Abstract

Romerillo (Chiliotrichum diffusum) is an unpalatable and invasive shrub occurring in over 1M ha of Magellan rangelands, which constraints livestock operations and reduces biodiversity. Low nutrient content and the presence hydrolizable tannins (HT) explain the low palatability of the shrub. We determined whether supplemental macronutrients (Exp. 1) or polyethylene glycol (PEG; Exp. 2), a compound that reduces bioavailability of tannins, enhance intake of romerillo by sheep. An in vivo digestion trial (Exp. 3) assessed the influence of nutrient supplementation on apparent DM digestibility in sheep fed romerillo. In Exp. 1, 28 yearling ewes were penned individually and randomly assigned to 4 groups (7 ewes/group), where they had supplements high in energy (HE; corn), high in protein (HP, canola meal), a choice between HE and HP (CH), or no supplement (Control; C). Subsequently, all ewes had ad libitum amounts of freshly cut romerillo followed by 1% BW of grass hay. Intake of romerillo was HP > C> HE (8.4, 6.3, 4.5 g/Kg BW, respectively; P 0.05), and ewes in CH selected a 67:33 proportion of corn:canola meal that only tended to reduce romerillo intake relative to HP (6.8 g/Kg BW; P= 0.074). Ewes maintained (HP, HE), reduced (C) or increased (CH) their BW during 26 d of experimental feeding (P 0.05). In Exp. 2, thirty-two yearling ewes were assigned to a 2x2 factorial design (8 ewes/group), with PEG (1-yes, 2-no) and Supplement (1-HP; 2-Mix:67:33 proportion corn:canola meal) as factors, and fed as in Exp. 1. PEG did not affect romerillo (3.4 % HT) intake (P > 0.05), but ewes supplemented with HP showed the greatest intakes of the shrub (6.6 g/Kg BW; P= 0.0002). In Exp. 3, 15 wethers were housed in metabolic crates and assigned to HP, C and Mix treatments (5 animals/group), and fed as in Exp. 1. Romerillo intake did not differ among groups, but the group HP tended (P= 0.0874) to show greater values of digestibility than the group C, and the supplemented groups presented greater DM retention values (P 0.05). Thus, protein supplementation or choices between energy- or protein-dense supplements in targeted browsing programs have the potential to enhance use of romerillo by ewes in Magellan rangelands while maintaining or enhancing animal BW. In contrast, PEG supplementation did not affect shrub intake and energy-dense supplements reduced romerillo intake relative to unsupplemented animals.