Editor’s note: This is Part 3 of a series of four articles titled “Dairy biological risk management.”

Human traffic on the dairy farm
Foot traffic also poses a risk of pathogen introduction and spread on a dairy facility. People walking through a farm include employees, neighboring property owners, sales and service personnel, veterinarians, hunters, hikers and other visitors. In order to keep track of who comes and goes, anyone who does not live on the facility should be required to sign a visitors’ log book and instructed on what areas are acceptable or unacceptable for foot traffic.

Restricted areas need to have clearly posted signs to remind visitors not to enter. It is important to ask visitors about prior contact with animals on other operations, and ask those at high risk of transmitting disease to take additional precautions (shower and change clothes or return at another time). Regardless, restricted areas should be delineated and animal contact should be minimized.

Producers should also consider requiring all visitors to wear clean coveralls and overboots. Providing clean coveralls for visitors will cover any “outside” organic debris on the visitor’s clothing and provide a barrier to disease introduction. The coveralls will also allow all organic material obtained on the farm during the visit to remain on that farm and prevent carrying it to another facility or into the home of the visitor. Disposable plastic overboots can be provided rather inexpensively (less than $1 per pair) and provide the additional benefit of protecting visitors’ shoes from manure and soil or mud.

Another option is to provide a footbath at the main entrance with a requirement that all visitors disinfect their footwear. However, there are limitations to the effectiveness of human footbaths. All gross debris must be cleaned off first and the disinfectant solution must be used under appropriate conditions (proper concentration, proper temperature, free of organic debris, frequent maintenance, etc.). A footbath that does not meet these conditions may in fact create a false sense of security, while providing little or no protection.

Zoonotic disease and health concerns of employees
According to the 2002 Census of Agriculture, the average age of a farmer is 55.3. As people age, their reflexes and immune systems decline. They aren’t as able to react to a fractious animal or recover from injury or illness. Considerations need to be made for those older, as well as the very young, at-risk individuals.

Illness may be more difficult to fight in this population, making prevention even more important. Producers often work with adult cattle and young calves, and there are many zoonotic diseases this population should be aware of. Listeriosis, brucellosis, salmonellosis, Q fever, tularemia, botulism, staphylococcus and streptococcus infections, E. coli, salmonellosis, cryptosporidiosis, leptospirosis, ringworm and the most serious – rabies – are all diseases adult cattle could pass to the dairy workers or their families.

There are ways to prevent such infections, such as wearing personal protective equipment (gloves, masks, rectal sleeves, waterproof gear, coveralls, boots and others) in situations that may predispose them to exposure. Calvings, abortions, rectal or vaginal palpation, artificial insemination, milking infected animals, passing esophageal tubes or balling guns, doing an oral exam, necropsies and handling vaccines or antimicrobials are situations that may cause abrasion of the dairy producer’s skin or expose their mucous membranes and they should protect themselves.

Other at-risk clients and their employees may include: children under the age of five, pregnant women and immune-compromised individuals. While the most profound immune suppression is caused by HIV/AIDS, other diseases and conditions that can compromise the immune system include tuberculosis, bone marrow or organ transplants, radiation, chemotherapy or chronic corticosteroid therapy, chronic renal failure or implanted medical devices (pacemakers, defibrillators, artificial heart valves, artificial knee or hip joints). Persons with diabetes, alcoholism with liver cirrhosis, malnutrition or autoimmune diseases, splenectomy patients and those on long-term hemodialysis also have compromised immune systems.

It is important to note some of these conditions or diseases may have a social stigma, making it difficult for a client or their employees to share their personal health information. This again makes it vital for veterinarians to educate their clients and their employees about zoonotic diseases.

Children are the future of farming and are a part of many dairy operations in the United States. It is important to understand what our young farmers may be at risk for. Children under the age of five have naïve immune systems, just like neonatal calves. There are many pathogens on a farm, some of which are zoonotic, so educating children and their parents about their risks and how to protect them is essential.

