I'm not aware of a predictable way to ensure more of one sex of calf verses the other sex via natural service. Females are XX and Males are XY, so at each conception there is a 50 percent chance of a male or female calf. Researchers have sought methods to sex semen for many years. In this research, they collect the bull and use a technique to separate the X and Y chromosomes. Following is an excerpt from an article from the 2003 Range Beef Cow Symposium on sexed semen: There is a method that works under laboratory conditions. X-chromosome-bearing bull sperm, which lead to females, have about 4 percent more DNA than Y-chromosome-bearing ones, which lead to males. By placing sperm in a solution of DNA-binding dye, X-chromosome-bearing sperm become more brightly stained than Y-chromosome-bearing sperm. By use of lasers plus a device called a cell sorter, it is possible to separate the sperm into three test tubes -- male, female, and unsexable, which is the majority. Those in the sexed test tubes accumulate at about 1,000 sperm per second, with an accuracy of just over 80 percent. Although 500 sperm per second of each sex is phenomenally rapid, in reality it is too slow to be practical for most purposes. For example, one straw of semen often contains 50 million sperm (30 million motile before freezing). At 500 sperm per second, it would take 100,000 seconds per straw or more than 24 hours to produce one dose of semen. The logistics of keeping sperm viable for such lengths of time at room temperature are considerable. The equipment is very expensive -- over $50,000 per setup -- and complicated to operate. Fertility probably would be lowered somewhat, and the long-term consequences of adding dye to DNA are unknown. However, procedures for sexing sperm have improved markedly over the next few years, and one practical application -- use of such sperm with in vitro fertilization, which requires few sperm -- may not be far off.

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