Genetic resistance of different genotypes of sheep to natural infections with gastro-intestinal nematodes

Abstract

During a 3-year period, from April 1991 to December 1993, in a flock with four lambing periods annually, faecal samples from lambs at weaning at the age of 3 months (no. = 1756), were examined for gastro-intestinal nematode eggs by the McMaster method. Faecal samples were also examined at the age of 9 (no. = 170), 12 (no. = 157), 15 (no. = 253) and 18 (no. = 85) months from the females only. From June to December 1993 packed cell volume (PCV) was also examined from lambs at weaning. Seven genotypes were used in this study. The faecal egg counts were affected by genotype, birth season, type of birth and rearing, sex and age. First generation cross of Sumatra X Barbados Blackbelly had lowest eggs per g of faeces (EPG) followed by Sumatra, St Croix, Sumatra X St Croix Fl and F2 and Sumatra X Java Fat tail. Lambs born in February-March when rainfall was low had lower EPG (V < 0-05) than those born in May-June or August-September. The EPG of lambs born and reared singly were significantly lower (P < 0-001) than those born twin, triplet or quadruplet. Female lambs had lower EPG than male lambs (P < 0-001). The EPG of lambs at 3 months were higher than at 9,12,15 or 18 months (P < 0-001). PCV was affected by genotype, sex, type of birth and rearing and season of birth. There was a positive correlation between PCV and weaning weight of lambs and a negative correlation between EPG and weaning weight. These results show that the crosses of St Croix and Barbados Blackbelly with local Sumatra sheep are at least as resistant or more resistant to gastro-intestinal nematodes than pure Sumatra breed and therefore these breeds can be used in cross breeding programmes to improve the body size of local Sumatra sheep.

Relative maturity and the development of immunity to gastrointestinal nematodes in sheep: an overlooked paradigm?

“…However, the reliance on such usage has come at a price: of anthelmintic resistance . In providing options for sustainable control methods which are less reliant on anthelmintics, considerable focus has been given to breeding animals displaying natural resistance to GIN . These approaches have generally been successful in identifying resistant genotypes based on phenotypic markers such as faecal egg count (FEC) and either plasma or saliva antibody levels , with a moderate‐to‐high heritability consistently reported.…”

“…Genotypic identification of resistant animals through molecular techniques such as quantitative trait loci, genomewide associated studies and candidate gene analysis has also been successful and has been suggested as a more reliable approach than use of more traditional phenotypic markers . Immunity to gastrointestinal parasites is known to be multigenic, with numerous candidate genes suggested based on evaluation of selection lines of sheep for divergence in immune competence or from breeds of animals noted for their ability to resist parasite infections . Nevertheless, immunity is not binary and regardless of genotype, animals show considerable variation in the timing and magnitude of immunological responses to GIN.…”

The Use of Microsatellite Markers to Study Genetic Diversity in Indonesian Sheep

“…In addition, there are also fighting type sheep, so called garut sheep. Indonesian thin and fat tail sheep have several advantages; especially they are well adapted to the hard environment, able to utilize low-quality feed, prolific (Inounu et al, 1986), early puberty (Sutama et al, 1988) and resistance to internal parasites (Romjali et al, 1998).…”

Microsatellite polymorphism in DRB1 gene (MHC class II) and its relation to nematode faecal egg count in Polish Heath Sheep

“…Variation has been observed both among the animals of the same breed and between animals from different breeds in their resistance to parasite infections (Stear and Murray, 1994;Romjali et al, 1997). Special attention is paid in the studies on this variation to the major histocompatibility complex (MHC) (Beh and Maddox, 1996).…”