Effect of implant strategy and Optaflexx administration on feedlot performance and skeletal muscle β-adrenergic receptor and insulin-like growth factor I mRNA abundance

Feedlot heifers (1,147) weighing 622 lb were used to evaluate the effects of implant strategy and Optaflexx administration. Implant treatments included Revalor-200 (R200) at arrival, or Revalor-IH at arrival and reimplantation with Finaplix-H on day 58 (RF). Optaflexx (200 mg/heifer daily of ractopamine-HCl) was fed the last 28 days. Treatments were randomly assigned to 16 pens. After 182 days, heifers were slaughtered, at which time carcass data were obtained and semimembranosus muscle tissue was excised for RNA isolation. Optaflexx administration significantly increased average daily gain (0.7 lb/day), feed efficiency (3%), hot carcass weight (10.5 lb), and ribeye area (0.42 square inches); decreased back fat thickness; and improved yield grade. There was no significant treatment effect on the expression of β1-adrenergic receptor (AR) mRNA, but there was a tendency for Optaflexx feeding to increase β2-AR mRNA concentrations. For β3-AR mRNA, Optaflexx treatment numerically increased β3-AR mRNA in heifers implanted with R200, but significantly decreased expression in heifers implanted with RF. Optaflexx also significantly decreased IGF-I mRNA in heifers implanted with RF, but numerically increased IGF-I mRNA in heifers implanted with R200. This data aids our understanding of the interaction between steroidal implants and Optaflexx in feedlot heifers. Knowledge about the modes of action of various growth promotants will aid in designing growth promotion strategies to enhance the efficiency of lean tissue deposition in feedlot cattle

Effect of Optaflexx and days on feed on feedlot performance, carcass characteristics, and skeletal muscle gene expression in yearling steers

Two-thousand two-hundred fifty-two yearling steers (690 lb) were used to evaluate the effects of Optaflexx and days on feed on finishing steer performance and carcass characteristics. Treatment groups included serial harvest dates of 150, 171, or 192 days. Within each harvest date, steers either received Optaflexx (200 mg/steer daily of ractopamine-HCl) for the final 28 days, or did not receive Optaflexx. All steers were initially implanted with Revalor-IS and were re-implanted with Revalor-S after 75 days on feed. At harvest, muscle samples from the inside round were obtained for mRNA analysis of the β- adrenergic receptors (AR). Optaflexx increased daily gains, hot carcass weight, and ribeye area, and improved feed efficiency. Optaflexx did not affect dressing percentage, USDA yield grade, or quality grade. Optaflexx did not change overall feed intake across the entire feeding period, but feed intake was increased during the 28-day period that steers received Optaflexx. As expected, greater days on feed decreased daily gains, overall feed intake, and the number of yield grade 1 and 2 carcasses, and worsened feed efficiency. Also, greater days on feed increased hot carcass weight, dressing percentage, and the number of prime and choice carcasses, as well as the number of yield grade 4 and 5 carcasses. Increasing days on feed decreased the abundance of mRNA for β1-AR and β3-AR, and increased the abundance of β2-AR mRNA. Optaflexx had no effect on abundance of mRNA for β1-AR or β3-AR, but it increased the abundance of mRNA for β2-AR. Optaflexx may affect expression of the β2-AR gene in skeletal muscle, which could impact the performance responses to Optaflexx feeding in steers

Two Types of Planning in Neighborhoods

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/68338/2/10.1177_0739456X8400300209.pd

Effect of Zilpaterol-HCl (Zilmax) on implanted and non-implanted feedlot steer performance and carcass characteristics

Zilpaterol-HCl (Zilmax) is a β2-adrenergic receptor agonist approved as a growth promotant in feedlot cattle for use during the last 20 to 40 days prior to harvest. It is orally active and improves performance and total body lean tissue. The recommended dosage is 7.6 grams per ton of feed on a 100% dry matter basis. Steroidal implants are used in feedlot animals to improve average daily gain, feed efficiency, and total lean tissue deposition. Little is known about how Zilmax and steroidal implants influence growth performance when used in combination. Our objective was to evaluate performance of steers administered Zilmax in combination with the steroidal implant, Revalor1-S

Effects of extended Zilpaterol-HCl withdrawal on performance and carcass traits of finishing beef heifers

Zilpaterol-HCl (Zilmax; Intervet/Schering-Plough Animal Health, Millsboro; DE) is an orally active β2-adrenergic agonist that is approved for use in feedlot cattle at the rate of 7.56 g/ton of diet dry matter for the final 20 to 40 days on feed. The minimum withdrawal time for Zilmax is 3 days. Zilmax increases hot carcass weight and dressing percentage, primarily as a result of increasing lean muscle mass and decreasing body fat. Zilmax also decreases marbling and increases shear-force values (i.e., less tender) of steaks. This study was conducted to determine whether the benefits of Zilmax would be retained with longer withdrawal times while overcoming undesirable effects on shear force and marbling

Supplementing feedlot steers and heifers with Zilmax increases proportions of strip loin, chuck clod, and top sirloin steaks exceeding Warner-Bratzler shear force thresholds, whereas aging moderates this effect

Ractopamine hydrochloride (Elanco, Greenfield, IN) and Zilmax (zilpaterol hydrochloride; Intervet/Schering-Plough, Millsboro, DE) are β-adrenergic agonists approved in the United States and several other countries to increase growth rate, improve efficiency of feed utilization, and increase carcass meat yield. Zilmax has been shown to improve feed efficiency by 26% and increase hot carcass weight, longissimus muscle area, and meat yield. However, a few studies have shown that Zilmax significantly increased Warner-Bratzler shear force values (decreased tenderness). The objectives of our research were to determine the effects of supplementing feedlot diets of steers and heifers with Zilmax for 0, 20, 30, or 40 days before harvest and the subsequent effects of 7, 14, and 21 days of aging on tenderness of steer and heifer Longissimus lumborum (from strip loins) and heifer Triceps brachii (from chuck clods) and Gluteus medius (from top sirloin butts) muscles