Dairy producers, herd managers, veterinarians, and consultants monitor production data, health events, and reproductive protocol compliance regularly; however, little time is spent evaluating semen storage and handling. Unfortunately, this can be a critical oversight, as every successful artificial insemination (AI) program begins with proper semen handling.
It is important to remember that sexed semen is a different product than conventional semen. To achieve 90% purity of a specific sex, sperm are treated with a fluorescent dye, and X and Y chromosome-bearing sperm are sorted with a flow cytometer/cell sorter based on intensity of fluorescence following exposure to a laser. At North American AI studs, on-site sperm sorting services are currently provided by Sexing Technologies (Navasota, TX).
DeJarnette et al. (2009) evaluated farm records from U.S. Holstein dairy herds and reported that the overall conception rate for sexed semen (for all services, in herds with ≥ 50 services) averaged 45% (range 27% to 70%), compared to 56% (range 34% to 83%) for conventional semen. Further, the conception rate achieved following AI with sexed semen averaged 80% of that achieved with conventional semen at first service (DeJarnette et al., 2009). The specific reasons contributing to lower fertility following AI with sexed semen, as compared to conventional semen, are currently unknown.
Despite decreased fertility and increased cost per dose as compared to conventional semen, the use of sexed semen has a higher economic value than the use of conventional semen in many situations (Cabrera, 2009). Keep in mind, however, that the single most important factor in the decision to use sexed semen is the current or expected heifer conception rate with conventional semen, which will determine the conception rate attained with sexed semen (Cabrera, 2009).
All frozen semen must be stored, thawed, and handled properly to maintain sperm viability and offer the greatest opportunity to obtain optimal fertility. Commercial AI studs, through stringent collection, processing, and quality control, provide a highly fertile product to their customers. When semen is purchased and transferred to a farm or professional AI technician’s liquid nitrogen tank, the maintenance of male fertility is in the hands of the producer, farm employees, and AI technicians.
The liquid nitrogen tank consists of a “tank within a tank,” with insulation under vacuum between the inner and outer tanks. Liquid nitrogen tanks should be stored in a clean, dry area, preferably on a wooden stand to avoid possible corrosion (due to contact with wet or damp concrete). Also, the liquid nitrogen tank should be securely fastened during transportation to avoid tipping the tank over and damaging the tank, which usually results in the premature loss of liquid nitrogen.
A detailed inventory of semen should be easily accessible so that straws filled with semen may be located and removed from the tank quickly to avoid exposure of semen to higher temperatures in the neck of the tank or even ambient temperature. When removing a straw from a liquid nitrogen tank, it is imperative that the technician keep the canister, cane, and unused semen straws as low as possible in the neck of the tank. A best management practice is to keep all unused straws below the frost-line in the neck of the tank. Keep in mind that although the temperature of liquid nitrogen is -320°F (-196°C), there is a temperature gradient in the neck of the tank. For example, a tank with a neck tube that measures 6 inches (15.2 cm) long may have a temperature of -103°F (-75°C) in the middle of the neck 3 inches (7.6 cm) below the top, while the temperature at 1 inch (2.5 cm) below the top may be +5°F (-15°C) (Saacke et al., 1978).
The temperature in the neck of the tank is important because sperm injury (as judged by sperm motility) occurs at temperatures as low as -110°F (-79°C) (DeJarnette, 1999). Furthermore, injury to sperm cannot be corrected by returning semen to the liquid nitrogen. As would be expected, the temperature in the neck of the tank becomes warmer as the liquid nitrogen level in the tank decreases. Therefore, another best management practice is to monitor the liquid nitrogen level in your tank regularly, and never let the tank go dry.
Sexed semen for commercial use is packaged in 0.25-mL straws with each straw containing 2.1 million sperm. Although 0.25-mL straws containing sexed semen may be handled similarly to 0.5-mL straws, the smaller diameter makes them more sensitive to semen handling errors. Research from ABS Global (2009) demonstrates the decline in sperm motility over time when sexed semen is not handled properly (Figure 1).
Figure 1. Progressive motility of sexed semen after thawing in a water bath at 95° to 98°F. Thawed semen was held at constant temperatures of either 98.6°F (recommended; denoted by a solid line with diamond endpoints), 108°F (heat shock; denoted by small dashed line with square endpoints), or 40°F (cold shock; denoted by large dashed line with triangle endpoints) (adapted from ABS Global, 2009).
As shown in Figure 1, providing thermal protection for sexed semen at 98.6°F results in the greatest maintenance (least decline) of progressive motility, as compared with sexed semen held at 108°F (heat shock) or 40°F (cold shock), both of which result in sharp declines in progressive motility over time.
To maximize the potential fertility in each straw of sexed semen, extreme caution must be exercised during semen handling. Fertility will likely be maximized when AI personnel:
Frozen semen must be stored, thawed, and handled properly to maintain fertility and offer the greatest opportunity to obtain optimal fertility. The range in fertility achieved following the use of sexed (and conventional) semen is quite large (DeJarnette et al., 2009) and may be due to many factors, including semen storage and handling errors. Consult your AI representative, university Cooperative Extension agent, or veterinarian to evaluate semen handling procedures. Handle sexed semen with care because every successful AI program begins with proper semen handling.
Joseph C. Dalton, Ph.D.
University of Idaho
1904 E. Chicago St. Suite AB
Caldwell, ID, USA 83605
ABS Global. 2009. Achieving maximum semen fertility with ABS Sexation. Available at: www.abspecplan.com.br/upload/library/Achieving_Maximum_Fertility_wABSSexation.pdf
Cabrera, V. 2009. When to use gender-biased semen: Economics. In: Proc. Dairy Cattle Reproduction Council Annual Meeting, Boise, ID, and Minneapolis, MN, pp. 83-91.
DeJarnette, J.M. 1999. Factors affecting the quality of frozen semen after thawing. In: Proc. Soc. for Therio. Ann. Conf., Nashville, TN, pp. 267-279.
DeJarnette, J.M., R.L. Nebel, and C.E. Marshall. 2009. Evaluating the success of sex-sorted semen in U.S. dairy herds from on-farm records. Theriogenology 71:49-58.
Saacke, R.G., J.A. Lineweaver, and E.P. Aalseth. 1978. Procedures for handling frozen semen. In: Proc. 12th Conf. on AI in Beef Cattle, pp. 46-61.