Genetic parameters estimation of resistance to gastrointestinal parasitism in traditional husbandry system of small ruminants in Senegal

Abstract

A protocol has been carried out in order to study the genetic resistance to gastrointestinal parasites on Senegalese breeds of sheep and goats. Faecal and blood samples have been collected on animals from different flocks of two areas of Senegal: the area of Louga located in a sahelian climate, and the area of Kolda located in a sudano-guinean climate. Sires identity was unknown in the husbandry system and pedigree were primarily based on dam-offspring relation. Traits analysed were faecal egg count (FEC) and packed cell volume (PCV). The study was conducted during two years: 1992-1993 for animals of Louga and 1993-1994 for animals of Kolda, with three samplings each year for FEC, two for PCV during rainy season. In Louga area, 193 goats and 184 sheep were collected the first year, 249 goats and 357 sheep were collected the second year, which corresponded to 60 flocks distributed in 15 villages. In Kolda area, the number of animals sampled was 322 goats and 349 sheep the first year, 297 goats and 428 sheep the second year. These animals were coming from 80 flocks distributed in 25 villages. Factors of variation of performances have been fitted in analysis models: village*season*year, age and lactation level for dams, village* season*year, age and sex for young. The heritability and the repeatability have been estimated using an “animal model”. The mean of the repeatability within year is 0.19 for FEC and 0.27 for PCV. Values of repeatability were smaller between years: 0.12 for FEC and 0.21 for PCV. The estimation of heritability was difficult: data structure didn’t allow to fit directly maternal environment and flocks effects, because of insufficient pedigree and small size of the flocks, respectively. Values of heritability estimated varied from 0 to 0.33 for FEC and from 0 to 0.38 for PCV, depending on sample analysed and model used. It was not possible to estimate genetic correlation between traits. However phenotypic correlations have been estimated between FEC and PCV, and between each one of these variables and the liveweight of the young. Constraints related to genetic study in traditional husbandry system have been discussed.