Response to challenge infection in sheep selected for resistance and susceptibility to Haemonchus contortus

Abstract

A study was undertaken to compare the host response on single and trickle infections of H. contortus in Malpura lambs selected for either resistance or susceptibility to H. contortus. Twelve Malpura male lambs (6 each from resistant - R and susceptible - S lines; 9-12 months old) were used during two periods of 10 weeks: single and trickle infections with an interval of three weeks. The host response was measured in terms of body weight, faecal egg count, haematological and biochemical characters for 10 weeks post challenge. Over the period of 10 weeks, a gain of 0.3 kg was recorded in lambs of R-line compared to a loss of 4.1 kg in S-line on single challenge. However, on trickle infection both the groups exhibited gain (5.7 kg in R-line and 5.2 kg in S-line) in body weight. On majority of occasions intensity of infection was lower in R-line compared to S line. Non-significant variation was observed in haemoglobin (Hb) and packed cell volume (PCV) among both the lines on single challenge. However, significant (P<0.05/0.001) variations among divergent lines (lower Hb value in S-line compared to R-line) were observed on trickle challenge. In both the forms of challenge, plasma pepsinogen level revealed non-significant variation. On slaughter, the mean number of adult H. contortus in abomasum varied non-significantly between 498.7±40.1 (R-line) and 576.7±270.1 (S-line). The worm length remained more or less similar in both the lines. Correlation between log FEC and body weight was significant (P<0.05) only in S line. Log FEC showed significantly (P<0.001) negative correlation with Hb and PCV in both the lines on single challenge. The correlation between log FEC and plasma pepsinogen level was significantly (P<0.05) negative in both the lines on trickle challenge. It was concluded that the animals selected for resistance can tolerate parasite challenge effectively with reduced intensity of infection, higher body weight gain and reduced pathogenic effect.