THE TROPICAL ADAPTATION OF BEEF CATTLE

an Australian study

by H.G. TURNER

The Australian tropics cover 36 percent of the country's area, and the raising of beef cattle is the main form of land utilization in this region of 2.8 million square kilometres.

Figure 1, showing mean temperature corrected to sea level, demonstrates that northern Australia is comparable in this respect to other tropical regions. But temperature is less moderated by elevation in Australia than it is in many other regions.

Figure 2 shows the distribution of beef cattle in Australia and some isohyets of rainfall. More than half of tropical Australia has a rainfall of less than 500 mm and only limited coastal areas receive more than 1 000 mm. The rainfall is strongly seasonal (monsoonal) and of low reliability. Conditions range from small but significant areas of wet tropics to major areas of aridity. There is little scope for arable cropping or fodder conservation and the industry is essentially pastoral and extensive. Because of low carrying capacities, it is difficult to moderate the natural range environment to which the cattle are exposed.

H.G. Turner is at the CSIRO Tropical Cattle Research Centre, Rockhampton, Queensland, Australia.

1. Mean annual world temperatures at sea level (Fahrenheit).

SOURCE: Thomas A. Blair and Robert C. Fite, Weather elements: A text in elementary meteorology, 5th ed., 1965. By permission of Prentice-Hall, Inc., Englewood Clifls, New Jersey, U.S.A.

2. Beef cattle distribution and rainfall in Australia.

Australia is free of the major infectious diseases such as foot-and-mouth disease, rinderpest, surra and pleuropneumonia, which are excluded by strict quarantine. The cattle tick (Boophilus microplus) and its associated blood parasites, Babesia and Anaplasma, are endemic throughout the less arid parts of the region; gastrointestinal parasites and biting insects, including the buffalo fly (Siphona exigua), affect the wellbeing of cattle.

Unlike most countries within the tropics Australia had no indigenous cattle and, by historical accident, the area was colonized by British breeds. In northern Australia the Shorthorn has been predominant, supplemented by the Hereford in limited areas, as the industry was established in the middle of the nineteenth century.

Introduction of tropical cattle

Whereas most tropical countries have indigenous Bos indicus cattle and look to the introduction of Bos Taurus to improve productivity, in northern Australia it has been necessary to introduce tropically evolved cattle. The approaches to the target of adapted, productive cattle from opposite starting points are instructive. In each case the focus of interest tends to be on the novel qualities to be introduced, sometimes to the neglect of those already established which are taken for granted.

Quarantine regulations have limited the sources and extent of importations of tropical cattle. The early entry of a few zebu cattle and of buffalo and banteng had little impact, the former being dissipated and the latter isolated as feral populations. In 1933, 19 Brahmans were imported from the United States and distributed among a number of herds. These were followed in the 1950s by further imports of Brahmans and Santa Gertrudis, by a small number of Africanders (also from representatives of the breed in the United States) and by Sindhis and Sahiwals from Pakistan. The latter were intended primarily for dairy breeding, but the use of Sahiwals in beef breeding has been explored.

Belmont programme

The breeding programme at Belmont, the field station of CSIRO's Tropical Cattle Research Centre at Rockhampton, started in 1954 with representatives of Brahman, Africander, Hereford and Shorthorn breeds. This centre was set up for the study of inherited factors controlling adaptation and economic performance under northern Australian conditions. After initial matings with all combinations of breeds, the following are the main lines established and carried forward, currently, to the F₄-F₅ generation:

Africander cross: half Africander, quarter Hereford, quarter Shorthorn; Brahman cross: half Brahman, quarter Hereford, quarter Shorthorn; Hereford-Shorthorn: half Hereford, half Shorthorn.

3. Young bull of Africander-cross line. This highly fertile and adapted line, under selection for growth, fertility and parasite resistance, has become established under the breed name “Belmont Red”.

These are referred to respectively as AX. BX and HS. In these and other subsidiary lines, a breeding herd of about 900 cows is maintained. They and their progency are grazed on natural and improved pastures representative of the area and exposed to the normal stresses of the environment. Performance is compared principally under these conditions, but some growing stock are studied more intensively in confinement.

The location of Rockhampton is shown in Figure 2, and its meteorological data are given in Table 1.

