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Animal carrying capacity, including concepts and definition, methods for assessment and use of standard stock units

B.K. SONI (*)

(*) B.K. Soni, Director General (Animal Sciences), Indian Council of Agricultural Research Krishi, Bhavan New Delhi. India.

It is now well recognised in all parts of the world that the most economic system of raising livestock is through maximum utilisation of the available plant materials, particularly the grassland or a grass cover. The alternate system of raising animals on concentrate feeds is not only costly but also tends to unnecessarily strain the already meagre resources of grains required for feeding the human population. The animal carrying capacity of any area has to be considered in this context and would, therefore, depend on a large number of factors, including the type of available soils; vegetation; ecology of the area; type and requirements of livestock production; and the possibilities of introducing new technologies for raising livestock in the area. There is, however, a great difference between the temperate world and the tropical world insofar as the problem of carrying capacity of land for raising livestock is concerned, and " pasture " and " grassland " are understood one way in the temperate region countries, while they have quite a different meaning in the tropics and arid and semi-arid areas. The improved pastures that may be produced in temperate or sub-temperate latitudes, centred around the key plants white clover or subterranean clover (Trifolium repens, T. subterraneum), will provide a maximum amount of feed for grazing or cutting of relatively high protein content suitable for a considerable part of the ration of animals. On the other hand, the crude protein content of natural pastures in the tropics tends to be relatively low and the crude fibre content rather high, perhaps because of climatic effects, or of soil fertility, or because of the physiological characteristics of the grass species that grow naturally or may be cultivated. Cenchrus ciliaris and Cynodon dactylon have the capacity to retain a relatively high protein content longer into the dry season there than their related species in the tropics.

Considerable work done in East Africa has shown that milk production and normal growth through a wide range of liveweight changes are limited either by crude protein, if this is lower than about 11 to 14 percent, or by total digestible nutrients if the crude protein is much higher than this. Since few, if any, natural grass stands in the tropics have anything approaching a constant crude protein content of around 12 percent, the limitations of tropical grasslands and the need for high protein cultivated fodder grasses and legumes become obvious.

The natural grass covers of the tropics include many and varied types of savannah, scrub and other non-forest vegetation, and the grass covers associated with open types of forest. The grass covers of India have been described and mapped. Similarly, the maps of grass covers for Latin America have also been compiled. The vast grassland areas are frequently said to represent a great potential and are underdeveloped resources for increased production of a wide range of livestock products. Although opinions may differ widely, it is probably true that this assumption is not realistic for the great majority of tropical and sub-tropical grasslands, at least as far as economic and intensive animal production is concerned. Certain types of tropical grass associations are of value for beef cattle production on the ranching system, others in the arid and semi-arid zones for sheep and goat grazing. In general, however, the higher forms of animal production such as dairy husbandry can only be maintained after the drying of the original stand and its replacement by newly sown or planted species. This does not mean, however, that the natural grasslands in the tropics and in the arid and semi-arid areas are of no value as parts of a dynamic form of livestock production.

In India, the position in respect of animal carrying capacity of grass cover has a direct bearing on socioeconomic conditions of the livestock raising community, inadequacy of grain production to meet human nutritional requirements and above all, an enormous livestock population that must be sustained. According to the 1972 census, India has 353.77 million livestock, comprising bovines, equines, sheep, goats, camels, and pigs. Converted into standard stock units, the total number comes to 226.5 million. The present feed and fodder resources are deficient by 36.2 percent as maintenance ration and by 80 percent as production ration. Approximately 21.8 million hectares of sub-tropical, semi-arid, and arid rangelands in India have to support 10.58 million standard animal units. Various investigations have been carried out in Indian research institutes to study in detail the extent of available nutrients from the grasslands in different parts of the country, together with studies pertaining to their chemical composition palatability and capacity to regenerate. The Central Arid Zone Research Institute, Jodhpur (Rajasthan) and the Indian Grassland and Fodder Institute, Jhansi (UP), are engaged in systematic research on this aspect, to evolve management systems for improving grasslands without disturbing the present livestock raising patterns, with the ultimate object of improving animal production and raising the incomes of farming communities in these areas.

