INCREASED PRODUCTION AND UTILIZATION OF PASTURE AND FORAGE

I. E. Coop

INTRODUCTION

In such a wide field as pastures and crops it is impossible in the time and space available, to do more than summarise the main lines of research and development of recent years having special reference to underdeveloped countries. In the long-term the greatest advances have been made in fundamental knowledge, such as - the basic physiology and biochemistry of plant growth, the significance of the C4 pathway in tropical plants, genetic engineering, embryo transfer in animals, remote sensing photography, the ecology of the world's grasslands. The pressing problems of rangeland degeneration, and social and economic change in human societies, are also better understood.

The immediate problem and the task of this paper is to descend to a lower practical level of what has been learned about the possibilities of increasing pasture and forage production, and of utilising feed grown in the most efficient manner.

Approximately one half of the sheep and three quarters of the goats in developing countries are within the tropics, the remainder being in a band from North Africa through the Near East to China. It is useful to have some classification of climatic zones governing plant growth, and for the tropics it is given below:

¹ From Unesco (1979)

² From Jahnke (1982) for Africa

A feature of research and development work in the tropics, with the exception of the arid zone, is that cattle rather than sheep and goats have been used, so that in the absence of good data on small ruminants one has unfortunately to interpret from cattle data. It is proposed to discuss briefly the recent pasture utilisation studies with sheep in the temperate zone and then move to the arid and semi-arid pastoral zones, followed by the cropping/livestock situation in the semi-arid and subhumid zones and finally to the subhumid and humid zones.

4 RD, Christchurch, New Zealand.

PASTURE UTILISATION IN THE TEMPERATE ZONE

Research activities, and the methods derived therefrom, for increasing ruminant production in developed countries follow fairly standarised lines - breeding and selection for improved cultivars, determination of plant nutrient (fertiliser) requirements, determination of animal feed requirements, grazing management studies aimed at integrating pasture growth and animal requirements with maximum efficiency on a year round basis. In the temperate zone under favourable conditions grass-legume pastures are capable of yielding 10–20t DM/ha/ annum on cultivatable land and 5–10t DM/ha/annum on hill land oversown with clovers especially (Trifolium repens).

While these studies have progressed on a broad front, in recent years special attention has been devoted to the most difficult and complex area - the efficient use of pasture under-grazing (Morley, 1981; Parsons et al., 1983). Techniques have been developed for measuring herbage mass, ratio of green to dead leaf, net DM growth of green material under various grazing pressures, the intake of the grazing sheep (or goat) at various levels of pasture availability, the pasture availability needed to promote given levels of production, and the residual pasture (DM/ha) at which production falls below critical levels. Concurrently research has determined the critical and non-critical nutritional periods in the annual cycle of the ewe, and the extent to which the resilience of the ewe to gain and lose body fat may be used to buffer seasonal peaks and troughs of pasture growth (Coop, 1982; Milligan, 1983).

Finally to put this into practice requires control of pasture growth and control or rationing of intake of the grazing sheep. This can only be achieved by adequate subdivision with fencing. This has been greatly facilitated by the development of electric fencing and in really intensive systems by the additional use of cheap portable electric fencing. Such fencing is also used for strip grazing of forage crops, in order to get maximum utilization of the forage.

The efficient conversion of pasture to animal production is a highly complex matter because of the interactions between the grazing animal and the pasture, interactions which vary with season. At low stocking rates percentage utilisation is low and continuous grazing is as good as, or better than, rotational grazing. However to obtain high animal production per hectare intensive grazing at high stocking rates is required in order to give a high percentage utilisation. In this case rotational grazing is superior. In practice compromises become necessary because pasture growth is seasonal, there are periods when utilisation is sacrificed in the interests of achieving high individual animal growth rates and others, such as in winter, when utilisation is much more important than liveweight gain.

The efficiency of utilisation of native pasture in extensive grazing systems running less than 2 sheep/ha is estimated in recent research to be below 30%. When such pasture is improved by oversowing, fertilisation and fencing, utilisation can be increased to 60–70%. On really intensively grazed cultivated pastures efficiencies of 70–85% are possible on a year-round basis. Some appreciation of intensive grazing and utilisation may be gauged from the current practice of wintering pregnant ewes in New Zealand, where the ewes are rotated, at a density of 1000 ewes per hectare, on a daily shift behind electric fences.

