Comparative evaluation of supplemental zilpaterol hydrochloride sources on growth performance, dietary energetics and carcass characteristics of finishing lambs

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Asian-Australas J Anim Sci. 2019;32(2):209-216

Publication date (electronic) : 2018 December 21

doi : https://doi.org/10.5713/ajas.18.0152

A. Rivera-Villegas¹, A. Estrada-Angulo¹, B. I. Castro-Pérez¹, J. D. Urías-Estrada¹, F. G. Ríos-Rincón¹, D. Rodríguez-Cordero², A. Barreras², A. Plascencia^2,, V. M. González-Vizcarra¹, J. F. Sosa-Gordillo¹, R. A. Zinn³

¹Facultad de Medicina Veterinaria y Zootecnia, Universidad Autónoma de Sinaloa, Culiacán 80246, Sinaloa, México

²Instituto de Investigaciones en Ciencias Veterinarias, Universidad Autónoma de Baja California, Mexicali 21386, Baja California, México

³Department of Animal Science, University of California, Davis, CA 95616, USA

^*Corresponding Author: A. Plascencia, Tel: +52-686-5636906 (111), Fax: +52-686-5636907, E-mail: aplas_99@yahoo.com

Received 2018 February 22; Revised 2018 May 1; Accepted 2018 June 4.

Abstract

INTRODUCTION

Zilpaterol hydrochloride (ZH), a beta adrenergic agonist, is an FDA-approved feed additive for beef cattle [1]. It was originally patented and marketed under the trade name Zilmax (ZIL; MSD, Summit, NJ, USA). However, following patent expiration outside the USA, additional “generic” forms of the compound have been approved for marketing in countries where the use of ZH as a feed additive is authorized. Notwithstanding potentially lower product costs, industry acceptance of “generic” forms of feed additives is limited [2]. The basis for this include: perceived differences in quality control during manufacturing and marketing; uniformity; purity; drug particle size and carrier, and their associated effects on product distribution during feed mixing and delivery; manufacturer product support; and demonstrated bio-equivalency. Supplementing finishing lambs with ZH at the rate of 6 mg/kg diet dry matter (DM) increase average daily gain (ADG), gain efficiency [3–5], carcass weight and dressing percentage [5,6]. These effects help to increase gain efficiency, particularly during the late finishing phase when cost of gain is greatest. The objective of the present study was to compare the effects of three approved sources of ZH (MEX SAGARPA, 2016; registration Q-0042-401, Q-7833-242, and Q-0273-205) marketed under the trademark Grofactor (GRO; Laboratorios Virbac México, Guadalajara, Mexico), Zipamix (ZIPA; Pisa Agropecuaria, Guadalajara, Mexico), and ZIL (MSD, Salud Animal Mexico, Estado de Mexico, Mexico) on growth performance, dietary energetics and carcass characteristics of finishing lambs.

MATERIALS AND METHODS

Diets, animals and experimental design

This experiment was conducted at the Universidad Autónoma of Sinaloa Feedlot Lamb Research Unit, located in the Culiacán, México (24° 46′ 13″ N and 107° 21′ 14″ W). Culiacán is about 55 m above sea level, and has a tropical climate. Average daily minimum and maximum air temperature during the trial was 25.9°C and 33.9°C (average = 29.9°C), respectively. Average daily relative humidity was 78.8%. All animal management procedures were conducted within the guidelines of locally-approved techniques for animal use and care: NOM-051-ZOO-1995: Humanitarian care of animals during mobilization of animals; NOM-062-ZOO-1995: Technical specifications for the care and use of laboratory animals. Livestock farms, farms, centers of production, reproduction and breeding, zoos and exhibition halls, must meet the basic principles of animal welfare; NOM-024-ZOO-1995: Animal health stipulations and characteristics during transportation of animals, and NOM-033-ZOO-1995: Humanitarian care and animal protection during slaughter process.