The arid region of India covers western Rajasthan, Southeastern Haryana, Kutch, and Northwestern Saurashtra in Gujerat State. Large parts of these areas are only suited for livestock farming. Considering the soil, vegetation, and water resources, 19 percent of lands in the arid region are of Class 6 and 7 as per the FAO use acceptability classification of lands for conservation purposes, and are suitable only for pasture and range development. Any attempt to increase the intensity of their use, especially for crop production, would reduce forage production potential and expose them to further degenerative changes. The problem in those lands is not only to increase farm production but to conserve available natural resources. With a view to increasing cereal production, more and more of these lands, which are unsuited for the purpose, have been put under cultivation. This has further assisted the forces causing degradation. Despite the increased area put under cultivation for common crops of the arid region, there has been a decline in the total yield of most of the cereal crops; this shows that the land is not fit for crop production and that utilisation for this purpose is resulting in a decrease of natural resources, which are already scanty.

In the arid areas of India, the rearing of livestock on a nomadic system is the main occupation of the local population for their sustenance. The local fodder resources for maintaining livestock are confined to the residual kadbis of cultivated crops (mainly millets) and grazing from common grasslands. In one of the major states of India, Rajasthan, the comparison of livestock population and land use statistics shows that in the arid districts, grazing areas available per head of bovine and per head of livestock are 1.1 hectare and 0.38 hectare, respectively, as against the corresponding figures of 0.47 and 0.22 hectares for the whole state. The number of cattle and buffalo for every thousand hectares of net cultivated area in the arid zone is 657, as against 939.5 for the state as a whole. Although the availability of land for livestock raising is more in the arid zone, the production level of kadbis as well as grass yield in these lands is low, seasonal and uncertain, and the quality is also poor. The inadequacy of fodder resources, as well as their availability only during the months of July-November, is responsible for the nomadism of the livestock breeders of these areas. Such conditions adversely affect the animal carrying capacity.

The major problems of rangeland can be attributed to various factors. Because of the aridity of the climate and over-stocking of the range, production per caput of ruminant animals is poor, mortality high, and fertility low, while those stock that survive are slow to mature. As a result of most natural pastures drying up in early summer, the high risks attendant on trying to carry young stock into a second year on range grazings, and the traditional divorce of livestock and crop production in the region, the stock owners are forced to sell unfinished animals for slaughter at extremely uneconomic rates. These could probably be doubled and finish improved by transferring stock to a higher plane of nutrition on cultivated forage crops or pastures.

Sheep are important species in the agricultural economy in India, especially in the arid and semi-arid areas with marginal and sub-marginal land unfit for agricultural production. Sheep are perhaps the most appropriate livestock species for utilising the sparse vegetation available or expected to be available in such areas through rangeland and pasture development. They can survive on extremely poor and low set vegetation because of their close grazing habits and ability to travel over long distances to obtain sufficient forage and water to subsist. On the same vegetation, other species of livestock would not be able to do so.

Because of the non-availability of suitable pasture lands for sheep grazing in most of the states of India, the sheep raisers migrate their flocks over extensive areas in the same state or even to neighbouring states. In Rajasthan around 5 lakh of sheep (1 lakh= 100,000), mainly from Nagur and Jodhpur districts, are in permanent migration. Permanently migratory sheep are mainly grazed in Madhya Pradesh, Uttar Pradesh and parts of Rajasthan. Around 10 lakh of sheep migrate for only 6 to 9 months. These sheep are also from the western districts of Rajasthan and follow definite routes and periods of migration toward Madhya Pradesh, Uttar Pradesh Haryana, and Gujarat. During migration the sheep graze on stubble in harvested fields and also in forest areas, where the shepherds pay nominal charges.

Over the last two decades, work on range management at the Central Arid Zone Research Institute has been in progress. It has been shown that grass production could be substantially stepped up through land development, fencing, reseeding, use of fertilisers, soil conservation, and water management. The results indicate that with adequate protection and controlled grazing the forage yield on the range lands could be practically doubled in about 3 to 5 years' time. It has been estimated that during years of normal rainfall, air-dried forage production in " very poor ", " poor ", " fair ", " good " and " excellent " grasslands is 200, 500, 750, 1,000 and 1500 kg/hectare, respectively, when protected. Fertiliser application and reseeding with better perennial grasses, suiting different soil and rainfall conditions give increased yields of forage material. Amongst the different soil and water conservation measures on rangelands, contour furrows are considered to be most suitable. The Institute has worked out the cost per hectare with regard to various measures of range development. The smaller the area of a block the greater is the cost of fencing per hectare, and blocks of less than 200 hectares have been found to be relatively costly to develop.

