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Small Ruminant Research 117 (2014) 142–150

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Small Ruminant Research

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Effect of zilpaterol hydrochloride on growth performance andcarcass characteristics of wether goats

M.A. López-Carlosa, J.I. Aguilera-Sotoa,∗, R.G. Ramírezb, H. Rodrígueza,O. Carrillo-Muroa,b, F. Méndez-Llorentea,b

a Unidad Académica de Medicina Veterinaria y Zootecnia, Universidad Autónoma de Zacatecas, Carretera PanamericanaZacatecas-Fresnillo Km 31.5, Gral. Enrique Estrada, Zacatecas 98560, Mexicob Facultad de Ciencias Biológicas, Universidad Autónoma de Nuevo León, Ave. Universidad S/N, Cd. Universitaria, San Nicolás de losGarza, Nuevo León 66450, Mexico

a r t i c l e i n f o

Article history:Received 11 August 2013Received in revised form 8 December 2013Accepted 30 December 2013Available online 7 January 2014

Keywords:Wether goatsZilpaterolGrowth performanceCarcass characteristics

a b s t r a c t

Zilpaterol hydrochloride (ZH) supplementation was evaluated on performance of growinggoats for the last 42 days before slaughter. Forty-eight Anglo-Nubian × Criollo animals (12per treatment) were randomly assigned to one of four treatments (ZH at daily doses of0.0, 0.1, 0.2 or 0.3 mg/kg of BW in diet) in a complete block design. Basal diet contained16.3% CP and 2.5 Mcal/kg ME. The ZH supplementation at doses of 0.1, 0.2 and 0.3 mg/kgof BW increased ADG by 22.1, 54.0 and 56.6%, and gain/feed ratio by 20.0, 40.0 and 60.0%,respectively. The DMI (g/kg of BW0.75) increased quadratically (P = 0.037). Carcass weightand dressing percentage (DP) augmented linearly (P ≤ 0.031) as level of ZH increased indiet. The ZH supplementation increased (P ≤ 0.023) longissimus muscle area (LM) and legperimeter (LP) with a linear improvement (P < 0.001) of LM area by 12.2% and 21.0% as ZHlevel increased in diet. The neck perimeter (NP) observed a quadratic trend (P < 0.035) withgreater values at 0.1 and 0.2 mg/kg of ZH. For each increment of 0.1 mg/kg in the ZH level,the percentage of fat in kidney, heart and pelvis tended to decrease by 4% (P = 0.089). Othercarcass characteristics were not significantly affected (P ≥ 0.311) by ZH administration, buttended to reduce (P ≤ 0.094) redness (a*) and chroma (C*) values in the longissimus mus-cle. It was observed a linear tendency to diminish pH (P = 0.072). However, no differences(P > 0.05) or trends (P > 0.10) were detected on purge loss (PL) or cooking loss (CKL). Growthdifferences between wether goats fed ZH doses of 0.2 or 0.3 mg/kg of BW were small, andtherefore lower dose of 0.2 mg/kg of BW seems enough to enhance growth. Moreover,the carcass characteristics showed minor differences between levels of ZH supplemen-tation, and therefore could be considered that the lower dose of 0.1 mg/kg of BW of ZHwas sufficient to improve these traits. It is concluded that addition of ZH to diets of wethergoats increased growth performance and carcass characteristics in a similar manner to thatreported for cattle and sheep.

© 2014 Elsevier B.V. All rights reserved.

∗ Corresponding author. Tel.: +52 478 9850202/492 1378304.E-mail addresses: aguileraivan@yahoo.com.mx,

jairo121974@yahoo.com.mx (J.I. Aguilera-Soto).

1. Introduction

The goat meat is an important source of nutrientsfor the consumers, especially in the developing countries(Devendra, 2010). It has been reported that the world popu-lation of goats is about 875.5 million head, and over the past30 years is the livestock species with the greatest annualgrowth rate (15.9 million head), in comparison to cattle (5.6

0921-4488/$ – see front matter © 2014 Elsevier B.V. All rights reserved.http://dx.doi.org/10.1016/j.smallrumres.2013.12.035

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million head), pigs (5.5 million head) or sheep (−3.4 mil-lion head). Over 95% of goat population is concentrated indeveloping countries, especially in Asia (61.6%) and Africa(31.6%), with the largest stocks in India (157.0 million head)and China (142.2 million head). Brazil (9.4 million head)and Mexico (9.0 million head) are the countries with thelargest number of goats in America (FAOSTAT, 2013).

From a health perspective, the consumption of goatmeat is recommended because of its lower content ofsaturated fat (Webb and O’Neill, 2008) and greater con-tent of iron, thiamine and riboflavin compared to meatfrom other farm animal species (Johnson et al., 1995). Goatmeat attributes are concordant with present day consumerdemands for leaner and nutritious meat (Webb et al., 2005);nevertheless, juiciness, tenderness, and texture are char-acteristics that goat meat must fulfill in order to achieveconsumer satisfaction (Grunert et al., 2004).

