Differences in prevalence of trypanosomosis in Nkedi Zebu, Ankole and crossbred cattle under tethering and open grazing management systems in Uganda

J W Magona, J Walubengo and J T Odimim*

National Livestock Resources Research Institute, P.O. Box 96, Tororo, Uganda.
magona.joseph@gmail.com
* Department of Livestock Health and Entomology, P.O. Box 531, Entebbe, Uganda.

Abstract

Grazing systems and breed composition are increasingly changing with livestock developments taking place in tsetse-infested areas of Eastern Uganda. A cross-sectional study was therefore conducted in Soroti and Bugiri districts from June to August 2009 to assess the prevalence of trypanosome infections in Nkedi Zebu, Ankole and Friesian/Zebu crosses (Crosses) kept under tethering and open grazing systems. A total of 2362 cattle were bled and examined for trypanosome infections using both the Haematocrit centrifugation technique (HCT) and Buffy coat technique (BCT).

The findings revealed that cattle kept under open grazing (n = 1612) had a lower mean packed cell volume (PCV) (28.6% 95% CI 28.4-28.6) and a higher prevalence of trypanosome infection (7.3%) than those kept under tethering (n = 451): mean PCV-30.2% (95% CI 29.7-30.7) and prevalence-6.7%. Overall, Nkedi Zebu had the highest prevalence (7.2%), followed by Ankole (7%) and Crosses (0%). There was no difference between the mean PCV of Nkedi Zebu (29.0% 95% CI 28.8-29.2) and Ankole (28.8% 95% CI 28.0-29.6), which were higher than that of Crosses (27.7% 95% CI 24.5-30.8). Trypanosoma vivax was the dominant species (62%), followed by T. congolense (20%), mixed trypanosome infection (14%) and T. brucei (4%).

In conclusion, tsetse and trypanosomosis strategies in Uganda that rely on tsetse control by use of tsetse trapping or insecticide treatment of livestock integrated with chemotherapy, could be improved by making them breed and grazing system focused.

Keywords: Prevalence, trypanosomosis

Introduction

The Zebu type, to which the Nkedi Zebu breed belongs, and Sanga type, to which Ankole breed belongs, constitute over 95% of the cattle population in Uganda, while exotic or crossbred cattle constitute only 5% (Magona and Mayende, 2002). Cattle are predominantly kept under open grazing management-different herds grazing extensively on communal pastures, while some are kept under tethering grazing management-individual animals tied by ropes against pegs on pastures neighbouring homesteads (Magona et al 2000). Variation in the prevalence of trypanosomosis is known to depend on breed and intensity of management, among other factors (Kalu 1995; Hendrickx et al 2000). The recent restocking programme in Eastern Uganda in which Ankole, Friesian or Friesian/Zebu crossbred cattle were distributed to farmers in tsetse-infested areas led to changes in breed composition. Moreover, increasing human population pressure on land has led to reduction in availability of grazing land, thus affecting the farmers’ choice of the grazing system. As much as the entire Eastern region of Uganda is dominantly infested with Glossina f. fuscipes and to a limited extent G. pallidipes (Lancien et al 1990; Okoth et al 1991; Magona et al 1997; Okuna et al 999: Magona et al 2005) that transmit bovine trypanosomosis, the current changes in breed composition and proportions of cattle under tethering and open grazing systems undoubtedly influence the prevalence and distribution of bovine trypanosomosis. Effective control of tsetse and trypanosomosis needs consideration of breed and grazing system, yet little is known about the distribution of trypanosomosis according to cattle breeds and grazing systems in Eastern Uganda. This study was therefore carried out in selected districts to address this issue.

Materials and Methods

Study areas

The location of Soroti and Bugiri districts is shown on the Map (Fig. 1). Savannah grassland is the main vegetation in the two districts. The annual rainfall ranges from 1200 to 1500 mm and is distributed in a bimodal nature. There are two wet seasons (March to May and September to November) and two dry seasons (December to February and June to August). The daily mean minimum temperature is 15ºC and mean maximum is 27ºC. Small seasonal variations occur in rainfall and temperature between the districts (Ford and Katondo 1976).

Grazing systems

The cattle sampled were kept under two distinct grazing management systems, including open grazing (extensive) and tethering (semi-intensive) system. Under the open grazing or extensive system, cattle were herded freely on communal pastures intermixed with tsetse-infested bushes, often allowing many different herds to intermingle. Of particular interest under this grazing system, is the high cattle-tsetse contact.   

