R. ShavulimoRegional Veterinary Laboratory
P.O. Box 450
Eldoret
Kenya
Summary
Resume
Introduction
Farm health monitoring
Resistance of goat breeds to haemonchosis
Discussion
References
An 8 mo study was carried out on-farm in Kenya on dual purpose (meat and milk) goats to assess the rate of worm reinfestation. Differential monthly egg counts indicated high concentrations of strongyles (460 epg) and strongyloides but low concentrations of tapeworms. Percentage composition of nematodes assessed by faecal culture was: Haemonchus, 51; Trychostrongylus, 40; Oesophagostomum, 8; and Strongyloides, 1. To compare the susceptibility of goat breeds to haemonchosis and to seek indications of genetic resistance, an experiment was conducted on 12 Small East African (SEA), 9 Galla and 13 Toggenburg x SEA goats. All animals were given a heavy dose of infective larvae. Mortality rates were 67% for Galla, 46% for Toggenburg x SEA and 25% for SEA goats. Deaths occurred earlier in Galla than in the other 2 breeds. SEA goats were able to survive a heavy worm infestation. No significant difference was seen in weight change, heamatocrit or faecal egg count in surviving infected animals.
Une étude portant sur une durée de 8 mois a permis d'évaluer le taux de réinfestation de troupeaux caprins mixtes (lait et viande) au Kenya. Les comptages mensuels d'oeufs montrent de fortes concentrations de strongyles (460 OPG) et strongyloides mais de faibles concentrations en cestodes. La structure de la population de nématodes établie par coproculture est la suivante: Haemonchus, 51; Trychostrongylus, 40; Oesophagostomum, 8; et Strongyloides, 1. Une expérimentation fut conduite sur 12 petites Chèvres d'Afrique de l'Est (CAE) et 13 Toggenburg x CAE pour tester la résistance des races caprines à l'haemonchose et pour relever des indices de résistance génétique. Chaque animal a reçu une dose massive de larves infestantes. Les taux de mortalité furent de 67 p.cent pour les Galla, de 46 p.cent pour les croisées et de 25 p.cent pour les CAE. Les mortalité furent plus précoces chez les Gallas que chez les 2 autres races. La CEA est capable de résister à une forte infestation. Aucune différence significtive n'a été décelée dans la variation de poids, dans l'hématocrite ou dans l'OPG chez les animaux survivants.
The Kenya goat population is approximately 7.7 million compared to 5.0 million sheep and 9.0 million cattle. About half the goats are on smallholder farms in pastoral areas and in the highlands. There are about 6000 animals which can be classed as improved goats (Stotz, 1983). Increasing the efficiency of goat milk and meat production through crossbreeding exotic with native goats would result in higher incomes and increase the availability of animal protein, but health problems remain a constraint to the introduction of exotic breeds.
Gastrointestinal nematodes, especially Haemonchus contortus, have been recognised as a major constraint to small ruminant production in the tropics (Allonby and Urquhart, 1975). The loss to Kenya's agricultural sector due to haemonchosis in sheep has been estimated at about US $ 26 million (Preston and Allonby, 1979). It is known that some sheep, including the Red Masai in Kenya, are able to survive in Haemonchus endemic areas with little or no veterinary attention (Allonby and Urquhart, 1973; 1975; 1976; Allonby, 1974; Preston and Allonby, 1978; 1979). There is less information on goat resistance. Sheep and goats are often considered to share common susceptibility to many diseases but significant differences have been noted in resistance between the 2 species (O. B. Smith, pers. comm.). It has also been noted that most sheep helminths are infective to goats, which appear to be more susceptible than sheep to a similar challenge (Dunn, 1978).
To determine the strategies for reducing disease problems in goats, a 1 yr survey was carried out on smallholder farms (Abinanti, 1982). A herd health programme was introduced in 1983 to monitor problems in crossbred dual purpose goats introduced on some farms in the same region. The results reported here cover a period of 8 mot In addition to farm monitoring, an on-station experiment to evaluate genetic resistance to Haemonchus contortus infection in the SEA, the Galla (both indigenous to Kenya) and the Toggenburg x SEA cross goat was carried out.
The farm study was conducted in 4 clusters of farms in Siaya, Kakamega and Kisumu districts of western Kenya. All 4 sites have bimodal rainfall with means between 1000 mm and 1300 mm for the medium potential Siaya district and 1750 and 2100 mm for the higher potential Kakamega and Kisumu districts (Sands et al, 1982). Farm size ranged between 0.90 ha and 1.09 ha (de Boer et al, 1984). Most of the goats were 3/4 Toggenburg with 1/4 SEA, with a few halfbreds of the same breeds (Khainga et al, 1984). Mean goat population was 135 does and 30 bucks of different ages. Differential worm egg counts using the modified McMaster technique were done on 5 g faeces of each goat each month.
