Effects of zilpaterol hydrochloride and implants in beef heifers I: feedlot performance, carcass characteristics, and intramyocellular lipid accumulation

Abstract Text: To assess the effects of zilpaterol hydrochloride (ZH) supplementation and implants on feedlot performance, carcass characteristics, and intramyocellular lipid accumulation, 33 crossbred yearling heifers were blocked by initial BW (464 ± 2 kg) and randomly assigned to three treatments consisting of no implant or ZH (CON); Component TE-200 implant on day 1 of the study, no ZH (IMP); implant and 8.3 ppm of ZH for 21 days with a 3-d withdrawal period (ZIL). Animals were fed a finishing ration once daily, ad libitum, with bunks managed to leave a minimum amount of unconsumed feed. After a 75-d feeding period, cattle were harvested at a commercial abattoir. At 36 h postmortem, carcass characteristics were collected and boneless strip loins were transported to the Kansas State University Meats Laboratory. To assess intramyocellular lipid content, 13^th-rib LM samples were cryopreserved, cut into 5-µm sections, and exposed to BODIPY 493-503 staining.  Final BW, DMI, ADG, and KPH were not affected by treatment (P>0.30).  The IMP and ZIL heifers had greater G:F compared to CON (P=0.04).  The ZIL heifers had greater (P<0.01) HCW than CON heifers and IMP heifers tended to have greater (P=0.07) HCW than CON heifers. The ZIL heifers had greater (P=0.03) dressing percent (DP) compared to CON heifers, and IMP heifers tended to have a greater (P=0.07) DP than CON heifers.  Heifers fed ZIL heifers also had greater LM area (P=0.01) compared to CON heifers, and IMP heifers tended to have greater (P=0.06) LM area than CON heifers. Heifers from the CON treatment had greater (P=0.01) amounts of backfat than ZIL heifers, and CON heifers tended to have more (P=0.09) backfat than IMP heifers. The CON heifers had greater (P=0.04) marbling than IMP heifers, but ZIL carcasses did not differ in marbling between the two other treatments (P>0.14).  For LM area, backfat, and marbling, ZIL and IMP carcasses did not differ from one another (P>0.37). Additionally, IMP heifers contained a greater (P=0.04) percentage of muscle fibers with intramyocellular lipid droplets than ZIL heifers.  The CON heifers tended to have a greater (P=0.08) percentage of muscle fibers that contained intramyocellular lipid droplets than ZIL heifers.  These data suggest that implanting cattle and ZH supplementation increase efficiency of lean meat production while decreasing adipose tissue accumulation in all depots except KPH.

Keywords:

Implants, Zilpaterol Hydrochloride, Intramyocellular Lipids