J. I . Restrepo and T. R . PrestonConvenio Interinstitucional para la Produccion Pecuaria en el Valle del Rio Causa
Apartado Aéreo 7482
Cali
Columbia
A first priority in any production programme for goats in the humid tropics is parasite control. Avoidance of reinfestation is more cost effective and biologically sustainable than use of anthelmintics. The features of this strategy are: complete confinement; uncontaminated forages; dry lying (slatted floors or non-edible litter that is changed frequently); and use of locally available feed resources according to the principles of balanced nutrients both for the rumen and for the animal.
Le contrôle du parasitisme est une des premières priorités dans tout programme caprin en zone tropicale humide. Les techniques permettant d'éviter la réinfestation des animaux sont moins coûteuses et biologiquement plus pérennes que l'utilisation des anthelmintiques. Ces techniques comprennent claustration complète, distribution de fourrages non contaminés, aire de couchage sèche (caillebotis ou litière non-consommable changée fréquemment) et utilisation de fourrages disponibles localement en respectant les équilibres alimentaires nécessaires aux micro-organismes du rumen et à l'animal.
Contrary to popular belief, goats are not more resistant to tropical climates than other species, do not subsist on a waste paper diet, and are not the dairy cow equivalent for resource-poor farmers. A principal characteristic of the goat is its dietary selectivity which has enabled it to survive in apparently harsh environments.
The major proportion of the world's goat population is found in the most arid regions of the tropics which shows not only the idiosyncrasies of the farmers in these so-called "difficult" regions, but also the influence of the environment which is favourable to goat rearing.
The high rainfall zones of the tropics present a contrast to the goat's preferred climatic and ecological environment. It is not, therefore, surprising that there is a high incidence of failures when enthusiastic farmers, government institutions and international bodies attempt to raise goats in such regions. A working hypothesis is that the principal biological factors which limit goat production in the humid tropics are (in order of importance): parasites of the digestive tract and of the lungs; nutrition; and other diseases.
General characteristics
Parasites are the major constraint to goat production in the humid tropics. In the Koboboya Goat Scheme in Fiji, 50% of the goat population (600 goats) died in the first 3 mo of the project during an outbreak of haemonchosis. In Columbia, there have been cases where all goats have died from parasite infestation. Parasitism is the major technical problem facing goat production in Fiji (Walkden-Brown, 1984), In the Solomon Islands, where the principal species are Haemonchus, Trichostrongylus, Ostertagia, Oesophagostomum and Moniezia, "worms are a major problem in intensive pasture-fed goats" (Simpson, 1984). In the Australian goat industry it is also believed that parasites are the most important cause of loss "while climate and high stocking rates are more important predisposing factors in goats than sheep, goats having a basic inability to resist gastro-intestinal parasites" (Baxendell, 1984).
Parasitism and management
The issues to be considered are that anthelmintic treatment is neither a satisfactory nor a sustainable solution and that there is a need to provide feed which is not contaminated by worm eggs, thus enabling the natural life cycle of the parasites to be broken.
The management systems tested comprised: tethering; housing at night following rotational grazing during the day; semi-confinement with uncontrolled grazing during the day; full confinement with feed derived from parasite-contaminated forages; and full confinement with parasite-free forages.
Tethering is not recommended because of the risk of strangling. The animal is essentially a prisoner and at the mercy of predators; and feeding is inefficient, being limited to a small area with little or no chance for selection. Free grazing, as a complement to semi-confinement, is not a popular system due to the risk of causing damage to neighbouring farms. Rotational grazing requires high investment in fencing and, if the pasture has a significant weed component, the weed percentage initially declines as palatable species are removed but unpalatable species subsequently increase (Simpson, 1984). An example of the limitations of rotational grazing systems is that when parasite-free forage was offered ad libitum, goats ceased grazing completely and took all their feed requirements from the cut forage.
It is important to consider the relationship between feeding system and parasitism. The only management system which guaranteed complete parasite control was full confinement complemented with the feeding of parasite-free forage. It is obviously desirable to control parasitism by management designed to prevent reinfestation than to use anthelmintics. In addition to the cost of such drugs, there are indications that they are partially metabolised by gut micro-organisms (R A Leng, pers. comm.).
The concept of parasite free forages
When cut forages are the basis of the feeding system, it is advantageous to ensure they are free of parasite eggs. This is especially important on the small farm where there is only 1 animal species and where recycled excrete is the main source of fertilizer.
Very high levels of parasitism have been found in fully confined goats which were being fed on elephant grass (Pennisetum purpureum) repeatedly cut on a short period basis and manured with fresh dung and urine. Reinfestation occurred repeatedly despite frequent use of anthelmintics. Sugar cane has been proposed as the best option in the tropics to provide the fermentable carbohydrate needed by ruminants. Because the optimum harvest interval is between 12 mo and 18 mo, both from the agronomic (Alexander, 1985) and nutritional standpoints (Alvarez and Preston, 1976), it is feasible to apply large quantities of goat excrement as fertiliser without the risk of contaminating the foliage as occurs when the optimum harvest interval is shorter. In an experiment where elephant grass and cane were compared in a simultaneous evaluation of different anthelmintics the goats fed sugarcane had no worm eggs in the faeces while goats fed elephant grass were severely infested.
