1. The objective of this study was to examine the influence of dietary soluble non-starch polysaccharide (sNSP) level and xylanase supplementation on productive performance, viscosity and pH along the gastrointestinal tract in laying hens. Excreta moisture content, ileal and caecal microbiota and short-chain fatty acid (SCFA) composition and apparent total tract nutrient utilisation were measured.

2. Hyline Brown laying hens (n = 144) were housed individually at 25 weeks of age and allocated to one of the four wheat-based dietary treatments in a 2 × 2 factorial arrangement, consisting of two levels of sNSP (High 13.40 g/kg or Low 11.22 g/kg), with or without xylanase (0 or 12,000 BXU/kg). Birds were fed the dietary treatments for 56 d.

3. Increasing dietary sNSP increased jejunum viscosity, degradability of total NSP, total tract flow of insoluble arabinose, and succinic acid concentration in the caeca (P < 0.05). Feeding high sNSP decreased excreta moisture content, total tract energy retention and free oligosaccharide, total tract flow of soluble and insoluble galactose and insoluble rhamnose and fucose, and ileal acetic and lactic acid concentrations (P < 0.05), and tended to reduce egg production (P = 0.058).

4. Supplementation with xylanase resulted in reduced jejunum and ileum viscosity, caecal pH, excreta moisture, flow of soluble arabinose and glucose and insoluble arabinose and xylose, caecal concentration of Lactobacillus sp. and isobutyric and succinic acid, and ileal concentration of Bacillus sp. and total anaerobic bacteria (P < 0.05). Xylanase application also increased energy retention and insoluble and total NSP degradation, and caecal abundance of Bifidobacteria sp. and valeric acid (P < 0.05).

5. These results reiterated the ability of xylanase to improve nutrient digestibility and reduce excreta moisture content in laying hens, and highlighted the importance of considering dietary sNSP level in laying hen diets.

Trace minerals, zinc (Zn), copper (Cu) and manganese (Mn) have been well documented as essential components in the diets of poultry since they are involved in various physiological and biological processes within the body in maintaining bird health and performance. Different sources of trace minerals can differently influence growth rate and bird health. Three experiments were conducted to assess the effects of different sources and levels of trace minerals on growth performance and gut health of poultry.

The first experiment (shown in Chapters 3 and 4) evaluated the efficacy of different sources of zinc (Zn) (oxide and sulfate forms - ionic bound forms) versus zinc hydroxychloride (covalent bound form) (ZH) and incremental levels of ZH on growth performance and intestinal health of broilers fed wheat-soybean meal-based diets from d 0 to 35. The dietary treatments consisted of a positive control treatment (50 mg Zn/kg from Zn oxide and 50 mg Zn/kg from Zn sulfate), a negative control treatment (NC) which contained no supplemental Zn; the remaining 5 treatments contained Zn as ZH at 20, 40, 60, 80, 100 mg/kg. The findings obtained in this experiment showed that Zn supplemented from ZH was more efficacious than ionic bound forms in improving growth, feed efficiency, and breast meat yield. Despite the finding that feed intake was not different among treatments, the lower inclusion (40 mg/kg) of Zn as ZH resulted in similar body weight gain (BWG) to birds given a higher level of Zn as the ionic bound forms (100 mg/kg). The results also suggest that lack of Zn supplementation can negatively influence tibia development and gut microbiota composition in broilers. Higher supplemental Zn (80 mg/kg) in the diet alters the cecal microbiota population in favour of Lactobacillus and can decrease the total bacterial load. Supplemental Zn sources and levels in the feed have the potential to manipulate the jejunal gut integrity at a molecular level. The optimal requirement of Zn as ZH for broilers would be 100 mg/kg to meet all metabolic requirements of birds.

