Prepuberal calves as oocyte donors: Promises and problems

The use of prepuberal heifers as oocyte donors in breeding programs could decrease the generation interval in cattle and increase the genetic rate of gain. While large numbers of follicles develop in response to exogenous gonadotrophins the oocytes they contain lack developmental competence until the animals are 6 to 8 months old. In vitro fertilization rates are normal but rates of cleavage and subsequent development are low. The oocytes are smaller than those collected from adult cattle and the cortical granules fail to disperse evenly during maturation. Oocytes from prepuberal calves release less calcium in response to challenges with InsP3. The lower peak height and altered pattern of Ca2++ oscillations when compared to oocytes of mature cows suggests that cytoplasmic maturation is incomplete in heifers 175 days of age or less. However, the development of ultrasound guided methods for the recovery of oocytes from calves greater than five months old and their improved developmental capacity as demonstrated by development to blastocysts and birth of live calves indicates that the prepuberal calf will play a significant role in animal breeding programs of the future by serving as sire darns or by expanding the influence of genetically superior animals in producer herds.