The purpose of this thesis was to select beneficial bacteria from the chicken intestinal tract and to screen them for their potential probiotic characteristics in order to use them against pathogenic bacteria, such as 'C. perfringens' and 'Salmonella'. Five experiments (Chapters 3-7) were conducted and out of four potential probiotic candidates, 'L. johnsonii' was eventually selected as a model organism and its effects on bird performance, gut microflora, gut morphology, and antibiotic effect were examined. Throughout this thesis, Cobb, male broilers were used. Each experimental chapter has been presented as a stand-alone paper, thus, this summary will only give an overview of the key findings of the thesis. Chapter 1 briefly describes the background information and justified the importance of research in the topic of interest, leading to the major hypothesis and objectives for conducting the five experiment contained in the thesis. Chapter 2, the literature review, covers the use of probiotics in poultry production, focusing on their modes of action and properties, and their potential as alternatives to in-feed antibiotics. In Chapter 3, four probiotic isolates were selected from 235 lactobacillus isolates of poultry origin using an antagonistic test against 'C. perfringens', 'E. coli' and 'S. sofia'. Quantitative and qualitative measurements revealed that these four candidates, 'L. johnsonii', 'L. crispatus', 'L. salivarius' and one unidentified 'L.' sp., were antagonistic towards 'C. perfringens', 'E. coli' and 'S. sofia' in vitro and were able to survive in feed for 7 days, in water and litter for more than 24 hours under practical production conditions. Chapter 4 presents data the efficacy of delivering 'L. johnsonii', 'L. crispatus', 'L. salivarius' and an unidentified 'Lactobacillus' sp. via feed in manipulating gut microflora environment and production performance was investigated. Results showed that none of the four candidates improved bird performance but they increased the small intestinal weight and tended to reduce the number of enterobacteria in the ileum. Among the four candidates, 'L. johnsonii' was the best in its effects on gut development and gut microflora, thus it alone was to be used in subsequent studies.

Meat chickens fed a high protein diet produce increased levels of putrefactive metabolites in the caeca such as ammonia, amines, phenols, indoles, skatole, cresol and branched chain fatty acids (reviewed by Qaisrani et al., 2015). Some of these metabolites are toxic and odorous (Mackie et al., 1998). A low protein diet formulated to provide all the required amino acids without excesses may reduce putrefaction and therefore the production of toxic and odorous metabolites in the hindgut and litter. This study was conducted to investigate the effect of a low protein diet on odorous metabolites emitted from litter.

A broiler experiment was conducted to examine the effects of sorghum particle size and milling type on the performance, nitrogen corrected apparent metabolisable energy (AMEn), digestive tract development, digesta pH, duodenal digesta particle size and digesta passage rate. Complete pelleted diets with identical botanical and chemical composition containing 750 g/kg whole sorghum (WS), sorghum ground through hammer mill with 1 mm and 3 mm screen (HM1 and HM3) and sorghum ground on a roller mill with 0.15 mm spacing (RM0.15), were made. Sorghum for diets HM3 and RM0.15 were milled to approximately the same mean particle size. Diet WS resulted in poorer (P<0.05) weight gain and feed conversion ratio (FCR) than the other diets from 11 to 21 days of age, while diet RM0.15 resulted in improved FCR. Apparent MEn determined between 25 and 28 days of age, however, was higher (P<0.05) for diet WS than for the other diets. This was possibly due to a longer adaptation time to a larger feed particle size, as indicated by a lower (P<0.05) pH in the gizzard and smaller duodenal digesta particle size for this diet. Diet HM1 gave similar performance as diet HM3, but resulted in a significantly smaller gizzard, a higher pH of the gizzard content, a lower pH of the duodenal content and larger particles in the duodenal contents, thus indicating that gizzard development and activity were compromised by this diet. Total tract passage rate of the liquid phase marker was slower (P<0.05) in the WS fed birds, but there were no differences in solid phase marker excretion rates.

