Definition of "estrus"

Bovine cervical mucus is more suitable for precise chemical and physical studies because much larger quantities can be obtained—as much as 150 ml may often be harvested from a single cow during estrus.

1963, A. J. Sobrero, “Sperm Migration in the Female Genital Tract”, in Carl G. Hartman, editor, Mechanisms Concerned with Conception: Proceedings of a Symposium Prepared under the Auspices of the Population Council and the Planned Parenthood Federation of America, New York, N.Y.: The Macmillan Company, page 174