Evaluation of epididymal semen quality using the Hamilton–Thorne analyser indicates variation between the two caudae epididymides of the same bull
Introduction
In particular cases, epididymal sperm is the only available source of male gametes for use in assisted reproduction programs. For example, this can be the case when spermatozoa have to be urgently retrieved from a severely injured or suddenly deceased donor, and can be vitally significant with a donor belonging to an endangered species. Valuable semen donors are not necessarily endangered in the traditional meaning of the word. Cattle breeding and selection programs have illustrated that the introduction of beef and dairy breeds in certain parts of the world has led to the near extinction of native breeds; for instance: in West Africa [1], Madagascar [2] and Brazil [3]. This results in dire consequences, because the available native gene pool is precious and irreplaceable to generate crossbred cattle that are adapted to local climate conditions, poor quality feed and endemic diseases [3], [4], [5], [6]. In some situations, superior males have to be handled, or captured under anaesthesia, and this might impair normal ejaculation. Moreover, theoretically, an ejaculate can be devoid of spermatozoa, which makes aspiration of epididymal sperm, or a testicular biopsy to recover sperm, necessary.
With these indications in mind, and given the fact that the locals for retrieval of the epididymal semen and processing of the sperm can be hours apart, interest in techniques for transportation and preservation of epididymal sperm is escalating. Collection of epididymal sperm further offers the possibility to acquire and use genetic material from elite males even after their death. Epididymal semen can either be used fresh, or be frozen and stored in genetic resource bank projects [7], [8], but the latter requires specialized equipment that is often unavailable in the field. The use of fresh or cryopreserved epididymal semen in assisted reproduction programs has already led to offspring in domestic and wild species including: horse, cattle, goat, dog, eland, mouflon, red deer, and chimpanzee [9], [10], [11], [12], [13], [14], [15], [16], [17], [18].
Unfortunately, studies detailing the factors that influence epididymal sperm quality have often been limited to examination of only a few individuals of a particular species; given the scarcity of pertinent data, it has been very difficult to make knowledgeable assumptions concerning epididymal sperm quality of other species. In addition, most protocols use one epididymis to evaluate sperm quality, while sperm from the corresponding one, from the same male, is frozen or stored [19], [20], [21], [22], [23], [24], [25], [26], [27], [28], [29]; but, it has yet to be shown whether the quality of sperm from both caudae epididymides is comparable. One would expect that sperm retrieval and preservation protocols have been developed based upon extensive research in Bos taurus bulls, particularly because domestic cattle may serve as a model for endangered Bovidae species; such as: gaur (Bos frontalis), wild yak (Bos grunniens), banteng (Bos javanicus), and kouprey (Bos sauveli) [30]. Apparently, this is not the case, and reports on the use, storage, fertility and characteristics of bull epididymal semen are rare.
Sperm quality, and the potential effects retrieval and storage protocols have on it, are traditionally assessed by the evaluation of morphological parameters. The desire to assess sperm quality in a more objective way is reflected by the increased use of computer assisted sperm analysis (CASA) in animals [31]. CASA was recently used to analyze epididymal semen in wild ruminants [32], [33], and it has also been utilized for sperm motility parameter analysis of ejaculated bull semen [34]; however epididymal bull sperm has, to our knowledge, never been evaluated with CASA. Therefore, the aims of this study are: firstly, to assess epididymal bull semen quality conventionally, and with CASA, and secondly, to compare the sperm quality of both caudae epididymides of the same bull. The hypothesis that sperm from either caudae epididymides is of equal quality has to hold true for experimental designs in which sperm of one epididymis is used as a control for sperm from the other epididymis (of the same individual) used in a treatment.
Section snippets
Collection of scrota and weighing of testes and epididymides
For both experiments, scrota of 46 bulls of different breeds (Holstein Friesian, Belgian Blue, Limousin), between the ages of 1.5 and 6 years, were collected in four different slaughterhouses in the immediate proximity of the laboratory. The gonads were transported to the laboratory and processed within 5 h after slaughter. Testes and epididymides were dissected free with a bistoury and the spermatic cord was systematically cut just above the caput epididymis. Each testis was weighed, first with
Results
Detailed data on weights of testes and epididymides, weights of caudae epididymides, and the results of conventional epididymal sperm assessment are summarized in a descriptive way in Table 1. From these data it is clear that considerable variation exists between bulls. As far as epididymal sperm quality was concerned, total motility ranged between 0 and 85%; only in one sample no motility was perceived. In addition, sperm morphology parameters were very different between bulls, with the
Discussion
In the present study, CASA results show a difference between epididymal and ejaculated sperm motion characteristics. In addition, these results have revealed that semen from both caudae epididymides within the same bull cannot be considered comparable in most quality parameters.
The results from the conventional assessment of cauda epididymal semen, such as the high sperm concentration, and the presence of, mainly distal, protoplasmic droplets, were expected, because the epididymis is known for
Acknowledgement
The authors thank M. Julian (JustMe Editing, Storrs, CT) for editing and critical reading of the manuscript.
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