Moreover, the specific odour and minor tenderness ofgoat meat are two important drawbacks that negativelyaffect its consumption. An alternative is castration of malekids before puberty and feeding with high-energy diets,in order to reduce odour and improve meat flavour andtenderness (Webb et al., 2005). However, consumer accept-ability could be affected due to the higher fat content inmeat (Goetsch et al., 2011).

Metabolic modifiers are compounds that improve theproductivity of commercially important domestic ani-mals, by improving their productive efficiency, increasingmuscle mass and concurrently decreasing carcass fat(Dikeman, 2007; NRC, 1994; Sillence, 2004). One ofthese compounds are the �-adrenergic agonists (�-AA) orphenethanolamines, which are orally active synthetic com-pounds that reduce adipose tissue deposition and increasemuscle mass by stimulating �-adrenergic receptors (�–AR)present on the surface of almost every type of mammaliancell (Johnson and Chung, 2007).

Zilpaterol hydrochloride (ZH) is a �-AA compoundapproved for use in animal feed in Brazil, México, UnitedStates and South Africa, whose effects on growth perfor-mance and carcass composition have been widely studiedin feedlot cattle (Avendano-Reyes et al., 2006; Delmoreet al., 2010; Elam et al., 2009; Rathmann et al., 2012), andsheep (Aguilera-Soto et al., 2008; Estrada-Angulo et al.,2008; López-Carlos et al., 2010, 2011, 2012; Macías-Cruzet al., 2013; Robles-Estrada et al., 2009). As in cattle andsheep, it is hypothesized that this compound could improvegrowth performance and carcass characteristics by increas-ing feed efficiency and reducing excessive fat in wethergoats under feedlot conditions; however, to date thereare no scientific reports for �-AA supplemented in goatsdiet.

The objectives of this study were to evaluate the growthperformance and carcass characteristics of wether goatssupplemented with ZH in diet for the last 42 days beforeslaughter.

2. Material and methods

The experiment was conducted in the Small RuminantExperimental Center of the Faculty of Veterinary Medicineand Animal Science of the Autonomous University of

Table 1Composition of diet offered to wether goats during the 42 days prior toslaughter.a

Item %

IngredientAlfalfa hay 32.0Oat hay 26.7Ground yellow corn 27.9Cotton seed meal 12.0Mineral premixb 1.4

Chemical compositionc,d

Dry matter, % 89.1Crude protein, % 16.3Total digestible nutrients, % 69.4Digestible energy (Mcal/kg DM) 3.0Metabolizable energy (Mcal/kg DM) 2.5Neutral detergent fiber, % 40.4Acid detergent fiber, % 24.3Ca, % 1.0P, % 0.5Crude fat, % 2.8

a As fed basis.b The mineral premix contained the following (DM basis): 50.0% lime-

stone, 35.7% sodium bicarbonate, and 14.3% sodium phosphate.c Values except DM are expressed on a DM basisd Analyzed values, except for TND, DE and ME that were calculated from

NRC (2007) feed composition tables.

Zacatecas, México (north-central México). Research proto-cols, animal care, and management procedures were madein accordance with approved local official techniques ofanimal care (NOM-051-ZOO-1995: Humanitarian careof animals during mobilization of animals; NOM-024-ZOO-1995: Animal health stipulations and characteristicsduring transportation of animals; NOM-033-ZOO-1995:Humanitarian sacrifice of domestic and wild animals).

2.1. Animals, housing and management

Sixty Anglo-Nubian × Criollo wether goats born in Mayand June of 2010 were acquired from a local flock at approx-imately 4 to 5 months of age and weaned 1 month earlier.Upon arrival, wethers were randomly assigned to groups of10 individuals per pen, identified with a sequentially num-bered ear tag, dewormed (Cydectin®, Fort Dodge AnimalHealth, México), and vaccinated against Clostridium spp.and Pasteurella spp. (Bobact 8, Intervet, México).

Wethers were initially fed with a mixture of good qual-ity alfalfa and oat hay during first week, and then weregradually adapted to consume the basal diet for the next2 weeks. The basal diet (16.3% CP and 2.5 Mcal/kg ME ona DM basis, Table 1) consisted of approximately 60% for-age (mixture of alfalfa and oat hay) and 40% concentrate(corn grain, cottonseed meal, and a mineral premix) andwas offered ad libitum at approximately 110% of consump-tion (as fed basis) from the previous d in 3 daily meals at07:00, 14:00 and 19:00 h.

Animals were fed with the basal diet during 4 weeksmore, and then 48 wethers were selected from the orig-inal group based on criteria of healthy appearance anduniformity of general condition. Wethers were ranked byweight and divided into three blocks (block 1 = 27.6 ± 1.1,block 2 = 25.1 ± 1.0, block 3 = 22.3 ± 1.0 kg; values representmeans ± SD) of 16 wethers each, and randomly assigned

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within block to four pens (four wethers in each pen), for atotal of 12 pens. Pens were roofed and with cement-floors(2.5 m × 3 m), and equipped with 1.5 m metallic fence-line,feed bunk and automatic waterers.