Necrotic enteritis, either in its clinical or sub-clinical form is known to cause massive economic losses in the broiler chicken industry. Currently, the use of in-feed antibiotics as growth promoters is discouraged. Therefore, mechanisms to control NE through diet include reduction of digesta viscosity, promotion of lower pH in the gastrointestinal tract (GIT) through acidification of feed, production of short-chain fatty acids and overall stimulation of beneficial bacteria growth. Intermittent lighting programs increase feed retention in the crop and reduce pH in the foregut compartments in comparison with standard commercial lighting programs and therefore may be a valuable, yet underexploited, barrier to prevent the invasion of the GIT by pathogens. In this experiment, a 2 × 2 factorial arrangement of treatments was employed in a randomized design to investigate whether intermittent lighting would increase broiler resilience to sub-clinical necrotic enteritis. A total of 390 Cobb 500 same-hatch, mixed sex, day-old chicks were assigned to 30 floor pens to test the effect of 2 factors, namely, lighting schedule (continuous, 18L:6D vs. intermittent, 1L:3D:1L:3D:1L:3D:1L:3D:2L:6D) and a subclinical necrotic enteritis challenge (challenge vs. no challenge). Challenged birds had lower feed intake and weight gain and poorer feed conversion ratio (FCR; P < 0.005). Intermittent lighting reduced feed intake (P < 0.05) without compromising final body weight gain. During the peak phase of 'Clostridium perfringens' Type A infection, the negative impact of the disease challenge on feed efficiency was lower for animals under intermittent lighting than for those under a 18L:6D schedule (2-way interaction, P < 0.005). Thus, in flocks that are raised under antibiotic-free production systems, intermittent lighting programs applied at least during the critical period for necrotic enteritis risks, i.e., d 18-24, may be a practical, non-medicated way to increase resilience of broilers to this disease.

Abatement of odour emissions has become an important consideration to agricultural industries, including poultry production. In order to study the link between diet and odour emissions, an experiment was conducted using twelve Ross 308 broiler chickens. At the age of 22 days, birds of uniform body weight were selected from a total of 288 male birds, adapted to metabolic chambers for six days and fed their respective diets for 15 days. Two treatments were compared using three replicates of two birds per chamber. The two wheat-soy diets were formulated according to the 2007 Ross 308 nutrient specifications for digestible amino acids but they differed in ingredient composition and metabolisable energy content. Thus, Diet A had 13.39 MJ/kg ME and used 60g/kg canola but no corn whereas Diet B contained 12.90 MJ/kg ME and used 150g/kg corn but no canola. The odorous emissions were measured using a Fourier transform infrared spectroscopy. A total of 24 volatile organic compounds were detected and quantified; eight being the major odorous ones: 2,3-butanedione, 2-butanone, dimethyldisulfide, methylmercaptan, 2-butanol, 3-methyl-butanal, phenol and m-cresol. From this pilot study it appears that there is a strong link between diet and odour emissions from broiler chickens.

It has been projected that world food consumption will be doubled between 2010 and 2050 and the meat consumption per capita will also be rising due to the improvement in economic status in the developing areas of the world (Godfray et al., 2010). Modern-day broiler chickens are superior to other animals in producing meat from feedstuffs. The broiler industry is expected to expand in the coming decades, at the annual rate of 2.5% per year, to fulfil the increasing demand for a high quality and relatively inexpensive animal protein source, short generation intervals and very low greenhouse gas emissions (Cowieson and Selle, 2011). However, the broiler industry is facing many new challenges to meet society's expectation of having clean and green products without compromising food safety and quality, animal welfare and environmental care. ... The present study aimed to provide an insight into the efficacy of betaine in broiler production through its two roles, by examining its osmolytic capacity in enhancing the efficiency of energy utilisation, digestibility of other nutrients and activities of the gut microbial community, and by evaluating its methyl donor function, which partially replaces dietary methionine and improves carcass quality.

