How do diseases enter a herd? There are two broad ways that disease agents can be transmitted, either Horizontally or Vertically. Vertical transmission means the spread of disease from mother to kid shortly before, during or shortly after birth (the perinatal period). It can occur via chromosomes, across the placenta or through colostrum. An important example for goat producers would be CAE which is spread via colostrum from mother to kid immediately after birth.

Horizontal transmission means the spread of disease between animals. Horizontal is more important then vertical transmission in most cases and is all that can occur in the absence of reproduction. For instance, in a pen of wethers there would be no possibility of vertical transmission.

Horizontal transmission is divided into Direct and Indirect transmission. Direct transmission between animals requires contact. This can be fence-line contact, introduction of an animal into the herd or an animal that went to a show and came back home. Animal movement is by far the most important method of bringing a disease from one herd to another. This is especially true of homologous animals (animals of the same species) but can occur with heterologous animals (animals of different species). In other words on the goat farm the most dangerous animal to bring into your herd is another goat. However, bringing in a cow can also expose your goats to very serious diseases as well.

Indirect transmission is either by fomites or by vectors. These are a little more complicated to control then direct transmission. Fomites are inanimate objects that carry disease. This would include the soles of your shoes when you walk through manure going from one pen of animals to another. Vectors of disease are animate objects that carry disease. This can include domestic animals, wild animals or insects. Vectors can be either mechanical or biological. Mechanical vectors just carry a disease agent whereas biological vectors play a role in the life cycle of the disease agent. Examples would be a cat carrying salmonella bacteria on its feet from one feed trough to another and a cat whose feces have Toxoplasma oocysts spreading disease by defecating in feed bins.

Bringing new animals into the herd

Let’s look at how these principles apply directly to your farm. The most common source of new infections is by bringing a new animal into the herd. It is necessary to bring new genetics into breeding herds on a regular basis. The safest way is to bring in only frozen semen or embryos. However, even these can serve as a source of disease. Once you have decided on an animal whose genetics are necessary for your herd what do you do next?

Step 1: Find out the disease history of the herd of origin, the results of previous testing in the herd and the status of the herd with any certification program. Disease history’s can be obtained from the owner of the herd and through the farm’s veterinarian. Have your veterinarian call their veterinarian. The questions you want to ask are:

1. “What diseases do you test for?”
2. “What diseases do you have?”
3. “What diseases do you not have?

If the herd is certified free of Brucellosis, Tuberculosis and Scrapie then those are 3 diseases you won’t have to worry about. If the herd doesn’t test for any diseases then they don’t know what diseases they have. If they have tested all goats for CAE and all were negative then they probably don’t have CAE. If they haven’t tested any for CAE then their status is unknown. All diseases are not created equal and some are much more important then others. The important thing here is to know what diseases they don’t have.

Step 2: Determine the pre-purchase disease status of the individual animal(s) that you are purchasing. You and your veterinarian would want to see all records on this animal that would show what immunizations it has had, which diseases it has been tested for and what problems it has been treated for. Next you are going to want to request a panel of tests to determine the disease status of the individual animal. The diseases you test for are diseases that there is some chance the goat may have. For instance, in the US it would be foolish to require a goat to be tested for Foot and Mouth Disease. However, it would be reasonable to want it tested for things like Johne’s disease. Some testing can be done only by examination. For instance to determine if a goat free of lice or foot rot someone has to look at it. Ideally this would be the veterinarian for your herd who does the examination. If it is not practical for your veterinarian to do the examination then the veterinarian who works for the source herd would be a suitable alternative. Veterinarians are legally and ethically bound to provide honest and accurate assessments of health status.

