Practical biosecurity in today’s dairy industry

We read and hear a great deal about biosecurity, but what it actually means in terms of changes we need to make in practical management is not always clear. Biosecurity refers to practices intended to make herds more secure against biologic risks, meaning contagious diseases.

The most significant risk factor for introducing a new disease onto a dairy farm is purchasing new animals. Yet, in the past year I have visited several dairy farms in the northeastern US in the process of buying cows; and most were doing nothing to protect themselves – and this is in a region where only a few years ago farms saw severe losses when a different strain of Bovine Virus Diarrhea (BVD) was introduced! While headlines about Foot and Mouth Disease and Mad Cow Disease have generated increased concern about biosecurity, the real threats to most dairy farmers remain the same agents that have been around for decades. These threats include Johne’s Disease, BVD, contagious mastitis, respiratory syndromes, Salmonella, and others. Keep in mind that routine health charts have little to do with biosecurity in today’s dairy industry.

Why the big gap between what is being preached and what is being practiced? Do dairy farmers simply ignore good advice, or are the writers and the speakers out of touch with reality, suggesting practices that are not feasible in most situations? In my opinion, neither of these is correct. I believe two other factors provide the explanation: risk tolerance and confusion.


Risk tolerance

Dairy farmers are used to taking risks. Just as many of us at one time did not wear seat belts despite general knowledge that it reduced the chances of severe injury in case of an accident, many producers will take a chance on new purchases, hoping that new diseases will not appear. They are often correct. All of us know of cases where new cows were brought in with no problems at all.

The danger with this type of risk tolerance is twofold. First, there is always the possibility that your herd will be the exception. A severe outbreak of illness and deaths within a week or so of adding animals is possible. The financial effects of lost milk, lost animals and veterinary expenses in these cases can be devastating.

The second danger is that the effects of a new disease may not be obvious for months or even years. Many farms battling with Johne’s or BVD have no idea when it was introduced into the herd. Unfortunately, you are not automatically ‘home free’ if you go two or three weeks after expansion without visible problems.

The second factor explaining the dearth of biosecurity is confusion. Many producers simply do not know what procedures are useful and practical.

Poor communication between veterinarians and their clients is part of this problem. Many farmers make major purchases of animals without consulting their veterinarian. The veterinarian first learns of the expansion when called to treat sick animals. On the other hand, not all veterinarians are prepared to advise their clients on this issue.


BE INFORMED: HAVE A PLAN

The best approach when adding animals is to understand the risks involved and prepare a plan to minimize those risks (Table 1). First, know the characteristics of BVD, Johne’s Disease, contagious mastitis, contagious foot disease and respiratory infections. If you are buying a herd and have access to those animals in advance, find out what tests can be done. Know what can be done after the animals arrive on the farm. Make sure key vaccinations are current in your own herd before making additions. Risk factors differ depending on whether your herd was previously closed, if you intend to make it a closed herd, or if buying cows will be the standard practice.


Tabla 1. Biosecurity precautions when purchasing cattle

• Maximize resistance of new and present stock
  • Have your herd up to date on vaccinations
  • Ensure good ventilation and cow comfort
  • Provide excellent nutrition
  • Always test calves from purchased cows for BVD
    
    
• If you have access to the herd before buying
  
  • Do bulk tank cultures for mastitis
  • Do bulk tank test for BVD
  • Look at somatic cell counts
  • Look for signs of foot or skin infections
  • Test 30 cows for Johne’s Disease
  • Test purchased animals for BVD (viral isolation)
    
    
• If you cannot test before purchase
  • Segregate new animals
  • Milk new animals last
  • Do CMTs, culture individuals

If you have the luxury of buying animals from an existing herd, have three or four bulk tank milk samples screened for mastitis organisms as well as for BVD. Test 30 cows with a Johne’s Elisa test. Test the cows you actually plan to purchase for BVD viral isolation; and if they are pregnant at the time of purchase, subsequently test the calves they deliver. The fee for these tests will vary from state to state, but will be rather small compared to the price of a dozen or more cows. Be sure to engage a veterinarian to help interpret the results. If tests come back satisfactorily, then you can buy cows from that herd with a relatively low degree of risk.

If testing before animals arrive is not possible, then every effort must be made to keep them in a separate group for two or three weeks. Milk them last. Use a footbath. Do a California Mastitis Test on each animal and culture those that show infection. Run a Johne’s Elisa and BVD viral isolation as soon as possible after the cows come on the farm. These procedures will allow infected cows to be culled and minimize the risk of damage to the rest of the herd. Again, it is crucial that the owner or herd manager and veterinarian work together.

If you intend to raise calves born to purchased cows, it is critical that those calves be tested for BVD. Make sure a test to find persistent infections is used because it is possible for a negative cow to deliver a positive calf months after the purchase occurred. This is probably the most common way that BVD is introduced into a previously clean herd. Besides testing new animals, do all you can to have your present herd fully up-to-date with vaccinations. Have ventilation, stall comfort and nutrition as good as it can possibly be. These factors will enhance the resistance of your present herd, and thus minimize the chances of a major disease outbreak.