In the Northern Hemisphere where winters are colder, greater reliance on hay and silage is made for winter feed. It is estimated that the percentage utilisation of metabolisable energy (ME) of the original pasture, when consumed as hay, is below 50%. For this, and for reasons of cost, the Southern Hemisphere grazing countries place emphasis on utilisation of pasture by the grazing animal with minimal use of conserved fodder.

Advances in grazing management and utilisation have nevertheless been made in northern countries. One example of this is the “two pasture” system developed for the wet cold hill country of Britain, whereby a smaller area of improved pasture is integrated with the larger area of unimproved hill land and utilised at strategic points in the annual cycle of the ewes. Another is the “three pasture” system aimed at minimising worm parasite problems. Finally in all the major grazing countries there is increasing evidence that cattle, sheep and goats can all be beneficial to one another, the special grazing characteristics of each being complimentary to the other. With coats this is seen especially in their preferences for weeds and pasture species not relished by sheep.

If proof is needed that modern pasture/sheep technology can lead to increased animal production the case of New Zealand may be quoted, where from approximately the same area of grazing land, sheep numbers have increased from 33 millions in 1950 to 53 millions in 1965, to 70 millions in 1982 with proportionate increases in meat and wool output. While only some of this temperate zone technology is immediately transferrable to developing countries, the objectives and the principles certainly are.

ARID AND SEMI-ARID ZONE RANGELANDS

The extensive rangelands of the arid and semi-arid zones of developing countries and the peoples they support are in varying degrees of crisis as a result of rangeland degradation, brought about by overstocking. The area is traditionally used solely by pastoralists under nomadic and transhumant systems, but the pressure of human population has led to the incursion of agriculturalists with their livestock into marginal areas, so putting an unbearable pressure on the rangeland vegetation.

Much has been written about the current state of rangeland vegetation, the social and economic impediments as well as the technical difficulties in reversing the deterioration (e.g. Unesco, 1979; Jahnke, 1982; Harrington, 1982 and Malechek, 1982). While there are cases or instances of potential improvements or improvements actually made, the concensus of opinion of authors is that the only solution short and midterm is to reduce grazing pressure. It is recommended that this be achieved by destocking, or by deferred grazing or some other form of grazing management which would permit a more even grazing and reduce severe overgrazing on critical areas. A recent FAO review (FAO 1984) commented that there is need for rehabilitation by the introduction of good management, that forage cultivation is not yet generally accepted and conservation of hay and silage rarely practised. There is a need to introduce forage trees and browze shrubs, but there was little likelihood of increasing forage availability in the near future due to pressure of livestock combined with the persistence of drought.

The productivity of the arid and semi-arid zone rangelands is low. Jahnke (1982), quoting other authorities, gives a figure of 2.5kg DM/ha/annum per mm rainfall, or It DM/ha/annum at 400 mm which is likely to be inefficiently utilised. Such yields cannot hope to generate enough income to provide incentive to introduce improved species even if this were technologically feasible.

While acceptance by the inhabitants and by Governments that reduction in grazing pressure is the only short term solution, one must not be entirely negative. Observation and development project results indicate that there are avenues for improvement and some specific examples of these are listed below.

1. Grain yields and sheep production were twice as great in South Australia through replacing fallow with subterranean clover and medic pasture, compared with Algeria having a similar Mediterranean climate but not integrating crop and sheep grazing (Allden, 1982, quoting Carter).

2. In the Drought Prone Areas Programme in Western India the introduction of Cenchrus ciliaris and Lasiurus sindicus increased DM yield from 0.4 t to 3t/ha/annum (Jain, 1983).

3. Depleted rangeland in China has been shown to be capable of yielding 3t DM/ha/annum by oversowing with milk vetch and fertiliser (Chinzagco project, pers. comm). In another site having 300 mm rainfall, all in summer, the yields of native grassland have been doubled with fertiliser alone, while in cultivated areas the use of newer cultivars of sorghums, maize, and annual grasses for silage, and native grass for hay has also doubled the number of stock carried as well as improving them greatly (FAO 1983).

4. The Syrian Arab Republic Rangeland Conservation and Development Project is one of the best known, reviving the ancient “Hema” system of grazing control, introducing Atriplex spp. planting fodder trees and creating lamb fattening cooperatives (Draz 1978).

5. The wide ranging development project in Morocco where Agropyron elongatum has been introduced into a Stipa-Artemisia ecosystem in a 300 mm rainfall area (El Gharbaoui, 1984).

