Biosecurity measures to control salmonellosis on NZ dairy farms
Background
Key features of Salmonella to understand to formulate an effective control programme are that Salmonella:
- Commonly enters farms in infected recovered or carrier animals imported onto the farm, or in wild animals
- Spreads between livestock by faecal-oral pathways
- May be shed in all body fluids, but especially manure, immediately before, during and for up to 70 days following recovery in adult cattle, and for 14 days in calves
- May persist in the environment in moist or wet (<85% DM) conditions, shaded areas and effluent for weeks or months
- Can infect any bird or mammal (including humans) or reptile species
The key factors that affect whether ingestion of Salmonella leads to clinical disease and its severity are the:
- Virulence of the serovar
- Dose/number of the bacteria that are ingested
- Strength of the host’s immunity, including any previous exposure to Salmonella or vaccination, and the presence of other dietary stressors including disruption of normal gut microbe balance or low dietary intake for 1 or more days
Of these factors, the first can’t be controlled on farm, but the remaining two can be targeted by management interventions.
Finally, 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.
Biosecurity protocols
Biosecurity protocols to control salmonellosis should be developed in a 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 found in the biosecurity measures Tables 1 and 2
- 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 also have benefits for control of other diseases
At the ‘farm gate’ protocols aim to prevent or reduce the risk of importing Salmonella onto or from exiting 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 e.g. herds that trade or co-graze stock or with known history of salmonellosis. |
| Quarantine new arrivals | Y / N | Isolate imported animals for 2 weeks and monitor for signs of disease (particularly appropriate for calves). | |
| Manage to enable closed herd policy | Y / N | Rear sufficient pregnant replacements so importing cows unnecessary. | |
| Y / N | Optimise cow health and reproductive performance to avoid preventable culling and mortality. | ||
| Y / N | Optimise heifer rearing practices so that those replacements reach weight targets and calve at optimum body condition as 2-year-olds. | ||
| Importing Salmonella onto farm with contaminated items or in contaminated feed or water | 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 access to areas with livestock or cattle feed | 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 | Additionally, delay access to previously flooded pasture or conserved feed or crops for as long as practical. | |
| Provide cleaning and disinfection area for visitors | Y / N | Provide piped water, brushes, buckets and disinfectants adjacent to bobby calf loading facility, calf rearing facilities and entry/exit point to dairy. | |
| 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, including bird-proof calf meal feeders. | |
| Y / N | Cover face of silage stacks between taking feed from them. | ||
| Y / N | Apply appropriate pest management plans. |
Behind the ‘farm gate’ protocols aim to minimise or eliminate the transmission of Salmonella between livestock on-farm if Salmonella has already entered (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. Continue isolation for as long as feasible according to age group. |
| In an outbreak handle all animals as if they are shedding Salmonella | Y / N | Symptomatic animals are likely only the “tip of the iceberg” (see “Human health risk” below). | |
| 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 | Apply system to both healthy and sick calves. Remove bedding, clean, rest and disinfect pens between batches of calves. | |
| Isolate high risk calves | Y / N | Calves born from cows suspected or diagnosed with salmonellosis should be isolated and considered at risk of developing the disease themselves. | |
| Infection spreading between stock via feed and water | Avoid contamination of feed with manure | Y / N | Avoid feeding cattle off the ground, or if not feasible, feed on fresh pasture breaks daily. |
| Y / N | Avoid staff walking across feed with manure-contaminated boots. | ||
| Y / N | Clean manure from vehicle tyres before they access feed storage areas. | ||
| Graze young stock separately from and ahead of 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 | If storing colostrum, use a preservative such as potassium sorbate (0.5% w/v) or consider using equipment to pasteurise colostrum/fresh milk or use powder milk replacer for calf feed. | |
| Prevent contamination of stored colostrum | Y / N | Prevent access by birds or rodents and only use stirring equipment that has been cleaned and disinfected. | |
| Clean and disinfect calf liquid feeding equipment | Y / N | Clean and disinfect colostrum- and milk-feeding equipment before first use and frequently (daily where feasible) during ongoing use. | |
| Don’t feed calves raw waste milk | Y / N | Milk from sick or antibiotic-treated cows is poor quality and possibly contaminated with disease-causing bacteria. | |
| 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 Effluent Management and Operation 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 and maintain strict hygienic measures. |
| 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 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 and that dry matter intake is optimal and consistent, especially over cow transition period. |
| 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 period. | |
| Provide sufficient space for all cattle to freely access feed from feed troughs | Y / N | Allow 0.7 – 1m per cow. | |
| Optimally manage transition cow diseases | Y / N | Apply effective programmes to monitor and treat diseases, particularly common peripartum disorders such as dystocia, mastitis, metritis/retained placenta, milk fever. | |
| Carefully manage mineral supplements (Mg, Ca, Na, Trace elements) | Y / N | Develop mineral supplementation programmes in conjunction with your veterinarian and/or nutritionist and follow recommended inclusion rates. | |
| Optimise use of supplementary feeds | Y / N | Develop herd feeding programmes in conjunction with your veterinarian and/or nutritionist. | |
| Optimise colostrum feeding of newborn calves | Y / N | Ensure every calf has 2 feeds of 2 litres of high quality (>22% Brix) colostrum within 12 hrs of birth. |
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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, immune-compromised, those taking antibiotics and those entering 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 them for 20 seconds
- Carefully follow hygienic food handling measures when eating or preparing food
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.
- Mohler, V. L., & House, J. (2009). Salmonellosis in ruminants. In Current Veterinary Therapy: Food Animal Practice (pp. 106–111).
- 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.
- 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