PRODUCTION OF YOUNG BULL BEEF

Numerous reports citing experiment data Experimental data for feetlot performance continue to claim advantages in gain rates and and carcass characteristics are available, howfeed efficiency for bulls in comparison with ever, for bulls and steers selected from the steers. Although most experiment data agree same breed, of approximately equal ages, and about such advantages, magnitudes differ con- fed identical rations without artificial growth siderably among the reports for good reason. stimulants the same number of days. The inforVariations in the design of bull-steer experi- mation is restricted to British breeds in an atments are almost as copious as the number of tempt to minimize variation due to breed difstations reporting results. Bulls and steers ferences, and selection criteria for experiment used in any given experiment are generally of data trim the number of reports reviewed to 14 comparable age and have been subjected to the [1-3, 5-9, 11-13, 15, 18, 20]. These data, collectsame feeding environment, but rations tend to ed from 947 head of cattle in nine states, are differ among experiments, as do breed, age, used to estimate differences in feedlot performand time on feed. Though some researchers ance and carcass characteristics between bulls feed to a predetermined slaughter weight and steers. which may differ for steers and bulls, others feed both on equal number of days. Likewise, PROCEDURE because some studies have been designed for carcass comparisons of steers and bulls, they The aforementioned experiments generally fail to provide critical feedlot performance data report bull and steer mean values for the folsuch as feed efficiencies. Carcass data may or lowing variables (or values from which they may not include slaughter weights, dressing can be constructed): initial weight, initial age, percentages, or yield of retail cuts. days on feed, feed efficiency, gain rate, final An ideal experiment, designed to estimate slaughter weight, dressing percentage, and differences in feedlot performance and carcass carcass grade. These mean values can be used characteristics between bulls and steers, could within a statistical model to test hypotheses start with twin bull calves maintained in the such as zero differences in feedlot performance same environment before and after one was and carcass characteristics between bulls and castrated, and fed like rations until they were steers. slaughtered at the optimal time. The carcasses Because the variance associated with gain then would be subjected to duplicate evalua- rate (or any other dependent variable) is extion criteria. Unfortunately, twinning in cattle pected to be constant for each animal across is not frequent enough to produce an adequate experiments, ceteris paribus, and different quantity of animals for such experiments. numbers of animals are used within experiEqually lacking are data to identify the opti- ments, the variance of the mean response is mal slaughter point, especially for bulls. From expected to equal 6 2 /ni where 62 is the constant an economic standpoint, optimal slaughter variance of observations across experiments time would be when marginal cost of gain and ni is the number of animals (either bulls or equals marginal value added to the animal, and steers) used in the ith experiment. A generalwould reflect the incremental effect of added ized least squares technique (GLS) is utilized weight on quality grade, dressing percentage, to avoid the inefficiency of ordinary least yield grade or retail yield, and palatability. squares estimation of a model containing Unfortunately, animal scientists conducting heteroscedastic disturbances. Specifically, such feeding trials have given too little atten- because the variance of the disturbances is of tion to this design issue.