Early- Life Determinants of the Age at Menarche.

Menarche, the first menstrual period, is a recognizable marker of puberty. The timing of menarche has important public health ramifications because an early age at menarche is associated with breast and endometrial cancers, obesity, type II diabetes, cardiovascular disease, and all-cause mortality. Secular trends and between-country variability in age at menarche suggest that the onset of puberty is responsive to changing environmental conditions. Nevertheless, the specific environmental factors that influence age at menarche remain largely unidentified. In this dissertation we first examined sociodemographic influences on recent trends in age at menarche using nationally-representative data from Colombia, finding that there was a recent ongoing negative trend in the age at menarche, most pronounced in higher socioeconomic status girls and among those living in urban areas. In the second aim we utilized the nationally representative dataset to examine the role of prenatal factors including season and altitude on menarche. We found that a higher number of gestation days exposed to the rainy season was related to an earlier age at menarche whereas a higher altitude of residence was related to a later age at menarche. We also noted that the association between gestation days exposed to the rainy season and altitude was only apparent among girls living in altitudes ≥2000 m. Finally, in the third aim we examined the relation between childhood red meat intake frequency and age at menarche in a longitudinal study among 456 school-aged girls from Bogotá, Colombia. We found that higher red meat intake frequency at 5-12 y was associated with an earlier age at menarche. We also incidentally discovered that higher frequency of tuna/sardine intake during childhood was related to later ages at menarche. In summation, this dissertation research shows that the age at menarche is responsive to early life environmental correlates including changing socioeconomic conditions, perinatal climate and geographic factors, and diet during childhood. This provides impetus to elucidate the specific mechanisms underlying these associations, which could ultimately lead to interventions aimed at promoting optimal pubertal development.PhDEpidemiological ScienceUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/120685/1/janerica_1.pd

Performance analysis of randomised search heuristics operating with a fixed budget

Jansen, T., Zarges, C. (2013). Performance analysis of randomised search heuristics operating with a fixed budget. Theoretical Computer Science, 545, 39-58When for a difficult real-world optimisation problem no good problem-specific algorithm is available often randomised search heuristics are used. They are hoped to deliver good solutions in acceptable time. The theoretical analysis usually concentrates on the average time needed to find an optimal or approximately optimal solution. This matches neither the application in practice nor the empirical analysis since usually optimal solutions are not known and even if found cannot be recognised. More often the algorithms are stopped after some time. This motivates a theoretical analysis to concentrate on the quality of the best solution obtained after a pre-specified number of function evaluations called budget. Using this perspective two simple randomised search heuristics, random local search and the (1+1) evolutionary algorithm, are analysed on some well-known example problems. Upper and lower bounds on the expected quality of a solution for a fixed budget of function evaluations are proven. The analysis shows novel and challenging problems in the study of randomised search heuristics. It demonstrates the potential of this shift in perspective from expected run time to expected solution quality.authorsversionPeer reviewe

Analysis of Randomised Search Heuristics for Dynamic Optimisation

Dynamic optimisation is an area of application where randomised search heuristics like evolutionary algorithms and artificial immune systems are often successful. The theoretical foundation of this important topic suffers from a lack of a generally accepted analytical framework as well as a lack of widely accepted example problems. This article tackles both problems by discussing necessary conditions for useful and practically relevant theoretical analysis as well as introducing a concrete family of dynamic example problems that draws inspiration from a well-known static example problem and exhibits a bi-stable dynamic. After the stage has been set this way, the framework is made concrete by presenting the results of thorough theoretical and statistical analysis for mutation-based evolutionary algorithms and artificial immune systems. </jats:p

Dietary protein and energy requirements of Venda village chickens

The objective of this study was to determine the dietary protein and apparent metabolisable energy (AME) requirements of local chickens. Freshly laid eggs of scavenging chickens collected in rural villages were hatched and randomly distributed to 27 floor pens, 10 chicks per pen. Chicks were fed 9 experimental diets that were combinations of three CP levels (140, 170 and 190 g kg−1 DM) and three AME levels (11.0, 11.7 and 12 MJ kg−1) during the starter phase (0–6 weeks) and combinations of three CP levels (120, 150 and 180 g kg−1 DM) and three ME levels (11.3, 12.0 and 12.4 MJ kg−1) during the grower phase (7–17) weeks. Significant differences within means on CP × AME interaction effect were observed in all parameters measured, except feed intake during starter period and dressing percentage (%) and breast yield of 17 weeks old chickens. The results of the present study indicated that during the starter and grower phases, unsexed chickens would require dietary combinations of 170 g CP kg−1 and 11.0 AME MJ kg−1 and 150 g CP kg−1 and 12 AME MJ kg−1 in their diets to optimise weight gain and FCR, and 150 g CP kg−1 and 11.3 MJ kg−1 to optimise ash content of muscles, protein content of the breast and fat content of the leg muscle. Supplementation of 27 g CP kg−1 feed to grower scavenging chickens would be enough to improve chicken production in the rural villages

Growth performance and digestive tract development of indigenous scavenging chickens under village management

The study was conducted on indigenous scavenging chickens under village management firstly, to evaluate the early development of the digestive tract to 28 days of age and secondly, to determine the growth performance of these chickens up to 20 weeks of age. One hundred and seventeen chicks, 13 chicks per age class (day 1, 4, 7, 10, 14, 17, 21, 24, 28) were randomly purchased from six rural villages in the Vhembe District, Venda, South Africa. The chickens were weighed and sacrificed for measurement of the different parts of its gastrointestinal tract. The liver and pancreas were also weighed. The relative weight of the storage organs and liver peaked at day 4 while that of the small intestine and duodenum peaked at day 10. The relative lengths of the small intestine and jejunum peaked at day 7, duodenum at day 10 and ileum at day 4. Four hundred and forty four (444) chicks from 13 households were recorded at two weekly intervals starting from day old until 20 weeks of age. The mean body weight obtained for males and females were 201.7 and 171.5 g at six weeks of age and 1048.1 and 658.6 g at 20 weeks of age, respectively. The indigenous chickens under village management were characterised by slow digestive tract development, poor growth performance and high mortalities. Further research needs to be conducted to determine the effect of early feed supplementation on the development of the digestive tract and the performance of indigenous chickens under village management

Litter characteristics of pine shavings, bio-secure pine shavings and sunflower hulls and its impact on broiler performance

The aim of this study was to investigate the physical characteristics of three litter materials, namely pine shavings (PS), bio-secure, fumigated pine shavings (BS) and sunflower hulls (SH) and its influence on broiler performance over a 33-day production cycle. The experiment was conducted in commercial poultry houses holding 42,500 chicks each, utilising a randomised block design with six house replicates per treatment. Litter samples were collected weekly for analyses of moisture, water-holding capacity, bulk density, pH and litter caking. Broiler footpad dermatitis was monitored at 21 and 31 days, together with acid detergent fibre (ADF) concentration of gizzard content, gizzard weight and small intestinal weight and length of 120 birds per treatment. Broilers across treatments consumed litter material which was evident in increased ADF levels of gizzard contents relative to feed. The SH contained more nutrients based on proximate analysis as compared to other treatments. Rearing on SH led to lower 7-day cumulative mortality, higher kilograms of broilers produced per square meter, average daily gain and slaughter weight. Improvements seen with SH did not alter commercial indicators, namely, production efficiency factor and feed conversion ratio. Litter converged toward similar physical characteristics at the end of production cycles when few differences were observed between treatments due to addition of feed, feathers and excreta