Performance attributes

Fertility

The calving percentages shown in Table 2 represent breed means accumulated over a number of years, corrected for the effects of age, lactational status and year (Seebeck, 1973a). These results were all obtained from a short annual mating period of seven weeks, with young (2-year-old) bulls and with singlesire matings (one bull to 30–35 cows). All three factors lower the level of fertility realized and emphasize differences in reproductive efficiency. In matings of F₁×F₁, the differences between breeding lines were not significant, although both AX and BX were more fertile than HS. In subsequent generations, AX maintained high fertility, HS dropped slightly, and BX fell dramatically; the breed differences are highly significant. Reciprocal matings between the AX and BX lines, made simultaneously with straight matings of each line, have shown that the differences is expressed in both males and females.

Within the BX and HS lines, cows that are progency of different sires differ significantly in fertility, with a heritability of 22–25 percent (Seebeck, 1973a). There is scope for improving fertility by selection, which would be enhanced by identifying the underlying genetic factors. Toward this end, the significance of morphological abnormalities of the female reproductive tract, semen abnormalities, serving performance, fertilization rates and postpartum anoestrus is being defined, and the endocrine bases of some of these differences are being elucidated.

Growth

The mean body weights of calves of the three breed lines are shown in Table 3. These represent 500–600 female calves of the F₂and F₃ generations born over a period of five years. The breeds did not vary significantly in birth weight, but thereafter the differences were highly significant. At 18 months, BX were 21 percent heavier and AX 16 percent heavier than HS. These differentials are somewhat lower than in F₁ progeny, the decline from F₁ to F₂ being greater in BX than in AX, and more in birth weight than in subsequent weights.

In breeding cows, mature weights are very similar in the different breeds, but they are approached at different rates and differ in seasonal stability. During a drought, weight changes of nonlactating pregnant cows from February to October were: AX -8.7 kg, BX +5.8 kg, HS -33.0 kg. However, the changes of lactating pregnant cows were all similar at about -33 kg, the BX thus being most affected by lactation (Frisch, 1973a).

Table 1. Mean temperatures and humidity at Rockhampton, Queensland

Mortality

Table 4 shows mean mortalities of breed groups in calves of F₂ + generations from birth to 15 months and in adult cows (Frisch, 1973b). At all stages, mortality was least in AX and greatest in HS. Comparison were similar in F₁ animals except that perinantal deaths were high in zebu-cross calves, especially those born to young British-breed cows. The mortalities of adult cows, averaged over a number of years, rose in two drought years to 5.6 percent in HS, 2.0 percent in AX and 1.5 percent in BX.

Carcass composition

The yield of carcass (dressing percentage) is higher, by about 2 percentage units, in BX than in AX or HS steers (Hewetson, 1962). The zebu-cross carcasses are leaner under some conditions but breed differences in fat content depend on stage of growth and plane of nutrition. Fat distribution shows some breed differences (Seebeck, 1973b). Distribution of muscle weight also varies, with AX better developed in muscles surrounding the spinal column and BX better developed in muscles of the upper hindquarter. In general, differences in yeild and quality of meat at a given liveweight, although significant in indicating the potential for genetic improvement, are of minor immediate importance in most market situations.

Pure zebu performance

The foregoing compares the performance of B. indicus × B. taurus halfbreds with a line representing their B. taurus parents. Directly comparable data on the performance of the zebu parental breeds are less extensive, and it must be remembered that representatives of these breeds have only a small genetic foundation in Australia. Nevertheless it can be stated that compared with the crossbreds the Brahmans and Africanders have lower growth rate, lower fertility and higher juvenile mortality, but lower postweaning and adult mortality.

Table 2. Calving percentages in Africander cross, Brahman cross and Hereford-Shorthorn lines

Source: Seebeck, 1973a.

Table 3. Body weights of Africander cross, Brahman cross and Hereford-Shorthorn heifers

Source: Kennedy and Chirchir, 1971.

Genetic adaptations to components of the environment

The preceding comparisons of performance were recorded in a specific field environment. Obviously they would not be identical in all environments. Adequate definition of the physical and biological environment as its affects cattle is difficult to express in absolute terms, and it is more meaningful to identify and quantify elements of the environment in terms of their comparative effects on animal performance. This gives a perspective of elements limiting performance, the importance of genetic differences in response to them, and the genetic strengths and weakness of particular breeds.

