Effects of Progressive Replacement of Corn Stover with Condensed Tannin-Containing Woody Biomass on Growth Performance and Reproductive Development of Prospective Breeding Ram Lambs

This study determined the level at which corn stover (CS) could be progressively replaced with condensed tannin-containing woody biomass (CTWB) from Quercus rugosa without compromising dietary acceptance, growth, energy utilization, or reproductive development in prospective breeding ram lambs. In Experiment 1, eight intact Rambouillet ram lambs (5 months old; 40.7 ± 0.2 kg initial body weight) were simultaneously offered diets containing 0–80% CTWB (CTWB-0–CTWB-80), equivalent to 0.00–20.96 g condensed tannins (CT)/kg dry matter (DM), in an 8-d preference trial. In Experiment 2, 36 intact Rambouillet ram lambs (6 months old; 49.97 ± 0.79 kg initial body weight) were assigned for 70 d to diets containing 0–60% CTWB and a calculated CT contribution from CTWB of 0.00–15.72 g/kg DM (n = 9/treatment). In the preference trial, CTWB-20 reduced CS from 80 to 60% without affecting the proportion of diet consumed or relative palatability index compared with CTWB-0, whereas inclusions ≥40% reduced both responses (p = 0.0143 and p = 0.0146, respectively). In the growth trial, CTWB-20, corresponding to 5.24 g CT/kg DM from CTWB, maintained growth performance comparable with CTWB-0 and produced a greater overall growth response than CTWB-60, reflected by greater final body weight (63.95 vs. 57.87 kg; p = 0.016), average daily gain (0.202 vs. 0.126 kg/d), cumulative body weight change (14.19 vs. 8.93 kg; p = 0.019), and gain-to-feed ratio (0.094 vs. 0.058; p = 0.011). Dry matter intake (DMI) remained similar (p = 0.278). As CTWB increased, expected DMI increased (p < 0.0001), the observed-to-expected DMI ratio decreased (p = 0.003), and the observed-to-expected net energy for maintenance (NEm) and gain (NEg) ratios increased (p ≤ 0.045), although observed NEm and NEg concentrations remained unchanged (p = 0.146). Rib fat thickness was maintained with CTWB-20 but decreased with CTWB-40 and CTWB-60 (p = 0.004), whereas longissimus muscle area, scrotal circumference, and sperm motility remained similar (p ≥ 0.157). Additionally, CTWB-20 was associated with greater sperm viability (p = 0.032), while all CTWB levels were associated with fewer morphologically abnormal sperm (p = 0.005). Finally, treatment did not affect income over feed cost or cost of gain (p = 0.217 and p = 0.735, respectively), indicating that partial replacement with CTWB did not adversely affect economic efficiency. Overall, 20% CTWB reduced CS from 60 to 40% and provided a favorable balance among dietary acceptance, growth, semen characteristics, and economic efficiency.