2.2. Treatments

Pens were randomly assigned within block to one offour dietary treatments consisted of the basal finishingdiet (control) or supplemented with zilpaterol hydrochlo-ride (ZH, Zilmax, Intervet, Mexico City, México) at dailydoses 0.1, 0.2 and 0.3 mg/kg of BW for the last 6 weeksbefore slaughter. Daily dosage of ZH was adjusted weeklybased on BW and feed consumed the previous week. ZHwas withdrawn from the ration 72 h before slaughter. Toaid slaughter procedures and carcass evaluation, and in anattempt to reach a target slaughter weight of 30–32 kg ofBW, each block was initiated in the experimental phasewith 3 weeks of difference, starting with the block of heavi-est wethers.

2.3. Growth performance data collection

Wether goats were individually weighed at the begin-ning (day 0) and every week until the end (day 42) of theexperimental period. The weighing procedure was carriedout before the morning meal (06:00 h) using an electronicscale (EziWeigh1, Tru-test Ltd., New-Zealand). Feed offeredand rejected were weighed and registered daily. To avoidan excessive rejection, the feed offered was adjusted daily,based on consumption of the previous day plus 5%. A sam-ple of feed rejected was collected once a week and dried ina forced-air oven at 100 ◦C for 24 h to determine DM con-tent, and used to estimate the corrected dry matter intake(DMI) (as-fed intake of feed multiplied by percentage DM).The corrected DMI by pen was divided by the number ofanimals in the pen to determine the average DMI/wether.The gain/feed ratio (G:F) was calculated by pen as kg weightgain/kg feed intake.

2.4. Slaughter procedure and carcass data collection

At the end of the 6 weeks trial period, wethers werefed with basal diet without ZH during 3 days previousto slaughter (withdrawal period from ZH). Wethers wereloaded at 07:00 h and transported less than 0.5 km to theabattoir of the Faculty of Veterinary Medicine and AnimalScience of the Autonomous University of Zacatecas. Uponarrival to the abattoir and immediately before slaughter,the wethers were weighed (pre-slaughter BW) for furthercalculations.

The wethers were slaughtered with a standard proto-col of immobilization via captive bolt stunning followedby exsanguination. Hot carcass weight (HCW) and thenon-carcass components skin, head, liver, hearth, lungs,spleen, kidney, mesentery, and full and digesta-free com-ponents of the gastrointestinal tract were weighed. Thegastrointestinal content was weighed and subtracted frompre-slaughter BW to obtain empty BW (EBW). Mass of non-carcass components was expressed in grams per kilogramof EBW. Carcasses were refrigerated for 24 h at 4 ◦C and

weighed to obtain cold carcass weight (CCW) and dressingpercent (DP). The difference between HCW and CCW wasused to calculate cooling loss (CL).

After 24 h chilling period, carcass measurements wererecorded. Carcass length was measured from the last cervi-cal vertebra to the last sacral vertebra, neck perimeter (NP)was measured at the level of the junction of the neck andthorax, leg perimeter (LP) was obtained at the base of theleg, and thoracic perimeter (TP) was measured at the levelof the 5th and 7th ribs.

The kidney, pelvic, and heart fat (KPH) were visuallyestimated based on the degree to which the KPH fills thebody cavity relative to the carcass size by the same trainedtechnician; whereas, subcutaneous fat cover (SFC) and car-cass conformation score (CCS) were classified accordingto McMillin and Pinkerton (2006). The SFC was evalu-ated on a scale of 1–3 (1.00–1.99 = minimal fat cover;2.00–2.99 = moderate fat cover; 3.00–3.99 = excessive fatcover. The CCS was also evaluated on a scale of1–3 (1.00–1.99 = heavy muscling; 2.00–2.99 = moderatemuscling; 3.00–3.99 = light muscling). Carcasses were sep-arated between the 12th and 13th ribs, and longissimusmuscle (LM) was measured with a planimeter, whereas fatthickness (FT) was measured at approximately 5 cm lateralto middle line, over the center of the LM with calipers.

2.5. Longissimus muscle characteristics data collection

At 24 h post-slaughter, instrumental color and pH ofthe LM were obtained. Color readings were taken onthe surface of the posterior LM exposure resulting fromthe 12th/13th-rib cut, after a 60-min bloom time. Colorwas evaluated using the CIELAB color space. Lightness(L*), redness (a*) and yellowness (b*) values were mea-sured (by triplicate each time and averaged) using aMinolta CR-400 spectrometer (Konica Minolta Sensing,Inc., Osaka, Japan), on the surface of the posterior LM expo-sure resulting from the 12th/13th-rib cut. Chroma (C*) andhue angle (h◦) were estimated as C* = [(a*)2 + (b*)2]1/2 andh◦ = tan−1(b*/a*), respectively. The pH analyses were per-formed in the LM between 1st and 2nd lumbar vertebrae,using a portable pH meter equipped with a puncture elec-trode (Hanna Instruments, HI–9025, Woonsocket, RI).

The LM located between 12th rib and 2nd lumbar verte-brae was removed from the right side of each carcass andfabricated into 2 cm thick steaks. Steaks were weighed andplaced individually in sealed plastic bags under vacuum.Steaks were refrigerated at 4◦ C for 3 days, and then frozenand stored at −20 ◦C until subsequent measurements wereperformed.

