Influence of the female reproductive tract on the motility and morphological characteristics of ram spermatozoa

In mammals, millions of spermatozoa are deposited in the posterior female reproductive tract but only a few hundred reach the oviducts and from these only one will fertilise an oocyte in a mono-ovulatory species. Investigating why so few spermatozoa reach the oviduct and what was so special about these spermatozoa was the central theme to the studies reported in this thesis. The studies were conducted in the facilities of the Biomedical and Tropical Veterinary Science precinct, James Cook University and used Merino sheep as the model. In initial studies, semen was collected from rams by electroejaculation and it was demonstrated that not only did ram spermatozoa in undiluted semen have a limited life span but that were differences between rams. Some rams had spermatozoa that survived for less than six hours whereas in others, spermatozoa survived for 30 hours. These differences between rams were not present in semen diluted in Tyroide’s-albumin-lactate-pyruvate (TALP) medium. Nearly all spermatozoa in freshly ejaculated semen were uncapacitated but after 12 hours incubation in Hepessynthetic oviduct fluid (HSOF), 70% were capacitated. Baseline information on the detailed motility and movement characteristics was determined with a computer-aided semen analyzer (CASA). The results demonstrated that there is a heterogenous population of spermatozoa in a semen sample and that some rams had spermatozoa that had a significantly larger head area than others. This result was supported in later studies by manual measurements of the width and length of heads of spermatozoa. Semen was collected each month for 13 months from a group of six rams. A range of measurements of the semen was made including volume, colour and velocity and movement characteristics of spermatozoa as determined by CASA. These data were correlated with meteorological data. The quality of semen was significantly influenced by the mean daily maximum temperature and hours of bright sunshine with the months January to March being the times when ram semen was of poorest quality. Samples of spermatozoa were collected from a range of sites in the reproductive tract of naturally-mated ewes at 3, 6 and 24 hours after mating. The spermatozoa were examined for detailed velocity and movement characteristics, capacitation status and dimensions of spermatozoa. A surprising result was the low and variable percentage (range 2%-22%) of motile spermatozoa in the uterus particularly at 3 and 6 hours after mating declining to a mean of 2.7% 24 hours after mating. No difference in the velocity and movement characteristics of spermatozoa between the anterior and posterior reproductive tract could be identified. However, two important and interesting results were found. There was evidence that the ovary bearing the pre-ovulatory follicle or corpus haemorrhagicum influenced the distribution of spermatozoa as significantly more spermatozoa were found in the mid and anterior ipsilateral uterine horn and oviducts than the contralateral side 24 hours after mating. The same occurred 6 hours after mating except there was only a non significant trend for the uterine horns. The second important finding was that the spermatozoa in the oviducts had a significantly smaller head than elsewhere in the reproductive tract. Analysis of the capacitation status of spermatozoa demonstrated that spermatozoa can undergo capacitation and the acrosome reaction in all sites of the reproductive tract and by 24 hours after mating most spermatozoa were capacitated and acrosome-reacted.