Health and productivity of traditionally managed Djallonke sheep and West African dwarf goats under high and moderate trypanosomosis risk

Trypanosome infections, packed red cell volume levels (PCV), body weight an d nematode faecal egg counts of village-based small ruminants were monitore d in two areas in The Gambia with either moderate or high trypanosomosis ri sk for 24 and 30 months respectively. Outflows from the flock and new-born animals were recorded and data on housing and management were compiled. Rep orted mortality rates were higher in goats than in sheep, but for both spec ies highest in the moderate risk area. The peak of trypanosome infections l agged the peak of tsetse densities by 1-3 months in both areas. Trypanosoma vivax was the predominant species found in the infected animals, followed by T. congolense. Trypanosome prevalence was, in general, higher in sheep t han in goats but only significantly higher during Year 1 in the moderate ri sk area. Trypanosome infection reduced the PCV level significantly and seas onal effects indicated significantly lower PCV levels during the rains. Try panosome infection si,significantly depressed weight gain in both species a t periods where infection rates were highest. In both species considerably lower weight gains were observed during the rainy season. Abortion rates we re higher in goats than in sheep in both study sites, and highest in the hi gh-risk site. Trypanosome infection in ewes in the high risk area increased lamb mortality significantly but had no effect on birth weights, nor on gr owth rates up to 4 months. Offspring mortality up to 4 months was generally high at both sites. Trypanosome infection in the dam between 3.5 to 7 mont hs post parturition significantly increased parturition interval in both sp ecies. Peak faecal egg output occurred at the end of the rainy season and w as highest for both species in the moderate risk site. Poor grazing managem ent was found responsible for a seasonal nutritional constraint. Based on t hese results, these breeds of sheep and goats can be considered as trypanot olerant since they are able to remain productive under high and moderate le vels of trypanosome challenge. Nevertheless, trypanosomosis affected their health and production level as shown by reduced PCV levels, depressed weigh t gains, longer parturition intervals and higher lamb mortality. In additio n, during the rains, helminth infections and poor management leading to nut ritional constraints had also a negative impact on health and production an d therefore influenced the innate resilience to trypanosomosis in those ind igenous breeds. Adaptations in management may have an equal impact as certa in disease control measures to improve biological and economical returns fr om small ruminants in tsetse infested rural areas. (C) 1999 Elsevier Scienc e B.V. All rights reserved.