The viability of including millrun (a byproduct of wheat milling) in diets for weaned pigs was assessed in two 26-day feeding experiments, the first using 48 and the second 128 individually housed, entire male pigs (Large White × Landrace) weaned at 28 days (average weight 7.4 kg). In Experiment 1, millrun included in iso-energy, iso-lysine diets at 0, 12.5, 25, 37.5, and 50% had no effect on performance or digestibility. Therefore, in Experiment 2, pigs received diets containing 50% millrun in a 2 × 4 factorial design. The two factors were: (1) feed form (dry or liquid) and (2) enzyme supplementation (0 or 300 g/g of a xylanase primarily targeting soluble non-starch polysaccharide (sNSP), 400 g/g of a xylanase targeting only insoluble NSP, or both xylanases. The inclusion of NSP-degrading enzymes had no significant effect on pig performance or diet digestibility. Feed conversion ratio (FCR) was improved by 0.10 ± 0.02 in liquid-fed pigs (P < 0.05). Apparent digestible energy and faecal gross energy (GE) digestibility were not affected by treatment, but ileal GE and crude protein (CP) digestibility were, respectively, 9.0 ± 3.4 and 2.5 ± 0.65 percentage units higher in pigs fed liquid diets (P < 0.05). Dietary treatment significantly affected the concentrations of sugar, starch, total NSP, and sNSP in digesta from different segments of the gut, without affecting pig performance. In conclusion, weaner pigs can be fed appropriately formulated diets containing 50% millrun without loss of performance. The FCR and CP digestibility were improved by liquid feeding, but not by the addition of NSP-degrading enzymes.

Wheat is a common raw material in Australian broiler diets because of its high starch and protein content. However, the main concern with wheat is the presence of soluble non starch polysaccharides (NSPs), especially arabinoxylans. Arabinoxylans may account for up to 61 g/kg of wheat dry matter (Choct and Annison, 1990). These NSPs are difficult to digest and may cause digesta to become viscous thereby reducing nutrient digestion and absorption. Many NSP degrading enzyme products are commercially available and are used in the poultry feed industry. This study was undertaken to compare the effect of different enzymes preparations on in vitro viscosity of different wheat varieties.

A trial was conducted to test the following hypothesis; broiler exposure to coarse insoluble fibre in the diet or litter will result in enhanced gizzard function and performance, improved adaptability to an intermittent feeding program and an increase in the occurrence of reverse peristalsis. Ross 308 broiler chickens were either intermittent or ad libitum fed a basal diet, a basal diet diluted with 15 % coarse hulls (barley and oats) or a basal diet diluted with 15 % finely ground hulls in a 2x3-factorial experiment (n = 17 birds/treatment). From 18 days of age, the birds were transferred to individual cages. Birds on intermittent feeding had restricted access to feed from 11 days of age. From 18 days of age, the restrictive feeding program consisted of four one-hour meals and one two-hour meal per day. AME value and faecal starch digestibility were determined by quantitative collection of excreta. At 31 and 32 days of age, birds were inoculated with CrEDTA via the cloaca. Weights were recorded and digesta samples collected from the gizzard, duodenum, jejunum, and ileum. There was no interaction between diet and feeding regime for any of the parameters measured. The addition of coarse oat and barley hulls resulted in birds with fuller, heavier gizzards (p < 0.001). Intermittently fed birds raised on the coarse hull diet exhibited an improved starch digestibility compared to birds not exposed to hulls (p < 0.001). The presence of chromium in all intestinal tract sections of birds from the six treatment groups, confirms that reflux occurs along the entire length of the gastro intestinal tract, irrespective of insoluble fiber content of the feed or feeding regime.

The possibility of preventing cannibalism through dietary manipulation was investigated in the 1940s and 1950s. For example, Bearse, Miller and McClary (1940) and Scott, Holm and Reynolds (1954) found that inclusion of oat hulls in diets decreased the incidence of feather pecking and birds showed superior feather condition. No other studies had been made on the role of nutrition in feather pecking and cannibalism until recently, when several dietary deficiencies were found to be related to feather pecking and/or cannibalism (Cain, Weber, Lockamy and Creger 1984; Cooke 1992; Ambrosen and Petersen 1997). Low levels of dietary protein (Cain et al., 1984; Ambrosen and Petersen 1997), of tryptophan (Shea, Mench and Thomas 1990; Savory, Mann and MacLeod 1999), and of lysine, methionine, and threonine (Ambrosen and Petersen 1997) have been reported to cause aggressive pecking and cannibalism in birds. Diets deficient in phosphorus and sodium have also been linked with the outbreak of cannibalism in chickens (Cooke 1992; Cumming, Chubb, Nolan and Ball 1995). Of particular significance are the findings of Esmail (1997) that addition of oat hulls to a layer diet reduced the incidence of feather pecking and cannibalism in a dose-response manner. Recent research by Hartini, Choct, Hinch, Kocher and Nolan (2002) also found that insoluble dietary fibre was very effective in reducing cannibalism mortality.