Evaluation of Feed Efficiency Traits with Post-Weaning Growth and Ultrasound Traits in Central Test Bulls
Type of DegreeThesis
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Since 1978, individual feed intake has been measured on bulls (n = 2,180) consigned to the Auburn University Bull Test along with weights, heights, scrotal circumference and ultrasound carcass traits. Test length since 1977 was reduced from 140 d to 112 d to 84 d. Eight breeds were analyzed using MTDFREML to estimate heritabilities of and genetic correlations between residual feed intake (RFI) and ADG, scrotal circumference (SC), ultrasound 12th rib fat thickness (USFAT), ultrasound longissimus muscle area (USREA) and percent intramuscular fat (USIMF). Breeds included were Angus (n = 857), Brangus (n = 41), Charolais (n = 380), Gelbvieh (n = 103), Hereford (n= 192), Limousin (n = 106), Santa Gertrudis (n = 106) and Simmental (n = 395). Traits were analyzed using three-trait analyses and a sire-maternal grandsire model with either age or weight as covariates. Fixed effects included length of test, breed and year. (Co)variance estimates were averaged across analyses to arrive at a final estimate. Heritability and genetic correlation estimates of all traits were on the lower end of reported literature estimates. These results may be due to consignment of elite bulls to a central test station. Results also suggest selection of animals with a lower residual feed intake should not increase individual size and should improve feed efficiency.