Feed transit time is the amount of time feed components are retained in the gastrointestinal tract and is often measured by giving a known amount of marker-containing diet and determining the first appearance of the marker in the faeces. Most markers used in digestibility studies are insoluble substances such as Cr203 and acid-insoluble ash which must be incorporated into the diets in substantial quantities for sufficient accuracy in subsequent determinations. Feeding birds a marker-containing diet in a given amount of time is difficult and inaccurate, and force-feeding birds using the Sibbald technique is tedious and not suitable for young broilers. The current paper describes a new fat-soluble marker, a long-chain alkane (C36H74), which can be easily and accurately administered to chickens orally.

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.

Coccidial co-infection, dietary inclusion of viscous grains and ingredients of animal origin protein are considered important predisposing factors for onset of necrotic enteritis (NE). High dietary glycine levels has been shown to increase the intestinal 'C. perfringens' population in broilers (Dahiya et al. 2005). As the causative agent for NE, the spore germination of 'C. perfringens' can be activated by the spore cortex-lytic enzyme (SCLE) coded by SleC thus to cause gastrointestinal disease. Investigations have shown that glycine forms a conjugated compound with bile salts playing a critical role in Clostridial germination (Sorg and Sonenshein 2008). This compound is recognized by the germinant receptor, CspC and is responsible for cleaving the N-terminal propeptide of SleC, expressing mature SCLE to activate its hydrolase activity. The current study assessed the impact of a high dietary glycine inclusion on performance of broilers under subclinical necrotic enteritis challenge.

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.

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.

Different energy evaluating systems have been used to formulate poultry diets including digestible energy, total digestible nutrients, true metabolizable energy, apparent metabolizable energy (AME), and effective energy. The AME values of raw materials are most commonly used to formulate poultry diets. The net energy (NE) system is currently used for pig and cattle diet formulation and there is interest for its application in poultry formulation. Each energy evaluating system has some limitations. The AME system, for example, is dependent on age, species, and feed intake level. The NE system takes AME a step further and incorporates the energy lost as heat when calculating the available energy for the production of meat and eggs. The NE system is, therefore, the most accurate representation of energy available for productive purposes. The NE prediction requires the accurate measurement of the AME value of feed and also an accurate measurement of total and fasting heat production using nutritionally balanced diets. At present, there is limited information on NE values of various ingredients for poultry feed formulation. The aim of this review is to examine poultry feed energy systems with the focus on the NE system and its development for chickens.