Animal agriculture has long relied on the addition of antibiotics to increase feed efficiency and to aid in the control of low grade intestinal infections, especially in young animals. This practice has come under increased scrutiny in recent years as the human population has had to contend with the development of so-called super bugs which are resistant to conventional antibiotic therapy.
For decades those involved in animal nutrition have defended the practice of antibiotics as feed additives but that has been discredited under the weight of a mounting amount of evidence to the contrary. Such use of antibiotics is now prohibited by federal statute and all use in veterinary medicine must be for the treatment of disease under the supervision of a practicing veterinarian.
It is the strong opinion of those in the regulatory field that the long-term use of antibiotics in feed led in large measure to the development of the various strains of bacteria highly resistant to many antibiotics widely used in human medicine.
In the ongoing search for alternative methods of treatment and control in diseases of all types, many tried and true measures have been modified and expanded. One of the earliest recorded preventatives to be introduced was the development of smallpox vaccine by Edward Jenner in 1798.
Jenner noted that those who milked the cattle in herds which had cowpox rarely contracted smallpox. He theorized that some factor in their everyday work was protecting them from that scourge. After a period of time he decided to subject healthy people to material scraped from the teats of cows affected with the disease. He scarified the skin of healthy subjects and wiped the scrapings from the teats onto the abraded skin. A new era in preventative medicine was born.
As the use of antibiotics continues to decline the search for alternative means of disease control continues. Newborn animals receive almost all of their early immunity from the ingestion of the antibodies contained in the colostrum of their mothers. The length of time this protection is effective varies among species but suffice it to say that it is short, something on the order of 24 to 36 hours. A rapidly occurring event occurs in the cells lining the gut wall of newborns that prevents the further passage of colostral antibodies.
The antibodies that are absorbed within that very short period of time after the first suckling persist in the newborn for varying periods of time depending on the species and the type of immunoglobulin being evaluated. In dogs and horses this may be for up to 22 days for the immunoglobulin designated IgG. It has been found that colostral immunity protects young animals against systemic infections during the first few months of life whereas the respiratory tract mucus is protective for only a few weeks.
Once weaned, young animals are prone to infection from a host of different bacteria and viruses that prefer to locate and do their dirty work in the lining of the intestinal tract. Most of the vaccines administered for protection against diseases outside of the gut are not very effective in providing protection in that region. Literally there are too many obstacles for an oral vaccine to overcome for it to be effective. There is the low pH in the stomach, the digestive enzymes and bile salts being secreted along the way all acting to inactivate a vaccine trying to stimulate immunity in that region. To date there has been little success in developing a vaccine that is effective in protecting against diseases in the GI tract. The administration of specific antigens on the other hand has shown some promise against some specific diseases.
Much has been written about the genetic modification of plants to render them resistant to application of commonly used herbicides resulting in some very heated exchanges regarding their use or misuse. Perhaps because of its limited use to date the question of vaccines derived from plants has not been scrutinized as carefully as that given to the food that our animals or we consume. Plant scientists working in this field suggest that nuclear transformed plants offer greater simplicity for the production of a vaccine product as seed lines can be developed and the growth of plant matter can be done using existing agricultural practices.
One can easily see the many advantages of a vaccination program that is based on the feeding of plant material that has been altered in such a way as to provide immunity against a particular disease by feeding the altered forage in the feed bunk or trough. Plant material that has been modified to provide or stimulate immunity offers many potential advantages. One would be storage. Plant material can be stored dried (think hay) for years without compromising its ability to provide protection when needed. This simple method of storage without elaborate refrigeration with its associated costs should do much to reduce the overall cost of production. Where seeds are employed they are able to work their way through the digestive tract without having their essential components compromised or destroyed by digestive juices.
The costs associated with vaccine production using plant material is much less when compared to that associated with conventional methods using mammalian tissues or microbial cultures. All that plants require are water, light, fertilizer and heat – most of which will be provided by Mother Nature during a normal growing season. One tobacco plant can produce over 150,000 seeds creating the potential for very large amounts of plant material from a rather small investment. In situations where time is critical and the need for vaccine of the highest priority, it is possible to achieve the production of vaccines in just a few weeks from cloning to actual production. This is not a theoretical situation; several companies have produced human influenza vaccine and monoclonal antibodies using this technology.
As the move to plant based vaccines and antibodies moves forward little work has been done to develop materials that can replace conventional antibiotics in destroying bacterial infections. Materials called lysins have the ability to destroy bacteria but getting these materials to the point where they are commercially available presents some real challenges. If a researcher attempts to use bacteria to produce such products the bacteria are destroyed in the production process and this is where plants once again come in. It has been found that by using the correct combination of technologies tobacco plants can be programmed to produce lysins that will destroy certain bacteria, viruses and fungi. Being plant material the administration of these lysins would be a matter of feeding the restructured plants to those animals who might be in need of treatment.
There are some rather remarkable developments taking place in laboratories around the country that most people know very little about. If the risk of side effects can be reduced, the costs controlled and overall benefit to the consumer increased, then it would seem that the research community has once again on the threshold of something very big indeed.