The purge loss (PL) and cooking loss (CKL) were deter-mined at 14 days post-slaughter. After storage, frozensteaks were tempered for 24 h at 4 ◦C, blotted dry withpaper towels and weighed. The PL was calculated using theweights taken before and after opening the vacuum pack-ages after 14 days of storage. The CKL was determined byweight loss after cooking steak samples of approximately2 cm3 and between 15 and 20 g. Samples were individuallyplaced in sealed plastic bags and heated in a water bath at75 ◦C until reaching an internal temperature of 70 ◦C. Tem-perature was monitored with thermocouples introduced

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in the core. After cooking, samples were cooled for 15 minunder running tap water, removed from packaging, blottedto remove excess surface moisture, and weighed. Both, PLand CKL were expressed as the percentage of loss relatedto the initial weight.

2.6. Statistical analyses

Data were analyzed as a randomized complete blockdesign using the MIXED procedure of SAS (2000). Modelincludes the treatment as fixed effect and block as arandom effect. For growth performance data analysis,pen was the experimental unit and initial weight wasincluded in the model as covariate. For carcass, organmass, and LM traits, individual carcasses were the exper-imental units. For carcass and organ mass data, theHCW was included in the model as covariate. For allanalyses, preplanned orthogonal contrasts were used totest (1) linear and quadratic effects of level of ZH feed-ing, and (2) differences between control and ZH feeding).Results are presented as least squares means ± SEM, andwere considered significant if P < 0.05, with trends identi-fied when the significance was between 0.05 and 0.1.

3. Results and discussion

3.1. Growth performance

Supplementation of ZH during 42 days in diet (ZH vs.control) improved (P < 0.001) final weight, total weightgain, ADG and G:F ratio. These variables increased linearly(P < 0.001) as levels of ZH increased in the diet (Table 2).ZH at doses of 0.1, 0.2 and 0.3 mg/kg of BW increasedfinal weight by 3.4, 8.1 and 8.4%, total weight gain by23.4, 55.3 and 57.4%, ADG by 22.1, 54.0 and 56.6%, andG:F by 20.0, 40.0 and 60.0%, respectively. DMI was unaf-fected (P = 0.321) by ZH supplementation (ZH vs. control),but when expressed as g/kg of metabolic BW, there was anincrease (P = 0.029) in those wethers supplemented withZH. Additionally, DMI increased quadratically (P = 0.037)with greater values at ZH levels of 0.1 and 0.2 mg/kg of BW(6.0 and 7.3%, respectively).

In agreement with our results, Mersmann (2002)reported that oral administration of �-AA to livestock usu-ally produce an increase in ADG accompanied in manycases by improvement in gain efficiency. For other rumi-nant species, previous studies reported an increment inADG, G:F, and final BW, with or without reduction in DMI,when ZH was supplemented in diet of beef cattle (Baxaet al., 2010; McEvers et al., 2012; Plascencia et al., 2008;Scramlin et al., 2010; Vasconcelos et al., 2008;) and sheep(Avendano-Reyes et al., 2011; López-Carlos et al., 2011,2012; Macías-Cruz et al., 2013; Robles-Estrada et al., 2009).In castrated male goats, Towhidi et al. (2011) reported animprovement in ADG, total weight gain and feed efficiencyat a dose of 0.2 mg/kg of BW.

In relation to the optimal dosage, the necessary ZHto stimulate growth performance was established in0.15 mg/kg of BW per day for beef cattle, equivalent at adietary concentration of 7.6 g per ton (8.3 ppm) of ZH (DMbasis) for the last 20–40 days on feed (FDA, 2006). In sheep,

Estrada-Angulo et al. (2008) and López-Carlos et al. (2010)stated an optimal daily response dose of 0.2 mg/kg of BWfor feedlot lambs; whereas, Ríos-Rincón et al. (2010) sug-gested a daily dose of 0.18 mg/kg of BW. In the presentstudy, greatest growth performance values were observedwhen wethers were supplemented with 0.3 mg/kg of BW,but the response was similar between doses of 0.2 and0.3 mg/kg of BW, thus it could be preferable to recommendthe lower dose of 0.2 mg/kg of BW.

In this study, dramatic increases were observed for ADGand G:F ratio at ZH doses of 0.2 and 0.3 mg/kg of BW perday. These increases were greater than previously reportedin most studies for beef cattle and sheep. For example, inbeef cattle Plascencia et al. (2008) reported a 37% increasein ADG and a 39% improvement in feed efficiency whenZH was fed at 0.15 mg/kg of BW for 40 days, and Scramlinet al. (2010) informed increases of 11% in ADG and 20%for G:F when fed ZH at 0.15 mg/kg of BW to beef steersduring the last 33 days of the finishing period. In sheep,López-Carlos et al. (2011) reported increments of 43% and35%, respectively when ZH was fed to finishing lambs for42 days at 0.2 mg/kg of BW; moreover, Ríos-Rincón et al.(2010) observed improvements of 40% and 28%, respec-tively in lambs fed ZH at 0.18 mg/kg of BW during a 35-daytrial.

