As has been shown in Chapter 1 much of the genetic improvement of cattle, sheep and goats in Europe which occurred during the 19th and 20th centuries has been obtained by changing the breed composition of the local populations. This was done either by infusion of blood from an outside breed or by grading up entirely to the improved breed. In many cases the improved breed had to be imported from another country.
The same thing is now happening in the tropical countries. While, as has been shown in Chapter 4, there is great scope for improvement by selection within the local breed, the most spectacular immediate increase in production can often be made by use of improved breeds from overseas. This means that the policy of importation is very relevant to a programme of livestock improvement. Its success will often depend on correct answers to the following questions:
Should both males and females be imported, or only males, or only semen?
At what age should animals be imported?
Which breed or breeds should be imported?
Should purebreds or crossbreds be imported?
How should the individual animals be selected?
The answers to these questions will depend not only on the environment - both managemental and climatic - to which the animals are going to be subjected and the product which is of interest, but also on the breeding system in which the animals are to be used.
The various breeding programmes involving imported animals or semen are discussed in Chapters 4 and 6. They may be briefly summarized as follows:
The formation or augmentation of a purebred population, or the servicing of such a population.
Grading up in order to replace the local breed gradually by the imported one.
Use in special governmental or institutional “nucleus” herds which are a source of sires or semen for purebreeding or crossing programmes in the general population.
Direct crossing on to the local animals.
Before importing a breed from a temperate region for purebreeding in a tropical area one must be sure that this is indeed the best policy. It must be remembered that in hot countries it is not with heat alone that the temperate breeds must contend. The high temperature, especially if combined with low or irregular rainfall, means poor quantity and quality of forage. In developing countries the standards of animal management and hygiene are usually not as high as in developed countries and the climate is an inhibiting factor in their improvement. The imported cattle are usually very sensitive to the local diseases - ticks and tickborne diseases are a special menace.
It is in the case of the range animals (beef cattle, sheep and goats), which cannot easily be protected from these hazards, that import of purebred temperate breeds to the tropics should be approached with caution. It will usually be better to try and improve the local breed by selection (see Chapter 4) or to use some crossbreeding system (Chapter 6). It is a striking fact that after over a century's attempts to raise British breeds of beef cattle in tropical northern Australia reason finally prevailed and there is now hardly a single commercial herd in Queensland, for instance, which does not contain zebu blood.
On the other hand when temperate livestock can be protected from the environmental hazards by adequate disease control, high nutritional level and good management (e.g. protection from solar radiation, regular spraying or dipping, reliable detection of oestrus, supplies of cool water) they can survive, reproduce and produce in hot climates. But these measures cost money and involve an intensive type of management. They can therefore be justified economically only in the case of animals producing a valuable product. Above all this means milk. It is chiefly improved breeds of European dairy cattle which are being imported for purebreeding in tropical areas.
High temperature during summer only or during the day only with the opportunity to cool down at night, is not in itself an impediment to milk production in European dairy cattle. Some of the highest yields in the world are recorded by Friesian cattle in the seasonally hot climates of southern California and of Israel. (The annual average yield of recorded cattle in Israel during 1977/78 was 7 858 kg.) Even in severe conditions of the Gulf (hot, dry and humid) average yields of 3 250 and 4 570 kg for first and second lactations respectively were obtained in a small herd of Friesians at Digdaga in the United Arab Emirates. The animals were extremely well fed and managed: they were housed only during the hot hours of the day, were fed an optimal diet and kept free from parasites and diseases. However, fertility problems were encountered. In spite of water sprinkling during the hottest periods, few cows were got in calf during the summer period (June-October) and the overall rate of reproduction was low (Ansell, 1976). Alberro (1981) describes a similar experience in Mozambique. With very careful attention to intensive food intake, parasite and disease control, and cooling of cows an average yield of 3 000 kg was obtained from a small herd of Friesians but fertility was low.
If Friesians can yield well in the Gulf region there is no reason why they should not be imported into other dry areas, especially in the Near and Middle East. But high management levels must also be imported.
