Terrestrial Animal Health Code
Terrestrial Animal Health Code |
Prevention and control of Salmonella in commercial bovine production systems
Introduction
Nontyphoidal salmonellosis is one of the most common foodborne bacterial diseases in the world with Salmonella Enteritidis and S.Typhimurium (including monophasic variants) being the predominant serotypes identified in humans in most countries. S. Enteritidis is primarily associated with poultry while S. Typhimurium may be present in many mammalian and avian hosts. These serotypes and several others occur at variable prevalence in bovines depending on the region. In some countries S. Dublin and S. Newport may also cause salmonellosis in humans.
Salmonellainfection in bovines is mostly subclinical, although clinical disease such as enteritis, septicaemia or abortion may occur. Subclinical infection, including a carrier state, can be of variable duration and can play an important role in the spread of Salmonella within and between herds and pose a public health risk.
Herd size and stocking density may influence the likelihood of introduction, dissemination or persistence of Salmonella; however, this is also dependent on geographical region, husbandry and other factors such as season and age.
Salmonella serotypes and their prevalence in bovines may vary considerably within and between farms, countries and regions. It is important for Veterinary Authorities and producers to consider serotypes of Salmonella, their occurrence and the disease burden in bovine and human populations when they develop and implement strategies for the prevention and control of Salmonella in commercial bovine production systems.
Definitions
For the purposes of this chapter:
’Commercial bovine production systems’: means those systems in which the purpose of the operation includes some or all of the following: breeding, rearing and management of bovines for the production of meat or milk.
’Intensive bovine production systems’: means commercial systems in which bovines are in confinement and are fully dependent on humans to provide for basic animal needs such as food, shelter and water on a daily basis.
’Extensive bovine production systems’: means commercial systems in which bovines have the freedom to roam outdoors, and where the bovines have some autonomy over diet selection (through grazing), water consumption and access to shelter.
Purpose and scope
This chapter provides recommendations for the prevention and control of Salmonella in commercial bovine production systems in order to reduce the burden of disease in bovines and the risk of human illness through foodborne contamination as well as human infections resulting from direct or indirect contact with infected bovines.
For the purposes of this chapter a bovine means Bos taurus, B. indicus, B. javanicus and B. grunniens, water buffaloes (Bubalusbubalis) and bison (Bisonbison and B. bonasus).
This chapter applies to bovines kept in commercial bovine production systems.
This chapter should be read in conjunction with the Codex Alimentarius Code of Hygienic Practice for Meat (CAC/RCP 58-2005), Code of Hygienic Practice for Milk and Milk Products (CAC/RCP 57-2004), Code of Practice on Good Animal Feeding (CAC/RCP 54-2004), and the Guidelines for the Control of Nontyphoidal Salmonella spp. in Beef and Pork Meat (CAC/GL 87-2016), and the OIE/FAO Guide to Good Farming Practices for Animal Production Food Safety.
Objectives of prevention and control measures
Prevention and control measures may focus on those serotypes of Salmonella of greatest consequence to bovines and public health. These measures will also contribute to the reduction of other serotypes.
Prevention and control measures in commercial bovine production systems may:
reduce the prevalence and amount of Salmonella entering the slaughterhouse/abattoir and therefore decrease the challenge to the slaughter and dressing procedures and the likelihood of bovine meat contamination;
reduce the likelihood of Salmonella contamination in milk;
reduce Salmonella contamination of the environment via bovine faecal waste, which in turn will limit infection of animals (including wildlife);
reduce the likelihood of infections in humans through contact with infected bovines or contaminated materials or water.
While control in the primary production phase can decrease the number of animals carrying or shedding Salmonella, controls after primary production are also important to minimise the contamination and cross-contamination of carcasses and meat products.
Good farming practices and, when appropriate, the principles of hazard analysis and critical control points (HACCP) should be taken into account when designing prevention and control measures.
Articles 6.13.5. to 6.13.16. provide recommendations for the prevention and control of Salmonella in commercial bovine production systems. These recommendations may also contribute to the prevention and control of some other infections.
Biosecurity
Biosecurity is essential to prevent and control Salmonella. A biosecurity plan should be developed according to the commercial bovine production system employed. The applicability of the measures, described below, will vary according to the type of commercial bovine production system.
