Residual feed intake, breed of sire and dam, and individual sire affect performance and carcass characteristics and rates of back fat and intramuscular fat of feedlot steers

One hundred and fifty eight Angus (A), Simmental (S), Angus-Simmental, and Simmental-Angus steers across two years across were classified into high (H), medium (M), and low (L) residual feed intake (RFI) groups. Steers in the H RFI group ate 1 kg more of DMI (P < 0.05) per day than steers in the L and M RFI group. Steers in the L RFI group had the highest feed efficiency by gaining 15% and 22% more per kg of feed than steers in the M and H RFI groups, respectively. Steers in the L RFI group had a phenotypic advantage for growth rate of 0.20 kg/d more (P < 0.05) than steers in the M and H RFI groups. Steers in the H RFI group had carcasses with more kidney, pelvic, and heart fat than carcasses of steers in the L and M RFI group. No differences were observed (P = 0.89) among RFI groups for meat tenderness using the Warner Bratzler shear force method. Our findings confirmed that management practices such as crossbreeding, and selection for RFI will reduce intake requirements of feedlot steers without affecting growth rate.;Six hundred and four steers from Angus (A), Simmental (S), Simmental-Angus (SA), 75% Simmental (75S) breeds was used across four different years from four separate ranches. Dietary treatments were: 75% dry rolled corn + 25% corn silage (75DRC), 50% dry rolled corn + 25% dry distillers grains with soluble (25DDGS), 40% dry distillers grains with soluble + 35% soy hulls (40DDGS), and 40% fresh wet distillers grains + 35% soy hulls (40FWDG); all replicated during the four years. Steers fed 40DDGS had the heaviest carcass (P < 0.05) with 16 kg more of HCW than steers fed the other diets. Carcasses of steers fed co-products had 0.21 cm more (P < 0.05) of BF than carcasses of steers fed 75 DRC. Carcasses of steers fed 75DRC diet had the lowest (P < 0.05) calculated yield grade (CYG). Steers fed 40DDGS exhibited the highest rate (P < 0.05) of intramuscular fat (IM) deposition. Rates of ultrasonic BF and IM deposition differed significantly among breed of sires. Steers sired by A deposited back fat 14% higher (P < 0.05) than steers sired by SA and 75S. Steers sired by A bulls had the highest (P < 0.05) rate of IM deposition. The rate of marbling over back fat was similar (P > 0.05) among breed of sires. This study confirms that there is no unique feature in the feedlot sector that could address the many biological and market challenges.;Progeny from sires with breed composition of Angus (n = 4 sires, A), Simmental (n = 8 sires, S), Simmental-Angus (n = 5 sires, SA), and 75% Simmental (n = 3 sires, QS) were used. Sires were assigned a random number followed by a letter indicating breed composition for identification purposes. High RFI (H RFI) group consisted of two A sires and one S sire. Low RFI (L RFI) group consisted of four S and two SA sires. For the medium RFI (M RFI) group, three S sires, three SA sires, three QS sires, and two A sires classified within this group. In average, sires RFI was 0.44 kg/d, -0.06 kg/d, and -0.48 kg/d for H RFI, M RFI, and L RFI group; respectively. Sire "3-S" had the highest estimated RFI value of 0.50 kg/d. Sire "15-S" exhibited the lowest RFI value. Initial weight differed (P = 0.0044) among RFI group of sires. Medium RFI Sire "4-QS" had the heaviest initial weight whereas, H RFI Sire "2-A" had the lightest initial weight with a difference of 58 kg (P < 0.05). The rate of ultrasonic marbling deposition was influenced (P < 0.0001) by sire and RFI classification. Sires classified as M RFI had slower rates than H and L RFI sires. Average rates of ultrasonic marbling (1/100*d-1) were 1.22 for H RFI sires and 1.23 for L RFI sires. Medium RFI sires had an average rate of 1.19 (1/100*d-1). Sire and RFI classification did not influence (P = 0.0948) the rate of marbling over a standard back fat endpoint of 1 cm. These suggest that selection for high rates of marbling deposition relative to back fat should maintain acceptable quality while allowing a high retail yield. Results from this study indicate that individual sire RFI is a potential selection tool to improve profitability by improving feed efficiency in the beef cattle industry. (Abstract shortened by UMI.)...