Assessing the impact of supplements, food aversions, and silica on medusahead (Taeniatherum caput-medusae (L.) Nevski) use by sheep

Abstract

We explored in sheep (1) the impact of supplements on medusahead intake and preference, (2) whether medusahead is aversive, and (3) if silica inhibits food intake. Groups of lambs (n=8) were individually penned and randomly assigned to 4 supplementation treatments: beet pulp:barley (70:30) (High Energy; HE), alfalfa:soybean meal (60:40; High Protein; HP), a choice of HE and HP (CHOICE), or no supplement (Control). After supplementation all animals had ad libitum access to medusahead in early reproductive – Trial 1, late reproductive – Trial 2, and thatch – Trial 3 phenological stages. On the last day of each trial, lambs had choices between medusahead and tall fescue hay. Lambs in HE tended to ingest (P<0.10; Trial 1) or marginally (P<0.05; Trial 2) consumed more medusahead than lambs in Control but intake values were low for all groups. Lambs in HE, HP and CHOICE showed greater intake of and preference for medusahead thatch than Control lambs during preference tests of Trial 3 (P<0.05). Lambs in HE, HP, and CHOICE ate more feed and had greater ADGs than Control lambs (P<0.05). In Trial 4, three groups of lambs (n=10) were fed beet pulp and then received intraruminal infusions of: (1) tall fescue hay (4g/kg BW), (2) lithium chloride (LiCl; 150mg/kg BW), and (3) medusahead (4g/kg BW). Medusahead infusions did not reduce intake of beet pulp relative to infusions of tall fescue hay (P>0.10), whereas infusions of LiCl conditioned a food aversion (P<0.05). In Trial 5, three groups of lambs (n=10) were fed: (1) alfalfa, (2) alfalfa-2.5% Silica, and alfalfa-4.5% Silica. Lambs in Group 2 had the lowest intake of alfalfa (P<0.05). Our research suggests that supplements can increase preference for thatch by sheep but their influence on intake and preference is only marginal for the other phenological stages tested. Our results also suggest that food aversions do not explain the low palatability of the weed, which may be better understood by the high concentrations of silica in its tissues.