Domesticated cattle are usually classified into two major groups, zebu (Bos indicus) and European (Bos taurus) cattle. These groups are considered to constitute two different species, although they are believed to descend from the same wild species, the aurox (Epstein & Mason, 1984). They have the same number of chromosomes, but differ in the morphology of the Y chromosome. There are also substantial physical and physiological differences between the two groups. Nevertheless they can readily be interbred, and produce fertile offspring of both sexes.
Most of the cattle indigenous to the tropics belong to the zebu species. The external trait which most clearly separates zebu from European type cattle is the hump over the shoulders or the posterior part of the neck. The term humped cattle is frequently used as a synonym to zebu cattle. The hump consists of muscle, connective tissue, and variable amounts of fat. The size and shape of the hump vary by breed, sex, and age of the animal. The function of the hump is not clearly understood. The earlier assumption that the hump was important as a store of fat for use during periods of feed scarcity has now been rejected.
Other conformation traits which are common to most zebu cattle are a narrow body, a sloping rump, and rather long legs. The hide is thin, loosely attached, and the brisket and dewlap are usually well developed, particularly in males. Size of the animals varies over a wide range, and breed averages from below 200 to above 400 kg for mature cows have been reported.
Zebu cattle are well adapted to the tropical environments, mainly because of the following attributes:
a) A high degree of heat tolerance, derived partly from low heat production and partly from a large ability to dissipate heat. A high density of efficient sweat glands increases the loss of heat through evaporation, and the short, sleek coat facilitates the convection to the surrounding air. It has also been maintained that the small body size contributes to the heat tolerance, as small animals have a higher surface to body mass ratio. However, the heat production at maintenance is proportional to metabolic weight rather than to actual weight, and the ratio of body surface to metabolic weight is almost independent of size.
b) Partial resistance to ticks, and thus to the many tickborne diseases occuring in tropical countries. Zebu animals have the ability to repel ticks by movements of the skin, but this is only part of the explanation of their larger resistance. It has been demonstrated that when animals are infested with tick larvae, fewer larvae develop into ticks in zebu than in European type cattle (Utech et. al. 1978). Zebu cattle are often claimed to posess a certain degree of resistance also to many other tropical diseases. To what extent this is a genetic property or has been acquired by immunization due to exposure in early life is questionable (Ansell, 1985).
c) Low nutritional requirements, because of small size, low metabolic rate, and possibly also more efficient digestion at low feeding levels.
The potential for milk production is poorly developed in most zebu cattle. The milk yield is low, often not much more than needed to feed the calf properly. The cows usually do not let down milk unless stimulated by the sucking of the calf, and adapt poorly to modem milking routines. Failure to let down milk when milked by hand or machine without the presence of the calf usually leads to complete cessation of milk secretion and consequently to short lactations. Zebu animals are late maturing, both physiologically and sexually, and heat symptoms are weaker than in European cattle. The fat and solids-not-fat content of milk is higher in zebu cattle than in most European dairy breeds.
Zebu cattle can, somewhat arbitrarily, be classified into a number of subgroups according to external traits, such as coat colour, size and shape of horns etc. A more useful classification might be on the basis of utility. A large number of zebu breeds have been described, but few of them have gained any importance outside their home region.
Sahiwal and Red Sindhi are the most widely used dairy breeds of zebu cattle. Both breeds originate from present day Pakistan, and are rather similar in external traits. They are usually greyish red or brown in colour, have short horns and a characteristic convex profile of the forehead. Records collected at the Indian National Dairy Research Institute indicate that the two breeds also perform similarly. Body weight of mature cows was 300 to 350 kg, and average milk yield about 2000 kg per lactation with 5 per cent fat (Bhatnagar et al. 1979 b). Individual cows of both breeds have produced more than 4000 kg of milk in a lactation. Both Sahiwal and Red Sindhi are rather small in numbers, but have been widely used for upgrading of local cattle in many countries, both in South-east Asia and in other continents. A collaborative programme for preservation and improvement of the Sahiwal breed in India has been established (Nagarcenkar, 1983). Eight institutional herds with altogether about 750 breedable females are included, and the programme is based on use of deep frozen semen in combination with progeny testing. In Kenya, a National Sahiwal Stud was established in 1962, and Sahiwal is used both as a pure breed, for grading of unimproved cattle, and for crossbreeding with European breeds (Meyn & Wilkins, 1974). Sahiwal has also made important contributions to most of the new breeds of mixed zebu - European ancestry.
