Salmonella infection in Irish dairy herds can have a significant impact on the productivity, profitability and welfare of infected cattle, but also have the additional risk of zoonotic potential to humans.
The two most common salmonella serotypes isolated in Irish cattle include Salmonella enterica serovar dublin and Salmonella enterica serovar typhimurium.
However, one strain, Salmonella dublin is species adapted to infect cattle and as such a carrier state exists. As a result of this carrier state, a high proportion of animals will fail to clear infection completely and will shed bacteria later in life during times of stress or management changes.
Diarrhoea is more often associated with Salmonella typhimurium infections. Salmonella induced abortion is most commonly associated with Salmonella dublin infection. Abortion most commonly occurs in the fifth-to-eighth month of pregnancy.
A study conducted in Ireland found that in unvaccinated herds positive for exposure to salmonella, total profits per farm were reduced by €7,731, €9,471, and €11,211 compared with the negative baseline (unvaccinated negative herds) based on milk prices of €0.24/L, €0.29/L, and €0.34/L, respectively.
In the same study, herds positive for exposure to salmonella were also recorded to have experienced a 316kg reduction in milk yield.
Table 1. Signs of salmonella infection
How does salmonella enter a herd?
- Cattle shed bacteria in periods of stress;
- Nose-to-nose contact with neighbouring herds;
- Farm visitors and vehicles;
- Waterways, birds, rodents, pigs and poultry;
- S. dublin can persist in slurry for up to one month and survive in the soil for up to one year.
Diagnosis
- Always consult your vet if clinical signs outlined in Table 1 are present on your farm;
- Tissue from an aborted foetus or faeces from an infected foetus/animal must be sent to the lab;
- Blood samples from suspect animals should be submitted for serology;
- Bulk milk tank analysis.
Control
- Vaccination;
- Maintaining a closed herd;
- Quarantine animals for four weeks if purchasing;
- Strict biosecurity should be particularly maintained around cases of abortion;
- Faecal material from clinical cases must not enter the slurry tank;
- A disinfection point should be in place for everyone who enters and leaves farm to use;
- Restricting access of livestock to external sources of infection.
Treatment
- Antimicrobials;
- Anti-inflammatories;
- Fluids to maintain hydration.
Vaccination
Currently in Ireland, Bovivac-S is the only vaccine available for the control of salmonellosis. Healthy calves from approximately three weeks-of-age can receive the primary vaccination course of two 2ml injections separated by an interval of 14-21 days.
Calves over six months-of-age and adult cattle should receive two 5ml injections 21 days apart. Generally, the risk of abortions due to Salmonella dublin infection in spring-calving dairy herds tend to start in September and peak in October and November.
It is recommended to ensure the primary course or booster is completed at least two-to-three weeks in advance of this risk period as detailed in Figure 1 (below).
Depending on the level of infection circulating in the herd, one annual vaccination should maintain a sufficient level of active immunisation.
Figure 1. Vaccination plan for calves over six months-of-age
Although Bovivac-S is not licensed for the control of abortion, research has shown that the proportion of Salmonella dublin-positive abortions from vaccinated herds was significantly lower than in herds which were not vaccinating.
Abortions due to Salmonella dublin in spring-calving dairy herds tend to start in September and peak in October and November.
It has been found that farmers often vaccinate too late and, as a result, miss the main period of risk. In general, it would be recommended to ensure the primary course or booster is completed two-to-three weeks prior to the onset of the main risk period, detailed in Figure 1.
In conclusion, the implications of a salmonella outbreak can be severe and result in significant financial, production and welfare costs.
Vaccination can form the cornerstone of control along with good calf management, strict hygiene protocols and high biosecurity standards.
More information
For more information, contact your local veterinarian practitioner and click here
