Use this URL to cite or link to this record in EThOS: http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.605811
Title: Ileal and total tract starch and nitrogen digestibility for broilers of wheat cultivars varying in hardness
Author: Elraghig, Mahmud
Awarding Body: University of Nottingham
Current Institution: University of Nottingham
Date of Award: 2012
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Abstract:
The nutritive quality of wheat as a main source of the energy in poultry diets is variable, particularly with respect to the low-apparent metabolisable energy (AME) values of some varieties. It has been speculated that the higher protein content and the stronger bonds between proteins and starch in hard wheat may be involved in a negative relationship between hardness and energy availability. The objective of the current study was to examine whether there was a difference in starch and nitrogen digestibility in broiler chickens when given wheat varieties with different hardness values. Each wheat sample was included at a fixed rate of 750 g/kg in a semi-synthetic diet. Each diet was offered ad libitum to 6 cages (2 birds / cage) from 20 to 23 days of age. Three experiments were conducted. In the first trial, twelve cultivars from the 2007 growing season with different hardness values from 34 to 86 and twelve cultivars were used in the second trial from the 2008 season with different hardness values from 10 to 68. In both trials samples were used in a broiler feeding experiment and laboratory analysis for ileal and total tract starch and nitrogen digestibility evaluation. In the third trial ten cultivars were used from the 2009 harvest season, four samples had different 'hard' mutations in Pinb-DI (2 lines with Pinb-DIb and 2 with Pin-DIe). The hardness values were from 10 to 73. This trial was focussed only on the ileal and total tract nitrogen retention and digestibility evaluation, to examine whether the genetic differences have any effect. Although there was a variation in starch digestibility for each diet in both trials 1 and 2, the effects of wheat hardness were not significant for either ileal or total coefficient of apparent starch digestibility of diets (P> 0.05). Similarly, there were no significant effects on the coefficient of apparent nitrogen digestibility (P< 0.05) in both experiments. Neither nitrogen nor starch content had a significant effect on starch digestibility. This gives an indicator that the difference between hard and soft endosperm not only depends on nitrogen and starch content but may also be based on the adhesive strength between the starch granules and surrounding protein matrix. It was concluded 11 that the variation in starch digestibility with wheats could not be attributed only to hardness of wheat and that other factors appear to be implicated in the low digestibility observed with some wheat samples tested in the current experiment. The digestible starch content increased from the ileum (digesta) and total tract (excreta) with 0.826 and 0.907, and the digestible starch content increased from the ileum (digesta) and total tract (excreta) with 0.889 and 0.922 in 2008 diets. The effect of region is to be expected, since starch is increasingly well digested as it passes through the gut. The results of trial 1 also showed that there were no significant differences in coefficient of apparent nitrogen retention or digestibility of diets based on wheat cultivars. The second trial results showed there were no significant differences in coefficient of apparent nitrogen retention or digestibility of diets based on wheat cultivars. Total nitrogen digestibility tended to show an increase with increased endosperm hardness (P= 0.082) The third trial results showed that there were no significant differences in ileal and total tract nitrogen retention. On the other hand there was highly significant effect of wheat hardness on total tract nitrogen digestibility (P<0.001), but there was no evidence of a linear effect. This is probably because the 10 samples used in this trial include 4 samples characterised by different genotype. These different genotypes showed a highly significant effect on nitrogen digestibility. In general, nitrogen digestibility coefficients based on excreta (total nitrogen digestibility) were numerically lower than those determined at the terminal ileum. This is probably due to the nitrogen synthesis of microbial nitrogenous compounds in the hindgut. When the end result of microbial activity is synthesis, the reverse situation will occur resulting in under estimates of digestibility. Evaluating the effects of wheat hardness on feed intake, nitrogen retention and digestibility of diets across the three trials, showed that the effect of endosperm hardness was highly significant and positively correlated with feed intake (r2 = 0.8157, P = 0.003). The year of harvest also has an effect on feed intake (P < 0.001) and there was a positive tendency that this effect was related to the endosperm hardness (P= 0.078). Statistical analysis indicated a 111 z highly significant effect of wheat hardness on ileal, total tract nitrogen retention and total tract nitrogen digestibility (P
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID: uk.bl.ethos.605811  DOI: Not available
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