Step 3: Assuming the goat is negative historically and on the current tests then we will bring it to our herd but keep it in quarantine. How long in quarantine? Well the answer is longer is better then shorter. Ideal duration is probably 60 days and the shortest interval you would use would be 30 days. What is a quarantine facility? A quarantine facility is an animal holding facility that is physically completely separated from the rest of your herd. That means no fence line contact, no aerosol contact, no manure runoff contact and no potential for spread by fomites or vectors. Ideally, it is far enough away that you need to drive there. A manageable protocol on a large farm is to have an employee that only takes care of quarantine. On small farms make sure that the quarantine barn is visited at the end of the day. Change boots and clothing before entering quarantine facilities and don’t go back to the main herd after you have been in the quarantine unit. Feed, feed buckets, bedding and manure can not be exposed to the nucleus herd. The most important issue here is transferring disease back to the nucleus herd but neither do we want the quarantined animals to be infected by the nucleus herd.

Step 4: At the midpoint of the quarantine period (30 days) a careful physical examination should be performed on the animal to make sure that it is free of physically obvious disease. At the same time consider retesting the animal for whatever critical diseases you are trying to exclude from your herd. There exists a distinct possibility that the purchased animal will test positive to a disease which it was negative for at time of purchase. The following situations could cause this scenario:

1. The animal was incubating the disease at the time of purchase.
2. The initial test was a false negative.
3. The stress of movement caused a latent infection to reactivate.
4. The animal was exposed to the disease in transit or after reaching your farm.
5. Some form of dishonesty or “laboratory error” has occurred.

Step 5: At this time it may be beneficial to administer an appropriate antibacterial to the animal either by injection or in the feed to attempt to eliminate agents of disease which may exist in a sub-clinical fashion. For a goat this would most commonly be a tetracycline. (Note: some veterinarians and producers are opposed to the use of prophylactic antibacterials (metaphylaxis). If you use antibacterials make sure it is used according to the label and that the withdrawal times are followed).

It will also be necessary to make the goat as parasite free as is possible. Ideally, this is done by checking a fecal sample for parasites and then deworming successively until the goat is parasite free. If fecal exams can’t be done, then dosing with three unrelated drugs will go a long way towards removing parasites from the incoming goat. For example dose with Ivomec, Albendazole and Levamasol simultaneously. At this time you would vaccinate the incoming animal for any know endemic diseases of your herd. So if you had Chlamydia in your herd you would want all new entries to be fully immune to Chlamydia prior to entry into the herd.

Step 6: The incoming animal should be acclimatized to your herd. This includes environment, feed, water and diseases. If you are buying a goat from Canada and bringing it to a hot humid place like Louisiana you will need to slowly acclimatize the goat to the environment. This will allow the animal’s innate resistance to be minimally stressed and will help the goat in preventing disease. The same holds true for feed and water. Sudden changes in food and water are viewed with suspicion with goats which means they may eat or drink less then they should. Hungry goats can overeat on a new ration and cause gastro-intestinal upset which may set the stage for infectious diseases. For some diseases we don’t have vaccines. The incoming animals should be acclimatized to diseases existing in your herd by contact between it and members of the herd.

Step 7: At the end of the quarantine period it would be wise to allow exposure of the new animal to a small sentinel group of animals. Sentinel animals are animals from your herd that act like a “canary in a coal mine.” If they don’t get sick after mixing then it is safe to assume that the rest of your herd will be safe. If they do get sick then they can be kept in quarantine until cured or removed from the herd. At any rate, at least your whole herd didn’t come down with the disease and you have proven to yourself that the incoming animal is not a carrier of disease.

Other sources of direct contact

In addition to bringing a new animal into the herd, direct animal contact can occur by fence line contact, show or sale contacts, or your goat may share a trailer ride with some other goats. All of these allow direct contact and exposure. That would mean that the exposed goat would need to go through quarantine period again to be safe. If there is an adjoining neighbor with goats then there will be fence-line contact. The solution to this is to double fence the perimeter. The space between the two fences is used as a corridor. When greeting new arrivals goats snort and blow nasal secretions. These droplets will travel up to 3 feet so make sure that animals are separated by at least twice that far (6 feet).

