Dear Colleagues,

In the last 5–10 years, the artificial insemination (AI) industry has been reshaped using sexed semen and the genomic selection of bulls, resulting in semen exposed to novel stressors during sexing procedures that include extensive dilution, exposure to lasers, shear forces of sperm moving at high speeds through tubing or channels and delays when cryoprotectants are added to semen. However, the fertility of sexed semen is reduced likely due to some or all of these stressors. Rethinking how these stressors might impact cryopreservation, capacitation, sperm interaction with oviduct cells, fertilization in vivo and in vitro, or even how we might modulate semen to improve in standard preservation all require revisiting. The second type of technology reshaping the AI industry is the use of genomic selection for bulls. The impact of this type of selection is that younger bulls now reside in AI centers, with many 1–3-year-old bulls now being the routine age range and few of the old standard 5+-year-old bulls being in use anymore. Younger bulls do not produce as much sperm/day, and are subject to more variation in semen quality. Many of these younger bulls have semen collected at puberty when sperm numbers are insufficient to inseminate large numbers of females in vivo. Instead, these sperm are used for in vitro fertilization, but little is known about how the conditions of in vitro fertilization should be adjusted for younger bulls. The variation in semen quality of the younger bulls is likely due to issues in spermatogenesis. A more complete understanding of spermatogenesis in the bull may help us understand on the cause and explain what can be undertaken to alter spermatogenesis as well.

The introduction of two major technologies has reshaped the cattle artificial insemination industry. Both technologies are driving the need for increased knowledge of sperm function and the regulation of fertility.  Semen sexing causes novel stresses on cryopreserved semen, suggesting we should reinvestigate the entire process of preserving sperm and how this impacts the physiology of sperm that allows fertilization and embryo development both in vivo and in vitro. The second technology, genomic selection, is allowing the selection of younger bulls, reducing the age of bulls in artificial insemination centers. There is a drive to collect these bulls as soon as they reach puberty and initially require the use of in vitro fertilization. Younger bulls also produce fewer sperm, accompanied by more fertility problems. Enhancing sperm production and investigations on how these sperm interact in the female tract are, thus, needed. 

We are pleased to invite you to co-create a Special Issue entitled “Cattle Reproduction: Sperm Regulation and Male Fertility”. In this Special Issue, original research articles, critical reviews and commentaries are welcome. Research areas may include (but are not limited to) the following: spermatogenesis, heat stress, male fertility, capacitation and the fertilization of bulls. We look forward to receiving your contributions. 

Dr. John Parrish
Guest Editor

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• spermatogenesis
• heat stress
• male fertility
• fertilization
• sperm capacitation
• sperm regulation
• sperm control
• artificial insemination