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[return to Table of Contents] One objective of this publication is to outline procedures for measuring and recording beef cattle performance data. Performance testing offers those engaged in beef production a way of measuring heritable differences among animals so producers can select animals which are expected to transmit superior performance to their offspring. A second objective is to achieve greater uniformity of terminology and methods of measuring performance traits. This is important in accomplishing rapid and accurate communication and developing cooperation among all segments of the beef industry in compiling and using performance records. The economic potential of performance testing in beef production is highly correlated with the level of communication and cooperation. It is not our purpose, however, to recommend a standard program applicable to all segments of the beef cattle industry. to assist breeders and others in more effectively using this information, we have prepared this publication to provide three basic types of information. First, we explain the importance of reproduction, growth rate, efficiency of gain, carcass merit, and linear measurements as economically significant beef cattle traits. Procedures and methods are provided for objectively measuring these traits which contribute to both productive efficiency and desirability of product. Second, we explain the use of Expected Progeny Differences (EPDs) as a procedure for increasing the accuracy of selection by using all available performance data on individual animals and their ancestors to estimate the value of these individual animals as parents. Third, we outline methods and procedures for incorporating information on objective measurements of performance traits into nerformance programs for seedstock producers, commercial producers, central testing, and sire evaluation. All recommendations are based on currently available research information and experience. A glossary at the end of the report contains definitions of terms that may be unfamiliar to the reader. Differences between individual animals in traits of economic value are inherited to varying degrees. Thus, systematic measurements and the use of records in selection will increase the rate of genetic improvement. 1.1: Importance of Performance Testing Differences in performance between individuals or groups of animals are due to either genetic or environmental causes. The observed or measured performance of each animal in each trait is the result of its heredity and the total environment in which it is produced. Genetically superior individuals can be more readily identified when the animals are maintained under the same management systems and their performance records are adjusted for known environmental differences. There are also many random or chance environmental variables which may contribute to errors in estimating the breeding value of animals. The importance of these variables, such as differences in fill (the contents of the animal’s alimentary canal) at time of weighing, can be appreciably reduced by following appropriate and uniform procedures. The weighing conditions should be the same for all animals that are to be compared. The rate of genetic improvement is dependent on: (1) the percentage of observed differences between animals that is due to heredity (heritability), (2) the difference between selected individuals and the average of the herd or group from which they come (selection differential), (3) the genetic association among the traits on which selection is based (genetic correlations), and (4) the average age of parents when the offspring are born (generation interval). Records of performance are primarily useful to provide a basis for comparing cattle handled alike within a herd. Large environmental differences due to location, management, health, and nutrition are likely to exist between herds or between different management groups within herds. Genetic differences between herds do exist, but only through a carefully controlled evaluation can these differences be assessed. Guidelines for a national sire evaluation program which takes herd differences into account are also described in this publication. To identify high-ranking individuals within a breed, it is necessary to first identify high-ranking individuals within herds. Thus, widesuread use of nerformance testing within herds is the first essential step to beef improvement.
1.2: Importance of Performance Records The principal features of effective records of performance programs are as follows:
Fertility and the various components which contribute to it have been found to be of low heritability. However, fertility is economically the most important trait in the beef industry and, in herds where fertility is low, a sizable selection differential can be achieved. Extremely low fertility or sterility are self-eliminating traits, but cattle of this kind need to be identified and eliminated from the herd for purely economic reasons. Thus, maintaining complete records on all cows and fertility records on bulls in breeding herds is recommended. Replacement animals should be selected from parent stocks that have above average fertility. Throughout this publication, the terms "weight ratio and gain ratio" are used to refer to the performance of an individual relative to the average of all animals in the same group. This ratio is calculated as: (Individual record / Average of animals in group) * 100 The above ratio is a useful device for quickly visualizing the relative rankings of individuals in a group. To some degree, it adjusts for environmental differences between groups. This means that two animals with equal weight ratios in two different herds or groups can be compared more validly on the basis of ratios than on the basis of actual weights. However, the possibility of true genetic differences between herds or groups limits the usefulness of ratios for between-herd or between-group comparisons. [return to Table of Contents] |