While warning against the importation of European breeds into unsuitable situations it is difficult to quote specific examples of such imports which have failed. Naturally if the importers have given bad advice or sent unsuitable animals or not treated them well enough, they do not want to advertise the fact. Likewise the governments or importing organizations that have been trying to deal with a herd of diseased, unthrifty, infertile or dying animals do not want to publicise their bad judgement or incompetence. But we could quote from our experience many examples to reinforce the warning that a very careful approach is needed to the import and breeding of temperate breeds in the tropics.
One case which has been well documented is the importation of Holstein-Friesian and American Brown Swiss cows onto well managed farms in the humid tropical lowlands of Bolivia (Wilkins et al., 1979). Of 696 cows and heifers imported 78 died within 12–18 months; others had to be slaughtered, were infertile or aborted. Calf mortality varied from 11 to 100 percent on the different farms. In the largest, of 301 live calves born, no less than 100 died in spite of skilled veterinary attention. Similarly Callow (1978) writes: “There are records of entire shipments of cattle dying, many shortly after importation, from disease and environmental stress”.
An importation having been decided on, one must then consider whether it is necessary to import both males and females. The advantage of importing females is that immediate results can be obtained. Within a few months the animals can be milking, or producing progeny for breeding or for meat. Naturally if there are no or few local cattle (or sheep), females must be imported. Females must also be imported if the aim is to form a nucleus herd. Otherwise there are several disadvantages. Firstly, it is expensive to buy sufficient cows to have a sizeable impact, and expensive in foreign currency, too. This, however, need not trouble countries that have plenty of funds (e.g. from oil or aid). Secondly, it is difficult to have available the accommodation and skilled personnel for managing large numbers of imported animals in a country which has no or little previous experience. This difficulty can be partly overcome by assembling the imported animals on large governmental, institutional or private farms rather than distributing them at once to the small farmer.
If females are imported the maximum genetic advantage is obtained by importing young pregnant females. They should, of course, be only in the early stage of pregnancy and should have been served by a purebred male of the same breed. Younger animals may have to be imported if they must be vaccinated (or otherwise immunized) against some local disease before a certain age. But calves and lambs are to delicate to travel.
Importations should be made in the cool season. This, of course, applies to males as well as females.
Under most circumstances it is usually preferable to import males only or semen only. This certainly applies to a crossbreeding programme. Even if the eventual aim is a purebred, a grading-up scheme is often the best way to achieve it. The purebred state can be reached by stages which gives time for a gradual improvement in feeding regimes, managemental skill and housing conditions. If it is found that conditions are not everywhere suitable for the purebred, grading can stop at the 3/4-bred or 7/8-bred level. This is, therefore, a very flexible approach. Above all, this grading can be used to help the small farmer and thus has a social advantage. While it may not be practicable or wise to issue him at once with purebred animals, by grading he can gradually increase the productivity of his herd. This applies particularly to dairy cattle.
Sires or semen will always be needed for use in a nucleus herd. If semen instead of bulls is imported then facilities for storing frozen semen must be available and especially a reliable source of liquid nitrogen. Naturally there must also be an AI system for the general distribution of semen from the nucleus herd.
The two extreme types of dairy cattle which are also the breeds most frequently imported into the tropics are the Friesian and the Jersey. Both are specialized dairy types but the Friesian is large and is outstanding in milk yield while the Jersey is small and its milk has a very high fat content. Naturally both produce meat as a secondary product but again the Friesian produces quantity and the Jersey quality. The other relevant difference between these two breeds is the higher heat tolerance of the Jersey. But the differences between the respective crossbreds (e.g. with zebus) are much less than the differences between the purebreds.
In general, then, Friesians should be used if the market demand is for liquid milk and beef, and Jerseys if it is for milk fat, especially in a hot humid environment. Furthermore, the Friesian can deal with large quantities of roughage whereas the Jersey has a maximum efficiency if the major part of its ration is in the form of concentrates. Friesian crosses will also make larger draught animals than Jersey crosses.