Livestock shows

Shows provide a real challenge to biosecurity programs. The ideal solution is to never bring home an animal from a show. For terminal meat class shows that is the obvious solution, for breeding class shows it is not a practical solution. Shows create an environment where animals of different species, breeds, age, sex, geographical locations, management systems and disease status come together for a brief period of time and intermingle. The animals are stressed from travel, noise, and unfamiliar settings. Stress can lead to increases in pathogen shedding and to increases in susceptibility to disease. A show is like elementary kids going back to school in the fall. There is always an outbreak of respiratory disease, diarrhea or the flu.

Before the show

Make sure that the exhibition center provides adequate housing, that pens are cleaned and disinfected and that ventilation is adequate. Make sure that all animals entering the show will be examined by the show veterinarian and that all state and local animal health laws will be enforced. Work with your veterinarian to establish a herd health program for your show goats and for the goats staying home that will be exposed to the show goat on its return. Do not mask signs of illness in your goat. If it is sick then stay home. Make sure that you have a Scrapie Tag for your goat (wethers excluded) and that you have any required health tests performed and that you have a current Certificate of Veterinary Inspection. Minimize stress on your goat by providing it with a pen that is as close to those in the exhibition facility as is possible and use the same bedding, feed and water source as you will have at the show. Keep fans on the goat at home, the white noise they produce will be the same as you will recreate at the show. Transport your goat in your own trailer. Avoid traveling in a commercial trailer or commingling with other livestock.

At the show

Keep your goats comfortable. Use adequate bedding and fans to provide white noise and ventilation. Use the same water, feed and hay that the goat was fed at home. Avoid sharing grooming equipment, feed buckets, manure shovels. If you loan out equipment disinfect it before using it on your goats. Discourage visitors from touching or feeding goats by putting signs up. Practice good personal hygiene yourself (wash your hands before handling your goat or your goats food). Try to get a corner pen so that animal traffic and contact is minimal.

After the fair

Disinfect all equipment that went to the fair. Don’t forget your trailer. Place the goat into your quarantine system and watch carefully for signs of clinical disease. Pamper your goat. Its more exhausted and stressed than you are.

Diseases from other species

In addition to other goats you need to prevent access of other animals to your goats. In general the more closely related the animal is to a goat the more dangerous it is in terms of disease transmission. Sheep and goats share the same parasites. Cattle and goats share a number of diseases. Unrelated animals are not necessarily safe. For instance Toxoplasmosis is a disease that causes abortions in goats. It is transmitted by the domestic cat which is a biological vector for the agent. Cats get infected by eating mice, the parasite completes its lifecycle in the cat and only in the cat and then the cat defecates in a feed bin and goats get fed grain which is contaminated with cat feces. Cats can also serve as mechanical vectors. It is amazing how much manure and disease agents can attach itself to the foot of a cat and it is amazing at how they can travel from pen to pen and trough to trough.

Now you might say “wait a minute, my cats control rodents on my farm and rodents transmit disease.” It is true that mice and rats can spread some important diseases like Leptospirosis which is spread in the urine of rodents. Cats are generally inefficient at rodent control and if you are relying on cats only then you will have a rodent problem. Rodents can be controlled by cats in addition to traps and baits but there are obvious dangers to the cats with this system. For the most part Toxoplasmosis is spread only by young cats (kittens). As the cat matures it becomes resistant to infection. Kittens can be avoided by spaying and neutering cats and maintaining a population of only adult cats.

Diseases introduced by fomites

The major categories of fomites that may expose your goats to new diseases would be: People, Trucks, Trailers, Feed and Water. People include friends, neighbors, buyers, veterinarians, employees and delivery personnel. Recognize that some of these are more dangerous to your goats than others. A friend from the city who has no livestock is a minimal threat. A veterinarian that has just come from treating a sick goat and is wearing the same boots and coveralls may be a serious threat.

Facilities with extremely high biosecurity standards discourage casual visitors from entering the livestock holding areas. When visitors do come they would require them to disrobe, shower and dress them in protective clothing and boots from the unit. Is all that necessary for you on your farm? Probably not, but again, think of the principles involved and implement it to the extent that is practical for your operation. It is best to keep people (especially other livestock producers) from getting in the casual habit of walking through your facility. People who go out to see the animals should have a real reason and the reason “just because they are cute” is certainly a valid reason; but those people must realize that a sick animal isn’t cute. If at all possible set up your pens so that goats can be observed from outside the pen or by putting all of your sale goats into a separate pen and not moving them back to the nucleus herd.

