Thesis (Ph.D.)--McMaster University, 2005. / Supervisor: Oded Bar-Or. Includes bibliographical references. Also available online.

These studies were designed to evaluate the relationships between residual feed intake (RFI) and performance of growing heifers and Brahman cows. Residual feed intake was determined for 77 heifers of diverse breedtypes (Angus, Brahman, Hereford, Holstein, Jersey and F1 crosses) during both the pre- and post-pubertal periods. Heifers were individually fed and allowed ad libitum access to feed for 84 +/- 6 d during the prepubertal feeding trial and 90 +/- 4 d during the post-pubertal feeding trial. Brahmaninfluenced heifers had lower RFI than heifers without Brahman influence during both the pre-pubertal (P < 0.05) and post-pubertal (P < 0.0001) periods. Residual feed intake determined during the pre-pubertal period was only a moderate predictor (r = 0.48; P < 0.0001) of RFI determined during the post-pubertal period. Residual feed intake was determined for 38 Bonsmara heifers over a 70-d feeding period. Heifers were fed a high roughage diet at 2.65% of body weight (BW). Weekly blood serum samples were analyzed for progesterone concentration by radioimmunoassay (RIA) to determine puberty. There were no observed differences between efficient and inefficient heifers for performance traits, age at puberty or conception, or cumulative achievement of puberty and conception. The postpartum performance of Brahman primiparous (n=16) and multiparous (n=38) cows previously evaluated postweaning for RFI was investigated. Females were weighed and evaluated for body condition score (BCS) at 28-d intervals prior to the start of the 2008 calving season. Weekly weights and BCS were collected beginning 21 d after calving. Blood serum samples were also collected weekly for progesterone analysis by radioimmunoassay (RIA), non-esterified fatty acid (NEFA) analysis by enzymatic colorimetry, and insulin-like growth factor-I (IGF-I) analysis by RIA. Females were exposed to vasectomized marker bulls after calving to aid in estrus detection. Eight and ten d following observed estrus, females were evaluated using ultrasonography via rectal palpation to determine the presence of a corpus luteum (CL). Efficient cows exhibited estrus, developed functional corpora lutea, and exhibited estrus with CL formation earlier (P < 0.05) than inefficient cows. Furthermore, a greater percentage (P < 0.05) of efficient than inefficient cows were pregnant at the end of the breeding season.

Developmental changes within the hypothalamus are necessary for maturation of the reproductive neuroendocrine axis. Recent reports have implicated several neuronal networks in this process, but genes involved in their regulation have not been elucidated. Using a well-established model for nutritional induction of precocious puberty, objectives were to 1) use microarray technology to examine changes in gene expression within the arcuate nucleus (ARC) of the hypothalamus in pre-pubertal heifers fed high or low-concentrate diets, and 2) determine if high-concentrate diets are required for nutritional induction of precocious puberty. In Experiment 1, early-weaned, cross-bred heifers were fed either a high-forage/low-gain (HF/LG; 0.45 kg/d) or a highconcentrate/ high-gain (HC/HG; 0.91 kg/d) diet for 91 d. Analysis of microarray data indicated that 346 genes were differentially expressed (P < 0.05) between HC/HG and HF/LG heifers. Expression of three key metabolic genes [neuropeptide Y (NPY), agoutirelated protein (AGRP), and growth hormone receptor (GHR)] observed to be differentially expressed in the microarray analysis was investigated further by quantitative PCR. Real-time RT-PCR indicated that expression of NPY, AGRP and GHR was lower (P < 0.05) in HC/HG compared to HF/LG heifers. In contrast, concentrations of insulin (P < 0.05), IGF-1 (P < 0.002) and leptin (P = 0.1) were greater in HC/HG compared to HF/LG. For Experiment 2, 48 heifers were used in 2 replicates (24 heifers/replicate) in a 2 x 2 factorial design to examine the roles of diet type (HF vs HC) and rate of gain (LG, 0.45 kg/d vs HG, 0.91 kg/d) on age at puberty. Heifers were fed HC/HG, HC/LG, HF/HG or HF/LG (n = 12/group) for 14 wk, and then switched to a common growth diet (0.68 kg/d) until puberty. Heifers in both HG groups reached puberty at a younger age (54.5 ± 1.8 wk) than heifers in both LG groups (60.2 ± 1.9 wk; P < 0.04). A marked increase (P < 0.01) in serum concentrations of leptin occurred in HC/HG heifers between 24 and 30 wk of age. This increase in circulating leptin was not observed in other groups. Overall, results indicate that nutritional regulation of reproductive neuroendocrine development involves the control of NPY, AGRP and GHR expression. The abrupt increase noted for circulating leptin in heifers fed HC/HG diets, if timed and sustained appropriately, could represent an important temporal cue for activation of the neuroendocrine system and the onset of puberty.

