Comparative Study of Conventional Protein Allowances and Theoretical Requirements of Growing Holstein Heifers

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Abstract
Studies are reported in which it was attempted to compare the response of Holstein heifers grown on the protein allowances of the 1936 Morrison feeding standard and on the estimates of Mitchell calculated by the factorial method. The growth data indicated there was no advantage in supplying more protein to Holstein calves from 150 to 350 pounds body weight than recommended in the 1936 Morrison standard. An intake somewhat below the lower limit of this standard produced as good gains as did higher levels. For heifers weighing more than 700 pounds the digestible protein allowances of Mitchell's estimates proved grossly inadequate. Data are presented to show that for Holstein heifers and with the feeds used the minimum protein requirements for growth were about 0.80 pound of digestible protein daily from 500 to 700 pounds, 0.90 from 700 to 800, and 1.00 pound from 800 to 1000 pounds. The factorial estimates of Blaxter and Mitchell for the calculation of theoretical minimum protein requirements for growing Holstein cattle have been recalculated with the inclusion of various changes for which experimental support has been cited. In general, the data from this study support the validity of the changes made.