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ARS Home » Plains Area » Clay Center, Nebraska » U.S. Meat Animal Research Center » Genetics and Animal Breeding » Research » Publications at this Location » Publication #154351
Title: GENETIC PARAMETERS FOR SIX MEASURES OF LENGTH OF PRODUCTIVE LIFE AND THREE MEASURES OF LIFETIME PRODUCTION BY SIX YEARS AFTER FIRST CALVING FOR HEREFORD COWS

Author
item MARTINEZ, G. - ARAGUA, VENEZUELA
item KOCH, ROBERT - RETIRED-UNIV. OF NEBR.
item Cundiff, Larry
item GREGORY, KEITH - ARS COLLABORATOR
item Van Vleck, Lloyd

Submitted to: Journal of Animal Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/12/2004
Publication Date: 7/1/2004
Citation: Martinez, G.E., Koch, R.M., Cundiff, L.V., Gregory, K.E., Van Vleck, L.D. 2004. Genetic parameters for six measures of length of productive life and three measures of lifetime production by 6 yr after first calving for Hereford cows. Journal of Animal Science. 82:1912-1918.

Interpretive Summary: Genetic parameters for length of productive life given the opportunity, measured as days between first calving and disposal conditioned on one of six opportunity groups, (e.g., L2 is length of productive life in days given the opportunity to live 2 yr after first calving), and lifetime production, measured as number of calves born, number of calves weaned, and cumulative weaning weight by 6 yr after first calving, were estimated using records of 1,886 Hereford cows from a selection experiment with three selected lines and a control line. Selection for length of productive life given different opportunities to be alive (additional years after first calving), and lifetime production measured as number of calves born, number of calves weaned, and cumulative weaning weight by 6 yr after first calving would be possible, but would be expected to be slow due to low estimates of heritability and possible lengthening of the generation interval. The high estimates of genetic correlations among measures of length of productive life (various opportunity groups) indicate that length of productive life measured through one year after first calving predicts productive life through 6 years after first calving with reasonable accuracy. High genetic correlations among these traits suggest that any of these measures of lifetime production could be used to select for improving productive life. Selection of the lines for weights at weaning and yearling ages seemed to have had little genetic impact on any measure of lifetime production.

Technical Abstract: Genetic parameters for length of productive life given the opportunity (LPL|O), measured as days between first calving and disposal conditioned on one of six opportunity groups, (e.g., L2 is length of productive life in days given the opportunity to live 2 yr after first calving), and lifetime production, measured as number of calves born (NB), number of calves weaned (NW), and cumulative weaning weight (CW) by 6 yr after first calving (CW6), were estimated using records of 1,886 Hereford cows from a selection experiment with three selected lines and a control line (CTL). Weaning weights were adjusted to 200 d of age and for sex and age of dam. Estimates of heritability and genetic and environmental correlations were obtained by REML with bivariate animal models with year of birth of cow as a fixed effect and direct genetic and residual as random effects. Genetic trends were estimated by regressing means of estimated breeding values by year of birth and line on birth year. Estimates of heritability (SE) for LPL|O ranged from 0.05 (0.01) to 0.15 (0.03). Estimates of genetic correlations (SE) among LPL|O ranged from 0.74 (0.14) to 1.00 (0.00), and estimates of environmental correlations ranged from 0.67 (0.05) to 0.98 (0.01). Estimates of heritability (SE) for NB, NW, and CW were: 0.17 (0.05), 0.21 (0.06), and 0.18 (0.01). Estimates of genetic correlations (SE) among NB, NW, and CW ranged from 0.96 (0.02) to 0.99 (0.01). Estimates of environmental correlations (SE) ranged from 0.93 (0.01) to 0.99 (0.01). Estimates of genetic correlations for L6 with NB, NW, and CW were near 1.00 (0.09). Estimates of environmental correlations (SE) ranged from 0.57 (0.03) to 0.60 (0.03). Estimates of genetic change per year (SE) for L6 were low for all lines and ranged from -3.53 (2.09) to 4.63 (2.11) d/yr. Genetic trends for NB and NW were negligible for all lines. Genetic trends for CW were low and ranged from -2.81 (1.67) to 3.29 (1.76) kg/yr. Differences in genetic trends between selected lines and CTL were not significant (P > 0.05). Estimates of environmental trends (SE) over all lines were: -104.00 (25.48) d/yr, -0.26 (0.02) calves/yr, -0.25 (0.02) calves/yr, and -55.10 (15.63) kg/yr, for L6, NB, NW, and CW, respectively. Selection for LPL|O or LP could be successful in a breeding program, but may be relatively slow due to the low magnitude of heritability and extended generation interval.