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

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.