Some investigators have hypothesized that estrogens and other hormonally active agents found in the environment might be involved in breast cancer increases and sperm count declines in humans as well as deformities and reproductive problems seen in wildlife. This book looks in detail at the science behind the ominous prospect of "estrogen mimics" threatening health and well-being, from the level of ecosystems and populations to individual people and animals. The committee identifies research needs and offers specific recommendations to decision-makers. This authoritative volume: Critically evaluates the literature on hormonally active agents in the environment and identifies known and suspected toxicologic mechanisms and effects of fish, wildlife, and humans. Examines whether and how exposure to hormonally active agents occursâ€"in diet, in pharmaceuticals, from industrial releases into the environmentâ€"and why the debate centers on estrogens. Identifies significant uncertainties, limitations of knowledge, and weaknesses in the scientific literature. The book presents a wealth of information and investigates a wide range of examples across the spectrum of life that might be related to these agents.

Introduction mammals and their environment; Internal responses to environmental stimuli; Environmental control of seasonal breeding: a commom final mechanism governing seasonal breeding and sexual maturation; Photoperiodic control of hormones, growth and lactation in cattle; Environmental influences on the sexual behaviour of Rhesus monkeys; Pheromones, social influences and population regulation in rodents; Pheromonal influence on mating behavior in female rats; Stress and fertility; The role of nutrition in mammalian reproduction; Nutrition and fertility in pedigree bulls; Nutritional and other factors in breeding performance of ewes; Environment and reproduction in tree squirrels with speial reference of the genus parexus.

A unique interdisciplinary overview of the way mammals reproduce, this volume synthesizes research done by laboratory physiologists, behaviorists, population ecologists, and animal breeders. F. H. Bronson has drawn together the disparate literature in these areas to provide students and researchers with a comprehensive and biologically integrated approach to the study of mammalian reproduction. Each chapter presents a wealth of issues and questions, summarizing the current consensus on interpretations as well as viable alternatives under debate. The book is principally concerned with how environmental factors regulate reproduction. Bronson proposes that a mammal's reproductive performance routinely reflects simultaneous regulation by several environmental factors that interact in fascinatingly complex ways. Environment is defined broadly, and the chapters give equal weight to ecological and physiological factors when considering how variables such as food availability, ambient temperature, photoperiod, and social cues interact to regulate a mammal's reproduction. Particular attention is given to seasonal breeding, and a taxonomically arranged chapter underscores the importance of comparative and evolutionary biology to an understanding of mammalian reproduction. Mammalian Reproductive Biology is a powerful argument for the value and importance of interdisciplinary approaches to research. Its almost 1,500 references constitute the most comprehensive bibliography to date on this topic. Bronson also gives detailed consideration to promising areas for future research. Well organized, carefully planned, and clearly written, this book will become standard reading for scientists concerned with any aspect of mammalian biology.

Using Science to Improve the BLM Wild Horse and Burro Program: A Way Forward reviews the science that underpins the Bureau of Land Management's oversight of free-ranging horses and burros on federal public lands in the western United States, concluding that constructive changes could be implemented. The Wild Horse and Burro Program has not used scientifically rigorous methods to estimate the population sizes of horses and burros, to model the effects of management actions on the animals, or to assess the availability and use of forage on rangelands. Evidence suggests that horse populations are growing by 15 to 20 percent each year, a level that is unsustainable for maintaining healthy horse populations as well as healthy ecosystems. Promising fertility-control methods are available to help limit this population growth, however. In addition, science-based methods exist for improving population estimates, predicting the effects of management practices in order to maintain genetically diverse, healthy populations, and estimating the productivity of rangelands. Greater transparency in how science-based methods are used to inform management decisions may help increase public confidence in the Wild Horse and Burro Program.

Genetic-based animal biotechnology has produced new food and pharmaceutical products and promises many more advances to benefit humankind. These exciting prospects are accompanied by considerable unease, however, about matters such as safety and ethics. This book identifies science-based and policy-related concerns about animal biotechnologyâ€"key issues that must be resolved before the new breakthroughs can reach their potential. The book includes a short history of the field and provides understandable definitions of terms like cloning. Looking at technologies on the near horizon, the authors discuss what we know and what we fear about their effectsâ€"the inadvertent release of dangerous microorganisms, the safety of products derived from biotechnology, the impact of genetically engineered animals on their environment. In addition to these concerns, the book explores animal welfare concerns, and our societal and institutional capacity to manage and regulate the technology and its products. This accessible volume will be important to everyone interested in the implications of the use of animal biotechnology.