of plant resources – the basic animal feeds for animals. Both farmers and producers within the framework of hygiene and good practice must pay attention particularly to the stage of drying and storing feed resources, in order to prevent microbiological contamination. With continuous collection and evaluation of microbial safety-related data during processing, distribution and use of animal feed, and application of adequate agricultural and management practices, microbial feed safety hazards may be considerably reduced and adequate feed quality ensured. Feed quality and safety are important prerequisites for sustainable development of livestock production.
