Peter J. Hansen
2026 Sigma Xi Fellow
Statement
“I was inducted into Sigma Xi in 1982 while a graduate student at the University of Wisconsin-Madison. I became active in the University of Florida Chapter soon after moving to Gainesville in 1983. My first office was that of Marshall (1993-1994), which is a now defunct office in our chapter. I served as President from 1999-200, Secretary from 2019-2020 and have been Treasurer since 2024. Among other activities, I used to organize a monthly seminar series sponsored by Sigma Xi.
Why am I so active in Sigma Xi? I love what it stands for – scientific excellence, public engagement, and support for young scientists. I want to advance those goals. Furthermore, Sigma Xi has enriched my life. The motto “Companions in Zealous Research” signifies much of what I value as a scientist. I am certainly zealous about science and being part of a like-minded community can be exhilarating. A university is a place where most branches of scientific inquiry are explored. Participating in Sigma Xi has brought some of those other branches of science into my own life. I have made friendships with scientists in disciplines far removed from my own and that was possible because of Sigma Xi."
Biography
Peter J. Hansen is a faculty member of the Dept. of Animal Sciences at the University of Florida, where has been on the faculty since 1986. He is currently a distinguished professor and L.E. “Red” Larson Professor of Animal Sciences. His research focuses on the biology of early pregnancy, enhancement of assisted reproductive technologies in cattle and development of methods to improve fertility and thermotolerance of cattle and other species.
Hansen received the B.S. in Agricultural Sciences from the University of Illinois in 1978 and the M.S. and Ph.D. degrees from the University of Wisconsin in 1980 and 1983. He did a postdoctoral fellowship at the University of Florida from 1983-1984 before joining the faculty of the University of Florida College of Veterinary Medicine as a visiting assistant professor in 1984. He took sabbatical leave at the University of Guelph in 1993.
In his career, Hansen has published over 420 refereed papers on topics related to reproductive biology, thermal physiology, and genetics (h index=100). One of the most satisfying facets of his career has been participation in education of early- career scientists. He has mentored 36 PhD students, 29 master’s students, 19 postdoctoral fellows and 57 visiting scientists. Hansen's contributions have resulted in new knowledge and understanding in multiple areas of reproductive biology, developmental biology, and genetics. As a graduate student, he documented how photoperiod can modify onset of puberty and length of the postpartum anestrus in cattle. As an assistant and associate professor, he elucidated mechanisms by which progesterone regulates maternal immune function during pregnancy to prevent compromise of the feto-placental unit. Later, he identified specific genes associated with genetic and physiological variation in fertility.
One major area of focus has been optimizing embryo transfer procedures in cattle to reverse the deleterious effects of heat stress on female fertility. Hansen observed that the preimplantation embryo undergoes changes in its ability to survive exposure to elevated temperature as it proceeds through development. In the cow, exposure to elevated temperature compromises developmental potential of the embryo at the earliest cleavage stages but the embryo is largely resistant to elevated temperature by the blastocyst stage (Day 7). Since Day 7 is when the embryo is typically transferred to the mother in cattle, Hansen reasoned that pregnancies established by embryo transfer would be resistant to disruption by maternal heat stress. This idea was shown to be correct in a series of experiments.
Hansen and colleagues also showed that a mutation in the prolactin receptor gene (i.e., the SLICK haplotype) identified in Senepol cattle can be incorporated into Holsteins to increase ability to regulate body temperature and decrease seasonal variation in milk yield. Hansen has now produced registered Holstein bulls carrying the slick gene; slick Holstein bulls marketed around the world mostly derive from these founder animals. Gene-edited slick animals have also been produced in a joint project between Acceligen, Semex, and the University of Florida. The first gene-edited cattle approved by the Food and Drug Administration of the USA resulted from this collaboration.
Recent research has focused on the phenomenon of developmental programming whereby specific events during development can cause changes in the health and function of the postnatal organism. Hansen demonstrated that programming in the preimplantation period occurs for cattle. The most important finding has been that addition of the methyl donor choline to culture medium of bovine embryos can result in birth of calves with increased weaning weight. Thus, the efficiency and sustainability of beef production can be enhanced by optimizing the environment of the early embryo.
Hansen has been recognized for his research many times including receipt of the highest awards given by the American Dairy Science Association (ADSA) (Land O’Lakes Award; 2010), the American Society for Reproductive Immunology (American Journal of Reproductive Immunology Award, 2013), American Society of Animal Science (ASAS) (Morrison Award, 2023) and the International Embryo Technology Society (Pioneer Award, 2025). He was the recipient of the Simmet Prize for Assisted Reproduction in 2026 sponsored by Minitüb and presented at the International Congress of Animal Reproduction, 2026). He is a Fellow of the American Association for the Advancement of Science, ADSA and ASAS and a Distinguished Fellow of the Society for the Study of Reproduction.
Hansen has served as President of the American Society for Reproductive Immunology (2004-2006), International Congress of Animal Reproduction (2012-2016), International Embryo Transfer Society (2013-2014), and Society for the Study of Reproduction (2022-2023). He was President of his local chapter of Sigma Xi (1999-2000). He has served on a variety of review and advisory boards including those for the New Zealand Ministry of Business Innovation and Employment (2015-2020), Genome Alberta (2021-2024), and Republic of Ireland Teagasc (Agriculture and Food Development Authority), 2025-present.