Tharparkar is a third breed originating from Pakistan. Animals of this breed are usually white or light grey, and slightly larger than the two breeds described above, but have similar milk yields (Bhatnagar et al.1979 a).
Most of the many Indian breeds are bred for both milk and draught. Kankrej (Guzerat) and Gir, both from the western regions of the country, combine good draught ability with acceptable milk yields, and have also a high potential for meat production. The same can be said about Ongole (Nellore), a breed originating from Southern India. Kankrej, Gir and Ongole have ail been exported to Central and South America, and have played an important role in the beef and dairy industry of that region.
Hariana is the predominant breed of Northern India. The bullock is highly recognized for its vigour and persistency for draught, and the cows produce up to about 1000 kg of milk per lactation. Hariana has been the local counterpart in many cross breeding programmes.
Most zebu breeds of African origin have been bred mainly for beef production. Boran has gained a good reputation as a dual-purpose breed. The home region of the Boran is the dry areas in Southern Ethiopia/Northern Kenya, and the breed has been widely used in improvement programmes ail over Eastern Africa, mainly for beef. The most promising dairy breeds of African zebu are probably Kenana and Butana, both originating from Central Sudan. Average milk yields of about 1500 kg per lactation have been reported for large herds of these breeds (Cunningham, 1983). The White Fulani cattle of the pastoral people of West Africa have also a fairly high potential for milk production.
The only major populations of humpless cattle native to the tropics are found in West Africa and in Latin America. The West African types consist of several breeds of small, shorthorned cattle. The most well known representative is the N'Dama, found in Guinea and adjoining countries. N'Dama is a triple-purpose breed, kept for milk, beef and draught. The animals are small in size (body weight of mature cows about 200 kg) but very hardy. N'Dama and some other breeds of the same group are found to be highly resistant to bovine trypanosamiasis, and are regarded as an important genetic resource for this characteristic.
America had no cattle when the continent was discovered by the Europeans. The descendants of the cattle brought by the conquistadors in the 16th and 17th centuries are therefore considered to be the indigenous cattle of Central and South America. These cattle, the criollo, are essentially of European type, but have evidently developed some adaptation to the tropical environment. A considerable number of different breeds has been developed, mainly for beef production. Among the more important dairy breeds are the Central American Milking Criollo and the Limonero cattle of Venezuela, which is derived from partly the same base. These cattle are claimed to have low early mortality, good fertility, and high fat and protein content in the milk. A major problem is the high frequency of failure to let-down milk unless the calf is present (Alba, 1978). A somewhat similar breed is the Costeno con Cuernos in Columbia. In recent years criollo cattle have to a large extent been replaced by zebu breeds, particularly Kankrej and Gir, and also by specialized European type breeds.
In some regions of the tropics the indigenous cattle can not easily be classified as Bos taurus or Bos indicus, but exhibit a mosaic of the traits typical for the two groups.
Sanga cattle, predominant in Southern Africa, are usually classified as a zebu type. The hump in Sanga cattle is less prominent than in zebu, and located at the posterior part of the neck (cervico-thoracic hump). Sanga breeds are kept mainly for beef production, and the milk yield is low. Recent research suggests that Sanga cattle have part of their inheritance in common with European cattle, e.g. the Y-chromosome is of the same shape as in European breeds (Meyer, 1984).
Intermediate types are also common on the frontiers between Bos indicus and Bos taurus territories, and along major routes of migration. An example is the Near East, where the native cattle, e.g. the Damietta in Egypt and the Damascus cow in Syria, obviously have been influenced by both groups.
Since the establishment of the first herd books in the late 1700's, most European dairy cattle populations have developed into clearly defined breed types. Selection for specialised dairy or dual purpose function has been accompanied by an increase in uniformity of colour and other external characteristics within each breed. In recent decades, the number of breeds has declined substantially. More than half of the dairy cows in Europe and North America now belong to one breed type, the Holstein Friesian.
Many of the temperate breeds have been used in crossbreeding in tropical countries. The more important among these are described below.
HOLSTEIN FRIESIAN. The origins of this breed are in the area running from the province of Schleswig-Holstein on the Danish-German border to the province of Friesland in the northern part of the Netherlands. The original cattle populations of these areas varied considerably in colour, but by the middle fof the ninteenth century the characteristic black and white colour pattern was predominant. Substantial exports from the Netherlands from 1860 onwards established the breed in a number of European countries, and in North America. Rapid expansion has taken place in this century, to the point where there are about 70 m. Holstein Friesian type cows, accounting for one-third of ail dairy cows in the world. It is the dominant dairy breed in Europe, where it is known as Friesian or Black-and-White, and in North America, where it is known as Holstein-Friesian or Holstein.
