The modern broiler chicken increases its bodyweight by 5000% in the first six weeks of life. Even so, the genetic potential of the bird is ever increasing. The intensive nature of the modern broiler meat production system also potentially increases risk of transmissible diseases. Thus, the stresses on the bird's physiological systems; skeletal/muscular, digestive, immune and cardiovascular, are also increasing. Augmentation of suitable husbandry practices with appropriate nutrition will allow improved broiler production and health, by helping the birds’ physiological systems serve their respective intended purposes. That is, nutritionists need to present a feed to the broiler that more accurately meets its needs, not only on a nutritional level, but also on a physiological level, such that the bird is more able to effectively digest and absorb the feed due to improved physiological responses to the feed itself. The nutritionist can only do so much when it comes to feeding for profit. Aside from the nutritional needs of the bird, economic constraint is the largest factor that must be considered when formulating a broiler diet. It is therefore important that feed production costs are reduced, and at the other end, feed efficiency is improved, essentially enabling a more profitable product per unit cost of feed.

Genetic selection of laying hens has produced lighter body weight while maintaining maximum egg production. Heavy birds have problems during the laying period such as fatty liver and large size egg. The body weight at point of lay and flock uniformity can be used to predict the production performance during the laying period. However, there is evidence that hens which are overweight produce poor quality eggs during the laying period. The first two studies were conducted to investigate the importance of body weight at point of lay and flock uniformity on eggshell quality and production performance on commercial farms, both cage and free-range production systems. A laboratory experiment was then set up using the information derived from the on-farm studies, and extended to analyse body conformation using computed tomographic scanning. The body weight and flock uniformity in the on-farm studies varied from farm to farm. The poor performance of many of the flocks also illustrates the likely variation occurring at a commercial level; poor compliance with average growth rate patterns and low uniformity standards. Hen age had the greatest effect on most egg quality variables. In the laboratory experiment, flock uniformity prior to point of lay was designed to be above the breeder standard. Body weight at point of lay significantly affected egg production and eggshell quality. However, there was no significant effect on bone breaking strength and bone dimensions. Body weight was significantly correlated with the composition of lean, fat and bone. Heavy hens deposited more fat than lean tissue. Body weight should be maintained at the level of breeder standards. Correct body weight and high uniformity of the flock at point of lay will result in good performance over the laying period with high peak production and good persistency of production and the production of good quality eggs. Management is the key factor to regulation of body weight during rearing and at point of lay.

Under control physiological conditions, the use of oxygen by cells of aerobic organisms generates potentially toxic reactive oxygen metabolites. A chronic state of oxidative stress may exist in cells because of an imbalance between pro-oxidants and antioxidants. The amount of oxidative damage increases as an organism ages and this is postulated to be a major causal factor of senescence (Sohal & Weindruch, 1996). Oxidative stress probably plays a major role in the progressive compromise in the ability to maintain homeostasis characteristic of the ageing process. Abnormally high levels of free radicals and the simultaneous decline of antioxidant defence mechanisms can lead to damage of cellular organelles, enzymes, as well as increased lipid peroxidation and altered protein and gene expression (Maritim et al., 2003).

The aim of this study was to investigate how the antioxidant status is affected by age and oxidative stress (±0.2 mM H2O2) in different functional regions of the rat kidney.

Antioxidant enzyme activities were shown to be attenuated with age under both control and stress conditions after peaking at 12 weeks old (young adult). Antioxidant enzyme activities were higher in the cortex by comparison with the outer and inner medulla respectively. GSH concentrations followed a similar pattern to the levels of antioxidant enzymes.

In all regions and under both stress and non-stress conditions the TBARS and lactate concentration showed a similar pattern with 12 weeks old < 36 weeks old < 5 weeks old and < 60 weeks old. The greatest concentration was measured in the 60 weeks rat under stress condition with the superficial cortex greater than the outer and inner medulla.

Protein expression of GPX1 detected by Western blot was shown to decrease with age under both control and stress conditions after peaking at 12 weeks (young adult). GPX1 expression was greater in the cortex by comparison with the outer and inner medulla respectively. On the other hand, GPX4 expression did not show much variation across the different regions of the kidney under control or stress conditions, although it did show a significant increase in expression in the inner medulla at 12 weeks under control. GPX2 expression was not detected across the different regions of the kidney under control or stress conditions.

mRNA was extracted from the superficial cortex, outer medulla and inner medulla. The expression of Gpx1, Gpx4 and Hsp-70 was analysed by quantitative reverse transcribed polymerase chain reaction (QRT-PCR).

