Evaluation of neutral detergent fiber, acid detergent fiber, and acid detergent insoluble ash to predict forage selection among heifers grazing pastures containing a binary mixture of brassicas and grass

An abstract of a study by Brunsvig et al examining diet selection by cattle grazing cool-season annual forages is presented. Estimates of brassica or grass intake did not differ in response to increased stocking rate when intake was estimated with NDF (P ≥ 0.52), ADF (P ≥ 0.48), or acid detergent insoluble ash (ADIA) (P ≥ 0.34). However, intake predictions using NDF and ADIA resulted in differences in time (quadratic, P < 0.01) but ADF did not (P ≥ 0.61). Interestingly, estimates of brassica and grass intake were 52% greater and 32% less when predicted using ADF in comparison with NDF. Similarly, estimates of brassica and grass intake using ADF were 35% greater and 38% less in comparison with ADIA. The overall pooled coefficient of variation for estimates of grass and brassica intake was 55, 60, and 65% for NDF, ADF, and ADIA, respectively.