If the Friesian breed is chosen then consideration should be given to the differences between strains from different countries. Preliminary results from the FAO strain comparison in Poland show that bulls from USA, Canada, Israel and New Zealand when crossed on to Polish Friesians, gave daughters with the highest milk yields; fat content was highest in Polish purebred and Dutch and New Zealand crossbred daughters. Liveweight after calving was greatest in Canadian, US and Israeli cross daughters and liveweight gain to 12 months of age was highest in Israeli, Swedish and New Zealand crossbred bulls (Stolzman et al., 1981; FAO, 1982). The environment of the strain in its homeland should also be considered when choosing which strain to import as well as the extent of concentrate feeding (e.g. high in Israel, low in New Zealand).
Although the FAO Expert Consultation on Dairy Cattle Breeding in the Humid Tropics (FAO, 1979) recommended that future efforts in crossbreeding should be concentrated on the Friesian and Jersey, it would be a mistake to ignore altogether other improved dairy breeds which are intermediate between Friesian and Jersey in milk yield, fat content and size. This applies particularly to the Ayrshire (with its improved derivative, the Finnish Ayrshire), the American Brown Swiss and the Danish Red. These have been tried in some tropical countries - e.g. Ayrshire in India, Sri Lanka and Kenya, Danish Red in Thailand and India, Brown Swiss in India and in tropical America.
Other breeds should also be mentioned. The Guernsey is similar to the Jersey but is larger, has a higher milk yield and a lower fat percentage. It has had little impact except in Kenya. The Dairy Shorthorn used to be an importand breed in the British Isles and in America but now it is almost extinct. However, one of its derivatives, the Swedish Red-and-White, has a high yield in its native country and merits trial elsewhere. Likewise its derivative, the Norwegian Red, is now the premier breed in Norway; it has been tried in Madagascar.
In Britain a sharp distinction used to be made between the dairy breeds (e.g. Friesian and Jersey) and the dual-purpose (milk-meat) breeds (e.g. Dairy Shorthorn and Red Poll). This distinction no longer has much meaning, since the Friesian produces more meat (as well as more milk) than the Dairy Shorthorn. On the European mainland no such distinction was made. No special beef breeds were maintained and all dairy breeds were expected to produce meat in the form of male calves and culled females. (The current French beef breeds are derived from former draught breeds). In central Europe, nevertheless, there are two breeds which truly merit the term dual-purpose since their milk yield approaches that of the Friesian and their meat production is greater. These are the Simmental (or Fleckvieh) and the Swiss Brown, both originating in Switzerland. Both have been exported to USA but in that country (and elsewhere) the Simmental has been treated solely as a beef breed and it is in that role that it has been exported to the tropics. On the other hand the Swiss Brown has been selected as a dairy breed (American Brown Swiss) and this is the breed known in the tropics - particularly the American tropics.
In many existing production systems (e.g. extensive pastoral husbandry) a high yielding adapted breed is a more suitable improver than a temperate breed. It was in this role that the Sahiwal, a dairy zebu breed from Pakistan, was first imported into Kenya (see Mahadevan et al., 1962; Trail and Gregory, 1981). There is a similar place for an improved Kenana-Butana in Sudan and for an improved Dairy Criollo in tropical America. But before these and other tropical dairy breeds (e.g. the Shami of Syria, the Red Sindhi and Tharparkar of Pakistan) can have a real economic impact it is essential to increase their milk yield by the type of selection programme described in Chapter 4.
For slightly improved conditions a new breed based on a crossbred foundation (usually European x zebu) is needed. There are now a few such available for import. The best known are the Jamaica Hope and the Australian Milking Zebu. Both of these are based on a Sahiwal x Jersey cross and contain 12–25 percent of the zebu blood. There is still some controversy about how good they really are but there is no doubt that their yields are higher than those of the pure Sahiwal. An experimental comparison in Jamaica has shown that, in that environment and with no feeding of concentrates, the Jamaica Hope is superior to the Friesian in milk yield, butterfat percentage, calving interval, fertility and, above all, viability. Poor reproductive performance and health problems decimated the Friesian herd to the point where only 18 animals (out of an initial 30) completed a first lactation and after two years only seven had completed a second; the corresponding figures for the Jamaica Hope were 30 and 28 (Wellington, 1979).
