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Libido, Sperm Characteristics, Sperm Output, and Fertility of Mature Dairy Bulls Ejaculated Daily or Weekly for Thirty-Two Weeks¹

Department of Animal Husbandry, Cornell University, Ithaca, New York

ABSTRACT

Ten aged dairy bulls were used to measure the effects of prolonged daily ejaculation on libido, sperm output, sperm characteristics, and fertility. The ten bulls were ejaculated once a week for a 4-wk. preliminary period after which five were chosen at random to be ejaculated once a day and five once a week for a 32-wk. experimental period.

The bulls ejaculated once a week required an average of 9.2 min. of active sexual stimulation and 2.9 false mounts before each ejaculation, as compared to an average of 16.0 min. and 3.7 false mounts for the bulls ejaculated once a day.

The weekly bulls yielded an average of 9.5 ml. of semen per ejaculate, 63% motile sperm, 1.89 billion sperm per milliliter of semen, 4.8 billion total sperm per ejaculate (per week), and 11.1 billion motile sperm per ejaculate (per week). The bulls ejaculated once daily yielded an average of 6.2 ml. of semen per ejaculate, 69% motile sperm, 0.81 billion sperm per milliliter of semen, 4.8 billion total sperm per ejaculate, 3.4 billion motile sperm per ejaculate, 33.8 billion total sperm per week, and 23.6 billion motile sperm per week. All of the differences between the two frequencies of ejaculation, with respect to the sperm output criteria, were statistically signicant (P < .05) except that for volume of semen per ejaculate.

Determinations of the per cent vitality stained sperm and the per cent of sperm with morphological abnormalities and estimation of the per cent of motile sperm in extended semen after three intervals of storage at –79. 5, and 15–25° C. revealed no significant differences between the two frequencies of ejaculation.

Measured by the per cent of cows not returning to service within 60 to 90 days after first insemination, the average fertility of 70% for 42,136 inseminations with sperm from the bulls ejaculated once a week was not significantly different from the average of 73% for 7,108 inseminations with sperm from the bulls ejaculated once a day.

The results of this experiment indicate that daily ejaculation of aged bulls for as long as 8 mo. is not harmful, either to the bulls themselves or to the quality of the sperm they produce. Ejaculating bulls two or three times on each of two or three days a week and storing the sperm in an improved extender, such as CUE, makes it possible for an artificial breeding organization to provide unfrozen semen with satisfactory fertility at all times from most stud bulls.

¹ The data are, in part, from a thesis submitted by the senior author to the Graduate School of Cornell University in partial fulfillment of the requirements for the degree of Doctor of Philosophy, February, 1959.

² Present address: Department of Dairy, Michigan State University, East Lansing.