In this century, significant differences have developed between the separate national populations of Holstein Friesian. These differences have been measured systematically in a large FAO-sponsored study in Poland (Stolzman et al., 1981). The trial indicated that North American types exceeded European Friesians in milk producing ability by about 15%, though with lower butterfat and protein levels; that North American types had higher mature body weights by about 6%; that European type Friesians had better beef potential, as measured by carcass conformation and meat/bone ratio; and that New Zealand Friesians, at lower body weights than North American types, had higher fat percentage and somewhat lower milk yield, giving an equivalent fat yield per lactation. Within the past ten years, most European Friesian populations have been making extensive use of North American genetic material, with the result that these inter-population differences have now largely disappeared.
Because it is the predominant breed in most devleoped countries, the Holstein Friesian benefits from the large scale investment in testing and selection being made, and in many countries annual average rates of genetic improvement for milk production are close to 1%.
BROWN SWISS. The breed known internationally as Brown Swiss has its origins in the Alpine regions of several European countries. In Switzerland, Austria and Southern Germany, the breed is known as Braunvieh, while in Italy it is known as Bruna Alpina, and in France as Brune des Alpes. In North America, it is known as Brown Swiss.
Internationally, the breed is much less numerous than the Holstein Friesian, numbering perhaps 4 m. cows, or 2% of world dairy cattle.
Trials within the last decade have confirmed that the divergence between the North American and European strains has paralleled that in Holstein Friesian, with the North American type having higher milk production, lower butterfat, and less suitability for beef production. As in the Holstein Friesian situation, the European brown populations have been using North American genetic material in a systematic way for about ten years. In addition, the Brown Swiss has been chosen as the source from which to broaden the genetic base of the Red Dane population.
While critical comparisons are lacking, large scale milk recording results in several countries suggest that Brown Swiss are somewhat below Holstein Friesians in milk capacity, though somewhat higher in butterfat percentage, and slightly better in beef merit.
JERSEY. The origins of the Jersey breed are on the island of Jersey in the English channel. The local cattle population, how numbering about 5.000 cows, has been closed to importation for over two centuries. Based on stock exported from the island, significant populations now exist in New Zealand, Denmark, Great Britain, and the USA, with smaller nuclei of the breed in many other countries. In Australia it has been used as the basis for the development of the AMZ, a synthetic Zebu × Taurus dairy breed. Likewise, it is a major contributor to the Jamaica Hope. Total numbers of Jersey cows worldwide amount to perhaps 2 m., or 1% of the world pouplation.
The characteristics of the breed are its small mature body size (mature body weight equals 60% of Holstein Friesian); early sexual maturity; high butterfat levels; poor beef capacity.
OTHER TEMPERATE BREEDS. Other temperate breeds which have in the past been used in crossbreeding on Zebu populations include the following:
DAIRY SHORTHORN. This breed, once dominant in Britain and Ireland, and highly influential in other countries, is now a small minority breed where it occurs, and is generally declining in numbers.
AYRSHIRE. A specialist dairy breed of Scottish origin, it is now mainly represented by the Finnish population, though the breed is also found in Canada, USA, Britain and a number of other countries.
RED DANE. This breed, which some decades ago was frequently used as an improving cross in other European Red populations, now represents 20% of the Danish cow population, and is involved in a systematic crossbreeding program with American Brown Swiss.
FLECKVIEH OR SIMMENTAL. This strongly dual purpose breed predominates in southern Germany. Substantial poulations are also found in Switzerland, Austria, France, Italy and some countries in Eastern Europe. It has been used as a specialised beef breed for crossing on other beef breeds in the United States and elsewhere. Some European populations, particularly the Swiss, have been using genetic material from North American Red Holstein sources.
NORMANDE. This strongly dual purpose population predominates in the Normandy region of northern France.
GUERNSEY. A specialised dairy breed, originating in the island of Guernsey in the English Channel. It is somewhat larger than the Jersey, though with many common characteristics. It is more numerous than Jersey in the USA.
MRY. This is a strongly dual purpose breed, which makes up one-third of the Netherlands cow population. The breed is red and white in colour, and has slightly lower milk potential than Friesian, but better beef merit.