Morada Nova sheep breed: Resistant or resilient to Haemonchus contortus infection?

[Display omitted] •Resistance against Haemonchus contortus was assessed in a Morada Nova flock.•More than 88% of the lambs had PCV≥24% even with high fecal egg counts (FEC).•Only susceptible lambs had decreased live weight due to parasitism.•More than 98% of the ewes had FEC below 4000 EPG.•PCV of the ewes was not affected by H. contortus infection. Morada Nova is a Brazilian hair sheep breed that is well adapted to the country’s mainly tropical climate and has good potential for meat and leather production. This breed is reported to be resistant to Haemonchus contortus infection, a highly desired characteristic due to the large impact of this parasite on sheep farming. Therefore, the present study aimed to characterize 287 recently weaned Morada Nova lambs and 123 ewes in relation to their resistance against H. contortus. The animals were dewormed and 15 days later artificially infected with 4000 H. contortus L3 (D0). They were individually monitored by periodic assessment of fecal egg count (FEC), packed cell volume (PCV), and live weight (LW). On D42, the sheep were again dewormed and submitted to a new parasitic challenge, following the same scheme. The animals of each category (lambs and ewes) were ranked according to individual mean FEC values, and classified as resistant (R, 20%), intermediate (I, 60%), or susceptible (S, 20%) to H. contortus infection. At weaning, high FEC were observed in all three phenotypes (P>0.05). After the artificial infections, there was a significant difference (P S), and LW (R=I > S). The infection levels (FEC) were negatively correlated with PCV (r = -0.66; P