Department of Animal Science


Date of this Version



Published for Proceedings, The Range Beef Cow Symposium XV December 9, 10 and 11, 1997, Rapid City, South Dakota.


Reproductive rate or efficiency, the number of live offspring produced from a herd of a specified number each year, is the main determinate of biological and economic efficiency of a beef cattle enterprise. Reproduction is a complex and continuous process that starts before birth and continues through puberty and a series of endocrine and behavioral events that include estrous cycles, breeding, conception, gestation, parturition, and lactation. The culmination of reproduction is live offspring produced for sale or for reentering the herd as replacements. Whenever any of these events are interfered with, reproductive rate and economic efficiency will decrease. In most beef cattle operations, the goal for reproductive rate is one calf weaned each year for each female that is two years old or older, but that rate is rarely attained because of limitations and interferences in the system. Many management (primary nutrition), genetic, and disease variables will affect reproductive rate, and these variables must be taken into account in managing a profitable ranch enterprise. However, there are cases where reproduction is interfered with even when we think we have "done everything right." Such is the case when cattle consume plant products that contain compounds that interfere with reproduction; an area referred to as reproductive toxicology. Two examples that we will cover in this review are plants that contain high levels of estrogens which potentially interfere with reproduction through effects on estrous cycles and conception and needles from Ponderosa pine trees which interfere with pregnancy maintenance during late pregnancy. There are other plant toxins that affect the general well being and health of cattle, but we will zero in on these two that primarily affect reproduction.