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Fertility in birds is dependent on their ability to store adequate populations of viable sperm for extended durations in sperm storage tubules (SSTs). The exact mechanisms by which sperm enter, reside, and egress from the SSTs are still controversial. Sharkasi chicken sperm showed a high tendency to agglutinate, forming motile thread-like bundles comprising many cells. Since it is difficult to observe sperm motility and behavior inside the opaque oviduct, we employed a microfluidic device with a microchannel cross-section resembling close to that of sperm glands allowing for the study of sperm agglutination and motility behavior. This study discusses how sperm bundles are formed, how they move, and what role they may have in extending sperm residency inside the SSTs. We investigated sperm velocity and rheotaxis behavior when a fluid flow was generated inside a microfluidic channel by hydrostatic pressure (flow velocity = 33 µm/s). Spermatozoa tended to swim against the flow (positive rheotaxis) and sperm bundles had significantly lower velocity compared to lonesome sperm. Sperm bundles were observed to swim in a spiral-like motion and to grow in length and thickness as more lonesome sperm are recruited. Sperm bundles were observed approaching and adhering to the sidewalls of the microfluidic channels to avoid being swept with fluid flow velocity > 33 µm/s. Scanning and transmission electron microscopy revealed that sperm bundles were supported by a copious dense substance. The findings show the distinct motility of Sharkasi chicken sperm, as well as sperm's capacity to agglutinate and form motile bundles, which provides a better understanding of long-term sperm storage in the SSTs.

A unique sperm behavior was observed in Egyptian chickens. Sperm showed a tendency to agglutinate forming motile thread-like bundles. Sperm agglutination behavior, kinematics, and some morphometric measures were studied in relation to sperm competition and fertility duration in Sharkasi and Dandarawi chickens. Sperm tendency to agglutinate was assessed by examining sperm morphology using scanning electron microscopy, Acridine orange-stained semen smears using fluorescence microscopy, and recording videos of sperm under phase contrast microscope. Sperm velocity and morphometric measures were evaluated using image-J software. To assess sperm competition, Sharkasi and Dandarawi hens were artificially inseminated by semen pools possessing equal number of Sharaksi and Dandarawi sperm. Artificial insemination was repeated ten times. The eggs obtained were incubated, and the hatchlings were discriminated as descending from Sharkasi or Dandarawi fathers according to their phenotype. To assess the fertility duration, Sharkasi and Dandarawi hens were inseminated by semen collected from roosters of the same strain. Eggs were collected for a period of 28 days post-insemination and incubated. Sharkasi spermatozoa showed higher tendency to agglutinate forming longer and thicker motile bundles. No significant differences were observed in sperm curvilinear and straight line velocity and in sperm morphometric measures between Sharkasi and Dandarawi chickens. Sharkasi roosters fathered 81.6% and 67.7% of the hatchlings produced by Sharkasi and Dandarawi mothers, respectively. The fertility period in Sharkasi and Dandarawi was 22 and 14 days, respectively. We suggest that the differences seen in sperm competitiveness and fertility duration can be attributed to sperm agglutination behavior.

To ensure survival, some unique features can be distinguished in birds that help them maintain reproduction. These features include the ability to store sperm for long periods within the utero-vaginal junction, a high sperm concentration per ejaculate, and polyspermy fertilization. Sperm face many challenges prior to fertilization. After copulation, most ejaculated sperm exit the female reproductive tract, and less than 1% continue in an attempt to achieve fertilization. In addition, egg size is substantially larger than sperm size because of the presence of the egg yolk. This results in a large number of sperm penetrating the egg away from the oocyte. These challenges have triggered evolutionary changes to maintain the existence of many species, such as the enormous relative size of the testis, which produces billions of sperm each day, and the ability to store viable sperm for long periods in the oviduct to ensure asynchronous fertilization. This chapter discusses several contemporary and sometimes controversial points regarding sperm behavior and their storage in the oviduct.

Sperm quality is a principal determinant of its fertilizing potency. The current study was conducted in an attempt to link some morphometric measures (sperm and flagellum length) and the concentrations of some ions in seminal plasma on the one hand to sperm swimming velocity on the other hand in three Egyptian local chicken strains (Dandarawi, Sharkasi and Fayoumi). Ten adult males (28 weeks old) from each strain were housed in individual cages. Semen samples were collected twice weekly for a period of 16 weeks. Some physical and chemical characteristics of semen including ejaculate volume (mL), sperm concentration, motility (%), and the concentrations of calcium, potassium, sodium and manganese in seminal plasma were measured. Sperm curve linear velocity (VCL), average path velocity (VAP), straight line velocity (VSL) and straightness (STR) were measured using computer assisted sperm analysis (CASA) software. The lengths of entire sperm, head plus mid-piece and flagellum (µm) were measured using image J software. There were no significant differences among strains in the percentages of total motile sperms and the percentages of sperms demonstrating progressive motility. Ejaculates of Dandarawi roosters had higher sperm concentration/ml (p<0.01), greater percentages of rapid swimming sperms (p<0.001) and higher values of VCL, VAP and VSL (p<0.0001) compared to those of Sharkasi and Fayomi strains. Significant differences were observed in sperm morphometry among the different strains where Dandarawi and Sharkasi had longer sperm and flagellum compared to those of Fayoumi (p<0.001). Chemical composition of seminal plasma revealed higher potassium concentrations in Sharkasi samples compared to those of Fayomi (P<0.05); while the concentrations in Dandarawi ejaculates were intermediate. In conclusion, Dandarawi sperm showed higher swimming velocity compared to both Sharkasi and Fayomi. Slower sperm velocity can be attributed to shorter flagellum and to higher potassium concentrations in seminal plasma in Fayomi and Sharkasi strains, respectively.