638 The influence of supplemental zinc and ractopamine hydrochloride on mineral and nitrogen retention of beef steers

Abstract Four hundred and thirty-two beef steers (346.3 ± 63.7 kg BW) were used to determine the effects of Zn source on feedlot cattle fed ractopamine hydrochloride. Cattle were blocked in groups of 54 by BW and housed in 48 pens containing 9 steers per pen. Pens within a weight block were randomly assigned to treatments in a 2 x 3 factorial arrangement, with factors being: 1) 0 or 30.1 mg of ractopamine HCl/kg DM fed during the final 29 days on feed; and 2) Zn source: 90 mg of supplemental Zn/kg DM from ZnSO4; Zn sulfate (67%) + Zn methionine (33%); and Zn from Zn hydroxychloride, fed through the entire feeding period. Cattle were fed a high concentrate finishing diet for 154 d and slaughtered at a commercial abattoir. Average daily gain, DMI, feed efficiency and carcass characteristics were determined after slaughter. Zinc source had no impact on live animal performance. Cattle fed ractopamine HCl had greater (P < 0.01) final BW, greater (P < 0.001) ADG, improved (P < 0.001) G:F, heavier (P < 0.01) HCW, and larger (P < 0.05) longissimus muscle compared to non-ractopamine supplemented steers. There was a Zn source by ractopamine interaction (P < 0.01) for dressing percentage. Cattle receiving ractopamine HCl with Zn hydroxychloride had a greater dressing percentage (P < 0.05) when compared to ractopamine HCl cattle fed other Zn sources. Cattle receiving ractopamine HCl with Zn sulfate had a lesser dressing percentage (P < 0.05) when compared to ractopamine HCl cattle fed other Zn sources. Additional Zn source by ractopamine HCl interactions were not significant. These data indicate that Zn source has minimal impacts on feedlot steer performance and carcass characteristics when supplemented to cattle receiving 0.0 or 30.1 mg of ractopamine HCl/kg DM.

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Effects of voluntary removal of ractopamine hydrochloride (Optaflexx) on live performance and carcass characteristics of beef steers

Translational Animal Science ◽

10.1093/tas/txab047 ◽

2021 ◽

Author(s):

P J Rincker ◽

J B Allen ◽

M Edmonds ◽

M S Brown ◽

J C Kube

Keyword(s):

Dry Matter ◽

Carcass Characteristics ◽

Carcass Weight ◽

Dry Matter Intake ◽

Beef Steers ◽

Live Performance ◽

Meet Residue ◽

Ractopamine Hydrochloride ◽

The Impact ◽

Linear Manner

Abstract There is a lack of consistency across the globe in how countries establish tissue ractopamine residue limits and which residue limits are applied to various tissues, particularly for edible noncarcass tissues. Therefore, some US beef slaughter organizations have recommended a 48-h voluntary removal of ractopamine before slaughter in order to meet residue requirements of specific export countries and maintain international trade. Our objective was to assess the impact of voluntary removal of ractopamine hydrochloride (Optaflexx®; Elanco, Greenfield, IN) up to 8 d before slaughter on growth performance and carcass characteristics. Crossbred beef steers (60 pens of 10 animals/pen) with an initial shrunk body weight (BW) of 611.8 ± 10 kg SEM were fed one of six treatments over 42 d. Treatments included a control that did not receive ractopamine, on-label use of ractopamine (0-d withdrawal), and 2, 4, 6, or 8 d of voluntary removal of ractopamine from feed before slaughter. The start of ractopamine feeding (30.1 mg/kg of diet dry matter for 32 d) was staggered so that blocks could be slaughtered on the same day. Dry matter intake was decreased by 0.5 kg/d when ractopamine was fed with a 0-d withdrawal (P = 0.04) compared to the control, but was not altered (P = 0.56) as the duration of ractopamine removal increased from 0 to 8 d. Final BW, total BW gain, and average daily BW gain were increased by feeding ractopamine with a 0-d withdrawal (P = 0.09) compared to the control, but these variables decreased in a linear manner (P = 0.10) as the duration of removal increased from 0 to 8 d. Gain efficiency was improved by 15% (P < 0.01) by feeding ractopamine with a 0-d withdrawal compared to the control, and gain efficiency decreased linearly (P = 0.06) as the duration of ractopamine removal increased. Approximately 2/3 of the increase in gain efficiency remained after 8 d of removal. Hot carcass weight was increased by 6 kg (P = 0.02) by feeding ractopamine with a 0-d withdrawal compared to the control. Measured carcass characteristics were not altered by ractopamine feeding or by removal before slaughter (P ≥ 0.24). The consequences of voluntary removal of ractopamine up to 8 d before slaughter were a linear decrease in live BW gain (0.64 kg/d), poorer gain efficiency, and numerically lighter carcass weight.

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291 Influence of feeding amino acid complexes of zinc and copper on growth performance and carcass response of finishing steers fed ractopamine hydrochloride

Journal of Animal Science ◽

10.1093/jas/skaa278.392 ◽

2020 ◽

Vol 98 (Supplement_4) ◽

pp. 212-213

Author(s):

Chanda Engel ◽

Gary Tibbetts ◽

Mark Branine

Keyword(s):

Amino Acid ◽

Animal Health ◽

Experimental Unit ◽

Beef Steers ◽

Individual Animal ◽

Acid Complex ◽

Amino Acid Complex ◽

Finishing Steers ◽

Ractopamine Hydrochloride ◽

Eden Prairie

Abstract A 42-d research study evaluated effects of feeding beef steers increasing levels of dietary Zn from Zn methionine (AAC-Zn; ZINPRO, Zinpro Corporation, Eden Prairie, MN) with or without supplemental Cu from Cu amino acid complex (AAC-Cu; Availa Cu, Zinpro Corp.) concurrently with ractopamine hydrochloride (RAC; Optaflexx, Elanco Animal Health, Greenfield, IN). One hundred-twenty steers (mean BW = 624 kg), ≤ 50 d from projected harvest were randomized to three pens (40 steers/pen) equipped with GrowSafe Systems (Calgary AB, Canada) feed bunk technology. Each pen was assigned to one of three treatment diets: 1) basal finishing diet + 30 mg Zn/kg DM from AAC-Zn (CON); 2) basal finishing diet + 90 mg Zn/kg DM from AAC-Zn (AAC-Zn90); or 3) AAC-Zn90 diet + 10 mg Cu/kg DM from AAC-Cu (AAC-Zn/Cu). Following allocation to treatments, cattle were acclimated to pen cohorts and GrowSafe feed bunks for 7 days. All steers were fed 300 mg RAC∙hd-1∙d-1 starting 35 d prior to harvest. Individual feed intake measurements began with RAC feeding and continued for 35 d until cattle were shipped for harvest. Carcass data were collected from each steer. Data were analyzed with individual animal as the experimental unit using PROC MIXED and PROC GLIMMIX procedures of SAS 9.4 (SAS Institute, Cary, NC). Numerically AAC-Zn90 fed cattle had heavier carcass weights than CON and AAC-Zn/Cu. Steers fed AAC-Zn90 had greater (P = 0.02) marbling scores compared to AAC-Zn/Cu. Steers fed AAC-Zn90 had lower backfat thickness (P = 0.02) and numerically greater marbling scores compared to CON. A biphasic program of feeding a lower level of AAC-Zn for the duration of the finishing phase followed by an increased rate of AAC-Zn during RAC feeding may optimize overall live and carcass response and improve total individual animal value.

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