Development of grassland will need to be accompanied by an adequate supply of seeds, particularly of perennial grass species. This is an important lacuna in areas where grassland management is taken up on systematic lines, as sufficient quantities of seed are not available. Therefore one of the important prerequisites for the grassland development programme would be production and supply of adequate quantities of seed.

Although there is an obvious need for closer integration of animal and crop production, which could be of mutual benefit to both sectors and conducive to the conservation and improvement of natural resources, very little real progress seems to have been made. There is evidence that much of the degradation of semi-arid rangeland has occurred recently, in some cases aggravated by the development of groundwater supplies, which has encouraged human population pressures. Reducing the permanent human population in range areas would greatly ease the grazing pressure; but there are great socioeconomic problems in resettling substantial numbers of nomadic peoples who have considerable skill in animal husbandry but little or no knowledge of crop production. Moreover the nomadic system, if properly controlled, is an efficient means of utilisation of meagre natural resources.

In order to arrest further deterioration of rangelands, it is necessary that a positive systematic programme should be introduced by the Government to restrict livestock numbers, in conjunction with measures to provide greater insurance against hazards such as impoverishment of fodder reserves. Such action programmes must be supported by positive steps to prevent further encroachment on the rangelands and to provide better outlets for livestock.

It is necessary to survey the natural grasslands within the livestock production area, on the fringes of that area and in more remote districts; to assess their present botanical and ecological status; to define the degree of deterioration, and to advise upon appropriate methods of ecological management or improvement, assisted perhaps by cheap methods of surface seeding with superior species. In tropical and subtropical latitudes where soil erosion is a problem, the role of all plant covers, whether natural or artificial, in conserving soil, helping to control the hydrologic cycle, and reducing desiccation, must be borne in mind when designing systems of controlled or free-range grazing on natural grasslands.

In order to plan and design a systematic and dynamic livestock production programme, it is essential that the herbage from natural grasslands should be analysed for its content of nutrients in different parts of the year. In considering the potentialities of natural tropical grasslands, it must be remembered that cattle can harvest a diet superior in quality to that of the forage as a whole with which they are presented, selecting more protein and less fibre. Thus milk production from a low quality pasture may be possible if the area available for grazing is sufficiently large to give the cattle scope for their selective grazing.

It is also necessary to know more about milk-producing potentialities of grasslands of the tropical and subtropical world and what can be achieved with slight adjustments in management. Some grasslands will be of value for the more extensive forms of dairy farming. Others will be more suitable for secondary roles in intensive systems of dairy farming, such as the maintenance of dry animals, the rearing of young stock, perhaps the fat teeing of male progeny, and the harvesting of low-protein hay.

It is necessary to introduce technological changes gradually. The farmer should be provided with incentives, and multidisciplinary studies involving animal production, agronomy and social and economic fields should be introduced. This can go a long way in improving the utilisation of grasslands and thus improving their animal carrying capacity.

Animal carrying capacity, as has been indicated above, covers a wide range of factors, all of which must be taken into consideration when assessing the suitability or effectiveness of grasslands. Particular emphasis must be given to livestock numbers, available vegetation, type of vegetation, and the purpose for which livestock are raised in a particular area. In India, for instance, the main emphasis in the raising of bovines is on milk production rather than on fattening for meat production. Nutritional requirements for these two purposes are ' different, and must be kept in view when assessing the suitability of rangeland. This also applies to sheep in this country, as by and large sheep are raised for production of wool in the northern parts of the country, while mutton production is incidental to wool production. Only in the southern parts of India are there specialised mutton breeds and animals raised for that purpose. Together with these factors the socio-economic conditions of the farming community and the pattern of agriculture in the area of livestock farming must also be taken into consideration.

In making any comparable studies in relation to management and carrying capacity of rangelands in different countries of the world, it is necessary to adopt standard livestock units. Specific studies in this regard, keeping in view various factors in relation to nutrition and growth of different species of livestock, need to be conducted in the major regions of livestock production. Such studies would, however, be time-consuming and expensive. It is, therefore, desirable that the unit equivalents suggested by FAO for different species of livestock be adopted by different countries till such time as more specific information becomes available.


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