Practical Biosecurity for Dairies: Where is the Evidence and Does It Really Matter?
John H. Kirk, DVM, MPVM
School of Veterinary Medicine
University of California Davis
An internet search taking 0.32 seconds on Google found 5,970 hits for Johne’s Disease. Another search had 9,790 hits for tuberculosis in cattle in 0.34 seconds. An even shorter search of 0.25 seconds found 27,900 hits for mastitis in dairy cows. Surprisingly, a search on dairy biosecurity turned up 26,000 hits in 0.40 seconds. It is interesting that the number of website references for the most important disease of dairy cows, mastitis, was almost equaled by the number of reference to dairy biosecurity. Obviously there is a lot of duplication and overlap in these biosecurity references as with most topics on the web. What might not be so obvious to many searchers of the internet is the lack scientific support for many of the strategies put forth in these hits. Many of the suggested practices are BMP’s or GMP’s that on the surface appear to be sound. The practices run the gamete from those intended to deal with the most highly contagious pathogens following the UK FMD outbreak to those dealing with the everyday dairy pathogens such as Staph aureus or mycoplasmal mastitis. The purpose of this paper is to determine where possible the extent to which the dairy biosecurity practices have scientific support or justification.
Biosecurity practices can be categorized in many different ways. One way is by the time on the dairy when the practices will be applied:
In-coming to the dairy
Replacements, returns from shows, bulls
Visitors to dairy, vehicles, vets, AI breeders
Movements between locations on the dairy
Boots and clothes
Dogs, cats, wildlife
Animals moving to market
Calves moving to calf ranches
Visitor and vehicles moving to other locations
In-coming to the dairy
A suggestion that is often made is to find out about the disease status of the herd of origin for purchased replacements or bulls prior to buying the livestock and bringing them home. This is really sound advice but many times it just isn’t possible due to problems in getting information or just because the animals are coming from many herds through an order buyer. In some cases verifiable information on specific disease may be requested or required prior to purchase. It may be wise to ask for certain diagnostic test prior to purchase. In many states, the Johne’s Disease status for herd is available. The risk of bringing in Johne’s is greatly reduced when buying from herd with documented low prevalence compared to herds in the general population that are not testing to determine their status.
Another often suggested practice would be to isolate or quarantine all livestock coming onto the dairy to include newly purchased animals (heifers, cows and bulls), livestock returning from shows and calves returning from calf ranches or heifer raising operations. Of primary concern would be infectious disease transferred by aerosols, manure or milk. The ideal quarantine facility should have a double fenced to prevent nose-to-nose contact and should not have shared waterers or feeders. Where greater separation is possible, it should be obtained, however, no hard data is available to suggest the minimal effective distance is really needed to prevent aerosol transfer. Some reports suggest a minimum of 100 yards of separation.
Older animals should be separated from young stock or calves. On large facilities to prevent spread through manure, workers could be restricted to the quarantine area. On smaller facilities, workers could work the quarantine areas last. At the very least, they could change coveralls and boots before working in the main herd. In most cases, an all in; all out strategy would be ideal with a holding time of at least 15 days. This holding time will allow for most infectious diseases to become clinical, recognizable and diagnosable prior to mixing the new animals with the existing herd. The owner’s risk aversion status may determine how much testing will be required and completed prior to mixing with the main herd. Any dying animals should receive a full diagnostic workup.
In the event of a disease outbreak, cleaning and disinfection may be necessary for the quarantine area. The pens may also have to be left vacant for a period of time.
It should be kept in mind that many infectious diseases exist in non-clinical forms or in an asymptomatic carrier status that will not be revealed in a quarantine period. Some diseases that fall into this category are Johne’s, BVD, Salmonellosis, BLV and contagious mastitis. However, the quarantine period will provide time for testing of diseases of concern. The new animals can be tested for diseases of concern and the results of testing made known before mixing with the herd. Milking cows could be milked last and cultured before totally mixing with the other milking cows. If undetected, these diseases may develop into full blown outbreaks at some later date.
Steps should be taken to control the perimeter access to the dairy facilities. Here is an area where under most circumstances (those where FMD or similar viruses are not involved) the suggestions may be on shaky ground. The question is how far should we go to reduce the everyday risk of introduction of disease in the absence of FMD? For instance, is it necessary to have the dairy completely fenced with lock gates with a call box at each entrance? Many perimeter ideas would results in a complete re-design of the dairy and structural changes that would be economically difficult to justify. However, deliveries and pick-ups should be made at the dairy perimeter whenever possible. This is to prevent vehicles from spreading agents around onto the dairy. The question here is how much do we actually know about the risk of infectious agent spread on vehicle tires? The primary concern here is for spread in manure from livestock trailers or liquids spilling from rendering trucks. Complete restriction of these vehicles to the dairy perimeter by using transfer stations will minimize risk. Preventing these vehicles from crossing cow walkways or from driving down feed alleys can also be predicted to reduce risk.