For people the most dangerous fomite is usually their shoes. People who have on boots that cannot be sanitized and that have been around livestock during the last week are a threat. For those people keep some disposable plastic boot covers handy or keep some spare boots around. For people with boots that can be sanitized a boot scraper, boot wash and sanitizing dip is a practical way to minimize the contamination they may carry. For visitors that will be handling animals on the farm hand washing and protective clothing is appropriate. Have a sink and soap handy for before and after visits. Hand washing after visits is especially important for children and people with compromised immune systems. Remember that goats can carry zoonotic diseases (diseases which are passed from animals to humans). The resulting diseases can sometimes cause serious human health issues. Protective clothing can be in the form of coveralls, apron, jacket, etc. Just make sure it is something that will cover the outer clothing of your visitor. At first your visitors will think that you are crazy when you ask them to follow these procedures. In the long run what you will find is that people who want to buy animals from you will appreciate the obvious efforts you make to keep them healthy and disease free.

Trucks and trailers

Trucks and trailers that are used for hauling livestock accumulate manure and other body fluids. If these vehicles are not washed and sanitized between loads they can serve as a very efficient fomite. If you are buying or selling an animal that will be transported by truck or trailer, inquire about the provisions the driver makes to insure the sanitation of his vehicles. Also ask about the presence of other livestock passengers on the trip. If your goats get on a trailer with goats from 10 other farms they will share the pathogens from all 10 farms. If you are trying to sell high health status goats you have a problem and need to find a new transporter.

When a vehicle comes to pick up your animals have it park outside the livestock area and bring the animals to the vehicle. This avoids the possibility of feces falling from the trailer into your biosecure area and it also prevents the possibility of an animal escaping from the vehicle and contaminating a large area. If you have a loading area on your farm place it at the quarantine area or the pen from where you sell goats. Similar arrangements should be made for feed trucks and other farm service vehicles. If they don’t have to enter your biosecure areas have them off load outside into your vehicle and transport the material to where it needs to go.

Feed

Feed can be a source of infectious material being imported onto your farm. Bovine Spongiform Encephalopathy (BSE) was transmitted all over the world by putting rendered ruminants into feed for ruminants. It is now illegal in the US and the rest of the world to use rendered ruminants in ruminant feed. More common than mad cow disease, feed can serve as a source of Salmonella infections. The feed can get contaminated at the mill, at the store, or on your farm by feces from birds, snakes or rats. This results in feeding grain mixed with Salmonella to your livestock. The solution is to buy feed from reputable suppliers and try to minimize storage times. On farm, keep the feed in rodent proof containers and avoid having spilled grain on the premises as it serves to draw birds and rodents.

Water

In most cases municipal water is a very safe source of drinking water for livestock. However, there have been instances where even municipal water was a vehicle of disease. Well water can be a source of contamination from runoff and may serve as a source of disease. Probably of more concern is surface water in ditches and ponds. Water that flows onto the property from other livestock enterprises should always be fenced off.

Diseases introduced by vectors

Vectors are animals or insects that spread disease. They can be either biological vectors and be a required part of the life cycle of the agent or they can just carry disease agents inside or outside their bodies. Many viral diseases are insect vectored. This would include diseases such as Bluetongue and West Nile Virus. The insect is necessary in both of these cases and the time the virus spends in the host is what makes it infectious. In the case of West Nile Virus, a mosquito would feed on an infected bird and then a week later feed on your goat giving it the disease. In this case, control would be difficult because the infected bird may have flown from hundreds of miles away. Obviously, it would take a very stringent biosecurity program to prevent the entrance of mosquitoes into the biosecure area. One solution would be to use mosquito repellant and immunize the goat against the disease.

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