One of the tasks on a dairy farm that often falls to the responsibility of young children is calf chores. Feeding, watering and bedding the calves is something kids are able to do without much supervision and gives them a sense of pride in helping out. It is important to remember what the E. coli example in the beginning of this series illustrated – children can succumb to disease if exposed.

Children who feed neonatal calves should be taught proper hygiene including things like washing hands before and after feeding the calves, wearing gloves if possible while feeding and never eating or playing around calf hutches. They should have designated calf chore clothing, and it should be taken off immediately after caring for the calves and put in a proper area so younger siblings do not contact it. Over time, children’s immunity will build up to many pathogens, but some will always remain a zoonotic disease threat.

Regardless of age, certain biological agents used for animals can pose a risk to those handling them. Oxytocin and prostaglandins have detrimental effects on pregnancy and should never be handled by pregnant women. Other products may have toxic potential if accidentally injected or absorbed via mucous membranes (e.g., the sedative detomidine, brucellosis vaccine). These items should be properly identified and precautions should be taken when handling these agents, such as:

• Storing products in a cabinet or refrigerator designed for that purpose. Food for human consumption should never be stored with biologicals.
• Injection needle caps should never be removed by grasping with the mouth.
• Hands should be washed after handling any biologicals.

Proper and frequent hand washing is the best way to prevent many zoonotic diseases. The following hand washing technique is recommended:

• Wet hands.
• Apply soap and rub hands together for at least 15 seconds.
• Rinse with water.
• Dry hands with a single-use, disposable towel (using a multi-use towel can spread disease between individuals).

Hands should be washed immediately after handling sick animals, after coming in contact with feces or urine from animals, after using the rest room and prior to eating to minimize the risk of zoonotic disease. Practicing and teaching these techniques can help protect the veterinarian, staff and clients from unnecessary exposure.

Another consideration on today’s dairy farm is the immigrant worker. The communication barrier may increase their risk of exposure, so working with knowledgeable translators and ensuring proper medical care will keep this at-risk population safe and continue their employment on the farm.

While the possibility of exposure and transmission of zoonotic diseases from animals to people cannot be totally eliminated, it can be minimized. By providing immune- compromised clients with correct and up-to-date zoonotic information, we can encourage them to keep their animals healthy and minimize exposure. This can be accomplished through:

• making producers aware of available information for them or their family members, who are immune-compromised, through conversations on farms, clinic newsletters and extension outreaches to local community organizations

• making dairy producers aware that immune status can be affected by many conditions

• speaking with immune-compromised clients regarding animal handling guidelines and recommendations

• providing a handout or brochure on zoonoses information with web links for further information

Routes of transmission
Pathogenic agents can be spread from animal to animal or animal to human, through a variety of transmission routes. Animals or humans can acquire disease-causing agents through inhalation or aerosolization, oral consumption or direct contact via fomites or vectors. Dairy cattle are often exposed to a variety of pathogens due to the environment in which they are housed and milked. Many disease agents can survive for extended periods of time in soil or other organic material.

While not a route of transmission, environmental contamination must always be taken into consideration. We will discuss each of these routes and recommend control strategies to manage disease risk in the coming sections.

Aerosol
The ability of pathogens to survive and be transmitted in the air varies by organism, as well as other factors such as season, temperature, humidity and wind speed. However, the greater the distance of separation between a carrier and a susceptible animal, the less likely transmission will occur. Direct contact between an infectious and susceptible animal will result in exposure, while pathogen concentration in the air decreases exponentially with distance. Therefore, increasing distance between wildlife, animals from other operations, and newly introduced animals should minimize exposure by the aerosol route.

Appropriate ventilation is extremely important in reducing airborne pathogen transmission. This becomes most important in the calf housing areas. Whether calves are housed in individual hutches, a greenhouse barn or a confinement facility, adequate ventilation, moisture control and temperature regulation are essential for healthy animals.