Mersmann (1995) argued that there are majorspecies differences in response to �-AA, indicat-ing a hierarchy of responses across species withsheep ≥ cattle ≥ turkeys > pigs > chickens. This authorassumed that one contributing factor to this hierarchyis that species closer to their maximal growth response(because of intense selection for growth rate), respondin a lesser extent to �-AA stimulation. In this sense, thegreatest response observed in this study may be attributedto the fact that Criollo goats have received little attentionin terms of selection for growth characteristics (Mellado,1997).

3.2. Carcass characteristics

The HCW, CCW, and dressing from wethers fed ZH(P ≤ 0.031) increased linearly as level of ZH increased indiet. But irrespective of the dose level used, these traitswere greater (P ≤ 0.008) in carcasses of wethers supple-mented with ZH. The CL, FT, SFC, carcass length and TPwas not affected (P > 0.1) by ZH administration (Table 3). Inaddition, supplementation with ZH increased LM area andLP (P ≤ 0.023), with a linear improvement (P < 0.001) of LMarea by increasing ZH level in diet. However, NP observeda quadratic trend (P < 0.035) with greater values at 0.1 and0.2 mg/kg of ZH. Moreover, both KPH fat and CCS tendeddecreased linearly (P ≤ 0.089) as dietary ZH increased.

In the present study, there was an evident increase inthe muscular tissue (HCW, CCW, DP, LM, CCW, NP andLP) and a reduction of KPH. These response are consis-tent with reports by Mersmann (1998), who argued thatorally administration of �-AA compounds in cattle, pigs,and sheep had two obvious effects: First, an increase inmuscle mass, result of an increase in muscle protein syn-thesis and a decrease in muscle protein degradation; andsecond, a decrease in fat mass, result of triacylglycerol

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Table 2Growth performance of wether goats fed diets supplemented with zilpaterol hydrochloride (ZH) for the last 42 days before slaughter.

Item ZH levelsa Contrasts (P<)

0.0 0.1 0.2 0.3 SEM Linear Quadratic ZH vs. Control

Initial weight, kg 27.7 27.5 27.7 27.1 0.9 0.637 0.779 0.810Final weight, kg 32.1 33.2 34.7 34.8 0.4 <0.001 0.220 <0.001Total weight gain, kg 4.7 5.8 7.3 7.4 0.4 <0.001 0.220 <0.001ADG, g 113 138 174 177 9.0 <0.001 0.219 <0.001DMI, kg/d 1.2 1.3 1.4 1.3 0.1 0.469 0.348 0.321DMI, g/kg of BW0.75 85.3 90.4 91.5 88.7 1.8 0.177 0.037 0.029G:F, kg/kg 0.10 0.12 0.14 0.16 0.01 <0.001 0.769 <0.001

ADG = average daily gain; DMI = dry matter intake; DMI, g/kg of BW0.75 = dry matter intake expressed on metabolic weight basis; G:F = kg weight gain/kgfeed intake.

a Zilpaterol hydrochloride (Zilmax, Intervet/Schering-Plough, Mexico) was supplied in the diet to provide daily doses of 0.0, 0.1, 0.2 or 0.3 mg/kg of bodyweight.

degradation and inhibition of fatty acid and triacylglycerolsynthesis in adipocyte. Moreover, carcass characteristicshave been consistently improved by oral administrationof ZH in other ruminants such as beef cattle (Baxa et al.,2010; Holland et al., 2010; Rathmann et al., 2012; Scramlinet al., 2010) and sheep (Avendano-Reyes et al., 2011; López-Carlos et al., 2010, 2012; Robles-Estrada et al., 2009).

In this study, back fat and subcutaneous fat cover wereunaffected by the administration of ZH. Reduction of subcu-taneous fat has been reported in male (López-Carlos et al.,2012; Salinas-Chavira et al., 2004) and female (Avendano-Reyes et al., 2011; Macías-Cruz et al., 2010) lambs fedZH. However, and according to our results, Estrada-Anguloet al. (2008) and Ríos-Rincón et al. (2010) reported noeffects on subcutaneous fat but a linear (P < 0.01) reductionin KPH fat of feedlot lambs supplemented with ZH.

Casey et al. (2003) argued that in goats, visceral fat(omental, mesenteric, kidney and pericardial) is the adi-pose depot that is first developed, followed by intermuscu-lar, subcutaneous, and intramuscular fat; therefore, younggoats have poor subcutaneous cover and in consequencethey are susceptible to high moisture losses during post-mortem chilling. In this study, cooling losses were about3%, which are in the expected parameter for goats close

to body weight 35 kg (Webb et al., 2005). Cooling loss wasnot increased by ZH supplementation probably because theexternal fat was unaffected.

