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| Healthy Diet - Healthy Livestock |
The direct effects of animal diseases on livestock productivity are significant and include reduced feed intake, changes in digestion and metabolism, increased morbidity and mortality and decreased rates of reproduction, weight gain and milk production.
The combined effects of these impacts have knock-on effects that limit important herd management decisions, constrain the selection of animals and breeds, as well as having potentially serious negative impacts on the livelihoods of resource-poor farmers and smallholders.
The interactions between disease, nutrition and genetic selection emphasize the need to control the effects of both epidemic and endemic diseases before programmes introducing enhanced livestock nutrition and improved breeds can make an impact. However, productivity and economic gains will not necessarily be achieved by disease control alone and an integrated approach is required.
On the other hand it is now widely understood that improved feeding and nutrition - with careful attention to the animals' seasonal requirements - has an important role to play in the control of diseases. Simply put, an animal with an adequate diet is more likely to be healthy than one with a poor diet. Similarly, certain breeds of livestock (typically the native breeds) have better natural immunity to disease, including abilities to cope with parasites.
It is important to recognize that better feeding of livestock covers:
- the quality or types of foods supplied, or given access to,
- the quantity of food,
- as well as adjusting for seasonal requirements.
Nutrition plays a major role in how well
animals are able to overcome the detrimental
effects of internal parasites. In fact, the signs of
parasitism can often be used as a symptom of
some other problem, usually poor nutrition (see Wells 1999).
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Nutrition-Health Interactions |
Some diseases that an animal can develop are entirely due to poor diet (rather than infection by bacteria or viruses). This may be because the feed contains a toxin that harms the animal directly, or it may be because the diet is deficient in a particular nutrient (energy, vitamin or mineral) and the animal then develops a "deficiency disease".
The development of infectious diseases can also be affected by the animal's diet, as the proper functioning of the animal's immune system (the system that fights off infectious disease) needs an adequate supply of protein, vitamins and minerals. Nutrition therefore also plays a key role in the balance of health and disease, which will decide whether an animal (when exposed to a disease-causing bacterium or virus) stays healthy or succumbs to disease.
A range of "tools" or techniques that take advantage of specific nutrition-health interactions are presented in a list of Tools and Fact Sheets for Smallstock Development |
For more tools  |
These, for example, include methods for utilizing the anthelmintic or anti-worm properties of plant tannins to combat infections by gastrointestinal worms.
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| Disease Resistance |
An animal that is well fed is better able to resist disease. This is partly because, in the balance of health and disease, an otherwise healthy animal is more able to stay healthy when exposed to infection than one which is already weakened through malnutrition. However, good nutrition seems to have a more direct interaction with health.
When an animal is exposed to a bacterium, virus or other infectious agent, the animal's immune system mounts a response to fight off that infection. This includes raising antibodies to fight the infection, as well as using white blood cells and other "killer" cells to attack anything (such as a virus) that it recognizes as "foreign". To mount this kind of response clearly needs energy, materials for manufacturing the antibodies and cells, and other factors involved in communicating messages in the parts of the animal's body involved with fighting infections. Specific nutrients needed for this work are thought to include, in particular:
- protein,
- the minerals zinc, copper and iron
- as well as Vitamins A and E.
Just as there are requirements, for example, for protein for growth or lactation, there are also requirements for protein for disease resistance. The requirements for these nutrients may be different (sometimes lower, sometimes higher) than the requirements for growth or lactation.
To maintain the animal’s health, then, these nutrients are needed. However, copper in particular can be extremely toxic especially to sheep. While it is important that the animal is supplied with these nutrients it is also important that excessive amounts are not given. Adequate nutrition will help to maintain health, but excessive supply of nutrients will not improve it further, and may even have a negative effect.
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| Importance of Dietary Protein in Combating Internal Parasites |
Animals develop resistance to helminth parasites, although goats are less resistant to nematode infection than other ruminant species. However, when nutrition is limiting, the immune response suffers to a greater extent than other functions such as lactation or reproduction. This means that the immune response is sensitive to changes in nutrient supply, and so improving the nutrition of sheep and goats (and other ruminants) at critical times of the year should increase their resistance to nematode infection. It has been observed that when goats' diets were supplemented with protein, their worm burden was reduced. Supplementing sheep diets with legumes (a source of protein) also reduced faecal egg count, although it had no effect on lamb mortality or growth rate. It has also been observed that if the diet is only supplemented with non-protein nitrogen (in the form of urea), no beneficial effects were observed, and supplementation with true protein was also required.
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| Vitamin and Mineral Deficiencies |
Vitamins are an essential component of a well-balanced diet and their major function is the metabolism and utilization of nutrients. The important vitamins for survival and growth of grazing animals are either manufactured in the rumen by the rumen microbes, in the body from sunlight, or are stored in sufficient quantity in the liver or contained in adequate amounts in available feed.
There are a number of minerals that are essential for life, and an insufficient supply of them may cause disease or even death. However, it is rare for deficiencies to occur with most of the minerals. Problems with some minerals are normally only encountered when their concentrations are too high.
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For more
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Metabolic Disorders |
Metabolic disorders are a group of non-infectious diseases caused by an imbalance between the supply of particular nutrients in the animal’s diet and the requirement for those nutrients. They are particularly common in pigs, sheep and goats in early lactation when the requirements for all nutrients are at their peak. However, deficiencies (or toxicities) from vitamins and minerals may also be included in this group of diseases. Many of these diseases are explained in more detail in the section on Animal Health.
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Bloat |
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Pregnancy Toxaemia, Ketosis
or twin lamb or twin kid disease |
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Milk fever or lambing sickness |
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| References and Further Reading |
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| Wells, A. (1999). Integrated Parasite Management for Livestock: Livestock Systems Guide. Appropriate Technology Transfer for Rural Areas (ATTRA). University of Arkansas, USA. |
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