Adult dairy cattle housed indoors also require appropriate ventilation to minimize airborne disease exposure year round and to minimize heat stress during certain times of the year. Times of congregation, such as moving cattle to the holding pen prior to milking, within the parlor and around feedbunks and waterers if cattle are housed outdoors, can influence the airborne pathogen load. Cattle should be moved slowly so as not to increase respiratory rate, which could induce coughing and expiration of pathogens from infected animals. Excitement and stress should be held to a minimum so as to minimize airborne disease transmission.

Oral
Oral transmission can occur through consumption of contaminated feed, water or the environment cattle may contact with their mouth. Items such as equipment, feedbunks, water troughs, fencing and other objects that they can lick; contaminated mineral, sodium bicarbonate and salt feeders; oral drenching equipment, esophageal tubes and numerous other objects found on a dairy operation can transmit pathogens orally.

Milk or colostrum
The first feedstuff consumed by a calf should be colostrum. Milk and colostrum are very effective means of transmitting disease organisms from dam to calf and from the environment to calf (via soiled or fecal-contaminated teats and udder). One might consider testing cows for diseases of concern (Johne’s, salmonellosis, bovine leukosis virus and others) and using colostrum from test-negative animals.

Single-source, dam-to-calf colostrum is generally considered the preferred feed source for neonatal calves. An alternative source is sometimes required. In this case, colostrum should be provided from an older, healthy cow from the same herd. Colostrum from such animals should be collected as aseptically as possible and can be frozen for up to one year without significant deterioration in quality.

To store colostrum, use one-gallon zipper-locked baggies. Fill it ¾ full with colostrum and lay it flat to freeze. Each bag should be labeled with the cow’s identification number, collection date and any other pertinent information. That way, should an animal test positive for an infectious disease, her colostrum can be removed from the supply.

Do not stack colostrum bags in the freezer until they are frozen. Condensation accumulates and the bags will freeze together if stacked too early in the freezing process. The one- gallon bags allow for ease of thawing due to their large surface area that can contact warm water in a bucket. The bag also stores enough colostrum for the first feeding to a newborn calf.

Pasteurization of colostrum is becoming more common so as to decrease the risk of pathogen spread to newborn calves. The benefit of minimizing the risk of disease spread versus the destruction of proteins, specifically immune globulins, needs to be weighed for each herd.

Post-colostrum feeding, calves should be fed pasteurized whole milk or high-quality milk replacer to prevent transmission of diseases. If milk is pasteurized, time and temperature of the batch should be monitored on a frequent basis to ensure proper destruction of organisms from lactating cows. Milk replacer should be stored in an air-tight container so as to keep out environmental contaminants and to minimize risk of oral spread of disease upon next feeding.

Feedstuffs
Control of feed sources and quality is just as important for the remainder of the herd. All feeds on a dairy should be evaluated for their risk of introducing or transmitting disease. This includes harvested feeds (silage, hay and grain), purchased protein sources, mineral mixes and other supplements. Feeds purchased from other sources should be accompanied by an acceptable quality assurance program and documentation. This should verify reasonable measures have been taken to protect the feed from contamination with potential disease-causing material. If a contamination is suspected, a representative sample of the feed should be collected and frozen for diagnostics.

The best feed can become a threat if not handled and stored correctly. This typically means preventing access and contamination from any animals, including wildlife, birds, vermin and scavengers, as well as dogs, cats, cattle and other livestock which may urinate, defecate or otherwise introduce disease. For certain feedstuffs like silage and grain, it may also mean proper protection from weather (to prevent spoilage and mycotoxin development), as well as special efforts in ensiling or processing to ensure appropriate conditions (anaerobic, low pH, etc.) are achieved to protect the feed from listeriosis, clostridium and mycotoxin proliferation. During harvest, it is essential wildlife carcasses are not ensiled because they carry the risk of contaminating the feed with botulinum toxin.

