Reproductive neuroendocrine activity and appetite are modulated at the hypothalamus by both nutritional status and photoperiod in the seasonal animal. The objectives of this work were (1) to measure circulating hormones and/or metabolites that relay information about peripheral nutritional status to the hypothalamus, (2) to identify which hypothalamic neuropeptides and receptors that are responsive to photoperiodic and nutritional feedback and (3) to establish which changes in peripheral signals and/or hypothalamic neuropeptides are associated with alterations in the activity of the reproductive neuroendocrine axis. Three main experiments were carried out. The first experiment (Chapter 1) utilised a 2 x 2 design to examine the separate and interactive effects of photoperiod and food restriction on hypothalamic neuropeptide and receptor mRNA expression and on GnRH/LH secretion. In the second experiment (Chapter 2), two components of nutritional status, BC and increased food intake were investigated since both are positively related to reproductive performance in sheep. In the final experiment (Chapter 3) the approach was to use an exogenous treatment to artificially raise plasma insulin in an attempt to "drive" some of the foregoing effects. Collectively these studies have lead to the first localisation AgRp, MCH, orexin, Mc3R, Mc4R gene expression in the ovine hypothalamus. They indicate that circulating insulin and leptin are major factors relaying information about nutritional status to the hypothalamus. In addition, they have dissociated BC and food intake as signals to the hypothalamus. Moreover these studies have provided no evidence that NPY, AgRp, POMC, MCH and ObRb play a role in driving seasonal changes in appetite and gonadotrophin secretion. However they do suggest NPY-ergic and melanocortin pathways are important in maintaining appetite/bodyweight/energy homeostasis or restoring energy balance following perturbation. Furthermore the results show that changes in nutrient-sensitive hypothalamic neuropeptide and receptor gene expression may not necessarily lead to alterations in the activity of the reproductive neuroendocrine axis. However, they do indicate that increased NPY biosynthesis during food restriction may be involved in the inhibition of pulsatile GnRH/LH release.

LD2668 .T4 1949 W51 / Master of Science

Digitized by Kansas Correctional Industries

Digitized by Kansas Correctional Industries

Typescript (photocopy). / Digitized by Kansas Correctional Industries

Typescript (photocopy). / Digitized by Kansas Correctional Industries

Typescript (photocopy). / Digitized by Kansas Correctional Industries

Mycotoxins are feed contaminants that are a major problem in the livestock industry because of their prevalence in feedstuffs and the difficulty of removing them. They can cause a wide range of issues at varying levels of exposure. Each species is affected by different mycotoxins and at different levels. Pigs are more susceptible to deoxynivalenol (DON), whereas ducks are more susceptible to aflatoxin.<br> Effects of mycotoxin contamination on animal performance are not fully understood. Therefore, the two experiments described in this thesis were conducted to determine the response of pigs and ducks to consumption of feed contaminated with DON and aflatoxin, respectively. In the first experiment, the effect of a mycotoxin binder on duck feeds contaminated with aflatoxin was examined. One-day-old male Pekin ducks (n=360) were randomly divided into four groups; each group had 6 replicate pens with 15 ducks per replicate pen. The positive control (PC) group was fed a diet that was free of aflatoxin B1, the negative control (NC) group was fed a diet that contained >75ppb of aflatoxin without a binder, the negative control with low binder (NC + 0.5) group was fed a diet that contained >75ppb of aflatoxin and 0.5 kg/ton of the binder, the negative control with high binder (NC + 1.0) group was fed a diet that contained >75ppb of aflatoxin and 1.0 kg/ton of the binder. The diets were fed in two phases, days 0-14 (phase 1) and 15-35 (phase 2). The results showed that during early phase 2, NC + 0.5 resulted in a higher rate of weight gain compared to NC (P<0.05); 2) NC + 0.5 ducks had higher feather quality than both NC and PC (P<0.05); 3) NC had higher relative liver weights (P<0.05); 4) blood glucose was higher in NC + 0.5 ducks (P<0.05); and 5) PC ducks had higher serum protein levels in the blood (P<0.05).<br> In the second study, effect of the same mycotoxin binder, used in the duck study, was examined in pigs fed diets contaminated with DON. A total of 128 pigs (Duroc × Landrace × Yorkshire, (1:1 barrows and gilts, aged 42 d) were randomly assigned to 4 treatments, 8 replicate pens with 4 pigs per. The treatments were DON, DON + liver protectant (1 kg/ton), DON + mycotoxin binder (0.5 kg/ton), or DON + liver protectant and mycotoxin binder. The study lasted 28 days and body weights (BW), feed intake (FI), and blood samples were taken on days 14 and 28. Body weights and feed intake were taken and used to calculate gain:feed (G:F). Aspartate aminotransferase (AST) and alanine aminotransferase (ALT) were measured in the blood serum. BW, FI, and G:F were not significantly different at any point during the study. AST levels were significantly reduced (P < 0.05) on day 14 in pigs fed the liver protectant but were not significantly different day 28.<br> In summary, effects of the use of mycotoxin binders in feed can be highly variable. This depends on the type of mycotoxin present in the feed, the amount of mycotoxin, and the species fed the diet. In the present study, the mycotoxin binder did not have an impact on the feed efficiency of the ducks or pigs. Effects of additional binders need to be evaluated for their effectiveness in mitigating the negative effects of mycotoxins.<br><br>

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