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Title: Genetic and Environmental Variation in Infestations with Ticks and Infections with Gastrointestinal Nematodes of Sheep in Semi-Arid and Semi-Humid Zones of Kenya
Authors: Ogore, Peter Busaka
Keywords: Genetic and Environmental Variation -- Ticks and Infections -- Gastrointestinal Nematodes -- Sheep --Semi-Arid and Semi-Humid Zones
Issue Date: Nov-1996
Publisher: Egerton University
Abstract: A total of 347. 213 and 169 lamb records were used to characterise the genetic resistance to gastrointestinal (GI) nematodes in Red Maasai (R), D0rper.(D) and their crosses at 3. 8 and 13 months of age, respectively. at Diani in the semi- humid Zone of coastal Kenya. Thereafter the remaining 160 yearlings were evaluated for tick resistance at Nguuni farm in the same region. At O1’Magogo in the semi-arid highlands of Kenya a flock of both R and D genotypes of 101 and 108 individuals from the 1992 and 1993 lamb crops. respectively, were evaluated concurrently for GI nematode and tick resistance. The indicators of resistance were: Faecal Egg Count (FEC) defined as the number of worm eggs in a gram of faeces; Packed Cell Volume (PCV) defined as the proportion of red cells to total blood volume: and tick count (TC) measured as total body count of engorged female ticks. Lamb survival rate was used as a measure of flock productivity. At Diani Estate there were no significant differences in live weights among genotypes measured between 3 and 13 months of age. Survival rate from birth to weaning was 91 % with no significant difference (P > 0.05) among genotypes. However, for post-weaning survival the mean was 60 % with a highly significant difference (P < 0.01) between R and D lambs (74 % and 27 %. respectively). The R and D genotypes differed significantly for PCV (P < 0.05) with R having higher PCV at 3 and 13 months of age. There was no significant difference among R and D genotypes differed significantly for PCV (P < 0.05) with R having higher PCV at 3 and 13 months of age. There was no significant difference among genotypes for FEC, although the R lambs consistently maintained lower FEC than D lambs at all ages. The effect of lamb breed was highly significant for TC with R lambs having lower counts than D lambs at all infestation periods both at N guuni and Ol’Magogo farrns. Heritabilities. estimated from paternal half-sib correlations, were characterized by large standard errors because of the small data set and limited number of sires. The heritability estimate for logarithm-transformed tick count in the second infestation period at Nguuni farm was low (0.13 i .24) but would be expected to increase to 0.20 or 0.24 if measuring of TC had been done 2 or 3 times within the same infestation period, respectively. The phenotypic correlation between TC on the ears and the total body count was 0.97 indicating that ear count alone was a good indicator of resistance to ticks in sheep. It was concluded that utilization of resistant animals is an attractive complementary approach to the use of chemotherapy as a means of increasing productivity of sheep under GI nematode infections. tick infestations and poor feed resources.
Appears in Collections:Faculty of Agriculture

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