Trypanotolerance in small ruminants of sub-Saharan Africa.

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.

Influence of an experimental Trypanosoma congolense infection and plane of nutrition on milk production and some biochemical parameters in West African Dwarf goats.

The interactions of trypanosomosis and plane of nutrition on health and productivity of multiparous and primiparous West African Dwarf (WAD) does were studied in a multi-factorial experiment including diet (supplementation or basal diet) and infection (infected or control). Experimental does were infected with Trypanosoma congolense at the beginning of the second week post-kidding and monitored for 16 weeks after infection. Trypanosome infection significantly reduced packed cell volume (PCV) (control: 30.1+/-0.3% versus infected: 22.2+/-0.3%; P<0.0001). Regardless of infection, the drop in PCV from the pre-infection period to the end of the experiment was more severe in animals under restricted diet (interaction dietxperiod, P<0.001). Trypanosome parasitaemia tended to be higher in the supplemented group than in the basal diet group (P>0.05) and multiparous animals had a higher parasitaemia (score: 2.6+/-0.1) than primiparous animals (score: 2.2+/-0.1) (P<0.05). Trypanosome infection as well as dietary supplement had a significant effect on lactation length. Milk off-take from trypanosome-infected does was significantly lower than that from the uninfected control group (17.5+/-3.2l versus 35.5+/-3.2l, P<0.001) and there was a positive effect of plane of nutrition (supplemented: 32.8+/-3.2l and basal diet: 20.2+/-3.5l, P=0.01). The drop in milk off-take due to trypanosome infection was more severe in the supplemented group (control: 46.7+/-4.7l versus infected: 18.9+/-4.2l) than in the group receiving a basal diet (control: 24.2+/-5.0l versus infected: 16.1+/-4.7l) (interaction infectionxdiet, P=0.04) due to the number of does from the supplemented group that were withdrawn from the experiment. The effect of trypanosome infection on doe's live-weight was only noticeable during the first 8 weeks of lactation and there was no significant effect on offspring growth rate unless the mother died. Plasma total protein (TP), albumin and cholesterol concentrations were significantly reduced by the infection but were significantly increased by supplementation. Supplemented does had a higher level of cholesterol and a tendency for a higher parasitaemia. Does of high parity also had a higher cholesterol level than primiparous does and, based on the number of animals that were withdrawn from the experiment, they showed a lower resistance to the infection.

Effects of an experimental Trypanosoma congolense infection on the reproductive performance of West African Dwarf goats.

Thirty-six West African Dwarf (WAD) goats were used to assess the effects of an experimental Trypanosoma congolense infection on their reproductive system. Estrous cycles were synchronised and when confirmed pregnant (n = 31), the does were randomly allocated into control and trypanosome-infected groups. After infection, the animals were carefully observed till parturition. Trypanosome infection caused an increase of rectal temperature, a significant drop in PCV (infected: 23.3 +/- 0.3%; control: 28.5 +/- 0.4%; P < 0.0001) and abortions in 27.8% of the infected does. Kids born from infected does had a lower birth weight than kids born from control goats (0.9 +/- 0.1 kg versus 1.6 +/- 0.1 kg; P < 0.0001). Eight out of 13 kids (61.5%) that were born alive from infected does died during their first week of life. Plasma pregnancy-associated glycoprotein (PAG) and progesterone concentrations were lower in the infected animals than in the controls. In general, PAG concentration in does which aborted dropped before abortion. Our results revealed that artificial T. congolense infection affected reproductive performance of WAD goats with abortions, premature births and perinatal losses being observed. Neither transplacental transmission of T. congolense nor histopathological lesions of the placenta could be demonstrated.

Performance of enzyme-linked immunosorbent assays for detection of antibodies against T. congolense and T. vivax in goats.

Indirect ELISAs using denatured antigen preparations of Trypanosoma (T.) congolense (TcAGd) and T. vivax (TvAGd) for detection of anti-trypanosome antibodies in bovine serum (I-TAB ELISAs), were adapted for serodiagnosis in goats. The diagnostic proficiency, the cross-reactivity with sera from heterologous trypanosome infections and the operational performance of the assays were evaluated on experimentally trypanosome-infected goats. The I-TAB ELISA (TcAGd) detected antibodies in all T. congolense infected goats (100% overall sensitivity) from 2 to 4 weeks post-infection (p.i.) until the end of the experiments. Specificity tested on 92 uninfected goats was 96.7%. Extensive cross-reactions of I-TAB ELISA (TcAGd) with sera from T. vivax or T. brucei infected goats were observed. The I-TAB ELISA (TvAGd) detected antibodies in 5 of the 6 T. vivax infected goats, specificity tested on uninfected goats was 100%. Cross-reactivity with sera from T. congolense or T. brucei infected goats remained limited. Infecting species identification based on the highest percent positivity (PP) in both systems, correctly identified all T. congolense infections, but misidentified in 2/19 occasions a T. vivax infection as a T. congolense infection. In the absence of T. brucei specific antigen coated plates, T. brucei infections were identified in, respectively, 7/9 and 2/9 occasions as T. congolense or T. vivax infections. Acceptable inter-plate repeatability was observed. The implications of results and technical requirements for ongoing applied research are discussed.