RELATIVE EFFICIENCIES OF WITHER HEIGHT AND BODY-WEIGHT INCREASE FROM BIRTH UNTIL FIRST CALVING IN HOLSTEIN CATTLE

Female Holstein calves from the Purina Research Center herd averaged 7 4 cm of height at withers and 40 kg of body weight (BW) at birth. At f irst calving (24 mo of age), calves averaged 138 cm of height at withe rs, 611 kg at precalving BW, and 547 kg at postcalving BW. Fifty perce nt of the total height increase occurred from birth to 6 mo of age, 25 % occurred during 7 to 12 mo of age, and 25% occurred during 13 to 24 mo of age. Twenty-five percent of the total BW increase occurred from birth to 6 mo of age, 25% occurred from 6 to 12 mo of age, and the rem aining 50% occurred from 13 to 24 mo of age. The increase in BW for 2- mo intervals, expressed as a proportion of the BW of the previous 2-mo interval, declined most rapidly during the first 6 mo, intermediately during the second 6 mo, and more slowly and progressively during the final 12 mo. Feed cost per unit of BW gain was lowest during the first 6 mo and then increased at a decreasing rate over the final 18 mo. Th e proportion of BW to height linearly increased over the 24-mo period. The increase in wither height as a proportion of the wither height du ring the previous period was greatest during the first 6 mo, intermedi ate during the second 6 mo, and lowest in the final 12 mo. Feed cost p er unit of height increase was lowest in the first 6 mo, intermediate during the second 6 mo, and highest with a rapid increase during the f inal 12 mo. The increases in relative BW and wither height are the mos t rapid and cost efficient during the first 6 mo of life.