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

Abstract

Five aged dairy bulls ejaculated once a week for 32 consecutive weeks required an average of 9.2 minutes of active sexual stimulation and 2.9 false mounts before ejaculation as compared to an average of 16.0 minutes and 3.7 false mounts for 5 bulls of similar ages ejaculated once a day for 32 consecutive weeks. 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 2 frequencies of ejaculation, with respect to sperm output criteria, were statistically significant (P < .05) except that for volume of semen per ejaculate. Determinations of the per cent vitally stained sperm and the per cent of sperm with morphological abnormalities and estimation of the per cent of motile sperm in extended semen after 3 intervals of storage at -79, 5 and 15-25[degree]C revealed no significant differences between the 2 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 7108 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 months is not harmful, either to the bulls themselves or to the quality of the sperm they produce. Ejaculating bulls 2 or 3 times on each of 2 or 3 days a week and storing the sperm in an improved extender, such as CUE, makes it possible for an atrificial breeding organization to provide unfrozen semen with satisfactory fertility at all times from most stud bulls.