Nutritional aspects of developing replacement heifers

Authors: FUNSTON, R - University Of Nebraska; MARTIN, J - Great Plains Livestock Consulting, Inc; LARSON, D - Great Plains Livestock Consulting, Inc; Roberts, Andrew

Submitted to: Journal of Animal Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/27/2011
Publication Date: 3/1/2012
Citation: Funston, R.N., Martin, J.L., Larson, D.M., Roberts, A.J. 2012. Nutritional aspects of developing replacement heifers. Journal of Animal Science. 90:1166-1171.

Interpretive Summary: Research in the late 1960s through the early 1980s indicated puberty occurs at a genetically predetermined size critical weight. Guidelines were established indicating replacement heifers should achieve 60 to 65% of their expected mature BW by breeding. Traditional approaches for postweaning development of replacement heifers used during the last several decades have primarily focused on feeding heifers to achieve or exceed an appropriate target weight, and thereby maximize heifer pregnancy rates. These heifer development systems may maximize pregnancy rates, but not necessarily optimize profit or sustainability. Since inception of target weight guidelines, subsequent research has demonstrated the pattern of growth heifers experience prior to achieving a critical target weight could be varied. Altering rate and timing of gain can result in periods of compensatory growth thereby providing an opportunity to decrease feed costs. Recent research demonstrates that feeding replacement heifers to traditional target weights increases development costs without improving reproduction or subsequent calf production relative to development systems where heifers were developed to lower target weights ranging from 50 to 57% of mature BW. It is expected that genetic changes in growth and onset of puberty that occurred in beef cattle over the last several decades may allow for developing heifers to lower proportions of their mature BW than traditional recommended. Growing heifers to lighter weights prior to first breeding provides opportunity for increases in production efficiency.

Technical Abstract: Studies in numerous species provide evidence that diet during development can mediate physiological changes necessary for puberty. In cattle, several studies have reported inverse correlations between postweaning growth rate and age at puberty and pregnancy rates in heifers. Thus, rate of postweaning growth was determined to be an important factor affecting age of puberty, which in turn influences pregnancy rates. This and other research conducted during the late 1960s through the early 1980s indicated puberty occurs at a genetically predetermined size, and only when heifers reach their target weight can high pregnancy rates be obtained. Guidelines were established indicating replacement heifers should achieve 60 to 65% of their expected mature BW by breeding. Traditional approaches for postweaning development of replacement heifers used during the last several decades have primarily focused on feeding heifers to achieve or exceed an appropriate target weight, and thereby maximize heifer pregnancy rates. Intensive heifer development systems may maximize pregnancy rates, but not necessarily optimize profit or sustainability. Since inception of target weight guidelines, subsequent research demonstrated the pattern of growth heifers experience prior to achieving a critical target weight could be varied. Altering rate and timing of gain can result in periods of compensatory growth thereby providing an opportunity to decrease feed costs. Recent research has demonstrated feeding replacement heifers to traditional target weights increased development costs without improving reproduction or subsequent calf production relative to development systems where heifers were developed to lower target weights ranging from 50 to 57% of mature BW.