Doctoral Dissertations

Date of Award


Degree Type


Degree Name

Doctor of Philosophy


Animal Science

Major Professor

Hugo Eiler

Committee Members

John D. Smalling, J. B. McLaren, Leon N. D. Potgeiter, Fred Hopkins


The objective of this research was to investigate the effect of blood concentrations of different chemical families of substances (markers) when injected intravenously, on the kinetics of their passage into the bovine ejaculate. Blood and semen were collected simultaneously and were analyzed for a given marker. The selection of markers for this research was based on biomedical significance and degree of chemical complexity. Markers were: Cortisol, progesterone, thyroxine, triiodothyronine, human chorionic gonadotrophin, Calicivirus (feline), penicillin, oxytetracycline, gentamicin, and carnitine. Steroids, amino acids, glycoprotein, and antibiotics readily passed (within 20 minutes) into the ejaculate from blood. Seminal and blood concentrations of these markers were positively correlated. The experiment with antibiotics showed that all antibiotics studied gained rapid entry into the ejaculate. It was established by vasectomy that gentamicin exclusively passed through the accessory glands. Within a given chemical family, markers with a greater affinity for its plasma carrier proteins passed slower than those with smaller affinities. T3 passed faster than T4, and cortisol faster than progesterone. Within a chemical family the molecular weight of a marker seems to be a secondary factor in determining the rate of transfer into the ejaculate from blood. Cortisol (MW 360) passed faster than progesterone (MW. 314). The relatively complex glycoprotein hormone HCG passed in detectable quantity into the ejaculate from blood. The quantity of HCG in semen was not large enough to cause spermatorrhea when frogs were injected with semen. This frog bioassay for HCG was not sensitive to the small amount of HCG in the semen. This could have been due to the relatively small dose of HCG injected into the bull. Conversely, bioassay experiments showed that all antibiotics used in these experiments were bioactive in semen. Neither Calicivirus nor carnitine passed into the ejaculate from blood. Due to the complexity of the RNA-containing molecule Calicivirus particle (MW. 10 million), it was not expected to pass. However, the fact that carnitine (MW.160) did not pass into semen in spite of a significant increase in blood concentrations was unexpected, since the epididymal source of carnitine is blood. The experiment with carnitine showed that regardless of the high affinity of the epididymis for carnitine, the injection of exogenous carnitine failed to increase (P > 0.05) the carnitine concentrations in the ejaculate. Furthermore, it was found that 79% of seminal carnitine is from epididymal-testicular origin and 21% was derived from accessory gland secretions. This series of experiments shows that the chemical composition of the ejaculate in the bull is rather fortuitous and depends in part, on the chemical composition of blood around the time of ejaculation. This could have a practical implication when trying to manipulate reproductive efficiency.

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