title: Impact of a leptin single nucleotide polymorphism and ractopamine hydrochloride on growth and carcass characteristics in finishing steers.
abstract: A total of 2,958 steers (mean initial BW = 549.6 ± 3.88 kg) were used to test for the interactive effects, of leptin R25C genotypes (CC, CT, or TT) and feeding of ractopamine hydrochloride (RH) on growth performance and carcass traits. Before application of the drug, steers were blocked by arrival at the feed yard, genotyped for the leptin SNP, allotted to genotype-specific pens, and assigned randomly within genotype and block to 0 or 28 d of dietary RH. All pens within a block were slaughtered on the same day. Final BW of steers fed RH was 9.1 kg heavier (P < 0.001), and RH-fed steers had greater (P < 0.001) ADG and greater (P = 0.001) HCW than steers not fed RH. Feeding RH did not (P = 0.723) affect DMI but it did increase (P = 0.001) with increased frequency of the T allele (8.62, 8.70, and 8.82 kg/d for CC, CT, and TT, respectively). Consistent with the effect of leptin on DMI, increased frequency of the T allele also positively affected 12th rib fat (P = 0.001) and empty body fat (P = 0.001). Regardless of RH-feeding duration, TT steers produced a greater (P = 0.001) percentage of USDA yield grade (YG) 4 or higher carcasses (6.46 vs. 2.98%) and a lesser (P = 0.023) percentage of YG 1 carcasses (16.0 vs. 21.9%) than CC steers. In addition, RH-fed steers produced a lesser (P = 0.034) percentage of USDA YG 4 or higher carcasses (3.70 vs. 5.31%) and a lesser percentage (P = 0.019) of USDA Choice or higher carcasses (57.5 vs. 62.5%) than steers fed the control diet. Results indicated that leptin R25C genotype impacted most traits associated with fatness, whereas feeding RH for 28 d affected HCW and ADG positively but impacted marbling and USDA quality grades negatively.
authors.affiliation: Department of Animal Science, University of Nebraska-Lincoln, Lincoln 68582-0908 pkononoff2@unl.edu.
authors.forename: P J
authors.initials: PJ
authors.lastname: Kononoff
authors.affiliation: Cactus Research, Amarillo, TX 79106.
authors.forename: P J
authors.initials: PJ
authors.lastname: Defoor
authors.affiliation: Cactus Research, Amarillo, TX 79106.
authors.forename: M J
authors.initials: MJ
authors.lastname: Engler
authors.affiliation: Cactus Research, Amarillo, TX 79106.
authors.forename: R S
authors.initials: RS
authors.lastname: Swingle
authors.affiliation: Quantum Genetix Canada Inc., Saskatoon, SK S7N 3R3, Canada.
authors.forename: S T
authors.initials: ST
authors.lastname: James
authors.affiliation: Quantum Genetix Canada Inc., Saskatoon, SK S7N 3R3, Canada.
authors.forename: F L S
authors.initials: FL
authors.lastname: Marquess
mesh_terms: D019943:Amino Acid Substitution; D000818:Animals; D001823:Body Composition / Q000187:drug effects; D002417:Cattle / Q000254:growth & development*; D019587:Dietary Supplements; D005838:Genotype; D006133:Growth Substances / Q000494:pharmacology*; D020738:Leptin / Q000235:genetics*; D008297:Male; D010627:Phenethylamines / Q000494:pharmacology*; D020641:Polymorphism, Single Nucleotide / Q000235:genetics*; D015430:Weight Gain / Q000187:drug effects
chemical_list: D006133:Growth Substances; D020738:Leptin; D010627:Phenethylamines; C060897:ractopamine
keywords: feedlot cattle; leptin single nucleotide polymorphism; quality grades; ractopamine hydrochloride; yield grades