Spermatozoa are unique cells because of their morphological and physiological characteristics. They are produced during the process called spermatogenesis. Spermatogenesis consists of three phases: spermatocytogenesis, spermiogenesis and spermiation, during which spermatozoa undergo several changes. Spermatogenesis takes place within the seminiferous tubules containing two types of cells—the germ cells and the Sertoli cells—that alongside the Leydig cells, which play an important role when it comes to normal fertility. Everything is regulated by the hypothalamic–pituitary–gonadal axis and specific hormones due to multi‐hormonal feedback systems. Spermatozoa possess morphological and physiological features, which are sometimes completely different from what is observed in various somatic cells. What is more, canine spermatozoa have specific characteristics making them special compared to the spermatozoa of other mammalian species. The metabolic energy production, which is crucial for the appropriate functioning of spermatozoa, can be fuelled by different metabolic pathways utilizing different chemical substrates. Inseparable from the oxidative phosphorylation process is the production of reactive oxygen species, which are both essential and toxic to spermatozoa. Furthermore, epididymis is a very important structure, responsible for the transport and maturation of spermatozoa, which are then stored in the last segment of epididymis—the epididymal cauda. Moreover, the retrieval of spermatozoa from the epididymides is crucial for the development of assisted reproduction techniques and sperm cryopreservation methods. The information gained from the research on domestic dogs might be transferred to their wild relatives, especially those species categorized as endangered.

Evaluation of sperm morphometry is an important criterion in the diagnosis of a male animal’s suitability for breeding. The aim of the study was to evaluate the morphometry of sperm from the epididymides of dogs subjected to routine castration using various staining methods. The study was carried out on semen collected from ten healthy dogs. Gonads were obtained from each dog during routine castration at a veterinary surgery. Then, the epididymides (caput, corpus, cauda) were isolated from the gonads, semen was collected from them and microscope slides were prepared. The slides for evaluation of sperm morphometry were prepared by four methods: DiffQuik, SpermBlue, eosin-nigrosin and eosin-gentian. A total of 2400 sperm were analyzed (240 sperm from the dog). The sperm collected from the caput and corpus of the epididymis were found to have larger heads and tails than those collected from the cauda of the epididymis. The staining method was shown to affect the morphometry of sperm taken from the epididymides of dogs. The staining methods differentiate the dimensions of the head of sperm in different parts of the epididymis but do not affect the length of the sperm tail. The occurrence of differences in the head dimensions of sperm may be linked to the use of different fixatives and chemical reagents in the staining procedure. Sperm stained by the EN method had the smallest head and tail dimensions. The greatest head area was noted in the sperm stained by the EG method. In the slides stained by the SB method, the sperm heads were relatively long but narrow. The methods used are suitable for the evaluation of sperm structure, and the possibility of using all four methods enables a full characterization of sperm collected from the caput, corpus and cauda of the epididymides of dogs.

The aim of the study was to analyze the incidence of spermatozoa with morphological changes in semen collected from canine epididymides. The study was conducted on five dogs with gonads obtained from them as a result of routine castration performed at a veterinary clinic. Epididymides were isolated after gonadal lavage with PBS fluid. Semen was collected by incising individual parts of the epididymis (caput, corpus, cauda) with a sterile scalpel, when placed in separate Petri dishes. Sperm morphology was prepared from the semen collected in this way. The preparations were stained with the SpermBlue method. The sperm morphology was assessed using a 100x immersion lens with a Nikon E-50i light microscope. In each preparation, the morphological structure of 200 spermatozoa was assessed, specifying the sperm cells with normal morphological structure and those with changes in their head, tail, and those with cytoplasmic droplets. Based on the performed study, it was found that there are differences in the incidence of sperm cells with morphological changes in individual sections of the epididymal duct. The largest share of spermatozoa with normal morphological structure was observed within the corpus of the epididymis. The most spermatozoa with head changes and with cytoplasmic droplets were found in semen collected from the epididymal caput. There were more than 14% more spermatozoa with head changes located in the epididymal caput than in the epididymal cauda (P ≤ 0.05). The semen collected from the cauda of the epididymis showed significantly more sperm cells with tail changes than in the remaining parts of the epididymis. As semen moved through the individual segments of the epididymis, the proportion of spermatozoa with head changes and cytoplasmic droplets decreased, while the proportion of spermatozoa with tail changes increased.

The aim of the present study was to analyze the frequency of occurrence of acrosome-reacted spermatozoa in semen stained with two methods, depending on boar semen storage time. The studies were conducted on ejaculates collected from 10 Landrace boars used in artificial insemination. The smears were prepared by means of two staining methods: SpermBlue and eosin-gentian dye. It was concluded that the proportion of acrosome-reacted spermatozoa depends on the staining method and ejaculate storage duration. When the smears were stained with the SpermBlue method, the number of spermatozoa with head defects, including acrosome reaction, was greater compared with the smears stained with the eosin-gentian dye. With the passage of semen storage time, a change in sperm count with an acrosome reaction was observed. In the SpermBlue-stained smears, the proportion of acrosome-reacted spermatozoa was the highest in the 96th hour of storage and was about 2.5%. An increase in the number of acrosome-reacted spermatozoa was observed in the semen stained with the eosin-gentian dye method in the following semen storage hours.