Production of marker bulls

Abstract

In order to be effective, a procedure for producing marker animals must meet four requirements. First, insemination of the female by the marker animal must be prevented. Second, transmission of venereal disease from the marker or from cow to cow via the marker must be avoided. Third, the marker must retain sufficient libido to actively pursue fertile females throughout the breeding period. Finally, the procedure must be economically feasible to perform, meaning that the procedure is technically simple to perform, is not inordinately expensive, and does not have a high morbidity or mortality. The multitude of precedures available indicate that no one procedure has yet been identified that optimally fulfills all 4 requirements. While each technique has its individual proponents, objective comparisons of techniques under equivalent field conditions are minimal or absent. The following paper will describe several of the more common procedures and discuss their ability to fulfill each of the 4 requirements.

Prevention of impregnation by the marker is achieved in three basic ways—prevention of viable sperm production, prevention of sperm transportation to the penis, or prevention of transportation of semen from the marker into the female reproductive tract. Elimination of disease transmission by the marker is approached in two ways—prevention of intromission or use of a disease free marker. Preservation of libido depends on maintenance of circulating hormone levels, and to some extent on preservation of neuroendocrine feedback occurring during the act of copulation.