It only takes one….

While we are focusing on herd expansions where a number of new animals are brought onto the farm, it is important to remember that it only takes one infected animal to cause problems. I am aware of a case where Johne’s Disease was brought into a herd with a clean-up bull. In another instance, a client working to upgrade herd genetics bought a high-priced purebred that unfortunately was infected with Johne’s. Biosecurity also means attention to other animals besides the milking herd and replacements. One client bought a few steers to fatten and brought BVD in with them. Any bovine can carry the common bovine diseases. Animals taken to shows or to custom heifer raisers can also be a source of infection on return.

While new animals are by far the most common sources of new diseases, other disease vectors include people, trucks and wildlife. Limit visitors, and be sure they take appropriate steps for disease control, including clean boots and clothing. Review traffic patterns and disease control practices on the farm with your herd veterinarian.

Standard health charts usually address tuberculosis and/or brucellosis, but do not consider any of the diseases that commonly cause problems today. Schedule a meeting soon with your veterinarian to design a biosecurity policy for your farm. If your veterinarian is not available for this, seek out a knowledgeable extension agent. Educate yourself about BVD, Johne’s, contagious mastitis, contagious foot disease and respiratory infections. Risk cannot be eliminated, but it can certainly be minimized.


Basic principles of biosecurity: minimize exposure, maximize resistance

There are two basic principles to follow in any endeavor to reduce the chance of infectious disease: minimize exposure to infectious agents, and maximize the resistance of the animals. When buying animals, we must deal with both those already on the home farm and the new ones that will be arriving.

In all cases, we can reduce exposure by providing excellent ventilation and keeping the environment clean and dry. The importance of these two factors cannot be over-emphasized, but they are often ignored. We can also reduce the exposure of the home animals by doing the testing outlined above, and avoiding purchases when testing indicates a high probability of disease. The animal’s environment includes the vehicle that will transport purchased animals. Know your hauler, and be sure the truck or trailer will be thoroughly cleaned and disinfected before the animals you have purchased are moved.

Maximizing resistance, or immunity, involves sound nutrition and minimal stress on all animals. Cow comfort, adequate space and relief from heat are important. Appropriate vaccinations must be current for both the purchased animals and the home population. The specific vaccines needed are beyond the scope of this paper, and should be discussed with your veterinarian.

Keep in mind that all animals carry some low level of infectious agents in respiratory and digestive tracts. When purchased animals are shipped, then put into a new environment, fed a different ration, and mingled with new herdmates, they are most certainly under stress. Stress lowers immunity, and this may allow initially low numbers of germs to multiply and cause disease. The sick animal then sheds germs into the environment, which exposes other animals. A disease outbreak can soon be underway, even though all animals started out healthy. Minimizing stress is very important, as is isolation of new animals if at all possible.


Specific diseases

There are many contagious agents that can be introduced through purchase of animals or other means. Following is a brief discussion of the more common diseases including BVD, Johne’s Disease, contagious mastitis, Salmonella, respiratory complex, contagious foot disease, Neospora, skin infections and Leucosis.


BOVINE VIRUS DIARRHEA

BVD is a viral infection and a very complicated syndrome. It is very prevalent in the dairy cattle population. Its primary effect is impaired fertility due to early embryonic death and abortion. In some cases clinical disease and death may be seen. Vaccination programs can minimize damage but cannot totally control this disease.

BVD can be present in the fetus of a healthy, pregnant cow if the cow was exposed while in the first trimester of pregnancy. That fetus may be aborted or may also be born at term and appear normal. This calf is a lifetime carrier of BVD; and can in turn be the source of infection to any animal it contacts. These carriers are referred to as ‘PI’ animals, meaning ‘persistently infected’.

BVD can be brought onto a farm by contaminated clothing, boots, or equipment, but most often comes with new cattle. In many cases the cows or heifers themselves are not infected, but have been exposed to the virus and are carrying an infected fetus.

Heifers sent to custom calf rearing operations and bred on those farms may be exposed and thus return carrying the infection in the womb. It is very important to test all incoming animals for the presence of BVD virus and to further test the calves born to any cows pregnant at the time of purchase.


JOHNE’S DISEASE

Johne’s Disease is most often spread by exposure to manure from infected cows. Young calves are at highest risk of getting the disease, while cows three years and older are most likely to shed it. Exceptions exist to both of those statements, but they are generally true. Therefore, the best way to control Johne’s is to separate young calves from older animals and to avoid using common equipment on both sets of animals.

There are no tests that can pick up Johne’s in all infected animals. Calves or heifers in the early stages of the syndrome will test negative even if they are incubating the disease. Therefore testing individual animals, especially young ones, will not provide protection. Testing a group of 30 second lactation and older cows will provide a good idea of the prevalence in a herd, and in turn help make the decision whether or not to purchase from that herd. Testing a group after arrival on the farm will help in evaluating the risk those animals pose to the existing herd, and allow you to manage accordingly.


