| Background |
In areas where local breeds of livestock have developed, or where they have been farmed for a considerable period of time, the animals and the system under which they are kept have evolved together. Under the process of natural selection, the animals that have survived and been most successful in terms of reproduction, are those that are best able to utilize the feed resources that are commonly available to them, that have the greatest resistance to the common, local diseases and parasites, and which respond best to the management practices that are employed by their owners.
These animals are ideally suited to the conditions in which they are kept. This does not mean that they are incapable of responding positively to improved conditions, only that they can survive and produce in their normal environment. An example of this is the Barbados Black-Belly sheep, which for years was famed for its ability to survive and reproduce without concentrate feeding, on poor quality, native pastures in the Caribbean. It was not until the last 25-30 years that it was realized that the breed could out-perform specialist European mutton sheep breeds in the region, if kept on improved, grass-legume pastures, or fed the same level of concentrates that were commonly given to the imported breeds.
For many years, leading farmers and research organizations, particularly in the developed world, have worked to breed and select superior animals with specific production characteristics. Thus, the British beef breeds (Angus, Hereford, etc.) have meat with a high degree of marbling (fat deposits within the meat), while the some of the European breeds (Limousin, Charolais, etc.) are famed for ‘double muscling’ with very little marbling. Many of these characteristics have been selected as a result of consumer preferences.
It has always been recognized that to achieve good results - and make the best of the selected characteristics - the animals must be provided with good nutrition, health care and husbandry techniques. The result of all this effort has been the production of a range of breeds of most domestic species of livestock that have the genetic capacity to utilize the best resources that can be provided, in order to grow at a fast rate and to produce high yields of meat, milk, fibre, eggs, etc.
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Improved breeds of livestock may die if raised under low levels of nutrition, health care and husbandry.
Under the same conditions, local traditional breeds will survive and continue to produce. |
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If animals that have been bred for almost ideal conditions are transferred to a situation in which nutrition, health care and husbandry are at a lower level than they need, they will be unable to realize their superior genetic attributes and they may even die. If that occurs, it represents a large loss to a farmer who has probably invested heavily in the purchase of superior animals. In Bolivia, it is recognized that improved lines of guinea pigs are superior to local breeds if kept under commercial conditions at altitudes in excess of about 2,500 m, but that they are very delicate when taken into tropical areas, where they are challenged by a poorer diet and a range of diseases that are not common at higher altitude. For this reason, slower growing but more hardy local breeds are recommended for most situations in the tropical lowlands.
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| Up-grading of Blood-lines |
If a farmer wishes to improve the productivity of his animals, the first step should be to improve the husbandry (feeding, health and management) of his existing animals, until he reaches the production potential of the local stock.
If higher productivity is then required, it will then be necessary to improve the genetic quality of his livestock and in general terms, the best way to achieve this is through cross-breeding with an improved line that exhibits the desired characteristics. In some cases, it is possible to use artificial insemination to introduce exotic blood into a herd of local animals. Where this is not possible, it is cheaper and easier to provide special care to a single, breeding male, than to the larger number of females that he will be mated with.
Usually, the first generation cross-bred animal will retain some of the rusticity and resistance of the mother, while showing some of the improved production potential of the father. If half-bred females are then mated to pure-bred exotic animals, the result will be three-quarter exotic. Obviously, animals should not be mated to their fathers, since this will introduce the real danger of negative, in-breeding effects. The second generation crosses will usually have a higher production potential than their half-bred mothers, but will be more delicate and so will need higher standards of management. In many situations in the tropics, it is unwise to go above three quarters exotic blood, as the loss of rusticity will often be counter-productive. These animals are often mated back to a local breed, to re-introduce a degree of tolerance to the practical limitations experienced on the farm. As such a system develops and matures, it is common to mate an animal that looks more like an exotic back to the local breed, while a cross-bred that looks more like the local breed would be mated to the exotic breed. The degree of exotic blood will then vary between three eighths and five eighths, which is often the optimal level of improved blood for small-farm systems in the developing world. The only draw-back here is that it requires continual access to males (or semen) of both the exotic and the local breeds and as more exotic blood enters an area, it can be extremely difficult to find pure-bred local males.
If conditions on a particular farm are so favourable that pure-bred exotic stock can be maintained, the fourth generation of crosses (fifteen sixteenths exotic) will, to all intents and purposes, be genetically indistinguishable from the pure-bred exotic parent line. These animals will have almost all of the production potential of the exotic, but with none of the resistance that was an important characteristic of the local breed.
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Cross-bred animals will be more susceptible to local diseases and parasites than are the traditional livestock breeds.
Cross-bred animals also require higher levels of animal husbandry, health care and supplementary feeding.
Farmers should be made aware of the increased costs associated with cross-bred or pure strains of exotic livestock. |
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In cattle, animals in the tropics should rarely be allowed to calve before the age of about three years and even in intensively managed dairy herds, average calving intervals are usually in excess of 15 months. There is, therefore, plenty of time to gradually improve husbandry standards on the farm in parallel with the improvement in genetic potential of the herd if it is up-graded by cross-breeding. In animals such pigs, as sheep and goats, where it is usually inadvisable to mate young females until they reach an age of about 12 months and a practical target is to have three litters in a period of about two years, up-grading through repeated cross-breeding is still feasible, as there is sufficient time between generations to improve husbandry standards to meet the necessities of the improved genetic potential. In animals such as poultry and guinea pigs, the generation time is so short that it does not allow for parallel improvements in genetics and management. Great care will be required in the up-grading of these animals, to avoid the severe losses that can occur if animal requirements outstrip the level of management that can be provided on the farm.
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