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 x 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.

Effect of wheat cultivar and enzyme addition to broiler chicken diets on nutrient digestibility, performance, and apparent metabolizable energy content.

A total of 5,000 one-day-old male broiler chickens were assigned to 8 different treatments in a 4 x 2 factorial design. Four wheat cultivars (Amiro, Guadalupe, Isengrain, and Horzal) and 2 levels (0 or 1 kg/t of feed) of an enzyme cocktail (Avizyme 1300, xylanase, 2,500 U/kg and protease, 800 U/kg) were used. Nutritionally complete mash diets contained 65 and 70% of the test wheat for the starter and grower period, respectively. Test wheats were used in diets for broilers, and growth performance and AME contents were measured. Broiler performance was measured in 4,800 broilers allocated to floor pens with 75 birds each and fed from 1 to 42 d of age. Digestibilities and AME contents of diets were measured in 200 broilers from 6 to 27 d of age individually allocated to battery cages. Chromic oxide (Cr(2)O(3)) at an inclusion rate of 0.5% in the diet was used as an indigestible marker. Apparent metabolizable energy was corrected by zero N balance to obtain AME(n). Wheat cultivar strongly influenced animal performance during the starter period (1 to 21 d of age). During the grower period (21 to 42 d of age), only BW and daily feed intake were influenced by wheat cultivar. Differences in daily feed intake were associated with differences in AME(n) intake during the starter period, but not during the grower period. Nutrient digestibility was higher with the use of enzyme. Animal performance was not affected (i.e., wheat cultivar differences were not eliminated by using enzymes). During the grower period, significant interactions were detected with regard to nutrient digestibility and AME(n). Differences in AME(n) content of wheat could not be explained by digestible starch.