Wheat starch digestion rate in broiler chickens is affected by cultivar but not by wheat crop nitrogen fertilisation

1. A study was set up to investigate the influence of wheat cultivar and wheat crop nitrogen (N) fertilisation on starch (ST) digestion rate in broiler chickens. A total of 288 broiler chickens were used in a 3 2 factorial design with diets based on three varieties of wheat (Apache, Caphorn and Charger), each grown at two N application rates (40 and 170 kg of N/ha). 2. Starch digestion rate was determined by measuring the remaining starch and the mean retention time (MRT) in 4 segments of the small intestine (proximal and distal jejunum and proximal and distal ileum) and in excreta, using chromic oxide as a marker. 3. Varietal differences in starch content (714-746 g starch/kg DM) were smaller than differences caused by crop N fertilisation (705-755 g starch/kg DM). Nitrogen application increased wheat crude protein (CP) content from 94 to 130 g/kg DM. 4. The majority of the ST in all diets was digested by the time the digesta reached the distal ileum (average 0·84 in the distal jejunum and 0·96 in the proximal ileum). 5. Starch digestion differed among wheat cultivars in the proximal jejunum (from 0·43 to 0·57, P <0·001). Afterwards no differences due to wheat cultivar or N fertilisation were found. 6. Starch digestion rate varied among wheat cultivars (from 2·45 to 3·28 h-1, P <0·001), but did not vary with N fertilisation, whereas dietary CP digestion rate was not affected by wheat cultivar or N fertilisation level. The digestion rate of ST was faster than that of CP (average 2·78 vs. 1·53 h-1). 7. The current study suggests that wheat cultivars can be classified on their rate of ST digestion independently of the N fertilisation applied to the crop during growth