Spilled feeds should be frequently cleaned up and disposed of, particularly adjacent to storage or feeding areas. Spilled feed attracts rodents, wildlife, fosters spoilage and serves as breeding ground for other pests.

Feedbunk and manger management is essential to ensure good quality feed for optimal dry matter intake. Adequate nutrition is required for an animal to remain healthy. In order to meet the high intake demands of lactating animals, feed should be made available throughout the day. Piling new feed on top of old presents an ideal environment for proliferation of spoilage and disease organisms during hot weather. Scraping feedbunks and mangers to remove all old feed should be done on a regular basis to ensure the spoiled feed does not get consumed or contaminates fresh feed piled on top.

From a disease standpoint, if feed is allowed to spoil, it serves as a great nutrient source for microorganisms to proliferate. Accumulation of old feed also serves as a breeding ground for flies and other pests, which can spread disease.

Often feed is offered to cattle on the ground at the same level where people walk and drive. At no time should anyone walk or drive through feed. Feces, urine and saliva can subsequently contaminate the feed and cause oral consumption of disease-causing organisms. Man-passes (people-passes) could be used so personnel are able to enter the cows’ pen without climbing through the feed bunk or over fences.

For animals on pasture, efforts to protect them from oral consumption of disease organisms include avoiding fertilization with high-risk materials (non-composted manure, frequently dragging the fields to break up fecal pats in drier climates (organisms die more rapidly when exposed to heat, sunlight and wind) and avoiding overgrazing, which forces animals to graze closer to the ground and nearer to fecal pats. Cattle should be kept away from pastures fertilized with high-risk materials for as long as possible.

Water
Water consumption is necessary for life and milk production. Animals fed in confinement or tiestall or stanchion barns should have water available throughout the day. Waterers can serve as a risk factor for disease if not maintained and cleaned properly.

Waterers should be monitored daily for functionality and cleaned when organic debris begins to accumulate. In trough-type automatic waterers, a rail should be installed two feet above the top rim of the waterer. This will minimize cows from standing or defecating in the trough, while allowing their heads to enter freely and consume water. Young calves should be offered fresh water throughout the day and a rail can be installed at 18 inches (or lower for younger calves) above their automatic water trough to prevent entry and defecation. Individual water buckets should be cleaned to avoid accumulation of organic debris.

Natural sources (creek, pond or cistern) are often used in pasture situations because of convenience and reduced expense. Natural water sources are at risk from contamination by wildlife, other livestock operations (leptospirosis, among other diseases) and other natural threats (blue-green algae, for example). The source should be protected as much as possible and monitored for problems.

Regardless of the water source, dairy producers should consider testing water quality every six months, and more often if there is a problem. Monitoring coliform counts, nitrates and nitrites, sediment, hardness and other minerals can be helpful to prevent disease and maximize milk production.

Manure and waste management
Because many of the diseases contracted through the oral route originate from fecal contamination, waste management is vitally important in controlling these pathogens. Manure should be transported to a designated storage or disposal area, out of contact with animals and with designated equipment. This equipment should not be used for other purposes, such as feed delivery, bedding, crop handling, etc.

If manure is to be stored, it should be kept in a well-constructed lagoon, with adequate capacity to handle large precipitation without overflow. The location should be such that, should an overflow occur, it would not expose animals to discharge. If this is not possible, the most susceptible animals should be protected from exposure.

Composting is considered by some to be a beneficial and viable method of handling manure. The advantages include a great reduction in volume and water content and a significant reduction in pathogen levels. Disadvantages include the time required for completion of the process, the equipment and labor demands, and loss of nutrients. If waste is not composted, producers should be cautious in what locations and at what times manure is applied.

Cropland can generally be considered a minimal risk of sustaining pathogens if the waste is applied early in the growing season. However, for some persistent pathogens, a single growing season is not sufficient to eliminate infectivity. Pastures are more of a risk, because there is no further processing to kill the organisms (like fermenting silage, drying hay, etc.). The safest recommendation would be to not spread manure on pastures in which susceptible animals would be placed. Similar or even greater cautions should be exercised in accepting manure or organic waste onto the farm from another source.

