Biosecurity measures to control salmonellosis on NZ dairy farms
Background
Key features of Salmonella– its persistence in the environment, how it affects animals and its public health importance:
- Salmonella commonly enters farms in imported animals or from wild animals and spreads between livestock by faecal-oral pathways.
- Salmonella may be shed in all body fluids but especially manure, immediately before, during and up to 70 days in adult cattle abd at least 14 days at least in calves, after clinical signs of disease resolve, depending on the serovar.
- Salmonella may persist in the environment in moist/wet (<85% DM) conditions, shaded areas and effluent for weeks or months as well as being shed from carrier/recovered animals for prolonged periods.
- Salmonella can infect any bird or mammal or reptile species (including humans).
- The key factors affecting whether ingestion of Salmonella leads to clinical disease and its severity are:
- Virulence of the serovar.
- Dose/number of bacteria ingested.
- Strength of host immunity including any previous exposure to Salmonella and presence of other stressors affecting the animal including disruption of normal gut microbe balance, low dietary intake for 1 or more days or other dietary stress.
- Strength of host immunity including any previous exposure to Salmonella and presence of other stressors affecting the animal including disruption of normal gut microbe balance, low dietary intake for 1 or more days or other dietary stress.
- Of these factors, the first can’t be controlled on farm, but the remaining two factors can be targeted by management interventions.
- Antibiotic resistant Salmonella are a real threat to public and animal health and therefore efforts to prevent and control disease outbreaks that don’t use antibiotics should be prioritised.
Transmission pathways
Biosecurity protocols
Biosecurity protocols to control salmonellosis should be developed in partnership between the farmer and their trusted vet advisor. The following steps can be followed to develop a salmonellosis control programme:
- Assess the risks of management practices on an individual farm basis (see accompanying biosecurity measures tables).
- Focus on controlling the management practices which likely have the greatest risks and which can be modified.
- Protocols should be reassessed in the event of an outbreak.
- Because many of the risks for salmonellosis in dairy herds are common to other infectious diseases, controlling these risks will have benefits for control of other diseases and animal production also.
At the ‘farm gate’ protocols aim to prevent or reduce the risk of importing Salmonella onto or exit from the farm (Table 1).
Table 1: Measures to control salmonellosis on NZ dairy farms ‘at the farm gate’
| Risk Factor | Control Measure | Measure Adequate? | Details |
|---|---|---|---|
| Importing Salmonella onto farm with infected cattle | Closed herd and no co-grazing policy | Y / N | If not feasible, develop an effective plan to screen and exclude animals from unknown or high-risk herds. |
| Quarantine new arrivals | Y / N | Isolate imported animals for 2 weeks and monitor for signs of disease. | |
| Manage to enable closed herd policy | Y / N | Rear sufficient replacements to calve so importing cows is unnecessary. | |
| Y / N | Optimise cow health and reproductive performance. | ||
| Y / N | Optimise heifer rearing practices. | ||
| Importing Salmonella onto farm with contaminated items or feed | Avoid use of equipment or vehicles from other farms used for manure management | Y / N | If not feasible then clean and disinfect equipment before use. |
| Prevent high-risk off-farm vehicles from accessing livestock areas | Y / N | e.g. dead animal collection trucks, livestock trucks. | |
| Purchase feed from suppliers with good pest control management | Y / N | ||
| Fence off water courses | Y / N | Delay access to flooded pasture or feed. | |
| Provide cleaning and disinfection area for visitors | Y / N | Provide piped water, brushes, buckets, and disinfectants. | |
| Importing Salmonella onto farm via infected feral animals or birds | Maintain boundary fencing to high standard | Y / N | Ensure boundary fencing is adequate to prevent entry of large feral animals. |
| Prevent access to feed by pests and vermin | Y / N | Use bird- and rodent-proof feed storage facilities. | |
| Y / N | Cover face of silage stacks between feeding out. | ||
| Y / N | Apply appropriate pest management plans. |
Behind the ‘farm gate’ protocols aim to minimise or eliminate Salmonella spread between livestock if Salmonella enters (Table 2).
