Goats are more susceptible to Haemonchus contortus infection than sheep under similar experimental settings

Due to differences in their feeding behavior, sheep and goats are often assumed to respond differently to helminth infections. The present study compared Haemonchus contortus infection profile between sheep and goats under the same experimental setting. Experimental infection was conducted using a randomized block design in four groups of intact sheep (InfSH and ConSH) and goats (InfG, and ConG). Groups InfSH and InfG (N = 7 each) received 10,000L3 of H. contortus whereas the control groups ConSH and ConG (N = 7 each) remained uninfected. Faecal egg counts and PCV were measured from Day 0 to day 56 post infection (PI). On day 56 PI, animals were humanely slaughtered and abomasal contents were recovered to measure worm burden, worm length and in utero egg count. The findings show that: (1) Haemonchus infected animals showed an increase in FEC starting from day 21 PI, (2) progressive reduction in PCV was registered from day 7 PI and continued to the end of the experiment while this remained at pre-infection levels in control groups, (3) FEC was much higher (P < 0.001) and PCV was significantly lower (P < 0.05) in infected goats than in infected sheep, (4) at necropsy, total worm burden with worm establishment rates of 63% and 28.87% were registered respectively for infected goats and sheep with significant difference (P < 0.05), (5) Female worms were significantly longer (P < 0.05) in InfG (22.8(+/- 1.2) compared to InfSH (20.5 +/- 0.67 mm) while (6) Mean worm fecundity was 974.8 +/- 239.4 and 1162.5 +/- 89.4 respectively for groups InfSH and InfG with no significant difference (P = 0.07), and (7) Parasite traits such as worm burden, FEC and female worm length were well correlated in sheep whereas few such patterns were observed in goats. In conclusion, under the same experimental infection, Arsi-Bale goats are more susceptible to H. contortus infection than Arsi-Bale sheep and hence deserve special attention when they are forced to live on grazing rather than browsing.