Genetic factors of sheep affecting gastrointestinal parasite infections in the Distrito Federal, Brazil

Abstract

Three sheep farms were used in the Distrito Federal, Central Brazil, to study the occurrence of parasites in the feces. A total of 1798 collections were taken over the period of a year. A total of 1205 were taken in Santa Inês breed (SI) in all three farms, 323 in Bergamasca (Berg), 54 in Ile de France, 49 in IlexSI, 103 in Morada Nova (MN) and 64 in TexelxSI, these last five groups being on a single farm. The animals were drenched soon after weaning and feces collected every 3 weeks to calculate fecal egg count (FEC), at least on two occasions on each animal. In some cases, blood was collected to determine packed cell volume (PCV) at fecal collection. Fixed effects included farm, breed/genetic group within farm, animal age (months), birth type (simple, twin) and sex. (Co)variance components were estimated for Santa Inês sheep using restricted maximum likelihood under an animal model. FECs were affected by month and farm showing that climate and management are important sources of variation for the parasites studied. While age and birth type of the lambs did not affect infection level, their genetic group was important, showing that breeding strategies can help control these parasites. Heritabilities for infection level in the sheep varied between 0.09 for Strongyloides and 0.31 for Moniezia expansa. Genetic selection strategies for sheep aimed at reducing these infections should result in more resistant animals.

Performance and parasite control of different genetic groups of lambs finished in irrigated pasture

“…This may be related to the triggering of immune responses and consequent resistance of animals to parasitism, a factor also reported by Abrão et al (2010) and reinforced by the work of McManus et al (2009) andLôbo et al (2009). In the latter, according to the authors, the heritability for EPG increased with infection.…”

“…This explains the pattern of EPG found in that research. McManus et al (2009) pointed out that genetic selection against these parasite infections can result in more resistant animals.…”

“…Some studies aim to evaluate the efficacy of anthelmintic drugs and risk of parasite resistance (Taylor et al, 2009), while others look for alternative substances and methods to control nematode parasites (AlonsoDíaz et al, 2010;Iqbal et al, 2010). Nowadays, more importance is given to the studies of genetic factors that influence the immune response of animals with the objective of identifying genotypes that have a greater genetic resistance to gastrointestinal nematodes (McManus et al, 2009). Bishop (2012) recommends a selection based on phenotypic measurements such as performance under conditions of nematode challenge, number of eggs per gram and measures of anaemia, such as packed cell volume or FAMACHA © score.…”

Os parasitas de ovinos

“…Os resultados foram coincidentes, independentemente da categoria avaliada e do tipo de infecção, natural ou artificial. O único estudo em que a raça Santa Inês mostrou-se comparativamente mais susceptível foi realizado no Distrito Federal (McManus et al, 2009). Nesse trabalho, demonstrou-se maior resistência da raça Morada Nova, casualmente uma das raças utilizadas na formação da raça Santa Inês.…”

Genetic diversity and assessment of 23 microsatellite markers for parentage testing of Santa Inês hair sheep in Brazil

“…They have a large, well-developed rump and largely black or brown pelts, which has appeared in a large proportion of the population in the last few years. This has led to reduced heat tolerance (McManus et al, 2009a) and resistance to endoparasites (McManus et al, 2009b). In addition, according to records of these flocks, the morphological changes that led to the creation of a New Santa Inês were possibly intensified by the introduction, from time to time, of some rams during mating season in order to increase the fertility of the flocks.…”