When including Salmonella as part of a biosecurity plan the following should be addressed:
location, design and management of the establishment;
veterinary supervision of bovine health;
management of the introduction and mixing of bovines;
training of personnel in their responsibilities and their role in animal health, human health and food safety;
prevention of contamination of feed and water, including for irrigation;
maintenance of records including data on bovine health, production, movements, feeding, water supply, medications, vaccination, mortality, and cleaning and disinfection of farm buildings and equipment;
availability of test results to the farm operator when Salmonellasurveillance is conducted;
removal of unwanted vegetation and debris that could attract or harbour pests around premises for bovines;
minimising the entry of domestic animals and wild birds into buildings for bovines and feed stores;
cleaning and disinfection procedures for buildings in which bovines are handled or housed, in accordance with Chapter 4.13.;
control of pests such as rodents and arthropods and regular assessment of effectiveness;
control and hygienic procedures for entry and movement of persons and vehicles;
cleaning and disinfection of equipment and vehicles identified as posing a risk;
storage and disposal of dead animals, bedding, faeces and other potentially contaminated farm waste in a manner that minimises the likelihood of dissemination of Salmonella and prevents the direct or indirect exposure of humans, livestock and wildlife to Salmonella. Particular care should be taken when bedding and faeces of bovines are applied to land used for horticultural crops intended for human consumption;
procedures for prevention of dissemination of Salmonella when an animal is suspected or known to be infected.
Location and design of establishments
for bovines
When making decisions on the location and design of establishments for bovines, it is recommended that reduction of the likelihood of transfer of pathogenic agents, including Salmonella, from major sources of contamination be considered. Sources of Salmonella may include other livestock establishments or areas of application or disposal of contaminated waste or effluent. Other sources and vectors of Salmonella include vehicles, equipment, water-courses, personnel, domestic animals, birds, rodents, flies and wildlife.
The design of intensive bovine production systems should consider the following:
management of faecal waste to minimise contamination of the establishment;
adequate drainage for the site and control of run-off water and untreated waste water;
use of materials for construction that facilitate effective cleaning and disinfection;
control of entry and movement of vehicles, equipment and persons;
preventing contamination of feed and water during storage and distribution;
handling and movements of bovines to minimise stress and spread of Salmonella;
separation of bovines according to likelihood of infection with, or susceptibility to, Salmonella;
restriction of entry of domestic animals, birds, rodents, flies and other relevant wildlife.
In extensive bovine production systems, location and design options may be limited; however, applicable biosecurity should be considered.
Management of introductions of bovines into the establishment
To minimise the likelihood of introducing Salmonella through introductions of bovines:
good communication within the bovine industry should be encouraged to raise awareness of the likelihood of introducing Salmonella through cattle introductions;
consideration should be given to minimising the number of sources of replacement bovines;
new genetic material should be introduced through the use of semen and embryos whenever practicable;
if possible, bovines should be sourced directly from herds of origin because live animal markets or other places where bovines from multiple properties are mixed for resale may increase the likelihood of spread of Salmonella and other infectious agents among bovines;
newly introduced bovines should be kept separate from the rest of the herd for a suitable period before mixing with other bovines;
when appropriate, testing of animals for Salmonella prior to introduction or mixing with other bovines should be considered to inform subsequent control measures, for example, when introducing bovines of unknown status.
Management of bovines on farm
To reduce the likelihood of transferring Salmonella among bovines:
bovines with suspected salmonellosis or otherwise sick should be separated from healthy bovines;
care of healthy bovines should be carried out prior to care of bovines with suspected salmonellosis;
priority should be given to the hygienic management of calving areas, for example keeping perinatal bovines separated from sick bovines and maintaining a clean environment;
bovines should be segregated according to age;
when possible, the 'all-in-all-out' principle for production cohorts should be used. In particular, the unnecessary mixing of different age groups, especially of calves, should be avoided;
consideration should be given to the potential for between-herd transmission of Salmonella via breeding, rearing and grazing of bovines from multiple sources on a single site, for example shared pasture, heifer rearing or sharing of bulls;
consideration should be given to the potential for between-herd transmission of Salmonella through direct contact between bovines across boundary lines or indirectly, for example through contamination of water courses.
