IN VITRO AND IN VIVO ASSESSMENT OF RATE AND EXTENT OF STARCH DIGESTIBILITY IN WESTERN CANADIAN WHEAT MARKET CLASSES AND CULTIVARS IN BROILER CHICKENS

Abstract

Two experiments were conducted to investigate the effect of Western Canadian wheat market classes and cultivars on rate and extent of starch digestibility in broiler chickens. The first experiment was an in vitro trial to determine starch digestibility rate and extent by mimicking chicken gastric and small intestinal (SI) phases. The study evaluated 18 spring wheat cultivars from eight Western Canadian wheat market classes. Each cultivar was replicated four times by growing them at four separate plots in a field nursery at Saskatoon, SK. Grain characteristics of these wheat cultivars were analyzed to determine the relationship with starch digestibility. The second experiment was designed to investigate genotypic variability of starch digestibility rate and extent, and also AMEn using broiler chickens. A total of 468 1-d-old male broiler chickens were randomly assigned to dietary treatments (6 cages/treatment, 6 birds/cage) from 0 to 21 day of age. The study evaluated two wheat cultivars from each of six Western Canadian wheat classes (selected according to the results of Experiment 1). Wheat cultivars were also subjected to in vitro starch digestion and grain characteristic analysis. Experiments 1 and 2 were completely randomized and randomized complete block designs, respectively. Wheat cultivars were nested within wheat market classes in both experiments. Differences were considered significant when P < 0.05. Pearson correlation was used to determine correlations. In vitro starch digestibility was affected by wheat market class and cultivar nested within class according to results of Experiment 1. Starch digestibility ranges of wheat classes for the selected SI phase times are as follows: 15 min – 33.1 to 49.1%, 60 min – 80.2 to 93.3% and 120 min – 92.4 to 97.6%. Low to moderate positive correlations were found for starch digestibility rate and extent with CP, ash, NSP and large granule size distribution, whereas negative correlations were found with total starch (TS), and small and medium granule proportions. According to Experiment 2 results, the starch digestibility ranges were: proximal jejunum – 23.7 to 50.6%; distal jejunum – 63.5 to 76.4%; proximal ileum – 88.7 to 96.9%; distal ileum – 94.4 to 98.5%; excreta – 98.4 to 99.3%. Wheat class affected wheat AMEn with levels ranging from 3203 to 3411 kcal/kg at 90% DM. In vivo starch digestibility in all four segments of SI and total tract starch digestibility were affected by wheat market class. Moderate positive correlations were found for in vitro starch digestibility with CP and large granule size distribution, whereas it was negative with TS, and small and medium granule proportions. There were moderate positive correlations for in vivo starch digestibility with wheat hardness and ash content. Significant and moderate strong positive correlations were observed between in vitro and in vivo starch digestion rate, but no correlations were found between AMEn and starch digestion rate. In conclusion, rate and extent of both in vitro and in vivo starch digestibility and AMEn were affected by Western Canadian wheat class, but starch digestibility did not predict wheat AMEn. The in vitro starch digestion model may have application in screening large numbers of samples for starch digestibility in poultry. Further, grain characteristics were related to differences in the rate and extent of starch digestion of Western Canadian wheat classes and cultivars, but to a limited degree.