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Cattle breeders demand products and services that improve efficiency and maximize profits. Research and development for these products, once done primarily in academic settings, now is occurring more within the private corporate sector who now fund research that was previously funded from public sources. These products often are patented and licensed to individual companies. Product availability is hastened, but sometimes at higher costs. Sex-specific sperm soon will be available to the cattle industry for use in high profile, genetically elite herds. Widespread availability of sex-specific sperm for commercial herds should follow within 2 years.
Sex-specific sperm for use with artificial insemination (AI) will enable producers to pre-determine the sex of calves from specific genetic matings, resulting in faster genetic gain within herds. This technology will reduce numbers of unwanted dairy bull calves that currently end up as dairy beef. Efficacious use of sex-specific sperm depends upon increased genetic merit and/or phenotypic gain for production traits, and increased economic efficiency of genetically superior females by the production of specific sex offspring. Managerial gains also will be realized with accurately predicted calf sex.
Hair color, milk production and rate of gain are examples of many traits determined by genetic code contained in the DNA (deoxyribonucleic acid). DNA, which is organized in packets called chromosomes, specifies what each cell does and when. Bovine sperm contain 30 chromosomes, one of which is the sex chromosome. Sex is determined by X- (female) or Y- (male) chromosome-bearing sperm. In mammalians, more DNA is contained within the X-chromosome (Table 1); for bulls, X-chromosome-bearing sperm have 3.8% more DNA content than Y-chromosome-bearing sperm. This forms the basis for separating sperm via flow cytometry/sperm sorting. DNA content is the only reliably proven difference between X- and Y-chromosome-bearing sperm (Johnson and Welch, 1999).