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Genetic variance and covariance components for feed intake, average daily gain, and postweaning gain in growing beef cattle
Feed is the single most expensive cost related to a beef cattle production enterprise. Data collection to determine feed efficient animals is also costly. Currently a 70 d performance test is recommended for accurate calculation of efficiency. Previous research has suggested intake tests can be limited to 35 d; however, decreased lengths in gain tests have been suggested to have detrimental effects on accuracy. The objective of this study was to estimate genetic parameters for growth and intake traits. On–test average daily feed intake (ADFI), on-test average daily gain (ADG), and postweaning gain (PWG) records on 5,606 growing steers and heifers were obtained from the U.S. Meat Animal Research Center in Clay Center, NE. The 3-generation pedigree contained 9,211 animals from 27 different breed groups. On-test ADFI and ADG data were collected from a minimum of 62 to 148 d testing days. Independent quadratic regressions were fitted for body weight on time, and on-test ADG was predicted from the resulting equations. PWG was calculated by subtracting 205-d weights from 365-d weights and dividing by 160 d. Heritability and genetic/residual correlations were estimated using multiple trait animal mixed models with ADG, ADFI, and PWG for both sexes as dependent variables. Postweaning gain and feed efficiency contemporary groups were fitted as fixed effects. Covariates included age on test, age of dam, direct heterosis, and breed origin. Variance components were estimated with ASREML 3.0. Heritability estimates ± SE for ADG, ADFI, and PWG of steers were 0.09 ± 0.03, 0.43 ± 0.05, and 0.37 ± 0.05, respectively; and corresponding estimates for heifers were ADG 0.14 ± 0.04, ADFI 0.39 ± 0.05, and PWG 0.42 ± 0.05. These estimates confirm genetic improvement of feed efficiency can be made. The genetic correlations between steer ADG and ADFI, PWG and ADFI, and ADG and PWG were 0.73 ± 0.12, 0.58 ± 0.06, and 0.81 ± 0.15, respectively; and corresponding estimates for heifers were 0.64 ± 0.13, 0.77 ± 0.05, and 0.65 ± 0.12. The genetic correlations between ADG and PWG for both sexes were strong. This indicates PWG is a strong proxy for ADG on-test and long test periods may not be necessary. A shorter testing period would allow more animals to be tested per year with a given set of facilities.
Keywords:
beef cattle, feed efficiency, genetic parameters