In this study, muscles from back (LM), neck (NP) andleg (LP) regions, responded in different extent to ZHadministration. This phenomenon could be explained bydifferences in the �-AR) subtypes present in individualtissues (Mersmann, 1998) because ZH is considered a�2-selective AR (Moody et al., 2000), or by differencesin muscle fiber types present in each group of muscles,because �-AA stimulates growth more specifically in fast-fiber type muscles (Holmer et al., 2009; Moloney et al.,1990; Vestergaard et al., 1994) and the relative propor-tion of any fiber type may vary according to species andanatomical site (Schiaffino and Reggiani, 2011; Te Pas et al.,2004). In agreement with our results, it has been reporteda regionalized effect of ZH as it increased the percentageof leg and hindquarter cuts, and decreased the percent-age some forequarter cuts as shoulder and neck, in beefsteers (Hilton et al., 2009) and ewe lambs (Macías-Cruzet al., 2010). In addition, Kirchofer et al. (2002) reporteda greater variation among fiber types within muscles ofthe chuck and the round, with greater presence of whitemuscle fibers in hindquarter muscles.

Table 3Carcass characteristics of wether goats fed diets supplemented with zilpaterol hydrochloride (ZH) for the last 42 days before slaughter.

Item ZH levelsa Contrasts (P<)

0.0 0.1 0.2 0.3 SEM Linear Quadratic ZH vs. Control

Hot carcass weight, kg 15.8 16.4 16.6 16.7 0.2 0.031 0.316 0.008Cold carcass weight, kg 15.4 15.9 16.1 16.3 0.2 0.018 0.352 0.006Dressing, % 49.9 52.1 52.5 53.4 0.8 0.017 0.465 0.008Cooling loss, % 3.0 3.1 3.0 2.8 0.2 0.511 0.548 0.893Longissimus area, cm2 9.9 11.1 12.4 12.0 0.4 <0.001 0.051 <0.00112th-rib fat thickness, mm 0.96 0.86 0.76 0.66 0.14 0.507 0.721 0.544KPH fat, %b 2.4 2.3 2.2 2.1 0.1 0.089 0.620 0.113Subcutaneous fat coverc 1.9 1.9 1.8 1.8 0.1 0.311 0.491 0.357Carcass conformationd 2.8 2.7 2.5 2.3 0.1 0.051 0.452 0.083Carcass length, cm 72.6 71.6 72.8 73.1 0.8 0.980 0.417 0.953Neck perimeter, cm 34.5 35.9 35.6 33.9 0.7 0.495 0.035 0.448Leg perimeter, cm 33.4 34.2 35.1 35.2 0.5 0.297 0.449 0.023Thoracic perimeter, cm 67.9 67.8 67.7 67.5 0.6 0.628 0.939 0.747

a Zilpaterol hydrochloride (Zilmax, Intervet/Schering-Plough, Mexico) was supplied in the diet to provide daily doses of 0.0, 0.1, 0.2 or 0.3 mg/kg of bodyweight.

b KPH, Kidney, pelvic, and heart fat, calculated as a percentage of hot carcass weight.c Fat cover score: 1.00–1.99 = minimal fat cover; 2.00–2.99 = moderate fat cover; 3.00–3.99 = excessive fat cover (McMillin and Pinkerton, 2006).d Carcass conformation score: 1.00–1.99 = heavy muscling; 2.00–2.99 = moderate muscling; 3.00–3.99 = light muscling (McMillin and Pinkerton, 2006).

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Table 4Organ massa of wether goats fed diets supplemented with zilpaterol hydrochloride (ZH) for the last 42 days before slaughter.

Item ZH levelsb Contrasts (P<)

0.0 0.1 0.2 0.3 SEM Linear Quadratic ZH vs. control

Hide 123 114 112 116 3.4 0.237 0.117 0.022Head 45.8 44.3 42.5 43.3 1.5 0.178 0.447 0.203Liver 22.7 21.0 19.3 21.0 1.0 0.143 0.134 0.087Heart 4.8 4.9 4.9 4.9 0.3 0.848 0.884 0.805Lungs 20.0 19.5 18.0 19.3 1.1 0.391 0.388 0.403Spleen 2.1 1.8 1.7 1.7 0.1 0.063 0.258 0.046Kidney 1.6 1.5 1.6 1.5 0.1 0.554 0.993 0.497Small intestine 20.8 22.6 23.6 20.5 2.2 0.963 0.261 0.597Large intestine 18.9 18.5 16.7 19.1 1.0 0.662 0.197 0.547Stomachc 37.8 33.7 35.6 39.0 2.3 0.565 0.120 0.566

a Non carcass components are in g/kg of empty body weight.b Zilpaterol hydrochloride (Zilmax, Intervet/Schering-Plough, Mexico) was supplied in the diet to provide daily doses of 0.0, 0.1, 0.2 or 0.3 mg/kg of body

weight.c Includes the rumen-reticulum, omasum and abomasum.

3.3. Organ mass

The relative mass (g/kg of EBW) of hide and spleenwas reduced (P < 0.05) in wethers fed ZH (Table 4), with atendency (P = 0.087) to reduce liver mass (ZH vs. control).In addition, spleen mass was reduced linearly (P = 0.063) asZH level was increased in diet. However, there were notdifferences (P > 0.5) or trends (P > 0.1) on other organs suchas head, heart, lungs, kidney, small and large intestine orwhole stomach (rumen-reticulum, omasum and aboma-sum) mass.

