Effects of sample size on neutral detergent fiber digestibility of triticale forages using the Ankom DaisyII Incubator system

Abstract

Accurate and precise determinations of fiber digestibility are essential for proper diet formulation for dairy cows. Our objectives were 3-fold: (1) regress in vitro neutral detergent fiber digestibility (NDFD) values from 48 triticale forages determined at multiple endpoints ranging from 12 to 240 h with Ankom Daisy^II Incubator system (Ankom Technology Corp., Macedon, NY) methods using 0.25- or 0.50-g sample sizes on concentrations of fiber-related analytes or growth stage; (2) directly compare NDFD values determined with 0.25- or 0.50-g sample sizes by Ankom methods after 12-, 24-, 30-, 48-, 144-, or 240-h incubations; and (3) compare NDFD values determined by Ankom methods after 30 and 48 h of incubation with those determined by traditional sealed-tube procedures obtained from a commercial laboratory. Generally, plant growth stage, which was quantified with a linear model suitable for serving as an independent regression variable, proved to be a better predictor variable for NDFD than neutral detergent fiber or acid detergent lignin. For direct comparisons of 0.25- and 0.50-g sample sizes using Ankom methods, the regression relationship for a 30-h incubation was explained by a linear model [Y = 1.206x - 1.1; coefficient of determination (R²) = 0.933], in which the slope differed from unity, but the intercept did not differ from 0. After a 48-h incubation, a linear model (Y = 1.014x + 7.1; R² = 0.964) indicated that the slope did not differ from unity, but the intercept was >0. A linear regression (Y = 1.040x - 1.8; R² = 0.861) of the 30-h incubation results obtained by Ankom methods using the 0.25-g sample size on those from the commercial laboratory indicated the slope and intercept did not differ from unity or 0, respectively. A similar relationship was obtained from the 48-h incubation (Y = 1.021x - 3.4; R² = 0.866). Relationships were poorer when the 0.50-g sample size was used by Ankom methods, particularly for the 30-h incubation, where the slope (0.824) was less than unity. Generally, NDFD values were greater for the 0.25-g sample size by Ankom methods, especially with 24-, 30-, and 48-h incubation times, and agreement with traditional sealed-tube methods was improved with the smaller sample size. Synchronization of results between Ankom and traditional methods needs to be further verified across a wider range of forages and harvest/preservation methods before definitive recommendations can be made.

Keywords: in vitro neutral detergent fiber digestibility; sample size; triticale.