Table 4. Mortality rates in Africander cross, Brahman cross and Hereford-Shorthorn calves and cows

Source: Frisch, 1973b.

Heat

The effect of the complex thermal environment occupied by an animal in the field cannot be predicted from experiments in climatic rooms. The effect of heat in a field situation has been estimated by clipping the animals; coats (Turner, 1962). Keeping Herefords clipped increased their growth during the six warmer months of the year by 13 percent. As clipping only partially relieved heat stress and lowered rectal temperatures to less than those maintained by zebu crosses under the same conditions, this is a minimum estimate of the importance of heat to a susceptible breed. Elementary parameters of the thermal environment in which these results were obtained are given in Table 1.

The superior heat tolerance of zebu crosses represents a significant advantage under warm conditions. Its main determinants are a sleek coat, high sweating capacity and low body heat production. Coat type is a good index of tropical adaptation in temperate breeds; it is related to sweating capacity (Schleger and Bean, 1971) and has a high heritability and genetic correlation with growth rate (Turner and Schleger, 1960).

Parasites and diseases

Breed differences in susceptibility to parasites have been studied by comparing responses to parasite control. In herds containing representatives of three breed groups, all run together at pasture and exposed to normal field infestations of the cattle tick (B. microplus) and gastrointestinal mematodes, one third of the animals were dipped twice or three times weekly to control ticks, one third were treated with anthelmintic every two or three weeks to control worms, and one third were left untreated. Gains of each treatment group of each breed in two different experiments (Figure 4) show that HS were profoundly affected by both ticks and worms whereas BX were unaffected by either and AX were somewhat affected by both. Genetic tick resistance, gained by breed selection, crossbreeding, and within-breed selection, is an important contributor to performance in endemic areas and the most efficient means of countering the tick. Genetic differences in susceptibility to gastrointestinal nematodes are obviously of similar importance. A criterion of helminth tolerance, as applicable for selection as are counts of mature ticks in selection for tick resistance, remains to be developed.

4. Liveweight gains of Africander cross, Brahman cross and Hereford-Shorthorn cross when dipped to control ticks, treated with anthelmintic to control worms, or untreated.

Sources: Experiment A: Seifert, 1971; experiment B: Turner and Short, 1972.

Infectious Keratocunjunctivitis (pinkeye) is an affection common everywhere, and is usually considered to be of minor nuisance value. It has been shown (Frisch, unpublished) that affected animals have markedly reduced growth rates and that there are major breed differences in susceptibility.

These are a few examples of the existence of genetic differences in susceptibility to diseases and parasites. Genetic solutions must be considered as economical and ecological alternatives to other control measures.

Feed utilization

Genetic differences in the growth response of animals subjected to stresses such as heat or parasites are expressed through some aspect of feed utilization. Susceptible animals suffer depression of feed intake or effects on digestion or metabolism (e.g., Seebeck et al., 1971). There are other inherent differences in feed utilization independent of environmental stresses. Voluntary feed intake per unit of liveweight is comparatively low in Brahmans, but they also have a lower maintenance requirement at a given liveweight (Frisch and Vercoe, 1969). It remains to be seen whether a low maintenance requirement, which is a component of efficiency and a great advantage under conditions of feed shortage, can be combined with a high feed capacity which promotes gross efficiency under conditions of abundant feed. For the present, a low maintenance requirement is of overriding importance where there is risk of seasonal feed shortage.

There is a tendency for zebu crosses to have slightly higher digestive efficiency than British breeds (Moran and Vercoe, 1972). Another genetic difference of potential importance for maintenance on low nitrogen diets is in the recycling of urea to the rumen. Zebu crosses maintain higher blood urea under certain conditions, and animals with low water intake and urine volume, advantageous in an arid environment, also conserve urea (Vercoe, 1967).

Genetic differences in the commitment of nutrients to fat or protein deposition, and in the relative depletion of fat or protein stores during weight loss, affect the efficiency of meat production.

