Preference for Condensed Tannins by Sheep in Response to Challenge Infection with Haemonchus contortus
Herbivores prefer feeds that supply required nutrients and avoid those with excess nutrients and plant secondary compounds (PSC). Nevertheless, PSC such as condensed tannins can provide beneficial medicinal effects to herbivores as they act against infective diseases such as parasitism. The objectives of this study were to determine: (1) if parasitized lambs increased preference for a tannin-rich feed after they experienced the beneficial antiparasitic effects of condensed tannins relative to parasitized lambs that did not experience such benefits, and (2) if preference for the tannin-rich feed in the former group decreased when parasite burdens subsided. Twenty two lambs were familiarized with beet pulp and beet pulp + 8% quebracho tannins (beet pulp + tannins) and choices were given between the two feeds (initial preference tests). Subsequently, all animals were dosed with 10,000 L3 stage larvae of Haemonchus contortus. Twenty-two days later, animals were exposed to beet pulp (Control group; n = 11) or beet pulp + tannins (Treatment group; n = 11) during 24 d. After exposure (during a parasitic infection) animals in both groups were given choices between the two feeds. Lastly, animals in both groups received an antiparasitic drench and were again given a choice between both feeds (after a parasitic infection). Lambs preferred beet pulp to beet pulp + tannins throughout the study (P < 0.001) and no difference in preference for the tannin-rich feed was detected between groups during initial preference tests (P > 0.05). However, during a parasitic infection, intake of and preference for the tannin-rich feed was higher for lambs that experienced the beneficial effects of condensed tannins while parasitized (Treatment) than for lambs that did not (Control) (P < 0.05). When parasitic infections were terminated by chemotherapy, differences between groups disappeared (P > 0.05). Preference by the Treatment group for the tannin-rich feed was lower after than during a parasite infection (P < 0.05). In contrast, preference by the Control group did not change during these periods (P > 0.05). Lambs in the Treatment group displayed lower FEC than lambs in the Control group (Group × Sampling Date; P < 0.05). These results show lambs learned about the antiparasitic effects of condensed tannins and increased their preference for the tannin-rich feed, which subsided after chemotherapy, indicating preference was due to parasite infection. These findings suggest management that allows animals to select tannin-rich feeds can enable parasitized animals to self-medicate.
J.Juhnke et al. 2012.Preference for condensed tannins by sheep in response to challenge infection with Haemonchus contortus. Veterniary Parasitology. 188 (1-2): 104-114