Both these breeds are based on the Jersey. In the future, breeds based on a Friesian cross should be available: active work in their development is proceeding in Australia, Brazil and India to mention only the most advanced experiments.
The European beef breeds can be roughly divided into two types:
the small early-maturing fat breeds producing quality beef such as the Aberdeen-Angus, Beef Shorthorn and Hereford, all of British origin;
the large late-maturing lean breeds which have but recently been developed from the local draught breeds. These include the Charolais, Limousin and Blond d'Aquitaine of France, the Simmental and German Yellow (Gelbvieh) of Germany and the Chianina, Marchigiana and Romagnola of Italy.
The British breeds are important historically since they were the first to populate the vast pastoral areas of the New World - North America, South America, Australia; they were also introduced into southern Africa. They are now coming under increasing competition from the large continental breeds either as purebreds in the temperate regions or as crossbreds in the tropics. The large breeds certainly grow more quickly and reach a larger size than the British breeds. But they need a higher level of feeding to do it. The British breeds were initially selected for ability to grow and fatten on pasture in summer and turnips and straw in winter. They only became too fat when their nutritional level was raised. The Beef Shorthorn has gone the way of the Dairy Shorthorn and the Aberdeen-Angus is declining in importance but the Hereford, the largest of the three, is increasing in size by selection and still has an important role both as a purebred and in crossbreeding. Its major disadvantage in climates with high intensity of solar radiation is its sensitivity to eye cancer. This shortcoming it shares with the Simmental - another white-faced breed lacking skin pigmentation. It can be overcome by selecting animals with cherry eyes - that is animals with red pigment around the eyes and particularly in the eyelids.
For crossbreeding the choice may fall on one of the large continental breeds, particularly for a terminal crossing programme. The disadvantage of these breeds is the high maintenance cost of the cow and the high incidence of calving difficulties which is directly associated with the size of the calf. Fortunately both of these troubles are avoided when the bulls are used for crossing on a small breed of local cow. When bred pure under temperate conditions there are small differences between these breeds in growth rate, carcass quality fertility and calving difficulty. In particular the Limousin has shown up best for ease of calving and the Italian breeds worst. However, these differences are not conspicuous when the breeds are used for crossbreeding in the tropics. The Simmental has been used very successfully - particularly in southern and eastern Africa - and the Marchigiana and Chianina have been successful crossing breeds on zebus in Brazil.
As indicated earlier, purebred European breeds are not suitable in most tropical areas. Breeds with both zebu and European blood have been formed in several countries and can be recommended for purebreeding or crossing in others. These include the Santa Gertrudis (from a zebu x Shorthorn origin in Texas, USA), the Bonsmara (from Africander x Hereford/Shorthorn in South Africa), the Droughtmaster (from zebu x Shorthorn in Queensland, Australia), the Belmont Red (from Africander x Hereford/Shorthorn in Queensland), the Canchim (from Charolais x zebu in São Paulo, Brazil) and several others. None of these, however, has made a great impact outside its country of origin. The Santa Gertrudis, for instance, has received much publicity and has been widely distributed in small numbers but it has never developed a large population. It is said to suffer from fertility problems; this would not be surprising in view of the low fertility of its parent breeds (Shorthorn and Brahman) and the inbreeding used in its formation.
For the most severe conditions consideration should be given to improved tropical beef breeds such as the American Brahman, the Boran of Kenya and the Africander of South Africa. These have been used widely in the American tropics and in eastern and southern Africa respectively. Probably the biggest success story in the export of tropical cattle has been that of the N'Dama breed native to Guinea and the neighbouring countries. On account of its resistance to trypanosomiasis it has been exported to all the other countries of West Africa as well as to those of west central Africa as far south as Zaire.
