Analysis of variability in nutrient digestibilities in broiler chickens

1. Forty commercial broiler chickens from two different breeding origins we re used for individual measurements of growth performance from d 7 to d 21. From d 21 to d 24 a balance experiment was carried out for the measurement of metabolisable energy (ME), digestibilities of lipids, starch and amino acids, viscosity of excreta water-extract, and amount of water loss. After this, the weight and length of the different parts of the gastrointestinal tract were measured for each bird. During the experiment, the birds were fe d with an experimental diet containing 5 g/kg of guar gum in order to incre ase the variability of responses. 2. There were no significant (P<0.05) differences between the two breeds in 21 d live weight, food:gain ratio, ME value or the digestibilities of lipi ds, starch and total amino acids. Significant (P<0.05) differences between the two breeds were observed for caecal size, excreta guar gum degradation measured using viscosity measurements, and vent score. 3. Pooling all the individual data, individual ME values were correlated (r (2)=0.33) with individual food:gain ratios, which shows that a great part o f ME variation was associated with individual variation. 4. Several significant (P<0.05) correlations were observed between individu al digestibilities and individual anatomical characteristics of the gastroi ntestinal tract. The most significant were concerned with the duodenum weig ht:length ratio correlated with ME (r=0.474) and the caeca weight:body weig ht ratio correlated with guar gum degradation (r=0.495). Covariance analyse s were carried out when correlations were significant and did not show sign ificant interactions with the breeding origin of chickens.