Interspecies Hybridization between Yak, Bos taurus and Bos indicus and Reproduction of the Hybrids

Yak are crossed with Bos taurus and Bos indicus cattle, including common local cattle breeds (via natural service) and via artificial insemination of frozen-thawed semen from improved breeds (e.g. Holstein Friesian). Female hybrids reach puberty and mate a year earlier than pure yaks. Nonpregnant F1 females usually have several estrus cycles in the same season and will generally calve every year. Calf survival is similar to that of the pure yak, however, abortion and dystocia are more frequent. Male hybrids are sexually active but produce no spermatozoa (the cause is uncertain) and therefore are sterile. Sperm production does not resume until at least the third backcross (15/16 yak or cattle), and often not until the fourth backcross. The F1 hybrids generally grow faster and larger than the pure yak, with production of milk and meat exceeding that of pure yak and usually exceeding that of local cattle breeds.