This thesis presents a review of the appropriate literature and results from the experiments that were conducted with water-soluble carbohydrate extracts from four Australian and New Zealand plants, 'Arthropodium cirratum' (Rengarenga lily), 'Cordyline australis' (Cabbage tree), 'Acacia pycnantha' ('Acacia' or Golden wattle) and the seaweed, 'Undaria pinnatifida' ('Undaria' spp. or Wakame). Plant extracts and commercially available prebiotic compounds, with a chemical composition of which was similar to that of the plant extracts were examined for their use as alternatives to antibiotic growth promoters (AGPs) in broiler chickens. ... The implications and significance of the major findings and an overview of effects of the studied plant extracts and prebiotic compounds, as alternatives for AGPs, on growth performance and health of broiler chickens are discussed. The major highlights of each experiment are presented in the relevant chapter in form of an abstract.

A total of 294 one-day old Cobb broiler chickens were used to investigate the effects of four lactobacillus strains on production performance. The chicks were assigned randomly to six groups with 7 replicates of 7 chicks per treatment. The six dietary treatments were: (i) basal diet (negative control, Tl); (ii) basal diet with added Zinc-bacitracin (ZnB, 50 ppm, T2), iii) one of four strains of Lactobacillus (tentatively identified as L. johnsonii, L. crispatus, L. salivarius and unidentified Lactobacillus sp., T3, 4, 5 and 6). The probiotic strains were selected from 235 lactobacilli isolates based on their in vitro antagonistic effect against Clostridium perfringens and Escherichia coli. Results showed that the addition of probiotic Lactobacillus spp. to the feed did not significantly improve body weight gain, feed intake and feed conversion ratio of broiler chickens raised in cages during the 6-wk experimental period.

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.

The effects of light intensity during rearing and beak trimming and dietary fiber sources on the incidence of cannibalism were investigated with 2,880 ISA Brown hens. During the rearing period, chicks were housed under two levels of light: dim light (i. e., 5 lx) and bright light (i. e., 60 to 80 lx) and two beak conditions: with or without trimming. At 15 wk of age, all birds were transferred to laying cages with five birds per cage. At 17 wk of age, four diets containing different concentrations of dietary fiber were offered: a commercial (wheat) diet, high insoluble fiber (millrun) diet, high soluble fiber (barley) diet, and high soluble fiber diet plus enzyme. Beak trimming had a profound effect (P < 0.001) on cannibalism with mortality occurring predominantly in untrimmed birds. Total mortality for the trimmed birds was 0.14 and 0.77% for the prelay (17 to 20 wk) and early lay periods (21 to 24 wk), whereas mortality was 13.4 and 37.7%, respectively, for the untrimmed birds. The beak-trimmed birds had lower feed intake than the nontrimmed birds (P < 0.05). Diet significantly affected cannibalism (P < 0.01). The highest mortality occurred in birds fed the commercial diet (13 and 29% for the prelay and early lay period, respectively). Diet also affected feed intake (P < 0.05), being lower (P < 0.05) on the commercial diet than on the higher fiber diets. Egg production per bird did not differ significantly between diets. Light intensity during rearing did not influence the incidence of cannibalism.

Phytobiotics represent a wide range of bioactive compounds that can be extracted from various plant sources. In recent years, some interesting and novel applications of phytobiotics in the production and wellbeing of monogastric animals have emerged, and these aspects are reviewed in the present paper. Recent studies at the University of New England indicate that water—soluble carbohydrate extracts from some Australian and New Zealand native plants can be used as potential phytobiotic compounds to modify the gut microflora in broiler chickens. Compared with other in—feed antibiotic alternatives, the evaluation of phytobiotics is still in its infancy and their potential use needs to be investigated with broader emphasis.

Previous research showed that mannanoligosaccharide (MOS) supplementation of broiler diets tended to reduce the number of coliform bacteria in the intestine of broiler chickens (Yang et al., 2006). The effects of MOS on the populations of mucosa-associated bacteria were further examined using an 'E. coli' challenge model.

Two enzyme assays, the radial diffusion and the dye-release methods, were modified and tested for their suitability in measuring β-glucanase activity in poultry feed. Enzymes A and B were incorporated into a barley-based broiler starter diet at three levels (500, 1000 and 2000 g/t). The measured β-glucanase activities were 35 U/g and 49 u/g for Enzymes A and B, respectively. A comparison of enzyme recovery rates from samples containing known amounts of the enzyme and from a buffer solution containing the same amount of the enzyme revealed that a fixed percentage of the enzyme bound to feed components in a dose responsive manner. Thus, enzyme recovery rates for the feed samples were not complete and varied between 66% and 97% for the radial diffusion assay and between 76% and 91% for the dyerelease assay. The two assays largely agreed with each other although at low enzyme concentrations, the dye-release assays gave higher recovery rates with lower standard errors. It may be concluded that both assays are useful in determining β-glucanase activity in feed and digesta samples, but the radial diffusion assay is cheaper to perform.

An experiment was conducted to determine the effect of sorghum particle size and milling type on broiler performance and feed apparent metabolisable energy (AME). Results show that AME was improved by feeding a pelleted diet containing whole sorghum, but the best performance (lowest FCR) was elicited by feeding a rolled sorghum diet at a common commercial grind size. Feed particle size may influence the rate of excretion of different fractions of the digesta and AME of a feed. AME may not be an accurate indicator of the nutritive value of grain as the same feed can have a different AME values based on physical structure.

Two experiments were conducted to examine the effect of graded levels of dietary chromium and leucine, and different fat sources on performance and body composition of broiler chickens. The results showed that chromium picolinate at 0.5 ppm significantly (p<0.05) lowered the carcass fat level. Gut weight and carcass water content were increased as a result of chromium treatment. Body weight, plucked weight, carcass weight, abdominal fat pad weight, breast yield and feed efficiency were unaffected by chromium treatment. Leucine did not interact with chromium to effect lean growth. Dietary leucine above the recommended maintenance level (1.2% of diet) markedly (p<0.001) reduced the breast muscle yield. The addition of fish oil to broiler diets reduced (p<0.05) the abdominal fat pad weights compared to birds on linseed diets. Fish oil is believed to improve lean growth through the effects of long chain polyunsaturated fatty acids in lowering the very low-density lipoprotein levels and triglyceride in the blood, in the meantime increasing glucose uptake into the muscle tissue in blood and by minimizing the negative impact of the immune system on protein breakdown. The amount of fat in the diet (2% or 4%) did not affect body composition.

The gut harbors more than 600 different species of bacteria, contains over 20 different hormones, digests and absorbs the vast majority of nutrients, and accounts for 20% of body energy expenditure. It is also the largest immune organ in the body (Kraehenbuhl and Neutra, 1992). Thus, anything that affects the health of the gut will undoubtedly influence the animal as a whole and consequently alter its nutrient uptake and requirements. Gut health is a complex term that can include the macro- and micro structural integrity of the gut, the balance of the micro flora, and the status of the immune system. Further complexity arises because of their interactions and the resulting changes in gene expression and possibly endocrine regulation. This, in turn, may affect the way nutrients are partitioned and utilized for organ development, tissue growth and immune system maturation (Kelly and Conway, 2001; Kelly and King, 2001). This paper will attempt to discuss the link between gut health and nutrition, mainly using data generated in poultry studies.