The effects of different zilpaterol hydrochloride feed supplements and extended ageing periods on the meat quality of feedlot bulls

Abstract

The aim of this study was to evaluate the possible effects of two different zilpaterol hydrochloride (ZH) beta-agonists - with further focus being placed on the viability of the generic Grofactor® product when compared to industry standard Zilmax® - on the carcass and meat quality characteristics of typical South African feedlot bulls (Bos taurus crosses). Additionally, meat quality attributes over an extended ageing period of up to 120 days were studied. The first objective was to evaluate the effects of dietary ZH-supplementation during the finishing period of feedlot bulls with either Zilmax® or Grofactor® on carcass characteristics namely, hot carcass mass (HCM), dressing percentage (DR%), carcass classification score, carcass compaction index (CCI), subcutaneous fat thickness (FT), carcass composition (bone: muscle: fat), as well as carcass pH and -temperature profiles from 45min to 24hours postmortem. The second objective was to critically evaluate the effects of feed ZH supplementation of feedlot bulls with either Zilmax® or Grofactor® on specific meat quality characteristics such as tenderness (physically measured with Warner-Bratzler shear force [WBSF] values), colour attributes (L*, a*, and b* obtained with a colorimeter as well as chroma and hue), drip losses and cooking losses over an extended ageing period of up to 120 days. The completely randomised control study consisted of 3 experimental groups receiving a finisher ration during the 30-day feedlot finishing period (with a subsequent 3-day withdrawal period); the first, a negative control (CT) received no ZH-supplementation added to the basal diet, second; ZH-based Zilmax® feed supplementation (ZM) and lastly ZH-based Grofactor® feed supplementation (GF). ZH-supplementation was mixed into the basal finishing ration at a recommended concentration of 105g ZH/ton. Each treatment was then randomly allocated to 3 replicates and fed from the first day of the finishing period (D0) for 30 days. The replicates amounted to each treatment being administered to 3 pens x 50 animals/pen = 150 animals. Due to the high costs of proximate and meat sample analyses, only 38 bull carcasses were randomly sub-selected from each treatment to be evaluated further (3 treatments x 38 bull carcasses = 114 carcasses and subsequent meat samples evaluated). No significant differences were observed between the two ZH-based molecules (ZM vs. GF) for any measured characteristic. Grofactor® performed similar to Zilmax®, supporting the viability of the generic ZH-supplementation with Grofactor®. Although ZH-supplementation did not yield significantly heavier live masses than CT over the finishing period, increasing the length of finishing period ZHsupplementation, improved the effect of ZH-supplementation i.e., after two weeks ZH bulls were 3kg heavier than CT (P = 0.64) and final slaughter masses differed with ZH weighing 5.4kg heavier than CT (P = 0.12). Compared to CT carcasses, ZH-supplemented bull carcasses were 8kg heavier (P = 0.001; η2 = 0.09), tended to have 0.9% higher DR% (P = 0.07; η2 = 0.03) and increased CCI (2.2 vs. 2.1; P < 0.001 and η2 = 0.13). The ZH energy repartitioning mechanism successfully increased carcass muscle% composition with 2.0% (P = 0.02; η2 = 0.05) and decreased the fat% composition with 1.8% (P = 0.05; η2 = 0.03) when compared to CT carcasses. ZH-supplementation did significantly decrease meat tenderness measurements of supplemented bulls when compared to CT on all ageing days (P < 0.05; η2 = 0.24). The WBSF values between CT and ZH differed with ZH being 0.5-0.8kg less tender for all ageing days. Post-mortem ageing did however significantly improve the decreased meat tenderness (P < 0.001; η2 = 0.38). ZH supplementation had no significant effects on any other meat quality characteristics. Post-mortem ageing of meat samples had significant effects on all meat quality characteristics investigated (P < 0.001; η2 > 0.30). And all meat quality characteristics had a trend to sharply decrease or increase in values measured from day 56 to 120. Meat colour lightness (L*) values fluctuated between increasing and decreasing from day 3 to 56, but ultimately increased from 39.7 on day 3 to 43.2 on day 56, only to have a drastic decrease to 36.0 on day 120 (P < 0.001; η2 = 032). The chroma values also fluctuated between increasing and decreasing from day 3 to 56, but ultimately decreased from 22.3 on day 3 to 17.1 on day 56, to then have a drastic decrease to 13.1 on day 120 (P < 0.001; η2 = 0.50). Hue angles drastically decreased from 0.4 on day 3 to 0.1 on day 7, then increased to 0.3 and remained constant up until day 120 (P < 0.001; η2 = 0.40). Interestingly ZH meat samples insignificantly had a slightly redder hue angle than CT. Meat drip loss, cooking loss and tenderness (as indicated by decreasing WBSF values) increased from day 7 (4.1%, 28.2% and 6.8kg, respectively) up to 56 days of ageing (10.8%, 30.1% and 4.3kg, respectively), then decreased on 120 days of ageing (8.9%, 22.1% and 4.6kg, respectively). Further studies would be recommended on the exact mechanisms which influence the tendency of post-mortem meat sample ageing to decrease in meat quality characteristic values from day 56 to day 120.