Condensed tannin intake and sheep performance: A meta-analysis on voluntary intake and live weight change

This study estimated the impact of condensed tannin (CT) consumption on dry matter intake (DMI) and live weight change (LWC) of growing sheep by means of a meta-analysis. A metabolic cost associated to CT intake was also estimated. Data included in the meta-analysis were obtained from scientific literature with the following inclusion criteria: (a) growing lambs fed ad-libitum without gastrointestinal nematode infection, (b) feed consumption data, (c) chemical composition of diets, and (d) CT consumption data. Data were analyzed as a whole data-set or grouped into three categories: (a) sheep consuming CT (CT group), (b) sheep not consuming CT (non-CT group) and (c) sheep consuming CT + polyethylene glycol (CT + PEG group). The effect of diet composition and quality (crude protein (CP), organic matter (OM), neutral detergent fiber (NDF), condensed tannins (CT), metabolizable energy (ME), dry matter digestibility (DMD), OM digestibility (OMD) and CP digestibility (CPD)) on DMI (g/kg0.75) was evaluated using regression analyses. The effect of diet composition and consumption of those same variables (g/kg0.75) on LWC (g/kg0.75) were also evaluated using respective regression analyses. The metabolic cost of CT consumption was estimated in terms of digestible crude protein (DCP) and ME requirements. The cost was estimated for a diet to sustain maintenance and a diet to supply 100 g/d LWC requirements. No effect was found of CT intake on DMI or LWC (P > 0.05). The DMI was best predicted by CP and DMD concentration (g/kg DM), when analyzed as a whole data-set. When analyzed as separate categories for CT and non-CT group was best predicted by ME (MJ/kg DM) (P < 0.05). For the CT + PEG group the DMI was best predicted by NDF (P < 0.05). The LWC was best predicted by DCPI2 when analyzed as a whole data-set. The best predictor of LWC was the DCP intake (for the CT data) and the ME intake (for non-CT data and CT + PEG data) (P < 0.05). Although CT intake do not have an effect on DMI and LWC, it was observed that at low dietary CP level increases DCP requirement and hence it does have a metabolic cost associated. The metabolic cost of CT consumption estimated for animals consuming a maintenance diet was 0.33 MJ of ME/kg0.75 and 1.04 g of DCP/kg0.75 and for animals fed a 100 g LWC diet was 0.13 MJ of ME/kg0.75 and 0.87 g DCP/kg0.75. Thus, a higher cost for CT intake was found for groups of lambs at low feeding level and the metabolic cost was reduced when lambs were at higher feeding levels.