Phenotypic markers to characterize F2 crossbreed goats infected by gastrointestinal nematodes

• We evaluated and characterize goats with different levels of resistance to gastrointestinal parasitic nematodes.
• We observed significant differences in phenotypic markers between groups.
• Resistant animals presented low EPG counts, high packed cell volume and total plasma protein than susceptible animals.
• The number of nematodes in the abomasums and small intestine was higher in susceptible group than in resistant.
• The animals identified as resistant had a better response to the gastrointestinal nematodes than animals identified as susceptible.

The aim of this study was to evaluate and characterize goats with different levels of resistance to gastrointestinal parasitic nematodes. During 93 days, 60 F2 crossbreed goats originated from ½ Saanen and ½ Anglo-Nubian animals were grazed in the same pasture. Feces and blood were collected on a weekly basis for eggs per gram counts of feces (EPG) and coprocultures and to determinate the number of eosinophils, packed cell volume and total plasma protein, respectively. On the same day, the animals were weighed, they body condiction was scored and their degree of anemia estimated by FAMACHA card. Based on the average values of EPG, the 12 animals with the highest average of EPG (susceptible group) and the 12 animals with the lowest average of EPG (resistant group) were selected, slaughtered and necropsied for counting and parasites identification. The resistant animals presented lower EPG counts (P < 0.0001) and 4.7 folder less parasites than susceptible animals. The resistant group also presented a higher average of packed cell volume (26.48%) and total plasma protein (6.24 g/dl) than susceptible one (24.04% and 5.82 g/dl, respectively). The average of number of eosinphils was similar among groups. The weight of resistant animals was higher than susceptible group (23.17 kg and 19.17 kg, respectively; P < 0.05), with better body condition score than the susceptible counterparts. The resistant animal had higher FAMACHA at class 1 (20%) than the susceptible one (5.26%), with FAMACHA 4 (4.21%). Haemonchus sp. was the most prevalent in the coprocultures, followed by Trichostrongylus sp. and Oesophagostomum sp. The number of nematodes in the abomasum was higher in susceptible group than in resistant one. The species identified were Haemonchus contortus in abomasum and Trichstrongylus colubriformis in small intestine. The EPG, packed cell volume and total plasma protein were useful phenotypic markers to identify resistant and susceptible animals to gastrointestinal nematodes infections.