Effect of a single dry season anthelmintic treatment of N'Dama cattle on communal pastures in The Gambia

The effect of a single anthelmintic treatment of cattle during the early dry season was studied. One hundred and sixty-six N'Dama cattle, 1–3 years old, were selected from five herds. There were 65 males and 101 females divided into two groups of 83 animals each. One group was treated with fenbendazole at 7.5 mg/kg body weight by mouth in November 1992; the other group remained as the untreated control. At monthly intervals from November 1992 to April 1993, each animal was weighed and the number of eggs/g of faeces (epg) was determined. The infective larvae (L3) were examined following culture of pooled samples from each group of animals. In April 1993, 6 animals (3 treated and 3 controls) from the herds under study were necropsied. The difference in the weight gains (4.6 kg) of the two groups was highly significant (p<0.0001). The difference in the weight gains and the epg between the treated and control groups was influenced by the age of the animals. Of the treated animals, one contained no nematodes, one contained only 25Oesophagostomum radiatum, and the third contained 25Cooperia L4. The three untreated animals were all infected. It was concluded that the treatment in early dry season, with an anthelmintic effective against both adults and larvae, led to a significant reduction in egg counts, to elimination of adults and hypobiotic larvae and, consequently, to an increase in the body weight gain by the treated animals.     

Response of Acacia senegal (L.) Willd. to inoculation with arbuscular mycorrhizal fungi isolates in sterilized and unsterilized soils in Senegal

The benefits of inoculation with six arbuscular mycorrhizal fungi (AMF) isolates (Glomus aggregatum, G. fasciculatum, G. intraradices, G. manihotis, G. mosseae, and G. verriculosum) were investigated on seedlings of Acacia senegal (L.) Willd., a multipurpose tree legume highly valued for arabic gum production. Mycorrhizal root colonization, plant growth and relative mycorrhizal dependency (RMD) were measured in A. senegal seedlings growing in soils from three geographical sites in Senegal (Dahra, Bambey and Goudiry) and two soil conditions (sterilized vs unsterilized) in the glasshouse. The impact of inoculation on mycorrhizal root colonization and plant growth depended on AMF isolates, soil origins and soil conditions. Mycorrhizal root colonization and plant growth were increased in sterilized soils regardless of soil origin and AMF isolates. The degree of RMD of A. senegal seedlings varied with soil origin, soil condition and AMF isolates. A. senegal showed the highest RMD values, reaching a maximum of 45 %, when inoculated with G. manihotis. However, in unsterilized soils, no significant effect of AMF inoculation on plant growth was observed despite significant root colonization with certain AMF isolates in Dahra and Goudiry soils. This indicates that the most infective AMF isolates were not the most effective and unsterilized soils may contain effective mycorrhizal propagules. In conclusion, it is important to consider the native mycorrhizal component of the soils before harnessing mycorrhizal inoculation programs for sustainable agroforestry systems.     

Prevalence and incidence of trypanosomosis in horses and donkeys in the Gambia

In a study of the prevalence and incidence of trypanosomosis in horses and donkeys in two regions of the Gambia, surveys were carried out at Niamina east and Bansang south with a high and low to moderate tsetse challenge, respectively. Eleven horses and 67 donkeys were sampled monthly from August 1997 to September 1998. Blood samples were examined for trypanosomes using the buffy-coat (BC) method and polymerase chain reaction (PCR). Three primer sets were used, specific for either Trypanosoma vivax (TVW), Trypanosoma congolense (GOL) or Trypanosoma brucei (ORPHON5J).The BC results showed that the prevalence (August 1997) and the average monthly incidence (September 1997-1998) of trypanosome infections in horses (45.5 and 16%, respectively) were significantly higher than in donkeys (6.2 and 9%, respectively). Using PCR, the number of detected cases was seven times higher than using the BC. T. congolense was the most frequently observed species, followed by T. vivax and T. brucei. This study confirms earlier observations by other authors that donkeys, which are exposed to a similar tsetse challenge as horses, are significantly less infected with trypanosomes than the latter.     

Estimation of enteric methane emission factors for Ndama cattle in the Sudanian zone of Senegal

Methane (CH₄) emission estimations for cattle in Sub-Saharan Africa (SSA) reflect limited production levels and diets that are high in cellulose forage. However, data on these livestock systems is lacking for their accurate evaluation. To provide guidance for climate change mitigation strategies in Senegal, it is necessary to obtain reliable estimates of CH₄ emissions from Ndama cattle reared in grazing systems, which is the predominant cattle system in the country. The objective of this study was to determine the annual methane emission factor (MEF) for enteric fermentation of Ndama cattle following the IPCC Tier 2 procedure. Our estimated annual MEF at the herd scale was 30.8 kg CH₄/TLU (30.7 kg CH₄/head/yr for lactating cows and 15.1 kg CH₄/head/yr for other cattle). These values are well below the default IPCC emission factor (46 and 31 kg CH₄/head/yr for dairy and other cattle, respectively) proposed in the Tier 1 method for Africa. Our study showed that feed digestibility values differ with season (from 46 to 64%). We also showed that cattle lose weight and adapt to lower feed requirements during the long dry season, with a resulting major reduction in methane emissions. The results of this work provide a new framework to re-estimate the contribution of grazing systems to methane emissions in Africa.

     

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.     

Contextualized re-calculation of enteric methane emission factors for small ruminants in sub-humid Western Africa is far lower than previous estimates

Tropical Animal Health and Production - Given the projected growth of methane emission by ruminants in developing countries, there is a clear need for reliable estimates of their contribution to...     

The susceptibility of Djallonké and Djallonké-Sahelian crossbred sheep to Trypanosoma congolense and helminth infection under different diet levels.

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.