A preliminary study on the evaluation index system of forage nutrients for the concept of “Standard Forage”

Leymus chinensis (sheep grass), Medicago sativa (alfalfa), Avena sativa (oats), and Sorghum bicolor (sweet sorghum) are four dominant forage species in northern China. This study reviewed forage quality standards from seven domestic and international institutions. Through field experiments conducted at the Xiertala Farm in Inner Mongolia, the dynamics of nutrient content throughout the entire growth period of these four forages were analyzed, and their harvest-stage quality was compared with national and international standards. The key findings are as follows: (i) the optimal harvesting periods for hay production were determined as follows: alfalfa at full bloom, oats at the waxy stage, sweet sorghum at the end of jointing, and sheep grass at the heading stage. Comparing the nutrient contents of the four forages with domestic and international premium quality standards revealed that only alfalfa approached supreme-grade standards (China/U.S.). (ii) Comprehensive analysis identified crude protein (CP), rumen degradable protein (RDP), non-fiber carbohydrate (NFC), and non-structural carbohydrate (NSC), etc., as key indicators influencing forage quality. (iii) Changes in ratios such as RDP:NFC, NFC:NDF, and SFA:UFA during the growth period were also examined, aiming to extend the evaluation perspective to the level of nutrient absorption and utilization by livestock. The exploration of these forage quality indicators lays a scientific foundation for establishing a standardized evaluation system for high-quality forage in northern China and facilitates the transition of the “Standard Forage” initiative from concept to practice.