Gene expression of Gpx1 was highest in the cortex, with a trend to decrease with age, after reaching a maximum at 12 weeks. By contrast, Gpx4 gene expression did not vary in a consistently significant fashion across the different regions of the kidney in all age groups, with the one exception of a significantly higher level of expression in the inner medulla at 12 weeks. In general there was a good correlation between enzyme activity, protein expression and gene expression for the antioxidant enzymes studied. The negative correlation between gene expression of Gpx and Hsp70 was striking although there is no data on protein expression of HSP70.

Thus, in stark contrast with the expression of both Gpx1 and 4, gene expression of stress protein Hsp-70 was elevated in the inner medulla, and was increased overall in the ageing rats at 60 weeks.

Overall then, the thesis provides general support for the free radical theory of ageing particularly as this pertains to kidney function.

Leptin is a cytokine hormone with multiple roles throughout the body. Previously leptin distribution and pharmacokinetics were poorly defined; here the pharmacokinetics of leptin has been examined in male and female mice at physiologic doses. These data were also used to create a predictive model for leptin distribution, allowing targeted research on leptin in the future.

Antibodies derived from ruminant mammary secretion can be used prophylactically to protect humans against disease. Although ruminant colostrum is a rich source of antibodies, colostrum is produced only for a short time, whereas milk, which is produced over extended periods, contains extremely low concentrations of antibodies. Therefore the aim of this project was to investigate underlying biological principles that could be employed to develop strategies aimed at enhancing antibody levels in ruminant milk while maintaining normal milk production. To address this aim, it was proposed that increasing the numbers of antibody secreting cells (ASCs) resident in the mammary gland during the lactation period would lead to enhanced local antibody production and in turn increased amounts of antibody in milk.

Daily torpor and hibernation in adult mammals and birds have been extensively studied, but there is still much to learn about these fascinating physiological states. Because torpor in marsupials is widespread, partially because many marsupial species are small in size and heterothermy is common in small species, a growing number of studies have successfully investigated the use of heterothermy in this group.

However, most available data on heterothermy in marsupials exist for adults, and very little for growing young, mostly due to the challenges of measuring body temperature (T_b) in very small animals. There is currently much well-placed interest in the relationship between heterothermy and climate change, and how increasing air temperatures (T_as) may influence the use of heterothermy in these species. However, an animal may be most at risk of being negatively affected by increasing or variable T_as when it is still developing, especially in the case of marsupials which have potentially vulnerable altricial young. While some studies have investigated the development of thermoregulation in these tiny animals, continuous temperature measurements, that do not disturb the animal, have not been obtained due to the lack of appropriate technology.

The species chosen for my study were fat-tailed dunnarts (Sminthopsis crassicaudata) and stripefaced dunnarts (S. macroura), which are small marsupials from the family Dasyuridae (carnivorous marsupials). These two species are common in the wild and are ideal for laboratory work as they are easy to maintain and breed in captivity. The central theme of my study was the development of thermoregulation and torpor in very small, developing dunnarts. My first aim was to find a method of taking continuous measurements of T_b in very small animals that would not interrupt torpor use, as conventional transmitters are too large to be used in such small animals. By testing and confirming the reliability and accuracy of small temperature-sensitive transponders, I was able to use these to obtain continuous T_b readings in animals only 60 days (d) old, at approximately 8 g, and still in the nest.

The second aim of my study was to measure the development of endothermy and torpor use in the fat-tailed dunnart (S. crassicaudata). When animals were placed at T_a of 18 °C at 40 d they were poikilothermic, rapidly cooling to T_a, at 48 d animals cooled more slowly and could maintain T_b at approximately 25 °C, and at 56 d animals were endothermic, maintaining a high, normothermic T_b at the low T_a. Animals at ~60 d entered an apparent state of torpor, but being unable to rewarm, became hypothermic. However, these animals could rewarm when given access to radiant heat. Basking in this instance was not an optional method of reducing the cost of rewarming, but was instead necessary to rewarm and avoid hypothermia, and therefore essential to be able to use torpor. The incidence of hypothermia decreased until ~120 d when all animals could actively rewarm, without the aid of radiant heat. This is the first time, to my knowledge, that torpor use in an animal that is not yet fully endothermic has been observed, and indicates that the development of thermoregulation in this, and likely other species occurs in three stages: poikilothermy, partial endothermy and heterothermic endothermy. This discovery may also have some evolutionary implications that need to be considered, as heterothermy was possibly an intermediate stage between poikilothermy and homeothermy in the evolution of endothermy in mammals. The observation of basking in juveniles could reveal the step that explains how pre-endothermic animals were able to move beyond the heterothermic stage in the evolution of endothermy.