Mean egg counts were highest for strongyles (460 ± 53 epg, range 100-20000), lower for strongyloides (257 ± 28, 100-8000) and lowest for tapeworms (20 ± 28, 100-4900). Strongyle eggs were predominant throughout the study with a lowest monthly mean of 282 epg. Monthly means for strongyloides remained relatively low until October when there was a sudden rise to 668 epg (Figure 1). Differential larval counts carried out from faecal cultures showed Haemonchus to be the most important strongyloid species (Table 1).
The experiment was carried out at Maseno Research Station on 17 SEA, 13 Galla and 19 Toggenburg x SEA male goats, aged between 9 mo and 11 mo at the beginning of the experiment. The animals were kept in a parasite-free barn with a concrete floor for 3 mo, before infection with 500 larvae/kg body weight. They were treated every 3 wk with Oxyclozanite + Levamisole (Nilzan) at the rate of 0.5 gm/kg body weight to remove residual worms and prevent reinfection. They were fed Sorghum sudanense (Sudan grass), Ipomoea batatas (sweet potato vines) and Pennisetum purpureum (elephant grass) ad libitum. Twice each week 5 g faeces and 2 ml blood were collected for determination of epg and packed cell volume. Weights were recorded once each week. Worm counts were undertaken on all dead animals. Infective larvae were recovered from faecal cultures, identified to generic level and quantified for infecting experimental animals (Georgi, 1974; Soulby, 1982; Njanja, 1985).
Table 1. Differential endoparasitic larval counts (% of total infestation) at 4 sites in western Kenya.
|
Cluster |
Worm species |
|||
|
Haemonchus |
Trychostrongylus |
Oesophagostomum |
Strongyloides |
|
|
Siaya |
61.36 |
36.36 |
2.28 |
0.00 |
|
Kaimosi |
57.14 |
41.43 |
1.43 |
2.50 |
|
Hamisi |
41.25 |
36.25 |
20.00 |
0.66 |
|
Maseno |
42.76 |
46.05 |
10.53 |
0.66 |
|
Mean |
50.63 |
40.02 |
8.56 |
0.79 |
Fifteen infected animals died, of which 3 (all Galla) were in the acute phase and the rest in the chronic stage (> 6 wk post-infection). Mortality, analysed using the exact test for a 2 x 2 contingency table (Bailey, 1983), was 67% for Galla, 46% for Toggenburg x SEA and 25% for SEA goats. With the exception of 1 animal which had a low count of 103 adult Haemonchus contortus, all dead goats had worms ranging between 1120 and 3624. Only 2 Galla had a mixed infection with Oesophagostomum (Table 2).
The results of the farm monitoring exercise showed Haemonchus contortus to be the most abundant parasite. Throughout the study, goats were on a monthly drenching programme but there was a continuous reinfestation even during the dry season (Jul-Sep). Evidence from other studies (Obi, 1982; Abinanti, 1982; Carles et al, 1983; Njanja, 1985) shows that haemonchosis in goats leads to considerable losses which may amount to as much as those in sheep. Although egg counts of 460 epg for strongyles are not high, other studies have shown that even subclinical infestation (defined as levels of infestation which do not show apparent symptoms of disease) significantly affect productivity (Spedding et al, 1960). In a similar study to the present one (Njanja, 1985), SEA goats tended to have lower worm counts than the Galla and the Toggenburg x SEA. In the current study the SEA had a lower infestation rate, a lesser change in body weight and lower egg counts, compared to Galla and Toggenburg x SEA. The SEA is widely distributed all over the East African region and survives well in Haemonchus contortus endemic areas (Stotz, 1983). The Galla is more restricted in distribution and confined to semi-arid areas where Haemonchus challenge is relatively low. Little work has been done to demonstrate survival mechanisms in such areas but, as disease resistance is likely to be an important element in any development programme, large scale experiments should be undertaken to try and establish what such mechanisms are.