Figure 1: Map of Uganda showing Soroti and Bugiri districts where the study was conducted

Under the tethering or semi-intensive system, individual cattle are exclusively tethered on pastures near homesteads using ropes. Exposure to tsetse depended on whether pastures were near tsetse-infested bushes or not and hence the cattle-tsetse contact was variable. Despite grazing cattle in tsetse-infested pastures, all farmers visited did not practise any tsetse control interventions at all.

Sampling of cattle

Using grids produced in a Geographical Information System (GIS), 10 and 15 equidistant geo-referenced points, that covered Bugiri and Soroti districts, respectively, were determined. Ground truthing of each point was carried out using a Global-Positioning System (GPS) and villages in which the points fell were selected for sampling of cattle.  Mobilization of cattle owners to bring their animals for sampling, the sampling method undertaken to select 100 cattle per point and blood collection have been previously described elsewhere (Magona et al., 2004b). Cattle of all ages and gender were sampled without any discrimination. Additional data regarding age, gender, breed, grazing system, packed cell volume, owner, village and sub-county were collected for each animal.

Blood examination

Each blood sample was examined for trypanosome infection using both the Haematocrit centrifugation technique (Woo 1969) and the Buffy coat technique (Murray et al. 1977) and used to determine the PCV on Haematocrit reader (Hawksley, Lancing, UK).  Trypanosome species identification was based on morphological differentiation on Giemsa-stained thin films.

Data analysis

Of the 2362 examined for trypanosomosis, only 2063 had full data entries. The prevalences of trypanosome infection and mean PCV were compared, according to breed and grazing system using c2 or Mann-Whitney U-test, performed using the Minitab software package (Minitab, State College, PA). A P-value of <0.05 was considered a significant difference. 

Results

Nkedi Zebu was the dominant breed constituting 94.5%, followed by Ankole (4.8%) and Crosses (0.7%). The majority of the cattle (78.1%) were kept under open grazing and few under tethering (21.9%).

The prevalence of trypanosome infections in cattle from the 10 and 15 equidistant geo-referenced villages in Bugiri and Soroti districts are shown in Table 1 and 2, respectively. In Bugiri, the prevalence ranged from 1-28% while in Soroti district it ranged from 0-12%. In addition, the prevalence of trypanosome infections under open grazing and tethering systems are shown in Figure 2. The overall prevalence of trypanosome infection in cattle under open grazing (7.3%) was higher than that of those under tethering (6.7%), but not significantly so (c2 = 0.19, d.f. = 1, P = 0.65).  Cattle under open grazing had a significantly (P< 0.05) lower mean PCV (28.6%) than those under tethering (30.2%).

Figure 2: Prevalence of infection due to different trypanosome species in cattle kept under tethering and open grazing, 2009

However, there were no significant differences between mean PCV of Ankole cattle under open grazing and tethering (P = 0.66) or Crosses under open grazing and tethering (P = 0.15) (Figure 3). But Nkedi Zebu cattle under open grazing had a significantly (P < 0.001) lower mean PCV than those under tethering. 

The prevalence of trypanosome infection in Nkedi Zebu, Ankole and crossbred cattle are shown in Tables 3 and 4. Nkedi Zebu had the highest prevalence (7.2%), followed by Ankole (7.0%). Crossbred cattle were free of infection. However, there was no significant difference among breeds (Nkedi Zebu vs Ankole; c2 = 0.005, d.f. = 1, P = 0.94; Nkedi Zebu vs Crosses; c2 = 1.08, d.f. = 1, P = 0.29). In addition, Nkedi Zebu had the highest mean PCV (29.0%), followed by Ankole (28.8%) and crosses (27.7%). But the differences among breeds were not significant (Nkedi Zebu vs Ankole, P = 0.71; Nkedi Zebu vs Crosses, P = 0.37; Ankole vs Crosses, P = 0.40).

The prevalence of trypanosome infection in Nkedi Zebu, Ankole and crossbred cattle are shown in Tables 3 and 4. Nkedi Zebu had the highest prevalence (7%), followed by Ankole (7%). Crossbred cattle were free of infection. However, there was no significant difference among breeds (Nkedi Zebu vs Ankole; c2 = 0.005, d.f. = 1, P = 0.94; Nkedi Zebu vs Crosses; c2 = 1.08, d.f. = 1, P = 0.29). In addition, Nkedi Zebu had the highest mean PCV (29.0%), followed by Ankole (28.8%) and crosses (27.7%) (Figure 3). But the differences among breeds were not significant (Nkedi Zebu vs Ankole, P = 0.71; Nkedi Zebu vs Crosses, P = 0.37; Ankole vs Crosses, P = 0.40).

