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Although a lot of information is currently available on trypanotolerance in cattle, until recently the trypanotolerant nature of small ruminants was not well known. Trypanotolerance in small ruminants is less pronounced than in cattle and should be considered as resilience rather than resistance. West African Dwarf (WAD) goats seem to be less trypanotolerant than Djallonke sheep. However, recent studies have shown that there is an important introgression of genes of trypanosusceptible breeds into WAD goat populations, which possibly explains the loss of trypanotolerance in these animals. Measures need to be taken to safeguard and upgrade the genetic purity of trypanotolerant goat and sheep breeds in Africa.

Forty pure West African Dwarf (WAD) goats and 35 of its F1 crosses with the Sahelian breed were used in a multifactorial experimental design to evaluate the effects of an experimental Trypanosoma congolense infection and interactions with natural helminth infections and different levels of diet on health and productivity of these two breeds. Trypanosome infection caused a severe drop in packed cell volume (PCV), but this was not significantly affected by breed. Neither deworming nor diet had any effect on the course of anaemia after trypanosome infection. The mean score of parasitaemia tended to be higher in crossbreeds than in WAD goats although this was not significant (P>0.05). Similarly, the antibody response to trypanosome infection was not significantly different between breeds. Parasitaemia level was significantly influenced by the level of diet with the group under high supplementation having a higher mean parasitaemia score than the group under low supplementation. Weight loss due to trypanosome infection tended to be greater in crossbreeds than in WAD goats (P>0.05). During this study, there was no difference in mean helminth egg output between crossbred and WAD goats. However, between weeks 4 and 10 after trypanosome infection (corresponding to a period of heavy rainfall and highly infective pastures), the mean egg output was higher in the crossbreeds. The immunosuppressive effect of trypanosome infections was revealed by a lower antibody response to Haemonchus contortus in infected animals compared to the uninfected controls. Trypanosome infection tended to increase strongyle egg output. This study did no reveal any superior trypanotolerance of WAD goats compared to crossbreeds.

The effects of artificial Trypanosoma congolense infection and dietary level on biochemical changes were observed in 24 ewe lambs (Experiment 1) and 42 breeding ewes (Experiment 2). All animals belonged to the Djallonké breed which is known to be trypanotolerant. For both experiments, there were four treatment combinations, of which two were kept on a restricted diet (L), the other two on an at libitum diet (H). Half of each dietary group was infected with T. congolense (LI, HI), while the remainder served as uninfected controls (LC, HC). Artificial T. congolense infection took place at the age of 200+/-7 days in Experiment 1 and at the peak of oestrus in Experiment 2. Irrespective of dietary levels offered, total proteins in lambs and ewes and albumin in lambs declined significantly (P<0.001) post infection. Plasma glucose concentration was reduced by the low dietary level and not by infection. Although plasma urea concentrations were slightly increased in the infected ewe lambs, adult ewes in the HI group demonstrated increased plasma urea concentrations (P<0.05) due to an interaction between infection and diet. Neither infection nor the imposed diet induced significant changes on plasma creatinine concentrations. Transitory peaks in non-esterified fatty acids (NEFA) and beta-hydroxy butyric acid (BHBA) levels in infected ewes on low dietary level indicated temporary changes in the energy metabolism of the host. It was concluded from this study that, inspite of their trypanotolerance, Djallonké lambs and ewes demonstrated an infection effect on host metabolism pattern due to T. congolense infection. These changes reflected to some extent trypanosome-induced alteration of the nutrient metabolism, which could not always be negated by diet supplements. Nutrition, as an independent factor, did confer added benefits against the debilitating effects of trypanosomosis under the conditions of the present study.

Forty two Djallonké and 27 Djallonké-Sahelian crossbred sheep were compared during 34 weeks for their disease resistance and productivity in a multifactorial experiment including trypanosome infection, helminth infections and dietary level. Eight treatment combinations were formed in which the two breeds were balanced. Pyrexia was observed following trypanosome infection and was not different between the two breeds. However, a significant higher parasitaemia level, a shorter prepatent period and a lower antibody response in the crossbreds following infection, indicated a significant reduction of the trypanotolerance and confirmed the genetic origin of the trait. Neither helminth infection nor dietary level influenced the onset and level of parasitaemia or the level of antibody response following trypanosome infection. Trypanosome infection, helminth infection and low supplementary feeding caused independently significant reductions in PCV level and weight gain but these declines were not worse in crossbreds as compared to Djallonké. Independently, of the studied factors, crossbreds were generally heavier than Djallonké and also grew faster, especially during the second phase of the study. Crossbreds had significantly higher mean nematode egg output (epg) compared to Djallonké sheep but reduction of epg following deworming was similar in both breeds. The lower epg in the Djallonké breed indicated an innate resistance to helminths and/or more efficient immune response. Trypanosome infection tended to increase epg, confirming the immunosuppressive effect of the former. The higher body temperature in the Djallonké compared to crossbreds suggested a better heat tolerance in the former breed. From this study it was concluded that Djallonké-Sahelian crossbred sheep inspite of a reduced trypanotolerance and lower resistance to helminth infection, posses a higher potential to intensify mutton production as compared to the pure Djallonké. However, appropriate measures should be taken to limit disease and stress factors in order to optimise production environment for this crossbred sheep.