Insuring the contents of purchased feeds is necessary to comply with the FDA Ruminant Feed Ban in the US preventing the introduction of BSE. Where uncertainty exists, it may be wise to require a letter certifying that the feed supplier is complying with all the Feed Ban regulations.
Controlling access of visitors from close contact with livestock may also be important for risk reduction. The primary concern is spread of infectious agents in manure into livestock housing or feeding areas. Signs can direct visitors to the dairy office. Most dairy owners or herdsmen have cell phones and visitors can be asked to call from the dairy office if no one is present. Otherwise, the visitors should be cautioned not to proceed further on the dairy. Visitors should be restricted to non-animals areas until granted further entry by the dairy staff. Protocols should be established with routine visitors such as the herd veterinarian, AI technicians and foot trimmers to allow them access to certain areas of the dairy. These protocols should also describe the necessary protective coverall and boots to be worn on the dairy (provide by themselves or the dairy). Visitors with manure soiled clothes or boots should never be allowed into livestock housing areas on the dairy. Dairy workers should be instructed to question any unaccompanied strangers seen on the dairy or to notify their supervisor of their presence.
International visitors require further questioning. The previous country where they have traveled from should be determined. Various websites can be checked to see if the country is an FMD-country or if other infectious diseases might be a concern. When the previous country is a concern, only visitors that have been in the US for over 5 days should be allow to proceed onto the dairy. To minimize risk, foreign visitors could be given a guided tour by car or bus and not permitted to enter livestock housing areas.
Many times we stop thinking about biosecurity at the perimeter of the dairy; however, it is also important to consider movement of potential pathogens on the dairy. Strategies to control spread on the dairy are the preventive measures that fill the gaps in the “in-coming” plans.
Training dairy workers about dealing with unauthorized visitors, the transmission of potential pathogens, the risk of “international foods” and protective clothing are the keys to controlling on-dairy movement. Dairy workers should fully understand that by controlling the movement of manure, they can control the movement of most potential pathogens about the dairy. This is particularly important with respect to salmonella, Johne’s, and cryptosporidia as some examples. Workers should know the areas on the dairy that are high risk for contamination of their boots and coveralls by potential pathogens. The high risk areas on the dairy are the fresh cow pens, calf raising areas, hospital pens and any quarantine or new arrival pens.
The high risk areas should be considered restricted activity areas. A minimal number of workers should be work in these areas. On large dairies, a few workers can be assigned to these areas and only work there. For instance, calf raisers should stay in the calf housing areas. On small dairies, wearing and changing gloves, protective clothing and boots before leaving the high risks areas will reduce the chances of spread. We were able to show that bacteria could move at least up to 400 feet on manure soiled rubber boots. How likely are boots to become contaminated by walking in manure in the high risk areas? We found in a study of 27 dairies that over 40% of the time boots became contaminated with salmonella by walking as few as 25 paces in the high risk areas (fresh cow and hospital pens) on California dairies. Keep in mind that it is not necessary to move an infectious amount of bacteria to cause problem. Dairies provide excellent growth materials for most bacteria so all that is really necessary is to just move enough bacteria to sustain life. Growth to harmful levels can easily take place almost everywhere the bacteria are carried.
Boot washing and disinfection can be part of solution or may give a false impression of providing control. When properly done, washing and disinfection of boots can be an effective BMP on the dairy. Washing with a drop hose in the parlor alone, even when the water may contain a disinfectant, will not be effective. To be effective, the boots must be washed and scrubbed with a brush to remove all visible manure and debris. This may require 5-10 minutes and the boots will probably have to be taken off so that the grooved bottoms may be thoroughly cleaned. Once the manure is completely removed, the boots can be sanitized or disinfected. This also takes time. The dairy needs to provide both time and proper washing and disinfecting equipment for the workers if they truly intend for this to be an effective control measure.
On dairies where it is not possible to provide effective boot washing facilities, changing protective clothing and disposable footwear should be considered. Clothing can be changed when coming into or out of high risk areas. Just leaving the soiled coveralls and boots at the high risk area is a practical BMP. Although expensive, disposable boots could be worn for the occasional visitor or workers coming into a high risk area.
Hand-washing facilities should be available in the high risk areas. This is particularly true for the calf raising areas when pinkeye or calf scours is present. Hands can easily become soiled with infectious agents. In some of these cases, the danger is for the health of the workers as well as the health of other calves. Wearing gloves is also a GMP for areas where frequent washing is necessary.
