Estimation of total-tract starch digestibility using fecal starch concentration in fattening Japanese Black cattle

Fattening Japanese Black cattle (Wagyu), renowned for producing marbled beef, derive essential energy from starch. While fecal starch concentration (FSC) can estimate total-tract starch digestibility (TTSD), equations developed for other beef production systems may not suit highly marbled beef production. This study developed a specific equation for estimating TTSD from FSC in Japanese Black cattle and compared it with data from other breed's production systems. Experiments with 49 Japanese Black cattle across four farms yielded 116 TTSD measurements. A database from 41 published studies on other cattle breeds (190 treatment groups, 2343 animals) was also analyzed. The Japanese Black cattle-specific equation (TTSD, % = 99.7 - 0.85 × FSC, %DM; R² = 0.89) showed a steeper slope compared to the literature-derived equation (TTSD, % = 100.1 - 0.54 × FSC, %DM; R² = 0.79) (P = 0.06). This difference reflects characteristics of Wagyu beef production, specifically lower dietary starch concentration (32.5 vs. 50.4%DM, P < 0.05) and higher DM indigestibility (29.5 vs. 22.5%, P < 0.05). A preliminary surveillance of commercial farms revealed substantial farm-to-farm variation in starch utilization, with TTSD ranging from 70.0 to 99.4%. This study provides a practical tool for monitoring feed efficiency in highly marbled beef production systems.