Variation in Birth and Weight Traits of identical Calves Produced Through Nuclear Transplantation

Abstract

The identical genetic makeup within groups of beef cattle produced through nuclear transplantation (NT) should reduce the number of animals required for statistically powerful research trials, assuming a lack of variability within genotypes. With this in mind, five groups of male, Brangus, second-generation NT pregnancies (seven to eight per group) being gestated in Holstein recipient females were obtained from Granada Biosciences (Wheelock, TX). Calving occurred from December 1991 to April 1992, and resulted in 24 live calves from 39 pregnancies. All animals were DNA fingerprinted to verify genotype within clone groups using restriction fragment length polymorphism analysis of genomic DNA. At birth, all calves were measured for head circumference (HC), shoulder width (SW), heart girth (HG), metacarpal circumference (MC), body length (BL), and birth weight (BW). All linear measures were positively correlated (P<0.01) to BW, and accounted for 84.5% of the variability observed in BW. Adjusted 205-d weaning weight (AWW) and adjusted 365-d yearling weight (AYW) were used to assess changes in variability within and among groups over time. Weight variability decreased 60% on average within genotypes as the animals matured. In one genotype, low variability (CV=6.3%) at birth with little change over time was observed. This uniformity may have been attributable to the surrogate dams being on a higher nutritional plane than earlier calving groups. These data indicate a reduction in observed weight trait variability within NT calves over time.