Specialized dairy breeds have been developed in India and the Murrah breed, and its derivatives in Pakistan (Nili-Ravi and Kundi), are usually considered the highest yielders. They have been imported as improvers into several countries of southeast Asia as well as into Iraq and Bulgaria. Nevertheless it is high time that controlled experiments were made to compare the overall performance (including meat production) of the Murrah with that of the other Indian breeds (e.g. Jafarabadi, Surti, Mehsana) as well as with breeds outside Asia (Egyptian, Italian, Bulgarian).
There are no specialized meat breeds but in several countries buffaloes are now exploited for meat, e.g. the dairy breeds in Bulgaria, Italy, Trinidad and Yugoslavia and the draught breeds (the Swamp type) in Australia and Thailand. This should lead to selection for beef characters.
All buffaloes have a tropical origin but this does not mean that they are heat tolerant. In fact they are semi-aquatic animals and under hot dry conditions they need frequent spraying or wallowing to maintain their body temperature.
Breeds have to be chosen according to product - wool, meat, milk or a combination. Most wool is produced under extensive management but for meat and milk management may be extensive or intensive. Sheep which are to be kept extensively (and this means the majority) should always come from a similar environment since they will receive little or no protective treatment.
Fleeced sheep should not be imported into a hot humid environment. There are a few wet tropical regions with a considerable population of fleeced sheep, e.g. Java, tropical America, but in Java (Mason, 1978) the fleece is a nuisance which is frequently shorn and discarded, while in tropical America the Criollo sheep are confined to the highlands (Mason, 1981a).
There is effectively only one fine wool sheep. This is the Merino with its many derivatives. While it flourishes in many dry regions whether hot (Australia) or temperate (Argentina, USSR) it should not be introduced where thorn or bush abounds (e.g. West Africa). But what should make any country pause before embarking on a policy of merinization is the current overproduction of apparel wool and the unsatisfied demand for carpet wool.
The Corriedale is a wool-meat breed that has been exported widely from its native New Zealand where it was formed at the end of the last century from a Merino x English Longwool cross.
If it is desired to introduce or improve a coarse wool breed there are several options open. In the dry areas of southwest Asia there are several outstanding carpet wool range breeds such as the White Karaman of Turkey and the Awassi of Syria and adjoining countries. All are fat-tailed.
There are numerous thin-tailed carpet wool breeds in Europe, Morocco, Pakistan and India, but insufficient comparative studies have been made to recommend individual breeds as improvers.
Most milk breeds of sheep are found in the Mediterranean region and the Middle East; for introduction into the tropics it is advisable to choose breeds from this region rather than the well known Friesian sheep of northern Europe (Germany and the Netherlands).
The choice lies between the range sheep such as the Sardinian (probably the highest yielder), Syrian Awassi and Churro (from Spain) on the one hand, and the more sensitive “household” breeds like the Chios of Greece and the Israeli Awassi which have the highest yields. All are coarse-wooled. The Roquefort cheese industry of France is based on the Lacaune breed but this does not seem to be a particularly high yielder.
Most of the improved meat breeds come from northern Europe, e.g. Suffolk and Oxford (England), Ile de France and Berrichon du Cher (France), German White-headed Mutton. Therefore they cannot be recommended for purebreeding in the tropics. They have been tried in the Mediterranean region but even there they have made no lasting impact. Under good management and intensive feeding conditions there may sometimes be a case for using these breeds in a terminal crossing system but it should be approached with caution. In the tropics temperate breeds have fared even worse (Turner, 1974).
Because of such failures attempts have been made, particularly in South Africa, to create breeds combining the adaptation of the local breed with the meat characters of the British. The most successful is the Dorper, from Dorset Horn x Blackhead Persian (a derivative of the hairy Somali breed). The Dorper has been used successfully as an improver in Kenya.
