Selection of tannins by sheep in response to gastrointestinal nematode infection1

Abstract

Herbivores learn to select compounds that attenuate the aversive effects of plant secondary metabolites (PSM), but can they increase intake of PSM they typically avoid when these PSM provide medicinal effects? We hypothesized that herbivores learn to increase intake of PSM-containing feeds when experiencing a gastrointestinal parasitic infection. Ten lambs with natural gastrointestinal parasitic burdens (PB) and 10 nonparasitized lambs (NP) were offered a choice of alfalfa (Medicago sativa) and alfalfa mixed with 10% quebracho tannin (Schinopsis quebracho-colorado; alfalfa:tannins) before and after they were conditioned with the postingestive effects of tannins. Preference for alfalfa:tannins did not differ between groups before experiencing the postingestive effects of tannins (P = 0.85) or when parasite loads were terminated due to the administration of ivermectin (P = 0.18). In contrast, when tested with a parasite burden, lambs in PB consumed more alfalfa:tannins (P = 0.08), showed greater preference for alfalfa:tannins (P = 0.07), and consumed less alfalfa than lambs in NP (P = 0.06). Ingestion of tannins by lambs in PB was followed by reduced fecal egg counts (FEC; P = 0.006), and there was a direct proportional relationship between preference for alfalfa:tannins and FEC (P = 0.07). In summary, parasitized lambs increased their intake of alfalfa:tannins when they experienced a parasite burden, which suggests they self-medicated with tannins against parasites. Self-selection of PSM has implications for the quest for alternatives to chemoprophylaxis in the treatment and well-being of parasitized wild and domestic animals grazing in pasturelands and in confinement.

Phytochemicals in animal health: diet selection and trade-offs between costs and benefits

“…Longer-term studies are needed to assess potential fitness benefits in parasitised livestock offered PSC-containing foods. However, we know that self-selection of condensed-tannin containing foods is triggered by parasitism in sheep and goats and that such behaviour reduces parasitic burdens (32)(33)(34) . We also know that sheep reduce their preference for tannincontaining foods when parasitic burdens subside (32,33) and that ingestion of condensed tannins induce penalties on performance (e.g.…”

“…However, we know that self-selection of condensed-tannin containing foods is triggered by parasitism in sheep and goats and that such behaviour reduces parasitic burdens (32)(33)(34) . We also know that sheep reduce their preference for tannincontaining foods when parasitic burdens subside (32,33) and that ingestion of condensed tannins induce penalties on performance (e.g. growth (35)(36)(37) ; see Table 1 for evidence of self-medication in animals).…”

“…Recent research suggests birds self-medicate with antioxidants (62) . Birds challenged by an increased production of reactive oxygen species after long flights (9) or under thermal stress (63) preferentially select foods high in flavonoids : parasitised animals (data taken from Villalba et al (32) ). : naive control animals; : parasitised animals (data taken from Juhnke et al (33) ).…”

Cattle and sheep develop preference for drinking water containing grape seed tannin

“…Trials with various concentrations of grape seed tannin (GST) in water were conducted to determine if sheep and cattle would develop a preference for water with GST in it and if they would prefer to drink water containing specific concentrations of this CT rather than water. Since there is now considerable evidence that ruminant livestock develop preferences for feeds and liquids that help them meet their nutritional needs and relieve ailments such as acidosis and gastrointestinal parasite infections (Burritt and Provenza, 1992;Kyriazakis and Oldham, 1993;Provenza, 1995;Phy and Provenza, 1998;Villalba et al, 2006;Villalba and Provenza, 2007;Lisonbee et al, 2009;Villalba et al, 2010), our hypothesis was: when consuming a high-quality forage diet, sheep and cattle would learn to prefer water that contained GST. However, because ruminants appear to need repeated exposure to a new flavor or food before they may develop a preference for it (Launchbaugh et al, 1997), we anticipated that sheep and cattle would require repeated exposure to increasing concentrations of GST in water before they would learn to prefer water containing this tannin.…”

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“…However, sheep under available pasture restriction, for example during Summer when the growth rate of the fast growing grass species has diminished due to the soil water restriction [13], the selection pressure is on broad leaf species because these species may have enough water soluble carbohydrate content to be palatable [14]. Several studies focused on sheep grazing behavior showed a pasture structure with a decreased broad leaf species while grasses and legumes species increased [15][16][17][18][19][20].…”