Nine experiments were performed to investigate how the synthesis and/or deposition of protoporphyrin IX (PP IX) into eggshell is influenced in brown-egg laying hens. The findings obtained in the first experiment (Chapter 2) showed that flock age and production system affected overall eggshell and egg quality. Egg weight was significantly higher in cage eggs, while albumen height was significantly higher in barn eggs. The mammillary layer ultrastructural variables showed no clear relationship with production system and flock age. Cuticle cover (ΔE*ab) was significantly higher in barn eggs compared with free range and cage eggs and was significantly higher in eggs from the 44 week old flock than for 64 and 73 week old flocks. In 1 gram of eggshell with and without cuticle, there was more PP IX in cage eggs followed by free range and barn eggs. The findings in experiment 2 (Chapter 3) indicate that eggs laid earlier in the day had deeper brown eggshell colour compared with the eggs laid later in the day. Egg position in a clutch had a clearer effect on eggshell quality in long clutches, as compared with medium and short clutches. The findings of the third experiment (Chapter 4) showed that different infectious bronchitis virus (IBV) strains affected the level of PP IX in eggshell differently. In unvaccinated laying hens, the mean PP IX per gram of shell was significantly higher on day 1 post-infection (p.i.) compared to day 7, after which PP IX increased with day p.i. In unvaccinated and vaccinated laying hens, PP IX decreased with increased day p.i. until day 12. The effect on loss of shell colour was more marked in the T strain infected group followed by N1/88, Vic S and A3 strains. Experiment four (Chapter 5) investigated reference gene stability in the shell gland in relation to time-points (time post-oviposition) of eggshell formation and nicarbazin treatment. The two most stable reference genes selected, HPRT1 and HMBS, were used for the normalisation of gene expression data obtained in experiment five (Chapter 6). The findings in experiment five showed that mitochondria per cell did not vary significantly with different time-points of eggshell formation and nicarbazin treatment. Genes involved in the synthesis of PP IX were regulated differentially in relation to time-points of eggshell formation. Feeding nicarbazin caused down-regulation of the ALAS1 gene that resulted in lower production of PP IX appearing in the shell gland tissue and eggshell. Experiment six (Chapter 7) investigated reference gene stability in the shell gland and spleen of infectious bronchitis virus (IBV) infected hens. The two most stable reference genes selected, TBP and YWHAZ, were used for the normalisation of gene expression data obtained in experiments seven and eight (Chapters 8 and 9). The RNA-sequencing findings in experiment seven showed that there were no differentially expressed genes (DEGs) involved in the mucosal immune system and eggshell formation in the shell gland between IBV challenged and control laying hens. However, there were 1608 and 1806 DEGs at 5 and 15 hrs time-points of eggshell formation, respectively. The Gene Ontology (GO) terms and functional gene analysis showed that the DEGs at 5 hr post-oviposition were mainly involved in ion transport and synthetic activities, while the DEGs at 15 hr were involved in energy metabolism and secretory activities, reflecting the peak stage of eggshell formation. The findings in experiment eight (Chapter 9) showed that IBV T infection significantly lowered mitochondrial count per cell in the shell gland region of the oviduct but not in the magnum or isthmus. The expression levels of nuclear DNA encoded genes involved in mitochondrial biogenesis and fission showed no clear correlation with mitochondrial count and were not significantly different between the control and challenged samples. The expression levels of all the genes except for PGC-1α were significantly affected by the time-points of eggshell formation. Experiment nine (Chapter 10) attempted to localize ALAS1, ALAD and FECH enzymes in shell gland tissue collected at different time-points (time post-oviposition) and in response to nicarbazin treatment. The findings showed that these antibodies did not recognise their respective proteins, possibly due to their amino acid sequences being derived from humans. PP IX fluorescence was not detected in Zenker Formol fixed tissue sections, stained or unstained, taken at different time-points and with or without nicarbazin treatment. Future work is suggested using chicken specific antibodies to localise cells involved in PP IX synthesis. Taken together, the findings in the current study broaden the understanding of factors affecting the synthesis and deposition of PP IX into eggshells.