They recommend, under these conditions, that cattlemen select stock for breeding on the basis of rate of gain rather than efficiency of feed utilization.

H. R. Guilbert and P. W. Gregory, working at the California Agricultural Experiment Station, also concluded that rate of gain did not satisfactorily indicate efficiency of feed utilization in groups differing in potential mature size and in earliness of maturity. If efficiency of feed utilization was to be determined independently of variations in type, size, and rate of maturity, some means of approximate control of the composition of gains was necessary, they believed. Hence, the steers used in their study were fed as much of a standard ration as they would eat and were marketed when they were judged to have attained a definite degree of finish. Relative rate of gain and relative feed capacity were determined, expressed in relation to the 0.75 power of weight. These indexes appeared to be closely correlated with each other and with efficient feed utilization.

Level of feeding is important when one tries to find a yardstick to be applied in the feed lot. Observations by Knapp and Baker indicate there is greater opportunity for genetic variation to be expressed when animals get all the feed they want. They recommend that a cattle raiser full-feed or self-feed steers if he wants to measure their differences in ability to grow. The recommendation, made also by others, is intended for use under usual conditions of fattening cattle for market as rapidly as possible after they are placed in the feed lot, and would not necessarily apply under other conditions of environment or management.

The length of the feeding period is likewise important. To find out more about this problem, data were used from steers fed for 293 to 356 days. Feeding for 168 days was found sufficient to indicate differences in efficiency of feed utilization between groups of progeny from different bulls, provided the data were adjusted for differences in initial weight. This feeding period is too short to allow steers to fatten sufficiently for market. Where individual feeding is practiced, however, some expense might be saved by feeding in groups after the efficiency of individuals has been determined.

Still another factor is the number of progeny that must be tested in order to determine the merit of a bull. We decided, after investigation, that we can get just about all the information we need about the sire's value by studying 8 or 10 of his offspring.

Ranchers, feeders, packers, and others find that one of their hardest problems is to appraise properly the worth of the carcass of a meat animal. Market grades are widely used, but they are largely measures of degree of finish or fatness. Knapp demonstrated that grades can be estimated rather accurately from measurements of height at withers and heart girth. Consumers, packers, and retailers want beef that contains just enough bone to give it form, enough fat for palatability and ripening quality, and a large proportion of lean meat. O. G. Hankins, Knapp, and I studied the 9-10-11 rib cut in 55 beef and 80 dual-purpose steers to determine its value as an indicator of carcass merit. This rib cut was separated into the lean meat, fat, and bone. Constituents were weighed, and the ratio of lean meat to bone determined. The average muscle-bone ratios were 2.55 and 2.28, respectively, for the beef and dual-purpose types. Approximately 15.6 percent of the variation in the 135 carcasses was accounted for by the differences between the two types. Highly significant differences were observed between sires within the two types, and accounted for about 22 percent of the total.

Sex also affects weight. Marvin Koger and J. H. Knox investigated the weights at weaning of steer and heifer calves on New Mexico ranges. They report that steers averaged 443 pounds and heifers 411 pounds, a difference of 32 pounds. The variable must be considered when comparing groups of progeny, or other groups, particularly when the proportions of the sexes vary.

Considerable emphasis is placed on selection of low-set, compact animals for breeding. The possibility of carrying this practice too far is indicated in a recent study by Knox and Koger. They fed 350 yearling steers, during a 9-year period, which were classified as rangy, medium, or compact. Rangy steers gained most rapidly, but when corrected for initial weight, differences in their favor were not statistically significant. There were no important differences in economy of gain among the three types, when this factor was considered in relation to initial weight. Likewise, carcass grade was about the same in all types. The rangy steers yielded a higher average dressing percentage than either of the other types. These workers conclude that it may be more difficult to develop rapidly gaining strains of beef cattle if size is reduced by too greatly restricting height and length to obtain compactness.