Abstract
Bag pore sizes and sample particle sizes were evaluated for measuring indigestible neutral detergent fiber (iNDF) concentration of feeds and feces in dairy cows. Four forage samples (alfalfa silage (AS), corn silage (CS), grass hay (GH) and wheat straw (WS), four byproducts [canola meal (CM), soybean meal (SBM), soy hulls (SH) and soy plus (SP)], four TMRs (with 20%, 40%, 60% and 80% concentrate), and two fecal samples [from the same cow fed high- (FSHS) or low-starch diets (FSLS)] were incubated in 2 cows for 288-h. Treatments were arranged as a 3 × 2 factorial: Three bag pore sizes (15 um (BS15), 25 um (BS25) and 50 um (BS50) with the same dimension of 5 × 5 cm, and two sample particle sizes (1 mm (PS1) and 2 mm (PS2). Fecal samples had only PS1, with BS15PS2 considered the standard to measure iNDF concentration of feed in dairy cows. Bag pore size affected (P < 0.01) iNDF concentration of all the tested samples, while sample particle size only affected (P < 0.01; Figure 1) iNDF of forage and TMR samples. The BS50, with either PS1 or PS2, resulted in the lowest iNDF concentration for all tested samples, and on average was 31% lower than BS15PS2. Concentration of iNDF of CS with BS25PS1 was not different from BS15PS2. For AS and TMRs with 20%, 40% and 60% concentrate, iNDF was not different between BS25PS2 and BS15PS2. For high NDF forage, e.g. GH and WS, BS25 with either PS1 or PS2, can replace BS15PS2 because there is no difference in iNDF concentration. In conclusion, BS50 is not recommended for iNDF determination, whereas BS25PS2 could be used to determine iNDF for AS, high fiber forage, and TMR with low to medium concentrate. Concentration of iNDF of fecal samples can be determined by BS25.