The influence of supplemental Zn-amino acid complex and ractopamine hydrochloride feeding duration on growth performance and carcass characteristics of finishing beef cattle

Abstract

Previous research indicates that finishing steer ADG and G:F increases linearly with increasing dietary Zn-amino acid complex (ZnAA) supplementation in cattle fed ractopamine hydrochloride (RAC). The objective of this study was to determine the influence of supplemental Zn-amino acid complex on growth performance and carcass characteristics of finishing steers fed RAC for 0, 28, or 42 d prior to harvest. This study was organized as 2 groups (GRP) of steers fed concurrently, for 91 (GRP 1) or 84 d (GRP 2). A total of 324 steers (463 ± 23.4 kg) were fed a corn-based finishing diet supplemented with 60 mg Zn/kg diet DM (as ZnSO). Steers were blocked by weight to pens of 6 steers, and assigned to receive either 0 (CON) or 60 mg supplemental Zn/kg DM from ZnAA ( = 27 pens per treatment). Receiving ZnAA for 49 (GRP 1) or 42 d (GRP 2) prior to start of RAC feeding had no impact on growth of steers ≥ 0.19). Forty-two d prior to harvest, pens were equally assigned within CON or ZnAA treatments to receive RAC at 300 mg∙steer∙d for 0 (NoRAC), 28 (28RAC), or 42 d (42RAC) prior to harvest, creating 6 final treatments ( = 9 pens per treatment). All steers within a GRP were harvested on the same day. Pen was the experimental unit, and the statistical model included the fixed effects of ZnAA, RAC, and block nested within GRP, and the random effect of pen. Ractopamine hydrochloride supplementation increased carcass-adjusted ADG, final BW, HCW, and ribeye area ( ≤ 0.007). There was an effect of ZnAA within 28RAC and 42RAC where carcass-adjusted ADG ( ≤ 0.10), and final BW and HCW ( ≤ 0.05) were greater in ZnAA supplemented vs. CON steers, and 28RAC steers supplemented with ZnAA had improved overall carcass-adjusted G:F relative to CON steers ( = 0.04). However, when steers did not receive RAC there was no effect of ZnAA on final BW, ADG, or HCW ( ≥ 0.78). Additionally, ZnAA supplementation had no effect on the difference in performance between steers supplemented with RAC for 28 vs. 42 d ( 0.21). In conclusion, under the conditions of this study supplemental ZnAA did not prevent the diminished response to RAC as days on RAC increased from 28 to 42. However, there appears to be a synergistic effect of ZnAA on RAC-induced cattle growth, as supplementing 60 mg Zn/kg DM from ZnAA to cattle fed RAC improved overall growth and HCW.

Roughage-free finishing diet based on whole corn grain and a mixture of additives for Nellore heifers

“…Furthermore, the values were within the standards observed in studies using high-grain diets for finishing beef cattle (Bohrer et al, 2014;Cônsolo et al, 2014Cônsolo et al, , 2015Genther-Schroeder et al, 2016;Contadini et al, 2017). It is worth noting that the results for rump fat were higher than those for fat thickness, since the deposition of adipose tissue begins from the end towards the middle of the carcass.…”

“…More recently, Genther-Schroeder et al (2016) worked with Angus crossbred steers in the finishing phase fed 88 mg kg −1 (diet DM) of a Zn amino-acid complex and reported no effects on DMI, ADG, gain:fat ratio, or carcass traits. Zhou et al (2017), on the other hand, reported greater DMI and milk yield in peripartum dairy cows fed diet supplemented with methionine (at 0.08 g kg −1 of DM), but no effect for choline (at 60 g day −1 ) supplementation.…”

Effects of supplemental zinc sulfate on growth performance, carcass characteristics, and antimicrobial resistance in feedlot heifers1

“…Our study indicated Zn supplementation up to 90 mg/kg DM (141.35 mg/kg total dietary Zn) minimally impacted carcass traits; however, Van Bibber-Krueger et al 2017observed an interaction between Zn and ractopamine hydrochloride (RH), where supplementing 100 mg Zn/kg DM decreased ribeye area and increased yield grade, but these effects were no longer observed after supplementing heifers with RH (Van Bibber-Krueger et al, 2017). These same results were not observed in steers fed 85 or 150 mg/ kg (60 mg Zn/kg DM from Zn amino acid complex) total dietary Zn (Genther-Schroeder et al, 2016). The lack of congruence among studies with steers and heifers may suggest different Zn requirements for males vs. females.…”

Effects of increasing supplemental dietary Zn concentration on growth performance and carcass characteristics in finishing steers fed ractopamine hydrochloride

“…In past work, we have noted that increasing ZnAA supplementation from 0 to 90 mg Zn/kg DM in steers supplemented with RAC at 300 mg•steer −1 •day −1 day linearly increased ADG (Genther-Schroeder et al, 2016a). A follow-up study reported that while 60 mg Zn/kg DM from ZnAA did not prevent the diminishing response to RAC typically seen as days on RAC increases from 28 to 42 d (Abney et al, 2007), ZnAA supplementation once again increased performance of yearlings fed RAC (Genther-Schroeder et al, 2016b). In this study, supplemental Zn from ZnSO 4 or ZnAA had minimal effects on growth performance in steers fed RAC at 300 mg•steer −1 •day −1 day.…”

“…Zinc (Zn) is essential for growth in animals. Research data from large pen feedlot studies (Larson and Branine, 2015) and previous university studies (Genther-Schroeder et al, 2016a, 2016b) have indicated that feeding Zn beyond the requirement of finishing steers may result in additional hot carcass weight (HCW) when cattle are fed ractopamine hydrochloride (RAC). However, this response may be related to Zn source and concentration, as others have not reported a relationship between Zn supplementation and RAC (Bohrer et al, 2014;Edenburn et al, 2016).…”