Adolescents engage in more risky behavior when they are with peers and show heightened susceptibility to peer influence relative to children and adults. Recent experimental studies suggest that peer influence on adolescent risk-taking may be mediated by activity in reward-related regions of the brain (Gardner & Steinberg, 2005; Chein et al., 2011). Because reward-related regions are modified by the hormonal changes of puberty, it is possible that the heightened influence of peers on adolescent risk-taking is more closely linked to pubertal development than chronological age. The current study examined whether the effect of peers on risk-taking was moderated by pubertal status. Participants (62 youth, ages 11-16) completed a performance-based measure of risky decision-making, once alone and once in the presence of two peers. Pubertal timing was assessed using self-report. Adolescents made riskier decisions in the presence of peers, and more advanced pubertal development predicted greater risky decision-making, controlling for chronological age. However, the relationship between pubertal timing and risk-taking was only apparent when adolescents completed the task alone. The effect of peer presence on risky decision-making was attenuated for adolescents with more advanced pubertal development. These findings suggest that the presence of peers may override biologically-based individual differences in propensity for risk-taking. / text

Replacement gilts and early parity sows constitute a large, and increasing, proportion of modern breeding herds. Breeding herd profitability is therefore increasingly dependant on the efficiency of gilt management strategies as well as litter size at first farrowing; however, incidences of reproductive failures and small first litter sizes are common within cohorts of replacement gilts. Hence, this thesis had two primary aims which were addressed in four experiments; one, to identify whether the puberty stimulation and mating strategies developed for genotypes of 20 to 30 years ago are suitable for today’s heavier yet leaner genotypes; and two, to better understand the influence of pre-pubertal growth rate and metabolic status on reproductive maturation, puberty attainment and potential litter size. In experiment 1, 192 Large White/Landrace crossbred gilts were used to compare the effects on puberty attainment of commencing boar exposure at 161, 182 or 203 days of age, and the effect of first mating gilts at either the pubertal or second oestrus on ovulation rate and early embryo survival. Gilts were artificially inseminated at the allocated oestrus, with the reproductive tracts collected at 22.8 ± 0.4 days after first mating (mean ± S.E.M), and the numbers of corpora lutea and viable embryos recorded. Delaying first boar contact until 182 or 203 days of age significantly (P < 0.01) reduced days-to puberty and increased the proportion of gilts attaining puberty within 10 days of start of boar exposure. Gilt age at mating had no effect on potential litter size; however, there was a tendency for gilts mated at their second oestrus to shed 0.6 more ova, and possess one more embryo at day 20 of pregnancy. Experiment 2 determined the effects of long- (chronic) and short- (acute) term moderate dietary restriction on ovarian development and oocyte developmental competence in 161- and 175- day old, pre-pubertal gilts. Both chronic and acute periods of moderate feed restriction reduced the number of medium follicles present on the ovaries of 161- and 175-day old gilts, as well as the proportion of oocytes reaching Metaphase II in vitro. However, feeding level during the 14 days prior to ovary collection had the greatest effect on follicular growth and oocyte quality. Experiments 3 and 4 investigated the effects of the same dietary treatments on the timing of puberty attainment in response to boar exposure and potential litter size following mating at the pubertal oestrus. Chronic dietary restriction during the pre-pubertal period delayed puberty attainment, but the timing of the pubertal response was unaffected by acute, moderate dietary restriction of previously well-fed gilts during the period immediately prior to, and coincident with, boar exposure. Acute dietary restriction or repletion stimulated an increase or decrease, respectively, in pubertal ovulation rates; however, neither the number of viable embryo present on day 22 of gestation nor embryo survival were affected by the nutritional treatments used in these studies. Overall, these results demonstrate that the timing and synchrony of puberty attainment is significantly improved when gilts first receive boar exposure at 182 days of age (or older). It is, therefore, concluded that sexual maturity, as measured by responsiveness to boar contact, occurs later in modern genotypes. It is also evident that within the age range investigated, delaying first mating until the second oestrus does not significantly increase either ovulation rate or embryo number at day 20 post-mating. Further, the current data provide the first evidence that despite profoundly affecting the size and morphology of the antral follicle pool as well as pubertal ovulation rates, subtle alterations in dietary intake have no affect on the number or proportion of embryos surviving the pre-and peri-implantation period. It is evident the litter size of gilts mated at the pubertal oestrus is not determined by the number of ova shed, with the current data demonstrating that increasing ovulation rates results in increased embryo mortality. / http://proxy.library.adelaide.edu.au/login?url= http://library.adelaide.edu.au/cgi-bin/Pwebrecon.cgi?BBID=1339082 / Thesis (Ph.D.) - University of Adelaide, School of Agriculture, Food and Wine, 2008