6. The introduction of Atriplex and Kochia spp. in Saudia Arabia (Hassan 1984),

7. The legumes Stylosanthes humilis and to a lesser degree S. guyanensis have been shown to be capable of being oversown or direct drilled on sites in the semi-arid zone.

There are also arid or semi-arid rangelands in the temperate zone (U.S.A., South America, South Africa, Australia) which have also degenerated under overstocking during the last 100 years and it is significant that in all of these stock numbers have declined. The most intensively studied are those in the U.S.A. and in a recent review of rangeland management and reseeding results, it is commented that “a considerable portion of western rangelands currently support vegetation assemblages greatly below their potential” (Herbel, 1984; Young et. a!., 1984). Wilson, A.D. (1982) in another review concludes that “there are no technological improvements in the pipeline that will lead to major productivity gains. The basic restrictions of sparse vegetation, low rainfall and a harsh climate are not subject to technological innovation”. Nevertheless there are instances that in all of these countries improvements are technically possible. To take but one example, Stevens and Villalta (1983) at high altitudes in Peru were able to establish ryegrass-clover pastures and to direct-seed lucerne into rangeland with large increases in sheep numbers carried.

The problem is that research and development projects in both developed and developing countries on which the possibilities if improvement have been shown, have high inputs of technical and economic aid. Whether they can survive in a straight commercial sense and whether it is economic to attempt to increase production is highly dubious. In the more favourable sites it may be so, but for most of it, the problem is to halt further deterioration. The poor income-generating power of the extensive rangelands dictates that any improvements must be ecologically sound and low cost, and should act in a catalytic role to permit better utilisation of the much larger area of unimproved land.

Research priorities suggested should include grazing management studies to provide more even grazing pressure, forage conservation, selection of species and cultivars extending growth into the dry period, integration with cropping systems. (Unesco, 1979; Malechek, 1982; Butterworth et.al,1984).

CROP - LIVESTOCK INTEGRATION

Crop production is an occupation of agriculturalists living in villages mostly in the semi-arid and subhumid zones. Traditionally some nomads have included the grazing of crop stubbles in their annual movement, while transhumant pastoralists have also made use of stubbles and crop residues during the dry period. The increasing sedentarisation or semi-sedentarisation of nomads and transhumants, together with movement of agriculturalists with their own livestock in the opposite direction into drier areas, is reducing the areas available for grazing and also increasing the risks of crop failure. The integration of cropping with sheep and goats is primarily in the semi-arid zone but extends into the subhumid zone. Although the cropping regime yields more DM/ha in the form of stubbles, straws and byproducts available for stock the increases in stock numbers more than offsets this. Nevertheless cropping systems and the more intensive and settled human existence in villages or permanent abodes, offers an environment much more amenable to technological change and improvement than does the rangeland. The following research developments in recent years are some of the more promising.

1. The breeding of improved cultivars of human feed crops - wheat, maize, sorghum, groundnuts etc. and research on fertiliser responses, together with an appreciation that in subsistence agriculture, fertilizer put on crops increases yield sufficiently to release land for planting in animal forage crops.

2. Research and demonstration has shown that forage production can be expanded considerably by inter-row sowing of legumes with the cereal, using improved cultivars of forage species, and especially replacing the traditional fallow with sown perennial or annual forage crops. Legumes such as Stylosanthes and vetches, and other tropical legumes in higher rainfall areas, are much preferred since their nitrogen level and nutritive value are high and they increase soil nitrogen for the next cereal crop. High yields have been obtained in Cyprus from barley and barley/vetch forage made into hay (Osman and Nersoyan, 1984; Unesco, 1979; FAO, 1983). If a move to greater use of forage crops and more efficient use of grazing stubbles is to be made then control of the sheep and goats becomes important. Attempts should therefore be made to gain acceptance of the electric fence by herders and cultivators.

3. Intensive fattening of lambs and kids, on locally grown roughage plus concentrates and byproducts, has a double advantage of controlled marketing with a superior product and more importantly of removing young animals to be fattened from the overgrazed rangeland, thereby reducing the grazing pressure. Lamb fattening trials have been reported from several countries showing typically that weaned lambs make gains of 100 – 250 g/day with feed conversion ratios of 6 to 10 according to the energy content of the diet. There is a need to examine what effect this has on the total system.

