Effect of soybean meal treatment with Cistus ladanifer condensed tannins in growth performance, carcass and meat quality of lambs

The effect of Cistus ladanifer (rockrose) condensed tannins (CT) on dietary protein utilization in lambs was evaluated. The experiment was conducted to test the hypothesis that treating soybean meal (SBM) with rockrose condensed tannins will improve dietary protein utilization allowing a reduction of the dietary crude protein content of lamb's diets without compromising growth performance, blood metabolites, carcass traits and meat quality. An experiment was conducted using growing lambs fed diets with SBM as the main source of protein, but differing in protein level (160 vs. 120 g/kg dry matter (DM)), treated or not with rockrose CT. Twenty four lambs penned individually were fed three diets based on grass hay and concentrate in a proportion of 15/85 (W/W). Concentrates were formulated to contain: 160 g of crude protein (CP)/kg DM with untreated SBM (Control); 120 g of CP/kg DM with untreated SBM (restricted protein, (RP)); 120 g of CP/kg DM with SBM treated with 15 g/kg DM of rockrose CT (RPCT). The daily feed amounts corresponded to 4% of live weight, and were adjusted weekly. Lambs fed RP diet showed the lower average daily gain (ADG) rates and lower protein efficiency. With CT inclusion a positive response on growth and on feed and protein efficiency was obtained, with ADG values similar to those obtained in lambs fed the Control diet and protein feed efficiency ratio higher than with the other diets. Carcass traits and meat quality were not affected by treatments. Through pre-treating protein sources with rockrose CT it is possible to reduce the protein content of diets without compromising lamb performance.