Research suggests that the temporary rise in adolescent antisocial behaviour (ASS) is attributable to a very large number of young people each engaging in a relatively small number of ASS's while progressing through adolescence. One possible explanation for the temporary increase in ASS during adolescence is that during puberty, the cognitive processes responsible for monitoring and controlling behaviour are disrupted. In support of this, recent research has found that adolescents' participation in ASS is positively correlated with the stage of pubertal development rather than age. Additionally, there is evidence that a temporary 'dip' in executive functioning (planning, organizing, decision-making) occurs at an age range (Le. 11-14 years) typically associated with the onset of puberty. This thesis reports a first test of a model which proposes a causal relationship between puberty, decreased executive function and increased antisocial behaviour. Self-report data on pubertal development, antisocial attitudes and ASS participation were collected from 323 boys and girls (ages 9 -17 years) attending New South Wales public schools. Executive function, (Le. updating, response inhibition, set-shifting) was measured in a 3D-minute individual interview. Data were analysed to determine if participants reported greater participation in ASS during puberty onset and whether this period was also characterized by a decline in executive function. In addition, it was investigated whether adolescents who attain puberty earlier than their peers participate in ASS earlier, longer, and at higher rates than their 'on-time' or 'late-maturing' peers, and whether there was an association between 'early' puberty and a persistent reduction in executive function. Results revealed that ASS participation was significantly associated with puberty onset timing, and some significant associations were found between antisocial attitudes and pubertal timing. There was some indication of decreased executive function at puberty onset and a link between early pubertal timing and a persistent reduction in executive function. Thus, there is some partial evidence to support the proposed model of adolescent ASS. However, complications in performing mediation analysis prevent concluding that executive function mediates the relationship between pubertal development and ASB. The implications of these findings are discussed with reference to future research in this field.

Thesis (Ph. D.)--University of Hong Kong, 2008. / Includes bibliographical references (leaf 187-209) Also available in print.

Thesis (Ph. D.)--University of Hong Kong, 2008. / Includes bibliographical references (leaf 187-209) Also available online.

Thesis (Ph. D.)--University of Washington, 1999. / Vita. Includes bibliographical references (leaves 148-168).

Thesis (Ph. D.)--University of California, Los Angeles, 1995. / Vita. Includes bibliographical references (leaves 247-259).