Användning av könssorterad sperma i nötkreatursaveln
Almost for as long as there has been breeding on bovine species, there has been a wish to have a higher proportion of offspring of either one or the other gender. In dairy cattle, heifers are more valuable, while in beef stock bulls are preferred. Semen is sorted based on the difference in DNA content between the X- and Y-chromosome in the genome of the sperm. X-chromosomes contain on average between 3,70 to 4,22% more genetic material than the Y-chromosome. Commercially it is the method of flow cytometry that is being used, which is always under improvement. There are differences in fertility between breeds, but there are no differences in precision of sorting between breeds. With unsorted sperm a 55 to 60% conception rate can be achieved on heifers, whereas with sorted sperm the conception rate is between 35 to 40%. In spite of the fears that the sorting process damages DNA and causes abnormal offspring, no reports confirm this. The genetic progress has been estimated to increase with 0,4 to 1,4 percent with sexed semen. To achieve the highest possible economical gain heifers should be used for AI with sexed semen, and not cows, since heifers have higher fertility. It is more expensive to use sorted sperm than conventional semen and the number of sperm in one dose is lower for sorted sperm. Many of the ethical aspects that exist with sorted sperm speak for its usage. These aspects include fewer cases of dystocia, increased bio security and higher biological efficiency.