4. Some arid and semi-arid areas have water available for irrigation, which is used mainly for cereal or cash crops (cotton) but some is available for forage. Water from the Nile is used in Egypt and Sudan, underground water in Libya and Saudi Arabia. Extremely high yields of lucerne (Medicago sativa ) and Egyptian clover (Trifolium alexandrinum) are obtained and provide a high protein source for cattle, sheep and goats.

5. Improving the utilisation of low quality roughages is also possible. Low protein levels characteristic of tropical forages during the long dry period are a limiting factor in animal intake and performance. (Minson, 1982). A considerable amount of research work has been done over the last 20 – 25 years on the use of urea to improve the voluntary intake of straws and other low quality roughages by cattle, sheep and goats. Trials conducted in pens have almost universally given good results but selective grazing by animals in the field has caused some doubts about its application in a grazing context (Coombe 1981). A more recent discovery is that alkali or ammonia treatment of straw can increase digestibility by 10–15units, e.g. from 45% to 55–60%. Encouraging results are being obtained from the technique at both the village level (Dolberg et.al., 1981), and the factory level (Creek et.al., 1984).

A much better understanding of protein requirements of sheep and goats has been developed during the last decade, with recognition of the significance of rumen nondegradable protein. This is of special importance in the tropics (Lindsay, 1984).

The outlook then for improvements in pasture and crop production, and of utilisation by sheep and goats in the cropping areas is reasonably encouraging. Whether it can keep pace with the increases in human population is another matter. Fortunately much of the research done in developed countries is less sensitive to environment in a cropping activity than in a grazing activity, and is therefore more likely to find application in the cropping scene. The most important fields of research in the cropping areas as far as sheep and goats are concerned are likely to be further integration of pastoral ism with cropping, conservation and forage production for the dry period, and improvements in the utilisation of straws.

Somewhat similar problems exist in the semi-arid/cold regions of the world such as in the arc from Turkey to China. Here the winter replaces the dry period of the tropics. In the USSR and Northern China for example, many pastoralists have been semi-or wholly sedenterised, and winter bases exist in villages or have been especially constructed. The growing of forage, partly for grazing but mostly for conservation as hay and silage, is a dominant feature of the system (Demiruren, 1982).

SUBHUMID AND HUMID ZONES

Though the line of demarkation between the semi-arid and subhumid zones is diffuse, there is a distinct trend towards tree crop agriculture as well as cropping, towards tall-grass pasture species and a greater density of villages, especially where associated with rice culture. This is accompanied by a shift in the relative importance of large and small ruminants. Whereas in developing countries sheep and goats outnumber cattle by nearly 2 : 1 in the arid and semi-arid zones, cattle outnumber sheep and goats in the subhumid and humid zones. As far as sheep and goats are concerned there are no longer any pastoralists and nearly all the animals are associated with village and cropping agriculture.

Tropical Pasture Development

Present native pastures consisting of Hyperrhenia, Andropogon, Themeda and many other species exist in a savanna landscape derived from forest or woodland. Soils are heavily leached, grazing is primarily with cattle and fire plays an important part in the grass, scrub, tree balance. The most important development in this area in the last few decades has undoubtedly been the selection, breeding and cultivation of improved cultivars of tropical grasses and legumes. The legume is particularly important because of the low nitrogen status of tropical soils. Though this work has been carried out in several tropical environments the driving force has been the CSIRO Division of Tropical Pastures in Queensland, Australia (Mannetje, 1982; Minson, 1982). Now there are established cattle ranches and cattle projects in most tropical countries with rainfall in excess of 800–1000 mm.

Unfortunately, in relation to sheep and goats, the basic grazing experiments and present projects are almost wholly involved with cattle. There are good reasons for this cattle dominance, but not for the exclusion of small ruminants. Very high yields of pasture DM are attainable - up to 30 – 40t/ha/annum but control of pasture growth, maintenance of the grass-legume balance, and ingress of weeds do present greater problems than with temperate pastures (Mannetje, 1982). Nevertheless the potential of these tropical pasture species for small ruminants with or without cattle should be explored. Some trials using sheep and goats have been recorded (Boulton and Norton, 1982; Potts and Humphreys, 1983; Susetyo et.al. 1983) but not yet on a farm scale. Some of the improved species, especially legumes such as Stylosanthes humilis and S. guyanensis, Macroptilium, Desmodium spp are also finding use as forages for establishment on fallows which are grazed by sheep and goats in both semi- and subhumid zones.

