Cattle Breeding

Use of Sex-Sorted S***m
Production of offspring of the desired s*x using s*x-sorted semen has become an established reliable technique in the dairy cattle breeding industry over the last two decades, where the major application is use of X-sorted semen on virgin heifers selected to produce the next generation of replacement animals. Although evolution of the technology has resulted in improved success, pregnancy rates are still somewhat lower than those achieved with conventional semen. Some of the reduction in pregnancy rate may be due to the lower concentration of s***m per dose (typically 2–4 million vs. 15–20 million in conventional, unsorted, semen straws). In superovulated cows, the use of s*x-sorted semen results in impaired fertilization rates and compromised yields of transferable embryos. Reduced fertilization with s*x-sorted semen may be due to low doses of s***m, an abnormal uterine environment due to supraphysiological concentrations of progesterone or atypical s***m transport in superovulated cows, damage to s***m during s*x sorting, or some combination of these factors. Thus, more research is required to optimize the yield of transferable embryos from s*x-sorted semen in superovulated donors.