In agreement with our results, Chikhou et al. (1993)observed a reduction (P < 0.001) in the hide weight ofFriesian steers supplemented with the �-AA cimaterol.Moreover, Scramlin et al. (2010) reported a reduction(P < 0.05) of hide weight from finishing steers fed ZH.The former authors argued that this phenomenon is dueto the large repartitioning effect of ZH that affects fatmetabolism (potentially lipolysis and lipogenesis) in non-carcass components such as the hide or viscera. Howeverother authors have not reported effects of �-AA on hideweight (Li et al., 2000). Sivamani et al. (2007) mentionedthat type 2 �-ARs are present in keratinocytes, but theirfunction in the epidermis continues to be elucidated.Abnormalities in their expression have been implicatedin the pathogenesis of various cutaneous diseases, and

are also involved on modulation of keratinocyte migra-tion and wound re-epithelialization. Nash et al. (1994)demonstrated a considerable protein repartitioning effectof �-AA towards muscle and revealed that the effects areaided by a reduced protein synthesis in wool and skin ofsheep treated with cimaterol. Further research is needed toelucidate if the origin of weight reduction of the hide is dueto the repartitioning effect with reduction in skin fat con-tent, decrease in protein synthesis or altered keratinocytemigration.

In the present study, the relative mass (g/kg of EBW) ofspleen was reduced (P = 0.046) by the inclusion of ZH in thediet. However, the physiological significance of this obser-vation is unclear. Spencer and Oliver (1996) conducted astudy to examine the effect of the �-AA clenbuterol onimmune function in sheep. Their study showed a reduced(P < 0.05) humoral antibody response in sheep treated withclenbuterol and immunized against somatostatin (SRIF),and a reduction (P < 0.05) of thymus (30%) and spleen (10%)weights (as indicators of lymphoid tissue growth) in theclenbuterol treated lambs, however reduction in organmass was not significant (P > 0.05). In addition, the authorssuggested that elevation of �-adrenergic status in sheep fed�-AA suppresses the immune system. The wethers fromthe present study did not showed any signs of clinical dis-ease during the period of study, but it was conducted by a

Table 5Longissimus muscle characteristics of wether goats fed diets supplemented with zilpaterol hydrochloride (ZH) for the last 42 days before slaughter.

Item ZH levelsa Contrasts (P<)

0.0 0.1 0.2 0.3 SEM Linear Quadratic ZH vs. Control

Instrumental colorb

L* 33.6 34.7 32.8 36.3 1.0 0.255 0.239 0.389a* 11.1 9.5 10.0 9.9 0.6 0.331 0.194 0.072b* 4.6 4.1 4.4 4.6 0.3 0.916 0.222 0.413C* 12.1 10.4 10.9 11.0 0.7 0.429 0.182 0.094h◦ 40.4 41.3 40.8 43.3 1.8 0.361 0.672 0.504

pH 5.8 5.8 5.7 5.6 0.1 0.072 0.438 0.299Purge loss, % 2.9 2.7 2.7 2.8 0.2 0.694 0.358 0.362Cook loss, % 27.8 33.0 35.6 35.2 3.6 0.137 0.447 0.111

a Zilpaterol hydrochloride (Zilmax, Intervet/Schering-Plough, Mexico) was supplied in the diet to provide daily doses of 0.0, 0.1, 0.2 or 0.3 mg/kg of bodyweight.

b Instrumental color at 24 h postmortem: L* = lightness (0 = black, 100 = white); a* = red to green (positive values = red, negative values = green); b* = yellowto blue (positive values = yellow, negative values = blue); C* = chroma = [(a*)2 + (b*)2]0.5; and h◦ = (hue angle) = tan−1(b*/a*).

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relatively short period of time and under controlled condi-tions.

In agreement with our results, López-Carlos et al. (2012)and Ríos-Rincón et al. (2010) have reported reductions inthe relative mass from liver of lambs treated with ZH in theorder of 20.7% (P < 0.05) and 9.5% (P = 0.01) respectively ascompared to untreated lambs. In feedlot lambs treated withother �-AA compounds, researchers have reported a massreduction in those organs of greater metabolic activity suchas liver (Kim et al., 1989; Spencer and Oliver, 1996) andheart (Koohmaraie et al., 1996). In Friesian steers treatedwith the �-AA L-644,969 Moloney et al. (1990) reported alineal reduction in weight of heart, lungs, liver and kidneys;whereas Chikhou et al. (1993) reported weight reductionsin liver and heart by effect of cimaterol supplementation.López-Carlos et al. (2010) studied the effects of two �-AA(ZH and ractopamine hydrocloride) on serum metabolitesof finishing lambs, and concluded that oral administrationof �-AA not compromised the general protein status or theprotein hepatic synthesis.