Figure 3: Mean packed cell volume of Nkedi Zebu, Ankole and crossbred cattle kept under different grazing systems, 2009

The proportions of different trypanosome species found in cattle in the different grazing systems are shown in Figures 4a, b and c. Trypanosoma vivax was the dominant species, followed by T. congolense, mixed trypanosome species and T. brucei. Whereas the proportions of T.vivax and T. congolense infections in cattle under open grazing and tethering were similar, major differences in the proportion of mixed and T. brucei infection were observed. Cattle under open grazing had a higher proportion of mixed infection (14%) than those under tethering (7%). In addition, T. brucei infections were found only in cattle under open grazing.

Figure 4a: Proportion of different trypanosome species causing infection in cattle kept under tethering, 2009

Figure 4b: Proportion of different trypanosome species causing infection in cattle kept under open grazing, 2009

Figure 4c: Overall proportion of different trypanosome species causing infection in cattle, 2009

Discussion

The aim of the present study was to assess the prevalence of trypanosome infection in different breeds of cattle under different grazing system with a view to using this information to improve tsetse and trypanosomosis control in Eastern Uganda, given the changing breed composition and proportion of cattle under different grazing systems. This study revealed that Nkedi Zebu was the dominant breed and the majority of the cattle were kept under open grazing.

Although the prevalence of trypanosome infection needs to be interpreted with caution due to low sensitivity of the parasitological tests used, these findings are valuable for improvement of tsetse and trypanosomosis control. Cattle under open grazing had a higher prevalence of trypanosome infection and a significantly lower PCV than those under tethering. This concurs with other studies elsewhere, that revealed the prevalence of trypanosomosis to be highest in extensively managed stock or in migratory cattle (Hall et al 1983; Kalu 1995), which could be partly explained by the fact that extensive management (open grazing) increases the cattle-fly contact.

Differences were also observed among the different breeds; Nkedi Zebu had the highest prevalence, followed by Ankole and Crosses. Other workers have similarly found the prevalence of trypanosomosis to be influenced by breed, being highest where taurine cattle are predominant and herds belong to several owners from rural areas (Kalu 1995; Hendrickx et al 2000) or in trypanosusceptible cattle, especially the crossbreeds (Kalu 1995).   

Trypanosoma vivax was the dominant species, followed by T. congolense, mixed trypanosome species and T. brucei. Similarly previous studies in Uganda have found T. vivax to the dominant trypanosome species (Magona et al 1998; Magona et al 2000; Okiria et al 2002; Magona et al 2004a).  The proportion of T.vivax and T. congolense infections in cattle under open grazing and tethering were similar, but major differences in the proportion of mixed and T. brucei infection were observed. Cattle under open grazing had a higher proportion of mixed and T. brucei infections than those under tethering, probably because tethering restricts free movement of animals, thereby reducing chances of animals being bitten, while free movement of cattle under open grazing increases cattle-fly contact. Increased likelihood of substantial tsetse bites is likely to increase chances of exposure to wider spectrum of trypanosome species infection i.e. T. brucei, T. congolense and T. vivax.  

Conclusion

• The findings suggest that there are differences in risk of cattle to trypanosomosis due to the grazing system and breed: two factors that are increasingly changing with livestock developments taking place in tsetse-infested areas of Eastern Uganda.

  
  

• Hence, tsetse and trypanosomosis strategies in Uganda that rely on tsetse control by use of tsetse trapping or insecticide treatment of livestock integrated with chemotherapy (Lancien et al 1990; Magona et al 1998; Magona et al 2004a), could be improved by making them breed and grazing system focused.

Acknowledgement

We are grateful to Michael Oretum, Geoffrey Odyek, Joseph Muboli and Robert Wabyanga for their technical assistance. This study received financial assistance from the FITCA Project (Uganda) for which we thank Mr. Ambrose Gidudu, the National Project Co-ordinator. This paper is published with permission of the Director, National Livestock Resources Research Institute (NaLIRRI), Tororo, Uganda.

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Received 23 November 2010; Accepted 15 February 2011; Published 19 June 2011

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