Author
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Macneil, Michael |
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Submitted to: Research Update for Fort Keogh Livestock and Range Research Laboratory
Publication Type: Popular Publication Publication Acceptance Date: 10/1/2002 Publication Date: 1/15/2003 Citation: MACNEIL, M.D. CAN BALANCING BIRTH WEIGHT AND GROWTH ENHANCE BEEF PRODUCTION. RESEARCH UPDATE FOR FORT KEOGH LIVESTOCK AND RANGE RESEARCH LABORATORY. p. 68-69. 2003. Interpretive Summary: Genetic selection to increase production tends to decrease net reproduction. Improving more than one unfavorably correlated trait at a time can be difficult. Reducing calf mortality by controlling birth weight while increasing later growth is an applied example of this problem. Genetic trends in maternal breeding values were used to indicate differences in milk production of the cows. A clear pattern of divergence between sublines emerged during the later years of this experiment, with the maternal effect being greater in YW than in YB. Based on this result and the relationship between maternal breeding value and actual milk production, it seems that genetic potential for milk production may have increased 52% more rapidly in YW than in YB. Taken together, the preceding results suggesting earlier maturity and reduced energy requirements resulting from smaller mature size and less milk production of cows the YB subline may increase biological efficiency and sustainability in some production systems, relative to cows of the YW subline. Technical Abstract: Simultaneous selection for low birth weight and high yearling weight has been advocated to improve efficiency of beef production. Two sublines of Line 1 Hereford cattle were established by selection either for below-average birth weight and high yearling weight (YB) or for high yarling weight alone (YW). Sires for both lines were progeny tested. Genetic trait in birth weight increased signficiantly in YW, but not in YB. Response in 365-d weight of YB was 61% of that obtained in YW. Breeding values for gestation length were greater in YB sires than in YW sires. Predicted breeding values for indicators of fat deposition tended to be greater in YB sires than in YW sires although YB and YW sires had similar breeding values for marbling score. Beef cows resulting from simultaneous selection for below-average birth weight and increased yearling weight had different growth curves and reducted genetic trend in maternal gain from birth to weaning relative to cows resulting from selection for increased yearling weight. Results demonstate the value of multiple trait selection for overcoming genetic antagonisms in beef production. |
