When projecting livestock environmental prospects for the 1990's, it is critical to recognize the multidimensional nature of managing livestock species under hot environments. This paper identifies potential critical physiological windows during the life cycle of the animal that are sensitive to heat stress and responsive to environmental modification. Ovarian follicular development appears to be sensitive to heat stress leading to reductions in intensity of estrus and subsequent fertility. Periods of follicular development that are sensitive to heat stress have not been defined. With current improved systems to alter the microenvironment of animals, the period of embryonic sensitivity to heat stress has shifted so that early embryonic losses are less. Potential recombinant proteins that may enhance embryo survival and correct deficiencies in placental function that are induced by heat stress warrant additional investigation. The postpartum period is a critical period in which a multitude of factors interact to influence animal productivity and its sensitivity to heat stress. Nutritional strategies to improve animal performance with the use of fat-supplementation are discussed. Environmental modification and housing systems need to not only maximize the efficiency of animal production but need to consider the potential impact on the environment relative to water use, soil and water pollution. Animal production and management systems need to consider both animal health and well-being issues. To optimize profit under conditions of greater societal constraints and available management alternatives, computer assisted management systems will become a critical tool.