Table 2: Measures to control salmonellosis on NZ dairy farms ‘behind the farm gate’ (calf-specific measures in bold type)
| Risk Factor | Control Measure | Measure Adequate? | Details |
|---|---|---|---|
| High levels of environmental contamination with Salmonella | Promptly diagnose, isolate, and treat suspected or confirmed salmonellosis cases | Y / N | Confirm cases and antibiotic sensitivity by bacteriological testing. |
| In an outbreak, handle all animals as if they are shedding Salmonella | Y / N | Symptomatic animals are likely only the “tip of the iceberg.” | |
| Separate all sick from colostrum cows | Y / N | Include confirmed or suspect salmonellosis cases among the sick. | |
| Use an ‘all-in, all-out’ calf management system | Y / N | Remove bedding, clean, rest, and disinfect pens between batches of calves. | |
| Isolate high-risk calves | Y / N | Calves born from cows suspected of salmonellosis should be isolated. | |
| Infection spreading between stock via feed and water | Avoid contamination of feed with manure | Y / N | Avoid feeding cattle off the ground. |
| Y / N | Avoid staff walking across feed with manure-contaminated boots. | ||
| Y / N | Clean manure from vehicle tires before they access feed storage areas. | ||
| Graze young stock separately from adults | Y / N | ||
| Prevent access of livestock to surface water or flood-affected feed | Y / N | ||
| Infection spreading to or between calves from environment and via milk and colostrum | Collect newborn calves > 1 times daily where feasible | Y / N | |
| Clean and disinfect calf collection trailer after each collection | Y / N | ||
| Clean and disinfect teats of colostrum cows before milking | Y / N | Thoroughly disinfect all teat skin with alcohol-based teat wipes before attaching cups. | |
| Ensure stored colostrum is properly preserved and nutritious | Y / N | Use potassium sorbate (0.5% w/v) or pasteurization methods for preservation. | |
| Prevent contamination of stored colostrum | Y / N | Prevent access by birds or rodents; use only sterilized stirring equipment. | |
| Clean and disinfect calf liquid feeding equipment | Y / N | Clean feeding equipment before first use and daily where feasible. | |
| Don’t feed calves raw waste milk | Y / N | Milk from sick or antibiotic-treated cows may be contaminated. | |
| Infection spreading and recycling between stock via manure and effluent | Ensure that dairy effluent or manure slurry or solids are spread on land according to best practice | Y / N | See DairyNZ guidelines and comply with regional council requirements. |
| Infection spreading between stock via equipment or personnel | Separate and hygienically manage sick animals | Y / N | Staff should handle or manage sick animals separately and after healthy ones, maintaining strict hygiene. |
| Minimise the number of people entering calf rearing facilities | Y / N | ||
| Provide/ensure clean PPE used by anyone entering calf rearing facilities | Y / N | Includes boots, leggings, overalls, disposable gloves. | |
| Infection spreading between calves because of facilities design and management | Clean and disinfect calf rearing facilities and equipment after all calves moved outdoors | Y / N | |
| Dispose of calf bedding in a way that doesn’t recycle pathogens back to livestock | Y / N | ||
| Install solid partitions between pens | Y / N | ||
| Compromised animal immunity (particularly neonatal calves and transition cows) | Optimise body condition score of transition cows | Y / N | Ensure heifers and cows are in correct body condition at calving. |
| Prevent heifer-adult cow dominance antagonism in critical periods | Y / N | Consider mixing rising 2-year-olds with mixed-age cows a few weeks prior to transition. | |
| Provide sufficient space for all cattle to access feed freely | Y / N | Allow 0.7 – 1m per cow. | |
| Optimally manage transition cow diseases | Y / N | Apply effective monitoring and treatment programs. | |
| Carefully manage mineral supplements (Mg, Ca, Na, Trace elements) | Y / N | Develop supplementation programs with veterinarians or nutritionists. |
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Human health risk
The disease control focus should not be only on cattle- farmers with salmonellosis in their livestock should:
- Be made aware of the significant risk of developing salmonellosis themselves or by members of their families and farm workers, especially children, the elderly, immuno-compromised or those taking antibiotics and especially from exposure in calf-rearing facilities
- Not drink raw milk from their herd.
- Not bring their outer clothing or footwear into the house.
- Wash hands thoroughly in warm soapy water and scrub for 20 seconds.
- Carefully follow hygienic food handling measures when eating or preparing meals.
Cleaning and disinfection
Organic matter e.g. manure, dirt, milk and milk fat must first be removed by brushing and/or warm water/detergent mix before a disinfectant is used on the surface. Organic matter deactivates disinfectants.
Disinfectants recommended or with label claims for control of Salmonella include:
- Chlorine dioxide (250 ppm- dx50, vetpak) (Holschbach,2018)
- Quarternary ammonium products
- Chlorhexidine products
For more information see
- Gay, J. M. (1999). Salmonella (Modules and Documents). Cornell University College of Veterinary Medicine Animal Health Diagnostic Center. link
- Holschbach, C. L., & Peek, S. F. (2018). Salmonella in dairy cattle. Veterinary Clinics of North America – Food Animal Practice, 34(1), 133–154. link
- Lombard, J. E., & Garry, F. B. (2025). Biosecurity practices for mycobacterium avium subspecies paratuberculosis infection, salmonellosis, and bovine leukemia virus on cattle operations. Veterinary Clinics of North America – Food Animal Practice, 41(1), 93–101. link
- Mohler, V. L., & House, J. (2009). Salmonellosis in ruminants. In Current Veterinary Therapy: Food Animal Practice (pp. 106–111). link
- Mohler, V. L., Izzo, M. M., & House, J. K. (2009). Salmonella in calves. Veterinary Clinics of North America – Food Animal Practice, 25(1), 37–54. link
- Parker, A. M., House, J. K., Hazelton, M. S., Bosward, K. L., Mohler, V. L., Maunsell, F. P., & Sheehy, P. A. (2016). Milk acidification to control the growth of Mycoplasma bovis and Salmonella Dublin in contaminated milk. Journal of Dairy Science, 99(12), 9875–9884. link