INTRODUCTION AND OBJECTIVES

Reproductive capabilities of mammals, birds and reptiles are influenced by nutrient provision at crucial stages of their life cycles. Nutrition of an individual inevitably depends also on that of its mother, irrespective of whether young are derived from egg-laying (birds, reptiles and prototherian mammals) or other (eutherian and marsupial) species. The maternal contribution is already pre-packaged as vitellus (yolk) at the time of oviposition in egg-laying species, and remains the sole nutrient source until post-hatch feeding commences. In contrast, most mammals rely on real-time maternally-derived nutrients throughout pregnancy and lactation.

Relative to maternal size, total nutrient requirements for production of mammalian offspring up to weaning are highly variable and exhibit enormous interspecies differences in relative distribution between pregnancy and lactation. An example is the kangaroo's trivial investment in pregnancy compared with the guinea pig's significant burden. Even within species, most notably those that produce litters, nutritional and genetic effects on numbers of ova shed and embryos surviving lead to major differences in maternal reproductive effort. It is against this background that we seek to identify feeding strategies which could enhance reproductive performance in endangered species. Central to this goal is greater understanding of specific nutrient roles in stimulating the expression of metabolic pathways that ensure reproductive success. In some cases the response to nutrition is immediate, operating directly upon target organs such as the ovary; in others full expression of nutritional effects is indirect and may not be manifest for months.