Sheep and Goats in the Village

The place of sheep and goats in the village is much the same as described for the arid and semi-arid zones. The scope for increases in numbers and production especially of goats has been emphasised (Devendra, 1980; Roy-Smith, 1982; Zulkifli et.al., 1980; Wilson, R. T. 1982), involving greater utilisation of the considerable byproducts available from cereal and tree crop production, the introduction of improved grass and legume species in available land and recognition of the part which the milking goat rather than the cow could play. The opportunity to exploit the production of tropical grasses and legumes is facilitated by the fact that many sheep and goats, especially in the humid zone, are fed under a cut and carry system, or are let out during the day time on a controlled grazing system. There is no doubt that small ruminant production in this zone could be increased and there are good reasons why it should. Most of the arguments about the relative merits of cattle, sheep and goats are based on personal factors, and on calculations of what ought to be, and there is a need for comparisons to be made on a strictly scientific basis. It is encouraging that recognition of animal production potential in the humid tropics is evidenced by the creation of the joint Australian/Indonesian Centre for animal research and development in Ciawi, Indonesia in 1975.

Utilisation of Pasture in Plantations

In the humid tropics there are large areas of tree crops such as coconut, rubber and oil palm. They are established in association with a tropical legume cover crop which in time regresses to grasses and weeds. Except in coconut plantations often grazed by cattle the herbage available is generally not used at all. Attention has been given by the Rubber Research Institute of Malaysia (Tan and Abraham, 1980) to using sheep to consume this herbage and to reduce the high cost of weed control. Promising results are being achieved, confirming that a considerable potential exists for the utilisation of this large feed resource.

Forage Trees and Tree Byproducts

The utilisation of edible trees and shrubs, and of tree byproducts such as leaves, pods and seeds has received considerable attention in recent years. The characteristics and feed values of tree crops have been reviewed recently by Hutagalung (1981). Particular attention has been given to leguminous trees-such as Leucaena, Gliricidia, Tagasaste spp. since the leaves of leguminous trees, and especially L. Leucocephala, have protein levels in excess of 20%. Recent evidence (Bamualim et.al., 1984) shows that the protein is a good by-pass protein, capable of enhancing intake of low quality roughages where these form the main diet. Acacia spp prevalent in many parts of the tropics can also be valuable in droughts (Snook, 1984).

Leguminous trees and edible shrubs are not confined to the subhumid and humid zones, but can contribute also in the semi-arid zone, and are likely to be utilised much more than in the past.

CONCLUSION

There is considerable scientific evidence that both pasture and animal production can be increased substantially in all except the arid zone. The major problems are lack of capital to implement improvement and uncertainty about its viability, economically. The greatest and quickest responses in pasture and forage production are likely to be in the subhumid zone, and also in cropping systems.

To maintain impetus in research it is suggested that priority be given to:

1. breeding and selection of pasture species for the semi-arid zone aimed at increasing the length of the growing period. Selection of low phosphate demanding legumes for this zone.

2. studies of the utilisation of tropical pastures by sheep and goats.

3. pasture conservation for the dry period, forage production on cropping land.

4. studies to increase the complementarity (or integration) of rangeland and cropping land.

5. continuation of studies aimed at improving the utilisation of low quality roughages by sheep and goats.

REFERENCES

Allden, W. G. 1982. In Nutritional Limits to Animal Production from Pastures. (Ed. J. 0. Hacker), pp. 45–65. Comm. Agr. Bur.

Bamualim, A., Weston, R. H., Hogan, J. P. and Murray, R. M., 1984. Anim. Prod. in Australia, 15: 255–258.

Boulton, P. and Norton, B. W.,1982. Anim., Prod, in Australia, 14:641.

Butterworth, M. H., Lambourne, L. J. and Anderson, K., 1984. Proc. 2nd Int. Rangeland Congr., Adelaide. (In Press).

Coombe, J. B.,1981. In Grazing Animals (Ed. F. W. H. Morley), pp. 319–332, Elsevier, Amsterdam.

Coop, I. E., 1982. In Sheep and Goat Production (Ed. T. E. Coop), pp. 351–375, Elsevier, Amsterdam.

Creek, M. J., Barker, J. J. and Hargus, W. A., 1984. World Anim. Rev., 15: 12.