Other strategies to reduce parasite reinfestation
The use of effluent from biodigestors with detention times longer than 30 d is another strategy which can be employed to break the reinfestation cycle of parasites, as it is possible that digestion of faecal organic matter by earth worms reduces the risk of parasite infestation. Earth worms are important as sources of high biological value protein in integrated farming systems which are considered to be appropriate vehicles for small ruminants.
Fibrous agricultural by-products and residues (cotton seed husks and rice straw) are other examples of basal feed resources which have a special value for goats because they are unlikely to be infested with parasites.
Recommendations for parasite management
High levels of performance can be obtained with goats when the management is such (slatted flood and parasite-free forages) that it minimizes parasite infestation. The aim should not be to develop "aseptic" conditions in which the animal is parasite-free but to develop management and feeding systems in which contamination is sporadic and at a relatively low level.
Parasite-free forage is the best way of reducing ingestion of infective organisms but should be coupled with a suitable type of housing. Feed troughs should be raised and fitted with an elevated step so as to force the animals to adopt a "browsing" position, helping to reduce the proportion of feed which falls onto the litter (thus cutting down waste) and also reducing the risk of further parasite infestation.
Pre-weaning nutrition
Research on rearing systems has so far been at the extremes of natural suckling by the mother and artificial rearing in isolated boxes. Few attempts appear to have been made to build on the experience of the resource-poor farmer. Such farmers generally adopt a partial suckling technique which produces some milk for family consumption without severely compromising the growth of the offspring.
An experiment in Columbia was set up to test the benefits of partial suckling. A control treatment, in which the kids were suckled for 20 min twice a day, was compared with a system of restricted suckling following hand milking in the morning and suckling without milking in the afternoon. Kids reared by restricted suckling were lighter at 150 d, mainly because of poor growth during the first 6 wk. Gains from 44 d onwards slightly favoured the restricted suckling group, indicating a compensatory response once the kids could take advantage of the freely available supplementary feeds. It is likely that, provided adequate supplementary feed is available, up to 250 ml milk/doe/d can be taken for human consumption without detriment to the final weight of the offspring.
Post-weaning nutrition
The principles followed, based on the "balanced nutrients" theory (Preston and Leng, 1986), have been used to develop feeding systems which have supported expected levels of productivity but with significant cost reductions and increased self-reliance.
Feeding the rumen provides readily fermentable sources of carbohydrates and nitrogen, complemented with micronutrients. Selection of the carbohydrate source should be governed by availability, price and degree of parasite contamination. Fermentable nitrogen (urea) and micronutrients are freely available as multinutritional blocks and from tree foliages which also supply some by-pass protein.
Nutrients not supplied as end-products of microbial digestion ("rumen" feeding) can be supplied by by-pass protein and long-chain fatty acids ("animal" feeding). The main supplement in this category is rice polishings which are rich in lipids, starch and protein. Most of these nutrients are in a form which allows them to avoid most of the rumen fermentation process (Elliott et al, 1978a; 1978b) and additional by-pass protein can be provided by tree foliages.
It is recommended that the basal diet (fermentable carbohydrates), multinutritional blocks and tree foliages are provided on a free choice basis and if possible in separate feeders. The rice polishings (cottonseed meal being an effective substitute) should be rationed at levels between 0.4% (growth and pregnancy) and 0.6% (lactation) of animal live weight.
Alexander A G. 1985. The energy cane alternative. Elsevier Science Publishers, Amsterdam, The Netherlands.
Alvarez F J and Preston T R. 1976. Performance of fattening cattle on immature or mature sugarcane. Tropical Animal Production 1: 106-111.
Baxendell S A. 1984. Diseases of goats. In: J W Copland (ed.), Goat production and research in the tropics. Proceedings Series No. 7. Australian Centre for International Agricultural Research, Canberra, Australia.
Elliott R. Ferreiro H M, Priego A and Preston T R. 1978a. Rice polishings as a supplement in sugar cane diets: the quantities of starch (glucose polymers) entering the proximal duodenum. Tropical Animal Production 3: 3035.
Elliott R. Ferreiro H M, Priego A and Preston T R. 1978b. Estimate of the quantity of feed protein escaping degradation in the rumen of steers fed chopped sugarcane and molasses/urea supplemented with varying quantities of rice polishings. Tropical Animal Production 3: 36-39.
Preston T R and Leng R A. 1986. Matching livestock production systems with available resources in tropical countries. Technical Centre for Agricultural and Rural Cooperation, Wageningen, The Netherlands.
Simpson G. 1984. Goats in the Solomon Islands. In: J W Copland (ed.), Goat production and research in the tropics. Proceedings Series No. 7. Australian Centre for International Agricultural Research, Canberra, Australia.
Walkden-Brown S W. 1984. Goat production and research in Fiji. In: J W Copland (ed.), Goat production and research in the tropics. Proceedings Series No. 7. Australian Centre for International Agricultural Research, Canberra, Australia.
