8E. Hare, H. D. Norman and J. R. Wright. Trends in Calving Age and Intervals for Dairy Cattle Breeds in the United States[J]. American Dairy Science Association,2006, (89):365-370.
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10E.Hare, H.D.Norman,J.R.Wright.Trends in Calving Age and Intervals for Dairy Cattle Breeds in the United States[J].American Dairy Science Association,2006, (89):365-370.