Prevalence and risk factors of conditions causing lameness in sheep under free range grazing system in Kajiado district, Kenya
Mugo, S G
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Lameness can be a cause of negative economic output in sheep farming owing to its adverse effects on productivity, reproductive performance and poor growth performance in lambs. The extent of lameness in sheep and its associated predisposing causes in Kenyan sheep rearing systems has not been elucidated. This study was carried out in sheep under free-range grazing system in Kajiado District, Kenya, from March 2010 to June 2010 with the following objectives (1) to determine the prevalence of conditions causing lameness, (2) to determine the possible risk factors predisposing the sheep to lameness conditions. This was a cross-sectional study in which each farm was visited several times, but each sheep on the farm was examined only once. Ten study farms were purposively selected from three divisions of Kajiado District, based on the willingness of the farmers to allow examination of their sheep and also on the stability of the farm's grazing routine from more nomadic tendencies. The data was collected either by filling a formal questionnaire with answers given through interviewing the farmers, farm managers or stockmen on animal-level factors, or by recording observations made on the farm regarding farm-level factors. The 10 farms had a total of 1916 sheep that met the study criteria. Out of these, 117 sheep were identified as lame during general locomotion scoring as they walked on a flat firm part of the ground. Each of these 117 sheep were examined closely for specific conditions or disorders causing lameness. Information on the actual disorders causing lameness was recorded. The location of the disorders on the limb, affected limbs whether fore or hind, and the affected claws whether lateral or medial were recorded in data collection sheets. The lesions causing lameness were photographed. A mark was put on each examined sheep to avoid repeat examination. Overall prevalence of lameness was 6.1 % (117/1916), out of which the conditions with relatively higher percentages of occurrence were sole erosion (3.8%, 72/1916), overgrown claws (3.2%, 61/1916) and tick-bite dermatitis (1.6%, 30/1916). Infective conditions such as foot rot and interdigital dermatitis had prevalence of less than 1%. The rest of the conditions such as shelly hoof, soil-balling, over-trimming and bone problems were incidental findings each in a single sheep. The conditions causing lameness occurred on the foot in 94% (110/117) of the lame sheep and on proximal parts of the limb in 6% (7/117) of the cases. The distribution of the conditions among the lame sheep was 43.6% (51/117) on the hind limbs, 23.1 % (27/117) on the forelimbs and 33.3% (39/117) affected both hind and fore limbs. Although there were several animal-level factors evaluated, the only factors found to be significantly associated with higher locomotion score were the number of limbs with lesions (X2 =11.15, P = 0.004), the affected limbs whether fore or hind (X2 = 9.20, P = 0.010), the affected claw whether medial or lateral (X2 = 16.98, P = 0.05) and the type of lesion (X2 = 4.71, P = 0.030). The only farm-level factor that was significantly associated with higher locomotion score was presence of traumatic objects in the grazing grounds This study concludes that the prevalence of lameness in sheep under free-range grazing system of dry zones such as Kajiado District is relatively low due to minimal farm-level risk factors. Similar prevalence studies should be carried out in high potential and wet areas of Kenya for comparison purposes.