For intensive production systems it has been shown that number of lambs is more important than growth rate in influencing the economic return. This character can be improved by crossing with a prolific breed, i.e. a breed with a large litter size. The north European Finnish and Romanov breeds are the best known but they should not be used in the tropics. There are several prolific breeds from the tropics and subtropics which average two or more lambs at a birth and can also breed every 8 months. These include the Chios of Greece and the D'man from the Saharan oases of southern Morocco. These are both subtropical fleeced breeds but the wool is of no great value. The same applies to the Priangan breed of Java which lives in a hot wet environment. For such a climate a woolless (hair) sheep would be preferable and there are at least two prolific breeds in this category - the Barbados Blackbelly and the White Virgin Island sheep, both from the West Indies. All these breeds and their crosses need very careful management in order to maintain alive the large numbers of lambs they produce (see Mason, 1980a).
For extensive husbandry in the wet tropics prolificacy is less important than ability to thrive in this unfavourable environment. Again a hair sheep is desirable and attention should be given to the varieties of American hair sheep, e.g. the Pelibüey of Cuba or the Tabasco of Mexico (see Fitzhugh and Bradford, 1982) or to the hair sheep of southern India, e.g. the Nellore or the Bannur. For a hot dry environment the Sudanese Desert sheep are clearly outstanding (see Wilson, 1980). Up to now the chief hair sheep used as an improver in both East Africa and tropical America, has been the Blackhead Persian.
Prospective importers of this last breed should not be deceived by the name and search for it in Iran. The Blackhead Persian is, in fact, an improved Somali developed in South Africa from imports of the blackheaded fat-rumped breed of Somalia.
The Wiltshire Horn has been imported into some tropical regions (e.g. the Caribbean) because it is an improved but woolless breed. But it is really a fleeced sheep which sheds its fleece at a very early age. It is unrelated to the hair sheep breeds of the tropics and should be considered along with the other European meat-wool breeds.
Because they are the most important meat and milk producers for the subsistence farmer in the tropics there is a great need for genetic improvement of goats. But because they have a low prestige value and are kept in small numbers and rarely under strict control, breeding programmes are difficult to apply. The result is that breeds of tropical milk goats do not compare in yield with the improved dairy goats of Europe. The best, or the best known, are the Jamnapari of India and the Shami of Syria. The former has already been used extensively in southeast Asia, and the latter in the Near East. A related European breed is the Anglo-Nubian which is an English breed of largely oriental origin. It thus combines comparatively high milk yield with tropical adaptation and has been more successful as an improver than the higher yielding Swiss breeds, the Saanen and the Toggenburg. These are not recommended for breeding pure in the tropics but are useful for increasing milk yield in a crossing programme.
Improved meat goats are even rarer than dairy goats. There has been no selection for growth rate and carcass quality in any temperate or tropical breed and it is high time such programmes were started. The nearest thing to a tropical meat goat is the Boer goat of South Africa but before it is used on a large scale on a local breed it should be carefully compared in a pilot trial to demonstrate that it really is superior when it is kept on the same nutritional level and in the same environment as the local breed.
(For further information on breeds see Devendra and Burns, 1982; Mason, 1981b).
If the imported breed is to be used for the production of crossbreds - that is crossbreds for breeding and milk production - it will certainly produce quicker results to import the crossbreds themselves if these are available. This is the thinking behind the activities of various commercial organizations in Australia and New Zealand which are selling crossbred Sahiwal x Friesian heifers, particularly to countries in southeast Asia such as Thailand and Malaysia where the advantage of milking crossbreds has been demonstrated but there is not a supply of either of the parent breeds. The material available now includes halfbred Sahiwal x Friesian heifers and bulls, ¼ Sahiwal ¾ Friesian bulls, and Sahiwal x Friesian/Jersey bulls.
This scheme appears to have a great future but importers will need a guarantee that the crossbreds really are bred from good Friesian cows and the best Sahiwal sires available. It could easily degenerate into a commercial racket when there is no breed standard and herdbook to guarantee breeding.
The first consideration, which applies to all species, is to import as wide a selection of genetic material as is available. If possible, animals should be from different herds and by different sires. If several must be taken from the same herd they should not be related. This is especially important if the animals are to be bred pure in a nucleus herd - inbreeding is a danger in such herds which tend to be comparatively small so the foundation stock should represent as many blood lines as possible.