Environment or genotype

In relation to the target of improving animal productivity there tend to be two schools of thought. One favours modifying environments to accommodate animals of the highest productive potential, the other favours neglecting any scope for ameliorating the environment and accepting the productivity of genotypes which withstand its rigours. Either is a prejudgement and neither alone gives optimum solutions. Freeing the environment of all limitations, in climate, disease, parasites and nutrition, is in some cases not feasible and in many not economical. Any managerial measure relying on inputs (buildings, mechanization, fertilizers, pest control) must be evaluated in terms of cost and benefit. Cost must be viewed not only in immediate monetary terms but with a long view of true costs of inputs such as fossil fuels and nonrenewable resources, and side effects on ecological balance. Cost-benefit evaluation of managerial inputs may be seriously misleading if limited to one genotype, ignoring genetic differences in response. Conversely, genetic solutions may be inefficient where scope for effective adaptation is limited and an environmental element can be transformed by minor inputs.

To optimize productivity it is necessary to study both factors: modification of components of the environment and genetic differences in response to them. The examples of such investigations at Rockhampton given in this articles have been more comprehensively reviewed by Vercoe (1974).

REFERENCES

Frisch, J.E. 1973a. Comparative drought resistance of Bos indicus and Bos taurus crossbred herds in Central Queensland. Aust. J. exp. Agric. Anim. Husb., 13: 117.

Frisch, J.E. 1973b. Comparative mortality rates of Bos indicus and Bos taurus cattle in Central Queensland. Aust. J. exp. Agric. Anim. Husb., 13: 127.

Frisch, J.E. & VERCOE, J.E. 1969. Liveweight gain, food intake and eating rate in Brahman, Africander, and Shorthorn x Hereford cattle. Aust. J. agric. Res., 20: 1189–1195.

Hewetson, R.W. 1962. Dressing percentages of Brahman and Africander cross and of British breed steers. Aust. J.exp. Agric. Anim. Husb., 2: 82.

Kennedy, J.F. & CHIRCHIR, G.I.K. 1971. A study of the growth rate of F₂ and F₃ Africander cross, Brahman cross and British cross cattle from birth to 18 months in a tropical environment. Aust. J.exp. Agric. Anim. Husb., 11: 593–598.

Moran, J.B. & VERCOE, J.E. 1972. Some factors affecting apparent nitrogen digestibility of roughage diets fed to cattle. J. agric. Sci., Camb., 78: 173–177.

Schleger, A.V. & BEAN, K.G. 1971. Factors determining sweating competence of cattle skin. Aust. J. biol. Sci., 24: 1291.

Seebeck, R.M. 1973a. Sources of variation in the fertility of a herd of zebu, British, and zebu X British cattle in Northern Australia. J. agric. Sci., Camb., 81: 253–262.

Seebeck, R.M. 1973b. The effect of body weight loss on the composition of Brahman cross and Africander cross steers. J. agric. Sci., Camb., 80: 411– 423.

Seebeck, R.M., Springell, P.H. & O'Kelly, J.C. 1971. Alterations in host metabolism by the specific and anorectic effects of the cattle tick (B. microplus). Aust. J. biol. Sci., 24: 373–380.

Seifert, G.W. 1971. Ecto and endoparasitic effects on the growth rates of zebu crossbred and British cattle in the field. Aust. J. agric. Res., 22: 839–850.

Turner, H.G. 1962. Effect of clipping the coat on performance of calves in the field. Aust. J. agric. Res., 13: 180– 192.

Turner, H.G. & Schleger, A.V. 1960. The significance of coat type in cattle. Aust. J. agric. Res., 11: 645–663.

Turner, H.G. & Short, A.J. 1972. Effects of field infestations of gastrointestinal nelminths and of the cattle tick (B. microplus) on growth of three breeds of cattle. Aust. J. agric. Res., 23: 177– 193.

Vercoe, J.E. 1967. Breed and nutritional effects on the composition of faeces, urine, and plasma from Hereford and Brahman X Hereford steers fed on high and low quality diets. Aust. J. agric. Res., 18: 1003–1013.

Vercoe, J.E. 1974. Studies on adaptation of cattle to tropical environments and the role of radioisotopes, and Tracer studies on the interaction between parasitism and animal production. In: Tracer techniques in tropical animal production. Vienna, International Atomic Energy Agency.