The survival of pathogens within manure depends on a variety of factors including sunlight, drying, freezing/thawing cycles, high temperature, high/low pH, exposure to oxygen, ammonia concentration numbers, types of pathogen present and the absorption of the pathogen to soil. Generally speaking, the risk of spreading disease will be lowered by exposing the waste material to environmental conditions. The most important means of accomplishing this is to adequately disperse the material. Dragging dry lots and pastures to break up and disperse fecal pats is an effective practice in drier climates. But similar to spreading manure for fertilizer, adequate time should be permitted between distributing the manure and returning animals to the lot or pasture. This ensures the organisms are exposed to the damaging environmental conditions listed above.

Fecal contamination from other species
Feces from other species can also serve to transmit disease to cattle. While it is virtually impossible to exclude wildlife from a pasture, every effort should be made to prevent access of animals to stored feed and feeding areas. Birds and vermin are quite effective at transmitting disease and are common in feed storage areas, confinement facilities and barns. Producers should recognize that even domestic animals pose risks because dogs, cats, goats, sheep and horses can all introduce disease to cattle.

Direct contact
Direct contact requires the presence of an agent or organism in the environment or within an infected animal. A susceptible animal becomes exposed when the agent directly touches open wounds, mucous membranes or the skin through saliva, nose-to-nose contact, rubbing or biting. Neonatal calves should be managed in such a way to limit methods of direct contact either with their dams or cohorts to minimize disease risk.

One of the most important efforts to reduce transmission via direct contact in adult cows is the isolation of sick or newly introduced animals. Ideally, a dedicated area or pen for isolation and separate milking facilities will help decrease the risk of diseases through direct contact. At the minimum, a dedicated pen within the operation is mandatory. Animals should be housed in this pen until they clear testing procedures or have had sufficient time to allow a disease pathogen to manifest itself. Additionally, incoming animals should be fed last, treated last, and milked last and all equipment should be cleaned and disinfected afterwards.

Unfortunately, not all infected animals show signs of disease. In order to minimize transmission from carrier animals, fence-line contact should be limited, both to animals from other operations (neighboring farms) and also to animals from different production groups on the same operation. Additionally, stocking density should be kept at the lowest acceptable level to minimize animal stress.

Reproductive
For the purposes of this document, reproductive transmission will encompass those diseases spread through venereal and in-utero routes. Venereal transmission, a type of direct contact, is the spread of pathogenic agents from animal-to-animal through sexual intercourse. In-utero transmission, another type of direct contact, is the spread of pathogenic agents from dam to offspring during gestation. Vaccination programs can be put in place for some of these reproductive diseases, but should only serve as an addition to proper biological risk management measures.

Disease risks associated with coitus vary depending on the type of reproductive service. Vertical or in-utero transmission often involves a chronically infected dam; however, it may also relate to exposure of the dam during a critical stage of gestation.

Test and cull strategies should be considered for certain vertically transmitted diseases. While whole-herd testing may be cost-prohibitive, producers should be encouraged to test suspect animals, such as repeat or “hard” breeders, cows that show erratic estrous cycles and animals that abort. Testing the dam and offspring of cows diagnosed with a disease that can be transmitted vertically should also be considered. This demands maintenance of complete and current records to facilitate identifying dams and offspring of affected animals.

Additional control measures relate to protection of the dam at critical stages of pregnancy. This varies by pathogen and generally necessitates the classification of pregnant animals as a susceptible population on dairy operations.  PD

References omitted but are available upon request at This e-mail address is being protected from spambots. You need JavaScript enabled to view it

—Excerpts from Center for Food Security and Public Health website

For additional resources on this topic, go to www.cfsph.iastate.edu/brm and look at the information related to dairy and producers.

Danelle Bickett-Weddle and Alex Ramirez, Center for Food Security and Public Health, Iowa State University