Behavioural and productive response to experimental infection with stage 3 larvae of Haemonchus contortus in feedlot bull-calves

Abstract Haemonchus contortus is a nematode parasite that establishes in the abomasum of ruminants, it has a cosmopolitan distribution and is a worldwide health problem for livestock. As a first line of defence against parasites, behaviour can help to prevent or fight infection, and may even serve as a method of early presumptive diagnosis. Parasites can affect performance of cattle and cause significant economic losses. The aim of this study was to determine the behavioural and productive changes induced by an experimental infection with H. contortus L3 in bovines. We used 32 dewormed bull calves, randomly divided into two groups, 8 no inoculated controls and 24 that were inoculated with 4000 L3 of H. contortus . Inoculation did not influence haematocrit or haemoglobin values at 0, 28 and 42 days post infection ( P > 0.20); however, an increase in the frequency of urination ( P  = 0.0001) and defecation ( P  = 0.0001), number of steps ( P P H. contortus , feedlot performance was not affected ( P  = 0.16), but during the last 14 days (29–42) inoculated animals gained 15% less weight compared to controls ( P  = 0.04). Over 42 days, inoculated calves showed a 28% poorer feed efficiency during the 42 days post-inoculation than controls ( P H. contortus obtained less net energy both for maintenance as for gain from diet ( P H. contortus , supporting the practice of deworming when eggs of this parasite are detected in the faeces even in low amounts.