title: Failure of photoperiod to alter body growth and carcass composition in beef steers.
abstract: In each of two experiments, 70 crossbred steers were blocked by BW and assigned to initial slaughter groups or to treatments in a 2 x 2 design. In Exp. 1, treatments were 168 d of photoperiod (8 h of light [L]:16 h of dark [D] or 16L:8D) and plane of nutrition (high energy [HPN] or low energy [LPN]). On d -22, 67 and 155, blood was sampled every 20 min for 8 h. Relative to LPN, HPN increased (P less than .01) ADG by 28%, carcass weight by 26% and accretion of carcass fat by 109% and carcass protein by 20%. On d 155, compared with LPN, HPN increased (P less than .01) serum insulin (INS; 1.09 vs .64 ng/ml) and lowered (P less than .05) growth hormone (GH; 2.14 vs 3.70 ng/ml), but prolactin was not affected. Photoperiod did not affect BW gains, carcass composition or serum hormones. In Exp. 2, treatments were 113 d of photoperiod (8L:16D or 16L:8D) and Synovex-S implant (presence [IMP] or absence [NONIMP]). On d 93, blood was sampled every 30 min for 10 h. Relative to NONIMP, IMP increased (P less than .01) ADG by 12% and accretion of carcass protein by 16%. Implants did not affect carcass weight or accretion of fat. Compared with NONIMP, IMP increased (P less than .05) GH (3.16 vs 2.39 ng/ml) and INS (.68 vs .46 ng/ml) but did not affect PRL. Photoperiod did not affect BW gain, carcass composition or serum hormones. We conclude that photoperiod fails to influence growth and carcass composition of steers.
authors.affiliation: Dept. of Anim. Sci., Michigan State University, East Lansing 48824-1225.
authors.forename: S A
authors.initials: SA
authors.lastname: Zinn
authors.forename: L T
authors.initials: LT
authors.lastname: Chapin
authors.forename: W J
authors.initials: WJ
authors.lastname: Enright
authors.forename: H A
authors.initials: HA
authors.lastname: Tucker
mesh_terms: D000704:Analysis of Variance; D000821:Animal Feed; D000824:Animal Nutritional Physiological Phenomena; D000818:Animals; D001823:Body Composition; D002417:Cattle / Q000254:growth & development*; D004435:Eating; D013006:Growth Hormone / Q000097:blood; D007328:Insulin / Q000097:blood; D008027:Light; D008297:Male; D011388:Prolactin / Q000097:blood; D015430:Weight Gain
chemical_list: D007328:Insulin; D011388:Prolactin; D013006:Growth Hormone