Trypanosome infections, packed red cell volume levels (PCV), body weight and nematode faecal egg counts of village-based small ruminants were monitored in two areas in The Gambia with either moderate or high trypanosomosis risk for 24 and 30 months respectively. Outflows from the flock and new-born animals were recorded and data on housing and management were compiled. Reported mortality rates were higher in goats than in sheep, but for both species highest in the moderate risk area. The peak of trypanosome infections lagged 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 than in goats but only significantly higher during Year 1 in the moderate risk area. Trypanosome infection reduced the PCV level significantly and seasonal effects indicated significantly lower PCV levels during the rains. Trypanosome infection significantly depressed weight gain in both species at periods where infection rates were highest. In both species considerably lower weight gains were observed during the rainy season. Abortion rates were higher in goats than in sheep in both study sites, and highest in the high-risk site. Trypanosome infection in ewes in the high risk area increased lamb mortality significantly but had no effect on birth weights, nor on growth 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 months post parturition significantly increased parturition interval in both species. Peak faecal egg output occurred at the end of the rainy season and was highest for both species in the moderate risk site. Poor grazing management was found responsible for a seasonal nutritional constraint. Based on these results, these breeds of sheep and goats can be considered as trypanotolerant since they are able to remain productive under high and moderate levels of trypanosome challenge. Nevertheless, trypanosomosis affected their health and production level as shown by reduced PCV levels, depressed weight gains, longer parturition intervals and higher lamb mortality. In addition, during the rains, helminth infections and poor management leading to nutritional constraints had also a negative impact on health and production and therefore influenced the innate resilience to trypanosomosis in those indigenous breeds. Adaptations in management may have an equal impact as certain disease control measures to improve biological and economical returns from small ruminants in tsetse infested rural areas.

The interactions between T. congolense infection and nutritional supplements on onset of puberty and age at first lambing were observed in 24 young Djallonké ewes. As experimental design, a randomised complete block design was used with four treatment combinations, of which two were kept on a restricted diet (L), the remainder on an unrestricted diet (H) and half of each nutritional group being infected with T. congolense (LI and HI), the remainder serving as controls (LC and HC). Infection with T. congolense took place at an average age of 6 months and 15 days. Mortality due to trypanosome infection was zero and clinical symptoms were not obvious. Intensity of parasitaemia and packed cell volume (PCV) drop following trypanosome infection were similar in both infected groups (HI and LI). High dietary supplementation resulted temporarily in a better haematopoietic response following trypanosome infection, measured as a macrocytic anaemia. Dry matter intake (DMI) was significantly depressed in the HI group immediately following infection. Trypanosome infection had a negative effect on live weight gain during the chronic phase, with the difference being most obvious in the HI group (interaction diet x infection; p< or =0.05). Whereas trypanosome infection had no significant effect, high supplementary feeding significantly reduced the age at first cycling. Age at first lambing was similarly reduced by the diet. Trypanosome infection tended (p< or =0.09) to delay age at first lambing with a mean difference of 31.5+/-22.4 days between infected and controls. Interactions between diet and infection for age at first cycling/lambing were not significant, indicating these effects were just additive. Neither birth weights nor growth rates of offspring born to the experimental animals were significantly affected by previous trypanosome infection, nor by the diet of the dam. In contrast, lamb mortality up to 3 months of age was significantly increased by infection of the dam and most losses arose in group LI. In conclusion, the effects of trypanosome infection on puberty and age at first lambing were indirectly mediated through depression of growth rates. Nutritional supplementation enabled a better erythropoietic response to T. congolense infection and better offspring survival rates but resulted in more depressed weight gains. The results however clearly indicated the delaying effect of insufficient feeding on onset of puberty and reproductive performance in young Djallonké sheep.

Ten West African Dwarf (WAD) female goats and twelve Djallonké ewes were artificially infected with a West African strain of Trypanosoma congolense and monitored during 36 weeks over an acute phase (weeks 0-12) and chronic phase (weeks 13-36) to evaluate their haematological and immunological response. Parasitaemia, packed cell volume, red blood cells, haemoglobin, white blood cells and trypanosomal antibodies were assessed. Mean corpuscular volume and mean corpuscular haemoglobin concentration were calculated. The infected animals showed a persistent parasitaemia together with a chronic anaemia and significantly lower packed cell volume, red blood cell count and haemoglobin. The infected sheep developed a macrocytic, hypochromic anaemia during the acute phase changing to normocytic, hypochromic during the chronic phase, whereas, the infected goats developed a normocytic, normochromic anaemia during the acute phase and normocytic, hypochromic during the chronic phase. A significant increase in WBC counts was observed only in the infected sheep during the chronic phase. Trypanosomal antibody titres were significantly higher in the infected sheep than in the infected goats. Both species are regarded as trypanotolerant but Djallonké sheep mount a better haematopoietic and immunological response to infection with T. congolense than WAD goats.

