Estimating fecal output and nutrient digestibility using acid detergent insoluble ash as an intrinsic marker in lactating dairy cows: technical note.

The current study was part of large experiments in a replicated 4×4 Latin square design where 4 dietary treatments (feed supplements) were examined. Fecal samples were obtained from the experiments via total collection (Experiment 1, n = 30; Experiment 2, n = 16). Feed and fecal samples were analyzed for acid detergent insoluble ash (ADIA) and nutrients, and those were used to estimate fecal output (FO) and nutrient digestibilites. Data within each experiment were analyzed using the Mixed procedure of SAS to determine diet, method (actual vs. estimated by ADIA), and their interaction on FO and apparent total tract digestibility of nutrients. A linear regression for FO between actual and estimated by ADIA was also conducted. The recovery of ADIA was 106% in both experiments. The use of ADIA tended to underestimate FO by 5% (Exp. 2, p = 0.09) and overestimate nutrient digestibilities by 2% to 5% (Exp. 1, p≤0.08). The linear regression resulted in the slope of 0.80 (against 1, p = 0.02) and the intercept of 1.93 (against 0, p = 0.21). In conclusion, ADIA is a potential marker for lactating cows in estimating FO when corrected by the factor obtained from the regression analysis.