Biosecurity in the Dairy Industry

Exploring Staphylococcus aureus

Introduction

It is often noted that improved biosecurity is one of the most cost-effective and feasible approaches to disease prevention and represents an alternative to reliance on routine antimicrobial use. Specifically, implementing higher levels of biosecurity can reduce the odds of diseases and improve productivity^2,3 on farms. 

With the emergence of new diseases and the increased threat of diseases entering the country (e.g. Salmonella Dublin, foot and mouth disease), implementation of biosecurity practices on dairy farms is critical. This FAAST review will highlight the key components of a successful dairy farm biosecurity program, using Staphylococcus aureus mastitis as an example as mastitis is a major contributor to the use of antimicrobials on dairy farms.

What is Staphylococcus aureus?

Staphylococcus aureus is a bacterial infection that is frequently found in Canadian dairy cows. In a one-time sample of Canadian dairy herds in 2015, 46% of herds were positive for this bacteria⁴.  

The presence of Staphylococcus aureus in a herd is recognized through an elevation in somatic cell count (SCC), or an increase in the number of clinical mastitis cases. Infected animals are likely to have chronically elevated SCC, as well as increased risk of culling, and reduced milk production^5,6,7.   

In addition to the health and welfare consequences of infection, Staphylococcus aureus also has a significant economic impact, with each infected cow costing the farmer an estimated $490⁸. Controlling this pathogen will lead to lowered antimicrobial use on dairy farms, since mastitis infections (the main use for antimicrobials in dairy cattle⁹) will be reduced. 

Biosecurity and Staphylococcus aureus

When thinking about controlling Staphylococcus aureus, it is important to consider transmission between individual animals and between farms. This pathogen is predominantly spread through the skin of infected animals, making infected cows the main source of bacterial transmission between cattle and between farms. Staphylococcus aureus infections are very difficult to eliminate once infection has taken hold, as the bacteria adheres to udder tissue within the mammary gland, causing a deep infection. 

Implementing external and internal biosecurity measures is critical in controlling the spread of Staphylococcus aureus.

External Biosecurity

Introduction of Animals

Staphylococcus aureus relies on the introduction of an infected cow into a herd to facilitate its spread. Maintaining a closed herd (no additions of cows to the herd from an external source), can prevent this pathogen from entering your herd.

If purchasing cows is required, the following strategies are highly recommended¹⁰:

1. Purchase from herds with a consistent bulk tank SCC < 200,000 cells/ml
2. Ensure that each cow entering has a SCC < 200,000 cells/ml over their lactation
3. Culture quarter milk of cows as soon as possible following arrival and consider animals as potentially infected (i.e. segregate and milk last) until results are available

People, Vehicles, and Equipment

Although humans, vehicles, and equipment are not carriers of Staphylococcus aureus, there are other dangerous diseases that can be transmitted through these routes. E.g. Salmonella Dublin, can be introduced by individuals entering a farm with boots or coveralls contaminated with manure, and the bacteria that causes digital dermatitis (or strawberry footrot) can be introduced through contaminated farm equipment. 

Ensuring that all farm visitors wear clean protective clothing and footwear, and all farm equipment is disinfected prior to use, can reduce the risk of disease introduction and prevent the spread of disease within your herd.

Internal Biosecurity

Management

Implementing simple management strategies on your farm can help to reduce the level and risk of infection from Staphylococcus aureus, and encourage elimination of this bacteria. This pathogen is thought to be spread from cow to cow at milking time (via…machinery? manual checks?); therefore, it is important to implement several practices at milking which include^11,12:

1. Wearing gloves when milking cows and cleaning or changing gloves if they become dirty
2. Application of a pre-milking disinfectant to the teat
3. Segregation of milking cows with chronically elevated SCC
   • Cows with elevated somatic cell counts can be identified and milked last to prevent the spread of Staphylococcus aureus to other uninfected cows 
   • Suspect cows can can be confirmed through bacterial culture

Beyond strategies implemented at milk time, other strategies include ensuring that milking equipment is routinely maintained and that the stalls where cows are housed are clean and dry. Flagging and culling cows that are positive for Staphylococcus aureus is also an important practice, as positive cows serve as a reservoir for infection within the herd. Cows that have a clinical case of mastitis or a chronically high SCC can be tested for Staphylococcus aureus through a bacterial culture of the animal’s milk. Infected cows should be identified with a band around their foot and milked last until they are culled to prevent transmission.    

Control of Staphylococcus aureus comes down to management! 

Cleaning and Disinfection

Staphylococcus aureus is predominantly transmitted from cow to cow at milking time, when the milking unit is placed on a healthy cow after having been used on an infected cow. A residual amount of bacteria is left in the teat cup after milking an infected cow, which can cause infection in healthy cows that are milked with the same unit afterwards. This is why it is important that the milking system go through a full wash after milking cows with Staphylococcus aureus.

When it isn’t possible to milk cows with Staphylococcus aureus last, reducing bacterial transmission can be achieved by cleaning and/or disinfecting the milking unit after an infected cow is milked. Flushing the milking cluster with cold water or a sanitizing solution is effective in removing Staphylococcus aureus from the milking unit and could reduce transmission¹³.

Personnel

The implementation of management changes to control Staphylococcus aureus is ultimately the responsibility of the farm personnel who work with the cows. Because of this, it is critical that all farm staff working with cows support and understand the rationale for why specific practices, particularly those related to milking, are implemented. Your veterinarian may be an excellent resource to help with training staff and explaining the “why” behind each management practice.

Take Home Messages

Staphylococcus aureus is a common and costly infection on dairy farms across Canada. The best way to prevent introduction of this bacteria to your farm is to avoid purchasing and introducing potentially infected animals to your herd. Staphylococcus aureus can be controlled using management strategies and test and cull/segregate options.