If the animals are being imported for breed comparison trials then a random sample of each breed should be imported, or at least a random sample of that portion of the population being selected for future breeding. In the FAO Friesian strain trial for instance, the bulls that provided the semen for the test were selected at random from young bulls entering the AI system for progeny testing in each cooperating country (Stolzman et al., 1981).
The major criterion for selecting dairy bulls is their progeny test i.e. the milk yield of their daughters (see 4.2.2). But it cannot be assumed without question that the bulls which produce the highest milking daughters under temperate conditions are necessarily those producing daughters with the highest yield under tropical conditions, or more important with the highest overall dairy merit (which will include milk let down, fertility, etc.). In other words there may be a genotype x environment interaction.
Cunningham and O'Byrne (1977) have reviewed the evidence for such interactions in dairy cattle. When the environmental difference was small as measured by the difference in milk yield of bulls' daughters in the two environments, the interaction was small. Put in another way the genetic correlation between the two environments was not appreciably different from unity when the ratio of production level between the two environments (high/low) was less than 1.4:1. These results were based on dairy bull progeny tests in herds at different management levels within a country or in different countries within North America or Europe. Under these circumstances bulls can be safely tested in the better environment for use in the poorer. However, the genetic correlation fell as the ratio between the production levels increased. When it was 1.6:1 (between Ireland and Britain) the genetic correlation was only 0.6. Extrapolating this regression to the lower production levels in the very different environments of the tropics would suggest low genetic correlations and hence a high degree of genotype x environment interaction. Buvanendran and Petersen (1980) have confirmed this by comparing the progeny test of the same Danish Red bulls based on daughters in Denmark and in Sri Lanka. The ratio of yields was 2.6:1 and the genetic correlation was only 0.08. If this result can be applied to tropical regions in general (results from Katpatal, 1977, suggest that it applies to India) then we must conclude that it is not reasonable to select dairy bulls for tropical conditions on the basis of progeny tests in temperate countries. It is quite sufficient to select bulls with average progeny tests. This is a conclusion of great economic importance because bulls with high progeny tests, and their semen, are much more expensive than average bulls and average semen.
The above argument applies primarily to purebreeding. If the bulls are to be imported for crossing there is even less reason to choose them on the basis of a high progeny test. They will be exploited primarily for the hybrid vigour obtained in the cross and not for the additive genetic effect measured by the progeny test.
Since beef bulls will also be used primarily for crossing the same argument applies to them. The results of performance test results on intensive feeding systems in temperate countries are irrelevant to the performance of animals on extensive grazing systems in the tropics. The difference in breed average can be relied on to supply the improvement in growth rate and carcass quality expected from the imported breed. The bulls must however be able to survive and maintain their fertility, especially if they are running with the cows on pasture. Individuals with a sleek coat should be selected. Turner and Schleger (1960) have shown that among European and European x zebu cattle, it is the sleek-coated animals which survive and grow better and are also more fertile. The absence of a woolly coat has a direct effect in facilitating heat loss but it is also associated with a physiological adaptation to tropical conditions - varying nutritional level, ticks and worms.
The importance of pigmentation round the eyes of white-skinned breeds has already been mentioned.
It has been emphasized above that, if sheep are to be imported, they should come from an environment as similar as possible to that into which they are being introduced. Also the choice of breed is more important than the choice of individuals within the breed. Therefore it is not necessary to discuss the criteria for selection of individuals - they will be the normal criteria of health, thrift, good udders, size and fertility.
One point should be noted. In a region of high solar radiation it is advisable to select a breed (or individual within a breed) whose skin is protected from the ultraviolet radiation. This may be by wool on the face, as in the Merino, or by pigmented skin and hair. This may apply to the whole animal but in the case of the fleeced breeds it is sufficient that the head is coloured or even that it has pigmented areas around eyes, nose, ears and mouth. This is also important as a protection against photosensitization such as that caused by the plant Hypericum in the Mediterranean region.