The second experiment (shown in Chapters 5 and 6) was designed to determine if nutritional (15 mg/kg) and pharmacological (200 mg/kg) levels of Cu hydroxychloride (CH) could effectively improve the growth performance and intestinal health of broilers, compared with Cu sulfate supplementation. The dietary treatments consisted of a negative control diet (NC) without any supplemental Cu, a basal diet supplemented with either 15 or 200 mg/kg Cu as CuSO4, and 5 diets supplemented with 15, 50, 100, 150, or 200 mg/kg supplemental Cu as CH. The results showed that the supplementation of Cu from CH was more efficient than Cu sulfate in promoting growth performance, both at nutritional and pharmacological levels. Birds fed 200 mg/kg Cu as CH gained more weight (77 g/bird) and had a lower FCR (3.2 points) compared to those fed 200 mg/kg Cu as Cu sulfate. This experiment demonstrated that the higher doses of Cu (up to 200 mg/kg) alter gut microbiota profile without compromising gut structural integrity or promoting tissue oxidation. Also, CH is more effective than Cu sulfate in making intestinal villi longer and reducing Cu excretion. Based on broken-line regression models, the optimal supplemental Cu as CH in the diet for the optimum body weight gain and FCR were estimated to be 109.5 and 72.3 mg/kg, respectively.

The third experiment (shown in Chapter 7) was designed to evaluate the effect of complete replacement of sulfate sources of Cu (15 mg/kg), Zn (80 mg/kg), and Mn (80 mg/kg) - (ITM) with hydroxychloride sources - (HTM) at the same inclusions on productive performance, egg quality, tissue mineralization and feed stability in Hy-Line Brown laying hens during post-peak production and under high ambient temperature. The results showed that HTM supplementation improved egg production, feed efficiency, eggshell quality, and egg mineral profile and produced darker brown eggshell color, although feed intake was not affected. These results are probably attributed to higher bioavailability of HTM compared with ITM in egg formation and pigment deposition into the eggshells, and in reducing the extent of oxidation in the feed, especially during high ambient temperature.

The results of these studies indicate that hydroxychloride trace minerals were more beneficial for broilers and layers over the ionic bound forms (sulfate, oxide) in improving growth performance parameters, intestinal health, productive production parameters, and egg quality of poultry. These effects may relate to the higher bioavailability, less reactivity with other minerals, greater oxidation stability of feed, and modulation of the negative effects of the high ambient temperature by trace minerals from hydroxychloride sources in poultry diets. The mechanism by which trace minerals as hydroxychloride contributed to lipid metabolism of broilers requires further research. An investigation into additional benefits of hydroxychloride trace mineral supplementation in post-peak laying hens could be of interest because commercial hens now lay for longer periods.

In this paper, we discuss the theory behind calibration curve experiments and their application to a zinc (Zn) bioavailability study with broiler chickens. Seven replicates of 16 male commercial broiler chicks were fed starter diets for 14 days. Six diets had different levels of a potential Zn source and one was a positive control with standard industry levels of Zn for comparison. Four commonly used methods of calculating bioavailability means and confidence intervals (CI) from a calibration curve (standard curve) experiment to estimate the bioavailability of a new zinc source in broiler chickens were compared. The methods compared were the following: 1) the Counter-Intuitive Method uses a multiple-range test to compare unknown test and standard samples; 2) the Intuitive Method uses standard linear regression and inverts the equation to predict Zn bioavailability for each replicate of test samples; 3) the Abductive Method uses Graybill's Equation, based on theory and observation, to estimate CI's; and 4) the Sophistic Method uses reverse regression, and calculates Zn bioavailability values directly from the equation. The Counter-Intuitive Method only gives information about which standards the test samples are, or are not, significantly different from respectively (average available Zn not predicted). The Intuitive Method ignores error about the standard curve and theoretically cannot estimate the CI directly (X̄±SEM = 107.5 ± 15.8 mg Zn/kg). The Sophistic Method underestimates and overestimates the test sample mean values above and below the mean of the standards, respectively (X̄ = 96.6 mg Zn/kg). The Abductive Method has an advantage over the other methods: The mean prediction estimation is consistent with theory (107.5 ± 6.1 mg Zn/kg; X̄±SEM). When test or "unknown" samples are near the mean of the standard samples, the CI is smaller than when near the extremes of the calibration curve. When calibration curve error is small (R² > approximately 0.95), there is little advantage to using the Abductive Method, but when calibration curve error is larger, as in many bioassays with growing animals, the Abductive Method improves the accuracy of the CI calculations. The Abductive Method was used to demonstrate the influence of the number of replicate samples on experimental power and cost.