Movement by dairy vehicles and equipment may also be a concern, however, the risk for these movements for other than perhaps FMD is mostly undocumented. Certainly the tires of trucks, feed wagons, pushup tractors and feed tractors can become contaminated as they drive through manure in cross-alleys and manure collecting areas. It would seem to be a GMP to avoid driving through manure and then into feed alleys or feed storage locations. Another commonly sited GMP is to avoid using the same front-end loader to carry feed, manure and dead animals. Perhaps on very large dairies it is possible to have a separate $90K loader but this is not practical on small dairies. Washing between uses is a possibility; however, it has the same drawbacks as washing boots.
Any equipment used to treat sick animals should be kept very clean. Particular attention should be paid to cleaning and sanitizing equipment used for oral medications such as esophageal feeders and drenching guns or tubes. Avoiding repeated uses of syringes and needles, mammary infusion cannulas, and multiple dose vials will prevent spread of pathogens from cow to cow or udder to udder. Many dairy still do not understand that some bacteria or fungi will grow and thrive in various antibiotics.
Animal, bird and insect control is found on most every biosecurity plan but it is often difficult to achieve. Most unwanted animals or insect have the basic needs of shelter and feed. Restricting their access to either a place to live and breed or to feed can be anticipated to reduce the numbers on the dairy. Most attention should be given to places where they live and breed as it is very difficult to keep them out of feeds. With respect to flies, this means attention to manure and spoiled feed buildups. Large dairy operations may opt for routine services that control flies and rodents. The only hope of controlling birds is to reduce the number of roosting and nesting places. On new facilities this should be a consideration in the construction plans, however, it is difficult to do on older facilities with open pipe construction and “I” or “L” beam construction.
Farm security should be considered in light of intentional tampering or unintentional accidents that might affect the milk or meat leaving the dairy. This requires a heightened awareness of who is coming onto the dairy and the changing attitudes of the dairy workers. Entry and access to hazardous materials and farm chemical storage buildings should be locked and only a limited number of workers should have keys to these buildings. The bulk tanks should be locked and water sources protected. Don’t make it too easy for a disgruntled employee or terrorist to gain access to these areas. Have an emergency plan and make sure all the workers know who to call.
Here we begin to think about restricting movement of food animals such as market dairy cows (formerly known as cull cows) and raw milk into the human food chain and the potential food-borne pathogens that they might take along with them. Here we are asking the dairyman to really think outside of the box or in this case the bulk tank. For many dairymen this is foreign territory as they use the slaughterhouse as a disposal facility rather than a food marketing option.
One key to protecting the human food supply is to make early decisions on treating, marketing or euthanizing sick or disable dairy cows. While it is pie-in-the-sky in many cases, I like to suggest that dairymen not send any cow to market that they would not want to serve to their own family for dinner. While finding the sick cow early is not that big a problem on smaller dairies, it is a significant problem on larger dairies that lack the individual cow contact. I believe it is a matter of priorities that has to be established by the dairy owner and passed down to the workers. If it is important to the owner; it will be important to the workers. In all cases, a quick decision on the disposition of the cow can determine the outcome of treatment or the quality of the cow arriving at the slaughterhouse or end a painful condition for a disable cow.
There is ample evidence to support that many cows become contaminated with potential food borne pathogens while being transported to market. For this reason, dairymen should be aware of the conditions of trucks and trailers that are used to transport their cows to market. However, until this becomes an issue that has direct economic impact on the individual dairyman, little attention will be focused on this issue. At that point, dairymen will insist on having clean trucks or trailers to take their cows to market.
In our area, most of the dairy workers are Hispanic. Because of their cultural background, they often prefer raw milk and gladly accept disabled cows as a source of meat. Both of these situations bring with them a significant public health risk to their families. Issues of sanitation are not always as important to these workers as well. Workers should never be permitted to leave the dairy wearing soiled clothing or boots.
Evidence? In some cases there is sound scientific evidence to support biosecurity strategies for dairies that can be applied in a practical manner. Dairies should take advantage of this information and implement these strategies. In other cases, the suggestions and conclusions that have been reached by many committees as well as individuals are sound strategies and make common sense without having been formally tested. As an example, just look at 4 or 5 internet references. The same strategies will probably be found in all of them. Some of these can also be implemented. However, with or without evidence to support these strategies, dairymen will only apply as many as necessary to quiet their risk aversion feelings. To many dairymen, setting up a biosecurity plan to dealing with a foreign animal disease like FMD is not on the radar screen. To others, dealing with Johne’s or mycoplasmal mastitis is a high priority. As veterinarians, it is our task to provide the assistance and guidance to provide the most sensible and secure plan that our dairymen are willing to undertake.