Table 2. Comparison of Kenya goat breeds for worm establishment rates, mortality rates, body weight changes and packed cell volume.
|
Parameter |
Breed |
|||
|
SEA |
Galla |
Toggenburg x SEA |
||
|
Larvae/kg weight |
6333 |
5417 |
5417 |
|
|
Establishment rate (% total) |
37 |
39 |
43 |
|
|
Mortality at 13 wk (% total) |
25 |
67 |
46 |
|
|
Weight (kg): |
|
|
|
|
|
wk 0
|
control |
11.7 |
10.7 |
11.5 |
|
infected |
12.7 |
10.8 |
11.9 |
|
|
difference (%) |
-8.5 |
- 0.9 |
-3.5 |
|
|
wk 13
|
control |
12.3 |
13.6 |
13.0 |
|
infected |
11.4 |
11.3 |
11.2 |
|
|
difference (%) |
-7.3 |
-17.6 |
-13.8 |
|
|
Packed cell volume (%): |
|
|
|
|
|
wk 13
|
control |
23.9 |
25.2 |
27.0 |
|
infected |
17.7 |
17.1 |
15.1 |
|
|
difference (%) |
-35.2 |
-32.2 |
-44.1 |
|
Abinanti F. 1982. Accomplishments of the animal health component in Kenya. Proceedings of the SR-CRSP Kenya workshop. Small Ruminant Collaborative Research Support Programme, Nairobi, Kenya.
Allonby E W. 1974. Ovine haemonchosis: Epidemiology, clinical signs and diagnosis. In: G M Urquhart and J Armour (eds.), Helminth diseases of cattle, sheep and horses in Europe. Robert Maclehose and Company, London, UK.
Allonby E W and Urquhart G M. 1973. Self-cure of Haemonchus contortus infections under field conditions. Parasitology 66: 43-53.
Allonby E W and Urquhart G M. 1975. The epidemiology and pathogenic significance of haemonchosis in a Merino flock in East Africa. Veterinary Parasitology 1: 129-143.
Allonby E W and Urquhart G M. 1976. A possible relationship between haemonchosis and haemoglobin polymorphism in Merino sheep in Kenya. Research in Veterinary Science 20: 212-214.
Bailey N T J. 1983. Statistical methods in biology (2nd edition). English Universities Press, London, UK.
Carles A B. Schwartz H J and Field C R. 1983. An interim report on some studies of productivity in two herds of Rendille goats and sheep. Proceedings of the 2nd SR-CRSP Kenya workshop. Small Ruminant Collaborative Research Support Programme, Nairobi, Kenya.
de Boer A J. Fitzhugh H A, Hart R D, Sands M W. Job M O and Chema S. 1984. Production of meat and milk from goats in mixed farming systems in the high potential tropics. In: J R Simpson and P Evangelou (eds.), Livestock development in sub-Saharan Africa: Constraints, prospects, policy. Westview Press, Boulder, USA.
Dunn A M. 1978. Veterinary helminthology (2nd edition). William Heinemann Medical Books, London, UK.
Georgi J R. 1974. Parasitology for veterinarians. W B Saunders and Co, Philadelphia, USA.
Khainga M S. Fitzhugh H A, Ochieng W O. Sidahmed A E, Brown D and Sands M W. 1984. SR-CRSP Kenya dual-purpose goats in western Kenya. History and record. Proceedings of the 3rd SR-CRSP workshop. Small Ruminant Collaborative Research Support Programme, Nairobi, Kenya.
Njanja J C. 1985. Control of naturally occurring nematode infections of goats in Kenya with ivermectin. M.Sc. Thesis. Washington State University, Pullman, USA.
Obi T U. 1982. Infectious diseases of goats in Nigeria: Impact on small ruminant production. Proceedings of the IIIrd International Conference on Goat Production and Disease 288.
Preston M and Allonby E W. 1978. The influence of breed on the susceptibility of goats to a single experimental infection with Haemonchus contortus in Kenya. Veterinary Record 103: 509-512.
Preston M and Allonby E W. 1979. The influence of breed on the susceptibility of sheep to Haemonchus contortus infection in Kenya. Research in Veterinary Science 26: 134-139.
Sands M W. Fitzhugh H A, Kekovole J and Gachuki P. 1982. Results of the small farm systems survey with implications for the potential for dual-purpose goats on small farms in Kenya. Proceedings of the SR-CRSP Kenya workshop. Small Ruminant Collaborative Research Support Programme, Nairobi, Kenya.
Soulsby E J L. 1982. Helminths, arthropods and protozoa of domesticated animals (7th edition). Baillière Tindall, London, UK.
Spedding C R W. Brown T H and Large R V. 1960. Internal parasites in grazing livestock. Proceedings of the 8th International Grassland Congress 718.
Stotz D. 1983. Production techniques and economics of smallholder livestock production systems. Farm Management Handbook of Kenya 4: 82-92.
