The responses of three nigerian indigenous goat breeds to primary and secondary experimental challenges with Haemonchus contortus
A study was designed to investigate if an initial infection is sufficiently protective to prevent the development of subsequent re-infection with H. contortus, and to determine whether or not the removal of primary infection could enhance stronger acquired immunity which is protective enough to prevent the establishment of a secondary infection. Responses of three Nigerian breeds of goat; Red Sokoto (RS), West African Dwarf (WAD) and Sahel White (SW) were investigated following primary and secondary experimental infections with Haemonchus contortus. Forty five (45) goats, (n=15) of each breed type were used in the experiment. During the primary challenge, (n=11) goats each of the three breeds were infected with 100 (L3) larvae of H. contortus by gavage weekly for 7 weeks, while four (4) goats each per breed served as control. On day 42 post infection, (n=12) goats, (4 per breed) of the infected animals were humanely euthanized and worm count determined. The second phase was carried out on the remaining twenty one (21) infected goats. They received the weekly infective dose of H. contortus by gavage up to week 10, when they were divided into 2 groups. The first group of 12 (4 SW, 4 WAD and 4 RS) animals were untreated, while the second group of 9 (3 per breed) animals were treated. The 2 groups were further reinfected with 2000 L3 of H.contortus each for a period of 7 consecutive weeks after a rest period of ten days. Clinical signs, worm establishment rate, faecal egg count (FEC), packed cell volume (PCV), eosinophil count, total serum protein and C3 complement were determined. The PCV, C3 complement and total serum protein of infected animals declined significantly (p<0.05) when compared to the control, after both primary and secondary challenges, irrespective of breed. Conversely, eosinophil count increased significantly (p<0.05). WAD showed improved parameters than other breeds, indicating better adaptability or greater resistance than the other breeds.
Keywords: Haemonchosis, Haematology, Nigerian goats, Primary and secondary infections, Resistance, Responses.