Measurements of Genetic Variation in Residual Metabolizable Energy Intake of Laying Hens1

ABSTRACT An experiment was conducted to determine heritability of the residual component of feed consumption. The effect of test period length was also examined to determine the shortest test period that would result in reliable data. Three hundred and thirty-five pedigreed White Leghorn hens were used. The experiment began when the hens were 26 wk of age and lasted for 28 wk. The residual component of energy intake was determined for each hen for time periods of 2,4, and 8 wk in length. These values were used to determine heritability. Analyses of the data for each period were performed in two steps. A reduced model, without pedigree information, was used to develop a regression model. A complete model was used for analyses of data. The procedure of starting egg mass output measurements 2 days after body weight measurements was more effective than starting records on the same days that body weights were obtained. The partial regression coefficients of ME intake decreased with age. Also the partial regression coefficients of ME on body weight change increased with the length of the test period. The partial regression coefficients of ME on egg mass increased slightly with age. Heritability of ME intake adjusted for metabolic body weight, body weight change, and egg mass output was highest (.567 ±.186) when the test was calculated by 8-wk periods. However, the range of estimates over time was lowest when made for 4-wk periods. (Key words: laying hen, egg production, energy intake, residual component, heritability