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close this bookAnimal Husbandry - Initial Environmental Assessment Series No. 2 (NORAD, 1994)
close this folderPart I: General account
close this folder3 Possible environmental impacts
View the document(introduction...)
View the document3.1 Overgrazing and soil erosion
View the document3.2 Pollution of air, soil and water
View the document3.3 Special impacts of livestock-based industries and transportation
View the document3.4 Loss of valuable genes
View the document3.5 Infection pressure and diseases, and impacts of medication
View the document3.6 Other ecological impacts, and consequences for landscapes
View the document3.7 Social impacts
View the document3.8 Impacts of other existing or planned activities

3.5 Infection pressure and diseases, and impacts of medication

When localizing a livestock project, the risk of serious diseases should be taken into consideration. Some livestock diseases can be transmitted to humans and wild animals and thus pose a threat to the environment. Generally speaking, the heavier the stocking rate in an area, the greater is the risk that infectious diseases may break out. An area in which a major animal husbandry project is established ought to have a satisfactory veterinary service.

Livestock production in tropical areas is vulnerable to a series of infectious diseases. Bacteria, virus, protozoa and worms which are rare or non-existent in temperate areas exist here. Examples are foot-and-mouth disease (virus), anthrax (bacteria), trypanosomiasis (sleeping sickness, caused by a protozoan) and various intestinal worms. Most of these diseases rarely have dramatic effects in extensive forms of production, but they can strike hard in intensive ones.

Many parasites flourish around water sources and feeding places, and full exploitation of few water points may increase the risk of diseases breaking out. Problems of illness can often occur in connection with a too intensive exploitation of areas in proportion to their capacity. Inadequate or incorrect nutrition or lack of minerals and vitamins can be decisive in regard to the extent of an outbreak of a disease. One should especially be cautious with regard to animals being kept in cages or bins (ea. poultry, pigs, rabbits).

Domestic animals introduced from outside often lack the power of resistance that local species have evolved throughout generations. In addition, pressure of infection may build up in the environment so that also local breeds become vulnerable to diseases. Conversely, local breeds and wild animals might pose a risk to imported breeds, partly by a direct pressure of infection and partly because preventive treatment/vaccination does not always reach the animals of all livestock keepers.

Experience shows that in the cool highlands in the tropics exotic livestock may be introduced or crossed with local breeds to the effect that the production capacity is greatly increased. Many diseases are less troublesome in the highlands and easier to control.

Many of the most common diseases can be controlled by means of a vaccination programme. Examples are vaccination against cattle plague, anthraz and some clostridial infections among various animal species. Vaccination is generally a cheap alternative as compared to drug treatment. Moreover, it is within the reach of many less prosperous livestock keepers. Curative drug treatment may be so expensive that only intensive forms of operation make use of such opportunities. When establishing a veterinary service, it is important to be aware of the limitations of such services when the majority of the livestock keepers are very poor. Preventive treatment by means of chemicals (spraying/cattle dip) also tends to be expensive and beyond the reach of extensive forms of animal husbandry.

Intensive animal husbandry often makes use of large amounts of drugs. In many places, it has been documented that drugs are used inappropriately or in incorrect doses. As a consequence, the desired effect is not achieved. Environmental impacts of medication can be considerable if it is not done safely. Especially two groups of drugs have been focused in this connection: parasiticides that are applied externally to the animal, and antibiotics that are given as injections or through the mouth, on their own or mixed with the feed.

Chemical insecticides being used to fight ticks, flies, horseflies, etc. are either very persistent (not easily broken down) in nature (chlorinated hydrocarbons such as DDT, Lindan) or, if not safely used, extremely poisonous for the users (phosphoric insecticides). Use of these insecticides is still widespread in many developing countries. Remnants of them may spread to the environment and accumulate in the food chain. In some places, high levels of such chemicals have been detected in an important nutrient such as mother's milk (cf. booklet 13 Use of chemical pesticides).

With regard to the antibiotics group (antibiotics and chemotherapeutics), great concern is attached to the development of resistant microbes that can infect humans and cause diseases that may be difficult to treat. For the same reason, treatment of many animal diseases has already become more difficult. If antibiotics are used as a growth-promoting drug, which often happens in connection with industrial modes of animal husbandry, special care must be taken. Much of the antibiotics that are given to animals finally end in the surroundings. This is most evident in connection with fish farming (see booklet 5 Aquaculture), but treatment of mammals will also cause a great deal of the drugs to end in the environment, either in their original form or as converted into other substances that can be equally harmful. It is still unclear how high the risk of establishing resistant environmental bacteria is, and what possible impacts this will have, but there is good reason to be aware of the problem.