The effects of Trypanosoma congolense infection and nutritional supplements on live weight changes during pregnancy, haematology traits and offspring performance were studied in 42 Djallonké ewes. A randomised block design was used to allocate ewes to four treatment combinations, of which two were on a restricted diet (L) and the remainder on an unrestricted diet (H). Half of each nutritional group were infected with T congolense (LI, HI), the remainder serving as controls (LC, HC). The degree of anaemia following infection was similar in both infection groups (P<0.0001), but the erythropoietic activity, as judged by the increase in mean corpuscular volume, was significantly greater in the HI group (P<0.01). Live weight gains during pregnancy attributable to higher supplements were significantly depressed by infection (P<0.01). Post partum weight was lower in the LI group as compared with the LC control. Diet interacted significantly (P<0.01) with infection and resulted in the lowest lamb growth rates in the LI group. It was concluded that dietary supplementation of trypanosome-infected Djallonké ewes during pregnancy and lactation improves productivity in terms of ewe live weight and improved lamb growth rates to weaning.

Interactions between Trypanosoma congolense and nutritional statue were studied in 42 ewes, bred at the peak of parasitaemia after synchronisation of oestrus. As experimental design a randomised block design was used with four treatment combinations (2 x 2 factors), of which two were on restricted diet (L), the remainder on an unrestricted diet (H) and half of each nutritional group infected with T. congolense (LI, HI) remainder serving as controls (LC, HC). Severity of parasitaemia was not influenced by supplementation and mortality rates were higher in the HI and LC groups, but these differences were found not significant. Progesterone levels during the synchronised cycle were significantly lower in the infected groups. Levels of pregnant specific protein B (PSPB) in pregnant sheep at days 21 and 26 and were not significantly affected by nutrition or infection, despite the tendency of a decrease in infected groups. T. congolense clearly affected establishment of pregnancy, as shown by lower rates of pregnancy and extended intervals between breeding and confirmation of pregnancy, nor was there any benefit of nutritional supplementation. Mean progesterone concentration during pregnancy, in those ewes which lambed, was not different between groups. The effect of the T. congolense infection on the outcome of pregnancy was not clear with the LI and HC performing well and poor pregnancy outcomes on groups HI and LC, although differences in litter size might explain these anomalies. It is concluded that the most pronounced effect of T. congolense was a negative influence on establishment of pregnancy, with nutritional supplementation unable to overcome this effect but having a beneficial influence on maintenance and successful outcome of pregnancy. However, individual exceptions indicate that some ewes cope better with the negative effects of infection and poor nutrition.

The interaction between Trypanosoma congolense and Haemonchus contortus was studied in 5 groups of 8 Djallonké sheep. Two groups received a single infection with either H. contortus or T. congolense, and 2 groups were infected with T. congolense followed by H. contortus (TH) or vice versa (HT). One group was kept as uninfected controls. Mortality due to infection was observed only in the dual infection groups. In the TH group, the effects were more acute whereas in the HT group they were more chronic. No significant differences in weight gain could be demonstrated between infected and control groups. Djallonké sheep are able to withstand a single infection with either T. congolense or H. contortus, which confirms their trypanotolerant nature and provides preliminary indication of resistance against helminth infections. However, when exposed to successive infections with both parasites, some of the animals lose this tolerance.

Ten West African Dwarf (WAD) does and 12 Djallonké ewes were artificially infected with a West African strain of Trypanosoma congolense and observed over two years. The infected animals showed a chronic anaemia together with a persistent parasitaemia but very low mortality and increase in body weights was not significantly different from the control. In the infected sheep significant differences were found in offspring production at three and five months due to a higher mortality among the lambs. The infected goats had more abortions and stillbirths and period to first kidding, total number of parturitions, production at birth, one, three and five months were significantly different from the controls. A productivity index was calculated and revealed that a chronic T congolense infection significantly decreases the productivity of WAD goats during two years whereas in Djallonké sheep, the loss in productivity is recovered after one year. Although both species are regarded as trypanotolerant, the Djallonké sheep show a better tolerance to a chronic T congolense infection that the WAD goats.

Two cloned strains of Trypanosoma congolense, of West and East African origin, were used to infect by intradermal inoculation two groups of young adult female Djallonké sheep and West African Dwarf goats. For a 3 month period post-infection, packed red cell volume (PCV), parasitaemia, body weight and clinical parameters were followed to evaluate their trypanotolerant nature and to control the pathogenicity of the two strains of T. congolense. Although the West African strain of T. congolense was more pathogenic than the East African strain, it seemed that the Djallonké sheep and the West African Dwarf goats, despite high levels of parasitaemia and a concomitant drop in PCV, showed a high degree of trypanotolerance, as reflected by zero mortality and an increase in body weight during 12 weeks of observation.