Effects of feeding Lespedeza cuneata pellets with Medicago sativa hay to sheep: Nutritional impact, characterization and degradation of condensed tannin during digestion

Abstract

Sustainable ruminant livestock production could benefit from feedstuffs containing condensed tannin (CT) if they maintained or improved livestock health and productivity while reducing the excretion of urinary nitrogen (N), which can be readily lost to the environment. Such feedstuffs would be most useful if they were easy and inexpensive to grow and could be field dried and pelletized for ease of transport and storage. One feedstuff that may meet these criteria is pelleted sericea lespedeza (SL; Lespedeza cuneata). Therefore, a 4 × 4 Latin square trial was conducted with four mature male sheep fed four proportions of pelleted SL with alfalfa (Medicago sativa) hay cubes, to determine effects on digestion and N excretion, and the fate of the CT during digestion. Pelleted SL contained (g/kg dry matter; DM) 182 CT, 23.3N, 341 aNDF, 227 ADF, 87 ADL and 55 ash, while the cubed alfalfa hay contained (g/kg DM) 28.5N, 381 aNDF, 284 ADF, 78 ADL and 137 ash. The SL pellets were consumed readily, but increasing their proportion in the ration DM from 0 to 0.4 linearly decreased apparent digestibility of DM from 59.7 to 49.9% and N from 74.7 to 53.4%, with associated reductions in urinary N excretion. Evaluation with 1H-13C heteronuclear single quantum coherence nuclear magnetic resonance (HSQC NMR) spectroscopy detected trace amounts of intact CT in sheep feces and analysis of the feces from the 0.4 lespedeza pellet ration using the HCl-butanol-acetone-iron assay indicated that 96% of the CT had been modified into non-proanthocyanidin components. Fiber analysis conducted with and without sulfite indicated an accumulation of sulfite-resistant CT-protein complexes in feces which likely contributed to the reduction in digestibility of fiber and N. This study has shown that SL pellets reduced urinary N excretion and diverted feed N to feces, but their inclusion in the diet reduced the apparent digestibility of DM and N. Complexes of CT, protein and fiber were the main contributor to the poor digestibility of aNDF and ADF in diets containing SL pellets. Findings presented here suggest a potential negative effect of these SL pellets on long-term sheep productivity in contrast to short-term productivity improvements due to the ability of the SL pellets to reduce gastrointestinal parasite populations.