Effects of inclusion of licorice (Glycyrrhiza glabra L.) leaves, a tannin-containing plant, in a low-protein diet on feedlot performance and carcass characteristics of fat-tailed lambs.

The protein-sparing effect of condensed tannins (CT) was investigated in growing lambs fed a low- or high-protein diet during a 50-day period. Isocaloric diets containing 106 g crude protein/kg dry matter (DM) (low protein; LP) or 138 g crude protein/kg DM (high protein; HP) were formulated using 70 % concentrate, 15 % corn silage, and 15 % dried licorice leaves, providing CT (4.1 g/kg DM). Twenty-four crossbred male lambs (3-4 months old, 23.9 ± 5.2 kg body weight) were assigned to one of four diets: LP with polyethylene glycol (PEG; 40 g/kg DM) supplementation (LP + PEG), LP without PEG supplementation (LP - PEG), HP with PEG supplementation (HP + PEG), and HP without PEG supplementation (HP - PEG). The effect of dietary crude protein level and CT on feed intake was not significant (P > 0.05). However, a positive effect on daily gain (P < 0.001) and feed conversion ratio (FCR; P < 0.01) was observed in lambs fed with HP diets. An interaction effect between crude protein level and PEG was observed, and consequently, FCR was higher in group LP + PEG (10.1; P < 0.05) than in groups LP - PEG (7.3), HP + PEG (5.3), or HP - PEG (5.4). There was also an interaction effect between crude protein level and PEG on kidney, pelvic, and heart fat, presenting a higher relative weight in group LP + PEG (12.6 g/kg) than in group HP + PEG (9.2 g/kg; P < 0.05), but no (P > 0.05) in groups without PEG supplementation. These preliminary results suggest that the use of CT can minimize the negative effect of low-protein diets on FCR in lambs.