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The right-angled triangle mixture experiment was designed to include fourteen diets with different concentrations of starch, protein and lipid. Experimental diets were offered to male Ross 308 broiler chickens from 10 to 23 d after hatching, and response curves and surfaces were generated to illustrate the influence of macronutrients on growth performance and nutrient utilisations. Despite the primary function of macronutrients, especially protein, may not be providing energy, macronutrients were expressed as energy derived from starch, protein and fat for statistical purposes in the mixture design. Energy derived from lipid had a greater impact on feed intake than energy derived from starch and protein. When we compared the influence of starch and protein on feed intake, 'equal distance rule' was observed, which means the animal consumes feed to the point on its respective nutritional rails where the shortage of starch exactly equals the surplus of consumed protein. Increasing the protein-derived energy intake increased weight gain in broiler chickens, whereas energy intake derived from starch and lipid had little impact on weight gain. Feed conversion ratio (FCR) may be reduced by either increasing protein energy intake or decreasing starch energy intake. As the slope of the contours was less than 1, the influence of starch energy intakes on FCR exceeded that of protein energy intakes. In conclusion, energy derived from protein is more important than non-protein energy in terms of weight gain, and a balance between protein and energy supplies is required for efficient muscle protein deposition.

A total of ten experimental diets with protein concentrations ranging from 154 to 400 g/kg and two lipid levels (46 and 85 g/kg) with identical energy densities were offered to 240 male Ross 308 broilers from 7 to 28 d post-hatch. Growth performance was monitored and nutrient utilisation (apparent metabolisable energy (AME), N-corrected AME (AMEn), AME daily intake, AME:gross energy ratios, N retention) was determined. The weight gain response of broiler chickens to dietary protein concentrations in diets containing high and low lipid levels was diverse, with the relevant quadratic regressions being significantly different (P0·05). AMEn was also linearly (P<0·0001) increased with dietary protein concentrations but regressions in diets with low and high lipid content were significantly different (P<0·03). Carcass protein content increased linearly with dietary protein content in diets containing high lipid concentrations (r 0·933, P<0·0001); by contrast, this relationship was quadratic (R 2=0·93, P<0·0001) in diets with low lipid levels. In conclusion, predictably, the effects of dietary protein concentrations on broiler performance were profound; however, the impact of dietary protein on performance in broiler chickens was modified by dietary lipid concentrations.

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We investigated the pattern of non-starch polysaccharide (NSP) digestion along the gut of pigs fed two different wheats, which were offered with or without xylanase supplementation. The two wheats used were pre-characterised before the experiment on the basis of low and normal feed intake of young pigs. Wheat type significantly influenced feed intake and growth rate in the first 7 days, however, by day 14 the only significant effect of wheat type was on growth rate. Xylanase supplementation increased the growth performance of pigs fed the poor quality wheat to a level similar to those fed the normal wheat. It also increased the daily gain of pigs fed the normal wheat. Wheat type had no significant effect on the digestibility of dry matter (DM), energy, free sugars or the different fractions of NSP in the duodenum, ileum or in the faeces. The duodenal gross energy digestibility values for the low and high performance diets were −27.4 and −47.5%, respectively, and xylanase supplementation significantly increased the digestibility of energy back to positive levels. Dry matter digestibility values followed a similar pattern. In the duodenum, xylanase increased (P < 0.05) the digestibility values of both soluble and insoluble NSP, whereas in the ileum, xylanase had a significant effect only on the digestibility of the soluble NSP fraction. Xylanase did not affect free sugar digestibility. The reduction in soluble NSP level coincided with a marked reduction in the amount of fucose, a prominent component of mucosal polysaccharides. This suggests that soluble NSP substantially increase endogenous losses. The absence of differences in the digestibility of the measured NSP between the two wheat samples suggests that the structures of the NSP, rather than just their amount and solubility, are important for the anti-nutritional properties of NSP in pig diets.

Increased intestinal permeability (IP) and inflammation are both linked with functionality of the intestinal barrier and in particular enterocytes. Currently, almost all assessment methods of the intestinal barrier function are invasive. The present study aimed to quantify selected proteins as novel biomarkers in excreta of broiler chickens to facilitate non-invasive assessment of gut barrier function using enzyme-linked immunosorbent assays (ELISA). It was further hypothesised that probiotics as feed additives may counteract gut barrier dysfunction. A 3 × 2 factorial arrangement of treatments was used with the main factors being gut barrier dysfunction models (control, rye-based diet, and dexamethasone-DEX) with and without probiotic supplementation (a three-strain Bacillus) using 72 male Ross 308 day-old chickens. Each of the 6 experimental treatments was replicated 12 times. On d 21 of age, fluorescein isothiocyanate dextran (FITC-d) uptake into serum was examined to test IP. Fresh excreta samples were collected on d 20. The biomarkers included alpha-1 antitrypsin (A1AT), intestinal fatty acid binding protein (I-FABP), lipocalin-2 (LCN2), fibronectin (FN), intestinal alkaline phosphatase (IAP), ovotransferrin (OVT) and superoxide dismutase [Cu-Zn] (SOD1). Only DEX increased (P<0.001) FITC-d passage to the blood on d 21 of age, indicating a greater IP. The excreta concentrations of A1AT, I-FABP and SOD1 were unaltered by the experimental treatments. DEX increased (P<0.05) FN concentration in excreta compared with control birds. Conversely, inclusion of rye in the diet reduced (P<0.05) FN but increased (P<0.001) OVT in excreta. Independently, DEX decreased IAP (P<0.05) in excreta compared with control and rye-fed birds. The excreta concentration of LCN2 tended (P = 0.086) to increase in birds injected by DEX. There was no demonstrable effect of probiotic addition on any of the studied parameters. Among the tested biomarkers, FN, IAP, and LCN2 revealed promise as biomarkers of intestinal barrier function quantified by ELISA kits.