CONTAGIOUS MASTITIS

Contagious mastitis is primarily regarded as Mycoplasma, Staphylococcus aureus, and Streptoccoccus agalactia. Other mastitis pathogens can certainly be spread from new animals to the existing herd, but are less of a threat. The best protection against these agents is to purchase cattle from herds with low somatic cell counts, and where bulk tank cultures prior to purchase do not show these germs. Do three or more bulk tank cultures over a two or three week time span to be confident of the results. Most labs do not do Mycoplasma cultures unless you specifically request them.

Once new lactating animals have arrived on the farm, arrange to milk them last or with separate equipment until you are satisfied that they are not a threat. Usually two weeks is long enough. Do CMT tests to identify cows and quarters that are likely to be infected; and get cultures done on suspect quarters to identify the cause. Sound mastitis control practices including individual prep towels, rubber gloves, teat dipping and dry cow treatment are important. New dry cows or pregnant heifers can also be infected with contagious mastitis, and may become a problem after calving. Milking them last until you are satisfied with their status is a good idea.


SALMONELLA

Salmonella is an intestinal pathogen causing fever, severe diarrhea and often death. Fresh cows and baby calves are most often affected. It can be introduced onto a farm with new animals, feed materials or by wild geese. The way to protect against Salmonella is to purchase feed from suppliers with control measures in place and to isolate new animals for a period of two or three weeks. Having separate pens for fresh animals and sick cows will be very important if you have to deal with Salmonella.


RESPIRATORY DISEASES

Respiratory disease outbreaks can be due to a wide variety of infectious agents and include Infectious Bovine Rhinotracheitis, (IBR), Bovine Respiratory Syncitial Virus (BRSV) Hemophilus, Mycoplasma, Pasteurella and others. Animals stressed by shipment often develop respiratory infections, and then spread them to others. Maintaining good ventilation and a clean, dry environment is very important. A sound vaccination program is crucial.


NEOSPORA

Neospora is a disease that will not spread from cow to cow, but must go through a canine intermediate host. Dogs that eat a placenta or aborted fetus can become infected, and the feces from the dog then serve to infect cattle. The disease then becomes established in the cow, and will infect her fetus when she becomes pregnant. That may cause abortion, but it can also lead to a normal, but infected calf. These calves will also be carriers, and are more likely to abort when they become pregnant. If they do carry a fetus to term, it will likely be infected, and the cycle continues.


CONTAGIOUS FOOT DISEASE

Foot infections include the well-known foot rot, plus hairy heel warts. In herds with no previous exposure to heel warts, severe lameness and milk loss can result when this syndrome is introduced into the herd. Footbaths or foot-spraying can control outbreaks, but these procedures are difficult to execute in dry cow or heifer pens. Inspect animals you intend to buy carefully and try to separate them for a week or two after arrival.

Ringworm, warts, and mange are skin infections that can certainly come in with new animals, or be picked up from a truck or trailer used to haul them. While they are relatively minor compared to other diseases, they are still annoying and must be treated.

If you see evidence of skin problems in animals you are thinking of purchasing, try to determine what the infection is and have it treated before taking delivery.


LEUCOSIS

Leucosis is not a large concern on most commercial dairy herds, but it is a problem for farms that hope to export animals or embryos. New animals can certainly be carriers of the leucosis virus; and testing is available that can establish the status of animals you might be preparing to purchase.


Conclusion

Recent headlines about exotic infectious diseases have caused a great deal of discussion about biosecurity and have made tight controls and import restrictions necessary. In all countries, however, the more common threats are same diseases that have caused problems for many years. These diseases, BVD, Johne’s Disease and contagious mastitis among others, can cause devastating economic losses. Protection requires that practical biosecurity measures be routinely followed.

The main source of new disease agents is purchased cattle, but other avenues exist as well. If you are buying cattle from an existing herd, do the testing outlined above prior to purchase. If that is not possible, it is still wise to test animals after they have arrived at your farm. Separate new animals from present stock to the extent possible. At the very least, milk them last. Do BVD testing for virus isolation on calves born to cows that were pregnant at time of purchase.

Work with your veterinarian to develop a sound vaccination program and a meaningful biosecurity program. Read articles and attend meetings to stay up-to-date. Insist that farm visitors take precautions to avoid risk to your animals. Veterinarians, AI technicians, foot trimmers and feed company representatives should arrive at your farm with clean boots, clothing and equipment. Don’t forget the basics of cleanliness, ventilation and sound nutrition in maintaining a healthy herd.

While you can never provide absolute, foolproof protection from contagious disease, you can greatly reduce the risk by adhering to the suggestions outlined above. Certainly some expenses and inconveniences are involved, but they are minor compared to the devastation that can occur with a major disease outbreak.