The genetic resistance to gastrointestinal parasites in Bergamasca sheep breed: Heritability and repeatability of faecal egg counts (FEC)

Bergamasca is a sheep breed mainly reared for the production of meat. Native of the Clusone plateau and the Bergamo valleys, it is now mostly spread in Lombardy (Bergamo), but it is also commonly found in other regions of Northern and Central Italy particularly as a crossing breed. This study was carried out in a single Bergamasca herd from Matelica (MC) to estimate heritability and repeatability of EPG (Eggs Per Gram) and OPG (Oocyst Per Gram) count as a preliminary investigation on the genetic resistance to parasitic fauna. Individual fecal samples of 75 adult Bergamasca ewes and 39 lambs have been considered coming from 5 subsequent withdrawals (from May 2007 to February 2009). Fecal samples were analyzed in order to determine EPG or OPG using the FLOTAC technique. Besides Coccidia and gastro-intestinal Strongylids (including Nematodirus sp.), samples were also analyzed in order to evaluate the presence of Strongyloides sp, Trichuris spp and Dicrocoelium dendriticum. For the statistical analysis data regarding EPG and OPG were transformed to the natural logarithm according to the formula y = log (EPG/OPG+25) to correct for heterogeneity of variance and to produce approximately normally distributed data. A mixed linear model for repeated measures was used to test the effect of the season on the considered variables and to estimate the repeatability. The heritability coefficients of EPG and OPG using daughter-mother regression and repeatability resulted in null values for all considered parameters.