Variation in broiler performance due to wheat source and enzyme supplementation
There is constant evolution in defining the value of feed grains for poultry, in particular rapidly growing broiler chicks. Based on many bioassay measurements, Scott (2005) indicated that 'feed value' should include not only nutrient level and availability, but also nutrient intake and retention as saleable meat. This is based on significant differences in voluntary intake that can negatively impact growth and feed conversion (Scott, 2005).
There are also significant impacts of cereal source on dressing yield (van der Klis and Jansman, 2002). A concern is that antigenic challenge due to protein profile of some cereal grains may significantly increase maintenance costs. Van der Klis and Jansman (2002) indicated that a high level of immune system stimulation reduced feed intake and daily gain with up to a 40 percent reduction in daily protein accretion.
The present study measures feed value and includes an estimation of immune response to sources of wheat-based diets fed without and with exogenous enzymes.
A broiler chick bioassay was used to establish the feeding value (nutrient level, availability and intake) of 34 wheat-based diets (75 percent inclusion) without or with feed xylanase and phytase.
As demonstrated in previous studies, high variation was found in voluntary feed intake and this was significantly correlated with lower growth and poor feed conversion. In the present study, the relative immunoglobulin (IgA, IgG and IgM) of blood plasma from chicks fed each dietary treatment was measured. There were no significant differences in these immune parameters between treatments, except for a reduction in plasma IgA with enzyme inclusion.
However, there were significant negative correlations between the immune parameters and growth and feed intake, signifying faster growing birds may have expended less energy on immune response and this may be due to grain source and/or enzyme supplementation.
The study seeks to evaluate relationships between physiological parameters and variation in production parameters, notably growth, feed intake and FCR.
Results indicated there were major differences in performance of individual cages of male broilers fed wheat-based diets with or without enzymes. There were also significantly large differences in feed intake between pens of birds. Both main effects (wheat source and enzyme supplementation) were significant, with no interaction indicating that enzymes had a consistent effect between wheat sources.
Both wheat source and enzyme supplementation had significant effects on FCR.
Of note were the moderately significant negative correlations between performance parameters (growth and feed intake) and the immunoglobulin levels of the plasma; there were likewise positive correlations between FCR and immunoglobulin level.
It could be hypothesised that faster growing birds experienced less 'challenge' (related to diet source and/or environment) and hence had lower immunoglobulin response. Alternatively, it could also indicate that faster growing birds have a lower immunoglobulin response and utilise nutrients devoted to this to achieve higher growth.
Although the results are not considered to be conclusive, they indicate that it may be important to establish the antigenic response to specific cereal grains and how this may or may not be alleviated by use of supplements, such as enzymes, to reduce negative gut challenges and minimise immune stimulation.
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Article made possible through the contribution of Australian Poultry Science Symposium (APSS) 2007.