RAPID: Elevated in Utero Temperature: A Suppressor of Fetal Development and Ruminant Fitness?

University Of Florida, Gainesville FL

Investigators

Abstract

A series of studies using the bovine calf as a model was recently completed to exame the impact of in utero heat stress on ruminant fitness during the immediate post-natal period. The studies indicate that calves that experience in utero heat stress are smaller at birth and weaning, have reduced passive immune transfer, and depressed innate immune function. A project designed to further examine the health and performance of cows that experience heat stress during the final 60 days of gestation is currently underway. The availability of calves that experience in utero heat stress under such defined conditions during late gestation presents a unique opportunity to gain further insight into environmental factors that alter neonatal health and development, and possibly induce life-long differences in immune function that alter fitness. RAPID funding of this application is essential to capitalize on this unique opportunity to gain insight into the fundamental biology of heat stress. The first proposed objective is to tease apart the cellular mechanisms responsible for the observed differences in immunoglobulin uptake, and to determine if in utero and early-life differences in immune status persist in later life. Intestinal capacity for immunoglobulin absorption could be reduced by heat stress in utero. That hypothesis will be tested by measuring tissue and cellular levels of IgG absorption and relative levels of apoptosis in neonatal calves from dams that experience heat stress or cooling during late gestation. To more fully assess the long-term impact of in utero heat stress, functional immune endpoints and growth in calves from heat stressed and cooled dams will be compared. Immune suppression observed in heat-stressed cows and/or their calves may also result from differences in their immune cell subsets compared to those that are cooled. To address this possibility, peripheral blood of cows 8 weeks pre- and post-partum and peripheral blood, spleen and thymus of calves sacrificed to address the first objective above will be evaluated by flow cytometry for the frequency of different types of immune cells including B cells, T cells, monocytes, macrophages and granulocytes. A broad understanding of the cellular mechanisms of immune function following in utero heat stress, and the impact on growth and survival to puberty, as an indicator of overall fitness will therefore be developed as a result of this project. The broader impacts of the proposed study include enhanced understanding of heat stress biology, and the potential to develop management interventions for farmed and captive ruminants with improved capacity to thrive under higher ambient temperatures. To accomplish these goals, continued graduate educational support is necessary. There is also a need to expand the diversity of those trained in the field of animal biology to better represent the general population. Two outstanding young women scientists of Hispanic ethnicity will work on this project as graduate students. The University of Florida also has a significant population of undergraduate students of Hispanic descent and two of those students have been recruited to introduce them to basic research methods, techniques in immunology, and data summary and presentation. The undergraduates will assist with all aspects of the animal care, sample collection, and conduct of immune function assays. Thus the proposal will add significantly to the capacity and diversity of students trained in animal biology at the University of Florida.