Semen Production, Fructose Content of Semen and Fertility of Dairy Bulls as Related to Sexual Excitement

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Abstract
The present widespread use of the semen of a dairy bull in artificial insemina- tion makes it necessary that his semen production be as efficient as possible. Any practice or practices that will increase his semen production, semen quality and fertility arc highly desirable, particularly, if he is an outstanding sire. Observa- tions and limited experimental data on male animals (1, 2, 3, 4, 5, 6, 11, 16, 19), as well as one objective experiment by Collins et al. (10) with dairy bulls indi- cate that sexual excitement prior to service is one of the factors which will mark- edly influence semen production. Collins et al. (10) clearly demonstrated that restraining as compared with not restraining dairy bulls prior to semen collection with the artificial vagina resulted in highly significant increases in semen production and semen quality. However, they gave no data on the percentages of usable ejaculates and fertility of the semen. Also, these workers could not make any comparisons between first and second ejaculates, since only one ejaculate was collected each time. Since many artificial breeding organizations average approximately two ejaculates from each bull at each collection period, characteristics of first and second ejaculates as re- lated to sexual excitement are important. Two of the most significant criteria of judgment of any practice involving dairy bulls are the efficiency of semen pro- duction and fertility of the semen. In view of the above-mentioned lack of data in the literature, two experiments were conducted to relate semen production, fertility of the semen and fructose content of the semen to three different controlled levels of sexual excitement of mature dairy bulls. Fructose content of semen was included because of its source and role in semen metabolism as shown by Mann (13, 14, 15) and because sexual excitement was believed to be a factor influencing the level of fructose. EXPERIMENTAL METHODS Experiment 1. This experiment was conducted with six mature bulls, two Jerseys, two Holsteins and two Guernseys, selected from the active stud of the