Preferences for foods varying in macronutrients and tannins by lambs supplemented with polyethylene glycol

Supplemental polyethylene glycol (PEG) increases intake when animals eat fo ods high in tannins, but little is known about how PEG affects preference f or foods that vary in concentrations of macronutrients and tannin. We inves tigated how varying macronutrients and tannins (commercially available extr acts from quebracho trees) affected food intake, and we assessed the degree to which PEG; (MW 3350) affected intake of tannin-rich foods by sheep. Fro m 0715 to 1800 daily, lambs were offered diets that varied in concentration s of macronutrients: high energy/low protein (75% barley/25% alfalfa), medi um energy/medium protein (35% barley/65% alfalfa), and low energy/high prot ein (100% alfalfa). Preference for these diets was determined in the absenc e of tannin, and then, in Trials 1 to 3, tannin was added in increasing con centrations (from 5 to 20%) to the diets with high and medium levels of ene rgy. In Trial 3, tannin (10%) also was added to the low-energy diet. Lambs were supplemented with either 50 g of PEG mixed with 50 g of ground barley or 50 g of ground barley alone from 0700 to 1715 daily; lambs always consum ed all of these supplements. In the absence of added tannins, all lambs pre ferred high energy/low protein > medium energy/medium protein > low energy/ high protein. As tannin levels increased, preference for the high- and medi um-energy foods decreased, and all lambs preferred foods that were lower in tannins and higher in protein. Lambs supplemented with PEG ate more macron utrients and tannins than unsupplemented lambs, and the effect became incre asingly apparent as tannin levels increased from Trials 1 to 4. We conclude that the effectiveness of supplemental PEG may be low if alternative forag es are equal or superior in nutritional quality and contain fewer metabolit es with adverse effects. In such cases, animals would likely prefer alterna tives to high-tannin foods.