Avian and Poultry Biology Reviews

Avian and Poultry Biology Reviews 14 (1), 2003

Efficiency of Thermoregulatory Control Elements in Precocial Poultry Embryos

Martin Nichelmann*1 and Barbara Tzschentke2

1Medical University, Minsk, Belarius

2Institut fur Biologie der Humboldt-Universitat zu Berlin, AG Perinatale Anpassung, 10115 Berlin, Invalidenstrasse 43, Germany

ABSTRACT

To explain all aspects of the efficiency of the thermoregulatory system in poultry embryos, the activity and the dynamics ofdifferent control elements have to be investigated systematically during the prenatal period. The relevant methodology and results, cited in this paper are mainly from our own group but are compared with related experiments described in the scientific literature. They may be summarised: Thermoregulatory behaviour is developed early in poultry embryos. Temperature of allantoic fluid (Taf) represents the internal body temperature in the last third of incubation because Taf and Tc are much the same at normal (37.5_C) and low incubation temperatures (34.5_C) after internal pipping. Fowl embryos show endothermic reactions from day 14 and Muscovy duck embryos from day 22. In precocial avian embryos, body core temperature increases in accordance with heat production. In contrast to heat production the efficiency of heat loss is high in precocial avian embryos. Development of physiological control systems starts with non-co-ordinated and proximate (immediate) non-adaptive reactions. In summary, endothermic reactions occur very early during embryonic development but their efficiency is limited. Due to the van't Hoff rule, low temperatures decrease the net heat production but the trajectories of endothermy are stimulated and related epigenetic adaptation mechanisms are activated. Using behavioural mechanisms the embryo is protected against super-cooling during the natural incubation process. The heat loss mechanisms are most efficient against heat stress, which may occur for only very short time during incubation, protect the embryo against disturbances caused by hyperthermia.

Keywords: endothermy, precocial embryos, heat production, heat loss, efficiency of thermoregulation, embryonic behavioural thermoregulation, physiological control systems

Avian Models for Research in Toxicology and Endocrine Disruption

Colin G. Scanes* and F. M. Anne McNabb

Department of Animal Science, Iowa State University, Ames, Iowa 50011, USA

Department of Biology, Virginia Tech, Blacksburg, Virginia 24061-0406, USA

ABSTRACT

There have been significant strides in our knowledge of the effects of toxicants on birds. This communication presents a brief review of avian toxicology with emphasis on effects of common toxicants that disrupt endocrine system function and control of reproduction, growth, development, stress and calcium-phosphorus homeostasis. For those hormonal systems that act through hypothalamic-pituitary axes, we emphasize current knowledge of the axis ``level'' at which the toxicants alter endocrine control. The classes of toxicants discussed are acid rain andyor aluminum, organochlorines such as polychlorinated biphenyls (PCBs), fungicides and insecticides, mycotoxins, (PCBs) and petroleum. The use of several types of avian models for endocrine disruption studies is discussed in the context of utility and practicality, developmental modes, species sensitivity and the choice of sentinel species. Promising new approaches for avian toxicological research are considered including shell-less embryos, continuous-flow administration of toxicants to avian embryos, gene microarrays, proteomics and metabolomics.

Keywords: toxicants, endocrine disruptors, avian models, reproduction, growth, development, thyroid, adrenal