Twenty-four Pelibuey×Katahdin (46.7±2.4 kg initial shrunk weight) crossbred intact male lambs were used in a 33-d growth-performance experiment to evaluate the treatment effects on growth performance, dietary energetics, carcass traits, and visceral organ mass. Prior to initiation of the study, lambs were treated for endoparasites (Albendaphorte 10%, Animal Health and Welfare, México City, México), and injected with 1×10⁶ IU vitamin A (Synt-ADE, Fort Dodge, Animal Health, Mexico City, México). Lambs then adapted to the control diet (Table 1) for a period of 7 weeks. Upon initiation of the experiment, lambs were individually weighed (electronic scale; TORREY TIL/S: 107 2691, TOR REY electronics Inc, Houston TX, USA), grouped by weight into six uniform weight blocks, and assigned to pens (1 lamb/pen). Individual pens were 6 m² with overhead shade, automatic waterers and 1 m fence-line feed bunks. Dietary treatments (Table 1) consisted of a corn-based finishing diet supplemented with no zilpaterol (Control), or the, same basal diet plus the label dosage (125 mg of product/kg diet, as-fed basis) as ZIL (MSD Salud Animal Mexico, Santiago Tianguistenco, Mexico), GRO (Laboratorios Virbac México, Mexico), or ZIPA (Pisa Agropecuaria, Mexico). According to the label, all products tested contained 4.8% ZH. Thus, the dosage of 125 mg of product/kg diet corresponds to a dietary ZH concentration of 6 mg/kg (as feed basis). Supplemental ZH was hand-weighed using a precision balance (Ohaus, mod AS612, Pine Brook, NJ, USA), and premixed for 5 min with the other minor dietary ingredients (urea, limestone, and trace mineral salt) before incorporation into complete mixed basal diet using a 2.5 m³ capacity paddle mixer (mod 30910-7, Coyoacán, México). To avoid contamination, the mixer was thoroughly cleaned between each treatment. The ZH was supplemented for 30 d followed by a 3-d preharvest withdrawal when all lambs received the non-supplemented basal control diet. The four dietary treatments were randomly assigned to pens within each weight block in a randomized complete block design. Lambs were allowed ad libitum access to dietary treatments. Fresh feed was provided twice daily at 0800 and 1400 h in a 40:60 proportion (as feed basis). Daily feed allotments to each pen were adjusted to allow for approximately 5% residual feed remaining in feed bunk at time of the morning feeding. Feed bunks were visually assessed between 0740 and 0750 h each morning, residual feed was collected and weighed for determination of daily feed intake. Adjustments, in daily feed delivery were provided at the afternoon feeding. Lambs were individually weighed at the beginning of the trial and at harvest. The initial shrunk body weight (SBW) was determined as full body weight×0.96 (adjustment for gastrointestinal fill). Upon completion of the study, all lambs were weighed following an 18 h fast (feed but not drinking water was withdrawn) to obtain final SBW. Final SBW was adjusted for hot carcass weight (HCW) by dividing the individual HCW by the average dressing percentage (0.6120) for all lambs.

Table 1

Composition of basal diet supplemented with different sources of zilpaterol hydrochloride

RESULTS

Assayed ZH concentrations were within the expected range (43.2 to 53.8 g/kg), averaging 47.8, 47.3, and 51.2 g ZH/kg of product for ZIL, GRO, and ZIPA, respectively. Thus, based on average as-fed intake, ZH intake averaged 7.92, 7.73, and 8.1 mg/d, corresponding to 0.157, 0.153, and 0.162 mg ZH/kg SBW for lambs fed ZIL, GRO, and ZIPA, respectively.

Treatment effects on growth performance and dietary energetics are shown in Table 2. Compared to controls, ZH supplementation did not affect (p>0.10) DMI, but increased (p<0.05) carcass adjusted ADG (36.7%), gain efficiency (34.2%) and dietary NE (26.0%). Accordingly, ZH supplementation markedly decreased (23.4%, p<0.05) the ratio of observed: expected DMI. At comparable levels of ZH intake, growth performance and energetic efficiency responses of feedlot lambs were not different (p>0.10) across supplemental ZH sources.

Table 2

Effect of source of dietary zilpaterol hydrochloride on 33-d feedlot growth performance and dietary energy of lambs

Treatment effects on carcass composition are shown in Table 3. Compared to controls, supplemental ZH increased (p<0.05) HCW (6.4%), dressing percentage (3.2%), and LM area (15.6%). Difference in HCW, dressing percentage and LM area among ZH sources was not appreciable (p>0.10). Compared to control, ZIL supplemented lambs had less (p<0.05) KPH and fat thickness (21.7% and 13.2%, respectively) and greater (28.7%, p<0.05) shoulder muscle:fat ratio.

Table 3

Effect of source of dietary zilpaterol hydrochloride on carcass characteristics

The ZH supplementation increased (p≤0.02) 10.9 and 14.3% whole cut weight of loin and leg, respectively, and increased 4.3% the proportion of leg (as percentage of cold carcass weight). These increases were reflected in greater forequarter (p = 0.03) and hindquarter (p<0.01) weights. Differences among ZH sources on whole cuts were not appreciable (p> 0.10; Table 4).

Table 4

Effect of source of dietary zilpaterol hydrochloride on whole cuts

Treatment effects on visceral mass are shown in Table 5. Compared to controls, ZH supplementation increased (4.6%, p<0.01) EBW and reduced (14.7%, p<0.01) liver/spleen weight (as g/kg EBW). Likewise, ZH supplementation tended (p = 0.08) to lower (8.9%) visceral fat. However, supplemental ZH did not affect heart/lung weight (p = 0.32), stomach complex (p = 0.29), or empty weight of intestines (p = 0.67). Lambs fed ZIL or ZIPA had less (15.5%, p<0.05) visceral fat as a proportion of EBW than control or GRO supplemented lambs.

