Guar bean (Cyamopsis tetragonoloba): evaluation as an alternative forage source in ruminants

This study aimed to determine the nutritional values, fermentation characteristics, saponin content, and in situ ruminal digestibility of guar bean (Cyamopsis tetragonoloba) dry matter and various silages adapted to hot climates. Harvesting was performed at the 75-day maturity stage, and the materials were categorized into five groups: guar bean hay (GH), guar bean silage without additives (GS), guar bean silage with 5% molasses (GM), silage containing 2/3 guar bean and 1/3 barley straw (GB), and silage containing 2/3 guar bean, 5% molasses, and 1/3 barley straw (GMB). The silages were fermented in vacuum bags for 60 days. Nutritional composition analyses included dry matter (DM), organic matter (OM), crude protein (CP), fiber fractions (NDF, ADF, ADL), water-soluble carbohydrates (WSC), organic acids (lactic acid, acetic acid, propionic acid, butyric acid, isobutyric acid, isovaleric acid), NH₃-N, CO₂ production, and total saponin levels. In situ incubation trials were conducted in rumen cannulated cows to assess the degradability of DM, OM, and CP. The results showed that GH and GS exhibited high CP levels (15.67–15.84%), low fiber fractions, and high relative feed value (RFV: 320–355), categorizing them as top quality. The addition of straw increased fiber content, subsequently reducing energy and protein content. The inclusion of molasses did not significantly improve fermentation characteristics in this study and had a negative impact on some values. The saponin levels of guar bean products ranged from 3.8% to 4.0% GAE, with high degradability levels observed. The findings suggest that guar dry matter and silage, particularly the GH and additive-free GS groups, offer high nutritional value (RFV: 320–355) and good in situ degradability due to their low fiber content. Consequently, guar bean shows promise as an alternative summer leguminous forage crop in arid conditions. However, considering the presence of high saponin levels, which are potential anti-nutritional factors, further in vivo feeding trials are essential to definitively evaluate its palatability, toxicity, and overall effect on ruminant performance before practical recommendations for feeding systems can be made.