Year of Publication

2003

Degree Name

Doctor of Philosophy (PhD)

Document Type

Dissertation

College

Agriculture

Department

Animal Science

First Advisor

Keith K. Schillo

Abstract

Most researchers studying sexual behavior of the bull have adopted the practice of severely restraining and sedating female stimuli, utilizing so-called "service stanchions" and quantifying behavioral events expressed by each bull. Based on these observations, bulls are classified as having high, medium, or low libido and ranked according to their ability to "service" the inanimate stimuli. It has been assumed that these methods represent appropriate measurements of reproductive behavior that will be expressed in a natural mating scenario and that bull sexual behavior can be studied in a manner that is independent of the context of the female. Hence, conventional methods fail to consider the appropriate contexts under which cattle interact sexually. Based on these issues, I investigated the role of unrestrained female stimuli in modulating the expression of male sexual behavior in domesticated bovine. Experiments were conducted to develop a paradigm for studying sexual behavior in bulls within a social setting that permits extensive interactions between males and females. The first experiment tested the hypothesis that female novelty and receptivity interact to govern the expression of mounting behavior in the bull. In this experiment, bulls that were exposed sequentially to 4, novel, estrual females expressed more mounts with intromission than when exposed alternately to two, estrual females or to the same estrual female over a four-hour period. Bulls exposed to a non-estrual female were not allowed to mount and intromit although they readily attempted to mount. A second experiment tested the hypothesis that mounting behavior of bulls exposed sequentially to 4, estrual females in 2 hours would be the same as that in bulls exposed to a group of 4, estrual females for 2 hours. Results suggested that in group mating situations there are differences in how males distribute copulations when presented with unrestrained stimulus females sequentially. Repeatability of sexual behavior was calculated by repeatedly testing bulls paired with either single or multiple unrestrained, estrual females on 8 different occasions and calculating the intraclass correlations. Overall, repeatability was low and indicated a large environmental component. This electronic dissertation contains multimedia video files which allow the reader to visualize representative examples of sexual behavior in Bos taurus.

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