Relationships between ruminal dry matter and starch disappearance and apparent digestibility of barley grain

Abstract

The objectives of this research were to examine relationships between ruminal dry matter (DM) and starch disappearance in barley grain and to determine how accurately in vivo digestibility of barley could be predicted from grain characteristics including ruminal disappearance of rolled and ground grain. DM and starch disappearances were determined when 10 different barley grains were incubated in the rumen of steers for up to 48 h in rolled and ground forms. In addition, apparent digestibilities of all-concentrate diets containing the 10 barley grains were measured with 20 steers (235±17 kg BW). Differences ( P<0.1) were detected between barleys for initial DM and starch wash-out from bags at 0 h and for slowly disappearing fractions. When barley was ground, barley cultivars with two-row morphologies had a higher ( P=0.04) DM wash-out at 0 h than six-row head-types. Rates of DM and starch disappearance from the slowly disappearing fraction ranged from 33 to 58% h −1 and from 49 to 80% h −1, respectively, but differences between barleys or between two-row versus six-row head-types could not be detected. Rate of starch disappearance was not correlated with rate of DM disappearance either when the hulless variety was included ( r=0.36, n=10) or not included ( r=0.21, n=9). Apparent in vivo digestibility of DM with all-concentrate diets containing 95% barley grain ranged from 80.5 to 87.4%, with diets containing the hulless variety Condor being the most ( P=0.05) digestible. Although correlations ( P<0.05) existed between in vivo DM digestibility and ruminal DM disappearance, acid detergent fiber (ADF) content of barley was more highly correlated with digestibility ( r=−0.77; P=0.01). DM disappearance from rolled barley grain was not related to in vivo digestibility. It was concluded that digestibility differences do exist between barley grains and that ADF content and ruminal disappearance are useful predictors of digestibility. Further, since ruminal DM and starch disappearance rates were not correlated, rates of starch disappearance in barley grain cannot be estimated from DM disappearance rates.