Demiruren, A.,1982. In Sheep and Goat Production (Ed. I. E. Coop), pp. 425–440, Elsevier, Amsterdam.

Devendra, C, 1980. J. Anim. Sci., 51:461–473.

Dolberg, F., Saadullah, M., Haque, M. and Ahmed, R., 1981. World Anim. Rev., 38: 37–41.

Draz, 0., 1978. Proc. 1st Int. Rangeland Congr., Denver, Colorado, U.S.A.

El Gharbaoui, 1984. Proc. 2nd Int. Rangeland Congr., Adelaide. (In Press).

FAO, 1983. Pilot Demonstration Centre for Intensive Pasture, Fodder and Livestock Production. Peoples Republic of China. FAO - CPR/79/001.

FAO, 1984. World Anim. Rev. 51: 2–11.

Harrington, G. N., 1982. In Grazing Animals (Ed. F. W. H. Morley), pp. 181–202, Elsevier, Amsterdam.

Hassan, A. A.,1984. Proc. 2nd Int. Rangeland Congr., Adelaide.(In Press).

Herbel, C. A., 1984. In Developing Strategies for Rangeland Management. pp. 1167–1178, NRC/Nat. Acad. Sci., Westview Press.

Hutagalung, R. I., 1981. In Intensive Animal Production in Developing Countries ( Ed. A. J. Smith and R. G. Gunn) pp. 151–184.

Jahnke, H. E., 1982. Livestock Production Systems and Livestock Development in Tropical Africa Kieler W. b. V. Vauk. 253 pp.

Jain, H. K., 1983. Proc. XIV Int. Grassl. Congr., p. 440.

Lindsay, J. A.,1984. Anim. Prod, in Australia, 15:114–117.

Malechek, J. C, 1982. Proc. 3rd Int. Conf. on Goat Prod. and Disease, pp. 404–408.

Mannetje, L. 't., 1982. Nutritioanl Limits to Animal Production from Pastures. (Ed. J. B. Hacker), pp. 67–85. Comm. Agr. Bur.

Milligan, K. G., 1983. Controlled Grazing Systems. Aglink FPP 681, N.Z. Min. Agr., Fish., Wellington.

Minson, D. J., 1982. In Grazing Animals (Ed. F. W. H. Morley), pp. 143–158, Elsevier, Amsterdam.

Morley, F. H. W.,1981. In Grazing Animals (Ed. F. W. H. Morley), pp. 379–400. Elsevier, Amsterdam.

Osman, A. E. and Nersoyan, N., 1984. Proc. 2nd Int Grassl. Congr., Adelaide. (In Press).

Parsons, A. J., Leafe, E. L., Collett, B., Penning, P. D. and Lewis, J., 1983. J. Appl. Ecology, 20: 127–139.

Potts, A. and Hymphreys, L. R., 1983. J. Agr. Sci, 101: 1–7.

Roy-Smith, F., 1982. In Intensive Animal Production in Developing Countries (Ed. A. J. Smith and R. G. Gunn), pp. 387–394. Brit. Soc. Anim. Prod. Pub. No. 4.

Snook, L. C, 1984. Anim. Prod, in Australia, 15:589–592.

Stevens, E. J. and Villalta, P., 1983. Proc. 14th Int. Grassl. Congr., p. 176.

Susetyo, S., Whiteman, P. C. and Humphreys, L. R., 1983. Proc. XIV Int. Grassl. Cong r., p. 412.

Tan, K. H. and Abraham, P. D., 1980. Proc. 1st Asian Australasian Anim. Sci. Congr., Malaysian Soc. Anim. Prod.

Unesco/UNEP/FAO, 1979. Tropical Grazing Land Ecosystems - a State of Knowledge Report. Unesco, Paris. 655 pp.

Wilson, A. D., 1982. In Sheep and Goat Production (Ed. I. E. Coop), pp. 309–330. Elsevier, Amsterdam

Wilson, R. T., 1982. Proc. 3rd Int. Conf. on Goat Prod, and Disease, pp. 186–195.

Young, J. A., Evans, R. A. and Eckert, Jnr. R. E., 1984. In Developing Strategies for Rangeland Management, pp. 1259–1300. NRC/Nat. Acad. Sci., Westview Press.

Zuikifli, S. D., Zulficar and Rachmat Setiadi, 1980. Proc. 2nd Ruminant Seminar, Ciawi, Indonesia. pp. 42–54.