Abstract
Abstract Forage inclusion within a dairy cow ration has both nutritional and economic benefits, as homegrown forages typically reduce feed cost while supplying the physically effective fiber needed for rumen function. However, low forage quality or limited forage inventory often requires producers to deviate from ideal high-forage diets. To better understand how forage inclusion strategies affect performance, this study evaluated relationships among formulation nutrient values, proximate analysis, and in vitro fermentation metrics (IFM) in commercial dairy rations. Fifty-eight TMR samples were collected from 30 dairies across the United States and paired with production data to identify key nutritional drivers of energy-corrected milk (ECM). Principal component analysis revealed two distinct ration clusters. High-forage/high-forage NDFom (HFHF) diets, defined as containing more than 50% forage and greater than 19.5% forage NDFom (FNDF), produced more ECM (53.27 vs. 50.93 kg/cow/day) and demonstrated stronger model predictability (R² = 0.72 vs. 0.34) compared to low-forage/low-forage NDFom (LFLF) diets (<50% forage and <19.5% FNDFom). HFHF rations were characterized by positive associations with FNDFom, microbial biomass (MBM), apparent dry matter digestibility (aDMD), and sugar–starch–soluble fiber (SSS), whereas total VFA production was negatively associated. In contrast, LFLF diets showed positive associations with FvNDFom and NEL 3× OARDC and negative associations with starch and total NDFom, reflecting different nutritional constraints under reduced forage inclusion. Results demonstrate that forage inventory constraints, rather than forage quality alone, distinguish ration type, and that optimizing forage NDFom and fiber digestibility remains central to supporting ECM. Because forage conditions vary widely among dairies, ration formulation must be adapted to each herd's inventory and fiber constraints to maximize performance.
Keywords: Dairy nutrition; forage inclusion; forage NDFom; ECM; PCA; fiber digestibility; IFM.