Abstract
The effects of steroidal growth implants alone or in combination with β-adrenergic agonist feed additives have not been studied thoroughly in mutton sheep in South African feedlot conditions. This study investigated the effects of a non-steroidal growth implant zeranol (Ralgro®), alone or in combination with zilpaterol hydrochloride (Zilmax®), on growth performance, carcass characteristics, and selected meat quality traits in 160 SA Mutton Merino ram lambs fed in a commercial feedlot. The experimental design consisted of two Ralgro treatment groups x two Zilmax treatments x two Zilmax feeding periods x 20 animals per treatment group. Lambs were randomly allocated to eight treatment groups, of which one half were implanted with Ralgro after arrival, followed by feed supplementation with Zilmax at two Zilmax feeding periods during the finisher phase, compared with negative control treatments (e.g. no Ralgro or Zilmax; Ralgro + no Zilmax; or no Ralgro + Zilmax). All lambs were fed the grower ration traditionally used by the commercial feedlot, which contained 16.89% crude protein (CP) and 2.94 Mcal/kg dry matter (DM). Zilmax was supplemented in the feed at 40 mg per animal per day and fed for 18 days or 25 days, plus three days withdrawal. Lambs that did not receive the Zilmax treatment were fed the basal diet without Zilmax feed supplementation. Ralgro significantly increased average daily gains (ADG) and cold carcass mass (CCM) of lambs. Lambs supplemented with Zilmax during the finisher phase had higher ADG, greater CCM and increased dressing percentage by ca.1.1% compared with those in the control group. Lambs fed Zilmax for 25 days had higher CCM than those fed for 18 days. The duration of the Zilmax treatment also decreased hide weight, fat thickness and shear force values (tenderness). Zilmax increased ADG and CCM in lambs, particularly if combined with Ralgro implants during the growing phase. The results from this study indicate that the combination of Ralgro implants with Zilmax feed supplementation during the finisher phase had additive effects and increased ADG and CCM of feedlot lambs.Keywords: Growth performance, meat quality, South African Mutton Merino, sheep, Ralgro®, Zilmax®
Highlights
Zilpaterol hydrochloride (Zilmax®) is a beta-adrenergic agonist (β-agonist) that is used commercially as Zilmax
The objective of this study was to investigate the effects of a non-steroidal growth implant (Ralgro), alone or in combination with dietary Zilmax supplementation on growth and carcass characteristics of feedlot lambs
A completely randomized control study was conducted to evaluate the effects of a non-steroidal exogenous growth implant zeranol (Ralgro), alone or in combination with Zilmax feed additive supplemented during the finishing phase on the growth, carcass, and selected meat quality parameters of mutton sheep fattened in typical feedlot conditions (Table 1)
Summary
Zilpaterol hydrochloride (Zilmax®) is a beta-adrenergic agonist (β-agonist) that is used commercially as Zilmax. It is a repartitioning agent and is utilized for its potential to promote growth (Ricks et al, 1984). The benefits of Zilmax supplementation in lambs are similar to those in beef, with increases in growth performance and carcass characteristics (Avendaño-Reyers et al, 2011; Estrada-Angulo et al, 2008; López-Carlos et al, 2011; López-Carlos et al, 2010). Zilmax is not yet available for use in the local mutton industry, and there are still inconsistencies in the effects, use, and efficacy of β-agonist supplementation and growth performance of feedlot lambs (Estrada-Angulo et al, 2008; López-Carlos et al, 2011; Nourozi et al, 2008)
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