In Vivo Digestibility, In Vitro Gas Fermentation and Enteric Methane Values of Sunn Hemp’s  (Crotalaria juncea L.) as Affected by Cutting Stages

<title>Abstract</title> <p> This study evaluated the effects of four cutting stages on the crude nutrient composition, <italic>in vivo</italic> digestibility, <italic>in vitro</italic> gas production, and enteric methane (CH ₄ ) production of Sunn Hemp’s (Crotalaria juncea L.). As vegetation progressed, crude protein (CP) decreased from 16.27% to 13.05%, while neutral detergent fiber (NDF) rose from 63.90% to 84.01%. <italic>In vivo</italic> trials with a year old wethers showed that dry matter (DM) and organic matter digestibility (OMD) peaked in the first two cuts (\(\:\sim\:\)65–71% and 71%, respectively) before falling significantly to 50–55%. Concurrently, <italic>in vivo</italic> metabolizable energy (ME) decreased from 10.67 to 7.07 MJ/kg DM (P &lt; 0.05). <italic>In vitro</italic> results showed a higher early fermentation rate (3–6 h) for the 1st cut, though 96-h total gas production remained stable (49.75–55.00 mL) across stages. Critically, advanced maturity shifted fermentation end-products, increasing acetic acid (AA) from 1.06 to 1.45 mg/mL and triggering enteric methanogenesis. Enteric CH ₄ emissions rose from 9.99 mol/mol VFA (1st cut) to 13.57 mol/mol VFA (4th cut) (P = 0.014). In conclusion, Sunn Hemp’s provides high-quality forage during the first and second cutting stages due to its superior protein and energy content. </p>