 |
Rural Industries Research & Development Corporation |
|| Home || Search || Contact || Publications Eshop || Privacy Statement ||
Rural Industries Research & Development Corporation
February 2003
RIRDC Publication No 02/151 RIRDC Project No SAR-13A
Executive Summary
Feed is the largest single cost factor (60%) in production
of chicken meat with the cost of energy being a major consideration given
that birds eat to satisfy an energy requirement. The Australian chicken
meat industry is highly dependent on supply of energy from cereals such
as wheat and barley that are known to vary widely in apparent metabolisable
energy (AME). In contrast, sorghum is generally assumed to be a relatively
consistent source of energy.
Cereal grains, combined with legumes and oilseed meals, provide not only the bulk of the energy and other essential nutrients for commercial poultry production, but are also the prime source of anti-nutritive components which are likely to have significant bearing on how effectively all dietary components are utilised by poultry. Of the known causes of variation in energy value of grains, soluble non-starch polysaccharides (NSP) stand out as a major determinant of the availability of energy and other nutrients.
This project examined the general hypothesis that feed-related and bird-related factors interact to produce a variable effect on the digestion of energy by individual chickens within the flock. A total of 12 experiments were conducted during this study. Breath tests were developed as non-invasive indicators of digestive function and gut microbial activity to be used in conjunction with conventional methods for measuring energy digestion in commercial breeds of chickens. The results provide evidence that gut function and bacterial colonisation of the gut are important determinants of digestive function, and that both are partially dependent on the sex of the chicken.
Up to 33% of the variation in AME was associated with physical features of the small intestinal mucosa, with ileal crypt depth being a key determinant. The breed and sex of chicken significantly affected villus heights of the mucosa in the jejunum and ileum, respectively. Re-modelling of the villus/crypt axis differed in male chickens depending on breed, but there were no breed differences observed in female chickens. These results are indicative of sex-related differences in gut morphology which is a key factor influencing the digestive capacity of the chickens. Whether effects of sex extend into biochemical functioning of the gut remains to be determined. Hence there is good reason to believe that gut morphology is a limiting feature of digestive function, but that other aspects are collectively more important given that 67% of the variation in AME remained unaccounted for.
The influence of gut microflora on the site of digestion of carbohydrate differed between male and female chickens, and according to type of grain used in the diet. Ileal digestible energy (DE) values for wheat and barley were unaffected by sex, whereaAME values were lower in male chickens compared with females. Energy excretion by male chickens rose in an exponential manner relative to energy intake, whereas the increase in females was linear. The differing effects of sex on DE and AME values of these grains strongly imply that post-intestinal processes and events associated with gut microflora were affected by the sex of the chicken. This poses questions as to what occurs in the gut to enable the microflora to change so radically in terms of numbers, species or activities according to the sex of the host animal.
In conclusion, the influence of gut microflora on between-bird variation in the digestive function of the chicken was partially dependent on the composition of the diet. Further work is needed to determine the fundamental reasons why bacterial colonisation of the gut is variable and why it differs substantially between male and female chickens. Then it may be possible to control the initial colonisation of newly hatched chicks and to maintain a health-promoting profile throughout the life of chickens in order to enhance efficient production, and product quality and safety.
|
