Use of gender-selected semen in beef cattle
The use of new technologies by the beef industry usually lags its development by researchers. An example of this would be gender-selected semen. The incorporation of this or any new technology is dictated by its necessity and positive economic advantage. Semen sorted for a specific gender (sexed semen) became commercially available in 2003 for dairy cattle but did not have significant use by the industry until 2006. On the other hand, the number of sires with sexed semen available for the beef industry was still 0 (zero) in 2007 but increased to 70 in 2011. The delayed use of gender-sorted semen by the beef industry may be related to the perceived economic return. For the dairy industry the economic benefit for heifer calves over bull calves is huge; however, in the beef industry gender differences in economic return exist but are not as dramatic. Therefore, for the beef industry to adapt this technology more knowledge is needed regarding how to capture economic returns from incorporating it.
First it is important to highlight that calves born from gender-selected semen will have similar production traits as their herd mates from conventional semen. For example: birth weight, calving ease, calf vigor, calf health, weaning weight, and mortality rates before weaning do not differ between calves from gender-selected and conventional semen. Second, with recent improvements in this technology conception rates with gender-selected semen are typically between 80% to 95% of conventional semen, in other words if AI conception rates are 60% with conventional semen, with gender-selected semen you would expect conception rates to be between 48% to 57%. One thing to be aware of to get the best possible conception rates is cows that exhibit estrus prior to AI have greater conception rates compared to cows that do not exhibit estrus behavioral. So, the use of gender-selected semen only in animals that exhibit estrus prior to AI will result in greater conception rates. Another method is the delay insemination of nonestrus cows to 20 hours after an injection of GnRH.
Even though gender differences are not as large in the beef industry as they are in the dairy industry, gender-selected semen has many applications which will depend on the herd. In commercial beef cattle a strategy would be to use gender-selected semen to produce replacement heifers. This strategy would start by selecting cows with desired maternal traits, such as age at sexual maturity, milk yield, fertility, maternal behavior, adaptation to the environmental challenges, and longevity. These animals would then be inseminated with gender-selected semen from sires with similar maternal traits. An advantage of this strategy would be the production of top replacement heifers and increasing the rate of genetic change in the herd. In addition, there would be a decrease in the number of steers produced from maternal sires. This benefits the herd as these steers often have decreased performance when compared to steers from terminal sires. When the number of cows to be inseminated with gender-selected semen is achieved the remaining cows can be inseminated to terminal sires knowing these calves will not be kept as replacement heifers. It also brings the opportunity to utilize different breeds, without affecting the herd’s genetic. Similar with herd bulls, since no heifers are expected to be retained from those animals a sire with terminal characteristics or different breed may be used. Another alternative, would be inseminate the remaining females with male selected semen from terminal sires, increasing the proportion of steers produced from terminal sires in the herd. Overall, the inclusion of gender-selected semen can bring economic advantages to the beef industry. However, there are situation in which the use of gender-selected semen can negatively impact the economic return of a herd too. If only female selected semen is used to inseminate the entire herd; this will optimize the selection of replacement heifers but the proportion of male:female calves will shift from an approximately 50:50 to a greater number of females what could affect economic returns due to lower prices for heifers sold to slaughter. If only male selected semen is used to inseminate the entire herd; this will optimize the genetic performance of steer calves for slaughter but removes any genetic benefit of AI on the future of the herd as replacement heifers can only be selected from calves born from the clean-up bull. Thus, the use of gender-selected semen in a beef herd has the opportunity to benefit the overall performance and future of the herd, but care must be given to implement this technology correctly.