Garland R. Dahlke

Feed Efficiency Calculator

and Implications The Feed Efficiency Calculator, a product from the National Program for Genetic Improvement of Feed Efficiency in Beef Cattle provides a tool to researchers and producers interested in calculating residual feed intake (RFI), residual gain (RG) and adjusted feed to gain values on tested animals. Introduction Calculation of residual feed intake (RFI) and residual gain (RG) from phenotypic data collected on the farm is not intuitive yet the results of this calculation have become fairly widespread in conversation and selection criteria among those involved in the genetic selection beef cattle seedstock. The RFI value results from determining the difference between actual dry matter intake and expected dry matter intake for a given animal at a measured level of weight gain or performance. RG results from determining the difference between actual gain and expected weight gain for a given level of feed dry matter intake. In both situations, the expected values are based on a regression calculation of group contemporaries and their performance.

Effect of estrus activity when evaluating feed efficiency in heifers

Introduction Feed efficiency measurements taken on individual heifers or bulls for the purpose of selection of replacement breeding stock tend to be taken when these animals are 200 to 400 days of age. During this time frame, many of these animals undergo puberty and the subsequent changes advancing sexual maturity initiates; however they do not all mature at the same rate. These changes tend to affect carcass characteristics due to the anabolic nature of the hormones associated with this stage of life, but also there are behavior changes that could have some effect on feed use. Estrus activity of heifers in the feedyard is discouraged and the use of additives such as melengestrol acetate (MGA) which suppresses estrus activity tends to improve feed conversion and weight gain in large pen studies. With this in mind along with the fact that puberty onset is variable within a weaning contemporary group, there was some concern that evaluation of feed efficiency may be confounded by the onset of puberty and estrus activity when evaluating heifers.