Feed and feed ingredients
Feed and feed ingredients can be sources of Salmonellainfection for bovines. For the effective control of Salmonella:
when appropriate, feed and feed ingredients should be produced, handled, stored, transported and distributed according to Good Manufacturing Practices, considering Hazard Analysis Critical Control Points (HACCP) principles and recommendations in accordance with Chapter 6.4.;
feed and feed ingredients should be transported, stored and fed in a manner that minimises contamination by faecal waste and, where practicable, minimises access by domestic animals, birds, rodents and wildlife.
Water
Water for drinking should be of an appropriate quality. When there is reason to be concerned about infection of bovines with Salmonella from contaminated water, measures should be taken to evaluate and minimise the risk. For example sediment in water troughs may act as a reservoir for contamination. Where practicable, untreated surface water should be avoided as a water source.
Additional prevention and control measures
The immune status of calves is important and therefore care should be taken to ensure that newborn calves consume adequate amounts of high quality colostrum in accordance with Article 7.9.5. (point 3 c)) and Article 7.11.7. (point 9)). Raw milk from infected cows should not be fed to calves.
Vaccination may be considered as part of a Salmonella control programme. Vaccine production and use should be in accordance with Chapter 1.1.6. of the Terrestrial Manual. The protective effect of vaccines is generally serotype-specific and is influenced by factors such as timing of vaccination in relation to exposure.
A number of conditions, for example liver fluke and infection with bovine viral diarrhoea virus, may increase the susceptibility of bovines to Salmonella; therefore, control of such conditions is recommended.
Stress may increase the susceptibility of bovines to Salmonella. Management of potentially stressful situations, such as mixing of groups of bovines, may reduce the likelihood of clinical disease or shedding of Salmonella.
Antimicrobial agents may modify normal flora in the gut and increase the likelihood of colonisation by Salmonella. In circumstances when antimicrobial agents are considered necessary for the treatment of clinical salmonellosis, they should be used in accordance with Chapter 6.10. Furthermore, antimicrobial agentsshould not be used to control subclinical infection with Salmonella in bovines because the effectiveness of the treatment is limited, they may increase the risk of Salmonella colonisation, and their use can contribute to the development of antimicrobial resistance.
Transportation
Vehicles should be properly cleaned and disinfected after transportation of animals, in accordance with Chapter 4.13.
When transporting animals from multiple establishments, the Salmonella status of the establishments should be considered to avoid cross-contamination of bovines.
In addition, the relevant recommendations in Chapters 7.2., 7.3. and 7.4. apply.
Lairage
Relevant aspects of lairage management include consideration of effective cleaning and disinfection between groups, minimising mixing of animals that have not continuously been kept together and managing stress.
In addition, the relevant recommendations in Articles 7.5.1., 7.5.3. and 7.5.4. apply.
Cleanliness of hides
Cleanliness of hides can be achieved by applying suitable practices during housing (for example additional clean bedding), transport and lairage. Dirty hides increase the risk of microbial contamination of carcasses during the slaughter process.
Surveillance for Salmonella in commercial bovine production systems
Surveillance data provide information to assist the Competent Authorities in their decision making regarding the requirement for, and design of, control programmes and in setting and verifying performance objectives.
Standards for diagnostic tests are described in the Terrestrial Manual. In addition, other sampling and testing methodologies such as testing of bulk milk or serum samples by ELISA may provide useful information on herd or individual animal status. Boot swab samples from communal areas in housing for bovines, slurry samples, or caecal or lymph node samples collected post-mortem can also be useful for microbiological testing. Some serotypes of Salmonella such as S. Dublin can be difficult to detect using microbiological methods.
If serology is used as the surveillance method, it may not be possible to distinguish between vaccinated and infected bovines.
Prevention and control in low prevalence regions
In regions where Salmonellainfection of bovines is uncommon, it may be possible to maintain low prevalence status or eliminate infection from herds through a combination of good farming practices, herdsurveillance, individual testing, movement controls, and removal of persistent carriers.
nb: first adopted in 2017.
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