Table 5

Effect of source of supplement zilpaterol chlorhydrate on visceral organ mass

DISCUSSION

Optimal daily ZH dosage for feedlot cattle is between 0.15 to 0.165 mg/kg body weight (BW) [16,17]. In practice, this corresponds to a dietary concentration of 6.7 mg/kg diet DM (6 mg/kg air-dry feed, 90% DM basis). Zilpaterol is not currently labeled as a feed additive for lambs. The numerous studies conducted thus far in feedlot lambs adopted the labeled dosage as indicated for feedlot cattle [3,5,6,18].

Enhancements in ADG, gain efficiency and dietary energetics when lambs were supplemented with ZH are consistent with previous reports [3,19]. In previous studies, ZH supplementation of finishing diets for feedlot lambs increased ADG by 20.1% to 40.6% and gain efficiency by 16.5% to 43.3%. The observed enhancements in ADG and gain efficiency in the present study fall within those ranges. However, the decrease (13.3% to 16.2%) in observed:expected DMI ratio due to ZH supplementation (23.4%) was greater than previously observed [3,5,19,20].

Increased HCW, LM area, and dressing percentage, and reduced backfat thickness with ZH supplementation has been a consistent response in feedlot lambs [18,21]. Increased LM area is partially explained by the greater ADG [22], whereas the increased dressing percentage is expected due to greater carcass protein accretion with no change in digestive tract fill [6,23]. The increased LM area is also consistent with increased shoulder muscle [21].

Increased carcass cutability due to ZH supplementation has been consistent response in feedlot cattle [16], with the more pronounced effect occurring in the hindquater [17]. However, in lambs, the effects of ZH supplementation on carcass cutability is less consistent. Whereas in some studies [4,24] supplemental ZH increased loin and leg (as observed in the present experiment), in others [25,26] supplemental ZH did not affect lamb carcass wholesale cuts. The basis for this is uncertain. Estrada-Angulo et al [3] observed that factors such as diet energy density, age, genetics, and ZH dosage level may influence response to supplemental ZH. Comparative effects of different ZH sources on carcass cutability has not been previously reported. However, because the dietary concentration of ZH was similar for each of the three sources, absence of effects of ZH source on carcass cutability is expected.

The effects of β-agonist on non-carcass organs has received limited attention. The β-agonist salbutamol decreased liver mass in pigs [27]. Likewise, supplemental ZH decreased liver mass in feedlot cattle [28]. Decreased liver mass has also been a consistent observation in feedlot lambs receiving ZH [5,23].

Effects of ZH on visceral organs has been attributed to the differences in the abundance of β-agonist receptors subtypes in these tissues [17]. In as much as an appreciable proportion of energy expenditure can be attributed to maintenance of visceral organs, especially the liver and gastrointestinal tract [29], reductions in visceral organ mass could contribute to the increased energy efficiency observed when dietary β-agonists are fed.

Increased carcass dressing percentage explained 66% (65 g/d) of the increase (98 g/d) in carcass adjusted ADG in ZH supplemented lambs. Enhanced daily gain accounts for 55% of the net economic value of ZH supplementation (benefit to the feeder), while increased carcass yield accounts for 45% of the net value (benefit to the meat packer and retailer). Thus, the economic benefit to ZH supplementation is optimized through integrated production and meat purveying systems (Table 6).

Table 6

Costs and income of different sources of supplemental zilpaterol estimated by animal during the experimental phase (33 d)

Avendaño-Reyes et al [30] compared GRO vs ZIL in crossbreed bulls (75% Bos indicus and remainder Bos taurus) in a 34-d finishing trial (30 days of ZH supplementation and 4 days withdrawal). Bulls ingested an average of 0.134 and 0.139 mg ZH/kg BW of GRO and ZIL, respectively. Supplemental ZH enhanced ADG and gain efficiency. However, growth performance responses were not affected by ZH source. Likewise, in the present study differences in growth performance responses in lambs fed different ZH sources were not appreciable.

Avendaño-Reyes et al [30] did not detect an effect of supplemental ZH source on carcass characteristics and organ weights of feedlot cattle. Likewise, in the present study differences among ZH sources on carcass characteristics and organ weights were not appreciable. In contrast, ZH sources differed in their effects on fat distribution. Compared with control, supplemental GRO and ZIPA did not affect (p>0.10) fat distribution. Whereas supplemental ZIL decreased (p<0.05) carcass fat thickness, KPH, and shoulder muscle:fat ratio. In as much as all ZH products provided a similar zilpaterol dosage, this outcome was not expected.

CONCLUSION

Supplemental ZH increases ADG, gain efficiency, carcass dressing percentage and LM area, while reducing observed to expect DMI in feedlot lambs. The magnitude of these responses were similar among ZH sources. Nevertheless, compared with non-supplemented controls, only ZIL appreciably decreases carcass fat. The basis for this is uncertain, but indicative that some practical differences in zilpaterol bio-equivalency may exist across commercial sources tested.

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