The �-ARs are present on almost every cell type, andcontrol an exceptionally large number of physiological andmetabolic functions; therefore, some effect on organ masscould be expected in animals fed �-AA (Mersmann, 2002).Williams et al. (1987) described an increase (P < 0.05) incarcass nitrogen retention but a reduction (P < 0.05) inthe nitrogen content of the non-carcass components andmajor organs of calves treated with clenbuterol. Moreover,the author proposed that because organs have a consider-able greater metabolic activity than skeletal muscle, smallreductions in mass might yield considerable savings innitrogen requirement for metabolic homeostasis.

3.4. Longissimus muscle characteristics

The ZH supplementation did not affect (P > 0.1) L* (light-ness), b* (yellowness) or h◦ (hue angle) values; however,tended to reduce (P ≤ 0.094) a* (redness) and C* (Chroma)values (ZH vs. control) of LM (Table 5). In agreement withour results, previous research showed a trend to result inpaler meat of beef steers (Avendano-Reyes et al., 2006;Hilton et al., 2009; Luqué et al., 2011) and lambs (López-Carlos et al., 2012) supplemented with ZH.

The decrease in instrumental color (a* and C* values)observed in the present study may be the result of apigment “dilution” effect in the muscle, probably due toreduced heme iron concentration (Geesink et al., 1993) andoxymyoglobin amounts (Carr et al., 2005) caused by hyper-trophy of the muscle fiber. In addition, various authors(Strydom et al., 2009; Vestergaard et al., 1994; Wheelerand Koohmaraie, 1992) reported hypertrophy of “white”fast-twitch muscle fibers and a change in fiber type pro-portion toward more glycolytic and less oxidative fibersin ruminants fed �-AA, which may contribute to a palerappearance of meat.

The color is an important criterion for judging freshnessand quality of fresh meat by consumers. In a study con-ducted by Sen et al. (2004) the color of goat meat was ratedbetter (P < 0.05) than mutton by consumers, which authorsattribute to a darker red color of fresh goat meat. In conse-quence, the reduction of a* and C* values could potentially

affect the consumer appraisal. However, Rogers et al.(2010) reported that colorimeter detects color differencesin strip loin steaks from steers supplemented with ZH thatcould not be observed by consumers or trained panelists.

The pH values at 24 h post-slaughter were similar(P > 0.05) in LM of wethers fed ZH or control diets (ZHvs. control); however, it was observed a linear tendencyto diminish pH (P = 0.072) as level of ZH increased indiet. Moreover, at 14 days post-slaughter no differences(P > 0.05) or trends (P > 0.1) were detected on PL or CKLas consequence of ZH supplementation. The pH, PL andCKL values observed in this experiment were similar topreviously reports for meat of goats (Ekiz et al., 2010;Johnson et al., 1995; Sen et al., 2004; Webb et al., 2005).In agreement with our results, other authors have notreported effects on pH (Avendano-Reyes et al., 2006; Neillet al., 2009; Scramlin et al., 2010), PL (Kellermeier et al.,2009) or CL (Kellermeier et al., 2009; Leheska et al., 2009)in LM of cattle fed ZH. In addition, López-Carlos et al.(2012) reported that pH, PL or CL were unaffected in lambssupplemented with ZH. Despite of the lack of statisticalsignificance (ZH vs. Control, P = 0.111), attributable to thehigh variability observed, there were a numerical incre-ment of 5.2, 7.8, and 7.4% in CKL of LM from wethers fed ZHat 0.1, 0.2 and 0.3 mg/kg respectively, respect to wethersof the Control group. In this respect, Aguilera-Soto et al.(2008) reported a greater (P = 0.2) CKL (5%) in LM of lambsfed 0.2 mg/kg of ZH, while Hilton et al. (2009) reported agreater CKL in LM of Holstein steers supplemented withZH in diet. These results have been attributed to the factthat ZH increases the proportion of moisture and protein,and simultaneous decrease the proportion of fat in muscle(Kellermeier et al., 2009).

4. Conclusions

Data from this study indicated that growth performanceand carcass characteristics were improved in wether goatsfed diets containing ZH at daily doses of 0.1, 0.2 or 0.3 mg/kgof BW for a period of 42 days. Most growth and carcasstraits increased linearly as dose of ZH augmented in diet.However, growth differences between wether goats fed ZHdoses of 0.2 or 0.3 mg/kg of BW were small, so lower dose of0.2 mg/kg of BW seems enough to enhance growth. More-over, the carcass characteristics showed minor differencesbetween levels of ZH supplementation, and therefore couldbe considered that the lower dose of 0.1 mg/kg of BW of ZHwas sufficient to improve these traits. Administration of ZHto wether goats had no detrimental effect on non-carcasscomponents or LM characteristics.

Conflict of interest

We wish to confirm that there are no known conflicts ofinterest associated with this publication.

Acknowledgements

The authors dedicate this article to the memory of grad-uate student Ana Maria Ocampo-Barragan, who devotedtime and effort to the completion of this experiment. We

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express our gratitude to undergraduate students Aldo Nor-iega and Victor Hugo Argüelles for its invaluable technicalassistance during experiment; and to the food process plantand abattoir personnel of Veterinary Medicine and AnimalScience College of the University of Zacatecas for assistancein the mixing of diets and slaughtering of experimentalanimals.

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