Intake of medusahead by sheep: influence of supplements, silica and individual animal variation.
Grazing represents a sustainable alternative for the control of medusahead infestations but intake of medusahead by ruminants is typically low. We determined in sheep whether (1) high-energy supplements enhance medusahead intake and preference relative to a treatment without supplementation and (2) individual differences in medusahead intake transfer to individual differences in the ingestion of a silica-containing ration. Groups of lambs (n=10) were individually penned and randomly assigned to three supplementation treatments: (1) Control (no supplement); (2) Calcium (Ca) Propionate (beet pulp:barley:Ca propionate, 67:30:3); or (3) Yeast (beet pulp:barley:yeast culture, 65:30:5). After supplementation, all animals had ad libitum access to medusahead in late vegetative to mid-reproductive (Trial 1), and late-reproductive phenological stages (Trial 2). Medusahead preferences were assessed by offering sheep a choice between medusahead and tall fescue hay. Plant part preferences were assessed by offering a choice between medusahead tops (mostly seedheads and awns) and mid-plant parts (mostly stems+leaves). Intake of medusahead was low and cyclic, declining towards the end of each trial (P<0.0001) and there were no treatment differences (P>0.10). Lambs preferred tall fescue hay to medusahead and medusahead tops to mid-plant parts (P<0.0001). Supplemented lambs gained more weight than control lambs (P<0.10). Thus, supplemented lambs performed better than nonsupplemented controls without reducing their intake of medusahead. In Trial 3, two new groups of lambs were formed based on their intake of medusahead during Trials 1 and 2 (n=10). One group consistently ate more medusahead and more of a ration containing silica (alfalfa:silica, 97:3) than the other (P<0.10). A significant and consistent degree of individual variation was measured among lambs - irrespective of treatment - regarding their ability to ingest medusahead and silica. This variation represents a promising option for maximizing use of medusahead by livestock in rangelands.