|Van Vleck, Lloyd|
Submitted to: Journal of Animal Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/20/1995
Publication Date: N/A
Interpretive Summary: A selection project was started at the U.S. Meat Animal Research Center in 1981 to increase economic efficiency of beef production by increasing twinning rate. After only 12 years of selection, twinning rate increased by a factor of nearly 10. Increased twinning rate will decrease the cost of producing feeder calves. The rate of twinning is reaching the range (about 40 to 50%) needed for commercial use of twinning technology. The rapid increase in twinning, a trait with low heritability, also demon- strates the power of indirect selection using a trait such as ovulation rate with higher effective heritability and with a large genetic correla- tion with the trait of economic value.
Technical Abstract: Estimates of genetic parameters for a two-trait twinning and ovulation rate model with genetic groups were: heritabilities of .03 for twinning and .07 for ovulation rates with a genetic correlation of nearly 1.00 and fractional permanent environmental variances of .06 for twinning and .05 for ovulation rate. Corresponding estimates when group effects were ig- nored were: heritabilities of .08 and .08 and fractional permanent environ mental variances of .02 and .04 for twinning and ovulation rates, respectively. Twinning rate (%) in the project at the U.S. Meat Animal Research Center has increased in all cows born in the project by year of calving from 3.4% in 1982 to 28.5% in 1993, a phenotypic increase of 25.1%. The estimated genetic change in twinning of cows by year of calving using the groups model has been 15.2%. The increase in average genetic value by year of birth has been 18.2% in twinning and 15.0% in ovulation rate from 1980 through 1991. Effects for seven selected groups of foundation animal ranged from -6.0% to 33.1% and influenced genetic trend.