Influence of age on the apparent metabolisable energy of diets containing maize or wheat for broilers
In a previous study, the apparent metabolisable energy (AME) of diets based on wheat, sorghum or maize for broiler chicks was observed to decline from day 5 to day 7 post-hatching and then to increase to day 14. The present study was conducted to confirm these results and to investigate the changes in AME over the first 21 days of life.
Two experimental diets containing either wheat or maize as the cereal base were formulated to contain recommended levels of major nutrients for broiler starters. The wheatbased diet was supplemented with a commercial xylanase. Each diet was offered to six replicate groups (8 birds/replicate) from days 1 to 21 post-hatching.
On days 3, 5, 7, 14 and 21, total excreta collection was carried out for 48 hour periods and feed intake recorded for the determination of AME. The AME results were subject to repeated measures analysis.
In both diets, the AME values were higher at day 3 and then declined during 5 to 9 days, before increasing at day 14 posthatching.
The decreases between days 3 and 5 were greater in wheat-based diets. No differences (P > 0.05) in AME were observed between 14 and 21 days of age.
These data confirm previous findings.
The higher AME values determined at day 3 may be due to favourable effects from yolk utilisation and a relatively sterile gut environment.
The subsequent drop between days 5 and 9 may be attributed to changing gut flora, declining influence of the yolk sac, inadequate secretion of digestive enzymes, or inadequate digesta mixing.
In general, the present data are suggestive of digestive inefficiency during the first week of life in modern fast-growing broilers. Supplementation with exogenous enzymes may be useful in this context.
Sorghum is one of the most common cereal grains used by the Australian poultry industry.
It can be included up to 60-70% of a broiler diet and may contribute most of the energy and a great portion of amino acids in the diet. Small differences in nutrient content or digestibility can affect the bird performance.
The objective of the present study was to determine the apparent ileal amino acid digestibility of locally grown sorghums and to examine the relationship between crude protein and amino acid contents in sorghum.
The amino acids in higher protein sorghums were more digestible than those in lower protein sorghums (P<0.01) except for methionine (P=0.02). Similarly significant positive correlations (r>0.85, P<0.014) between digestible crude protein and digestible amino acid concentrations have been found in sorghums.
The digestibility of lysine varied among sorghum samples and was generally lower than other essential amino acids (except for threonine and histidine). However, digestibility of lysine tended to be higher in high protein cultivars compared to low protein cultivars.
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Article made possible through the contribution of the Australian Poultry Science Symposium (APSS) 2006.