Variation in apparent and true ileal amino acid digestibility in barley using a rat model

The study aimed to determine ileal amino acid and total tract energy digestibility coefficients for a range of barleys. The laboratory rat served as a model nonruminant animal and digesta samples were obtained using the slaughter method with chromic oxide being used as a dietary marker. In a preliminary study the effect of time interval after the feeding of a single meal of ground barley and before sampling of ileal digesta on the apparent ileal digestibility of total nitrogen (N) and of the effect of the length of terminal ileum sampled were investigated. There was no significant effect of time of sampling but there was an effect (p<0.001) of site in the ileum. The final 10 cm of ileum was considered appropriate for the sampling of ileal digesta for barley-fed rats. In the main study 20 barley samples comprising 14 different cultivars which had been grown in the same year but in three distinct geographical locations in New Zealand were given as sole sources of protein to growing rats (n=120). Digesta were collected (final 10 cm of ileum) 4 h after the commencement of a single meal. The barley samples had variable contents of crude protein, amino acids, neutral detergent fibre, acid detergent fibre, acid detergent lignin and gross energy. The mean (n=6) apparent ileal N digestibility ranged from 0.74 to 0.85 while the equivalent range for true N digestibility was 0.84 to 0.94. Apparent and true ileal amino acid digestibility showed considerable between-sample variation. Digestible energy ranged from 13.0 to 15.1 MJ/kg dry matter. There was a significant effect of the geographical locality where the barleys were grown on amino acid digestibility for most of the cultivars studied.