Effects of Ractopamine Hydrochloride on Growth Performance and Carcass Characteristics in Wool and Hair Lambs

Abstract

This study aimed at evaluating the effects of ractopamine hydrochloride (RAC) on growth performance and carcass characteristics of wool and hair lambs. For this purpose, 48 lambs averaging 31.3 kg body weight, of which twenty were wool (Ramboullet x Suffolk) and twenty eight were hair (Tabasco) lambs, and four levels of RAC (0, 10, 20, and 30 mg/kg diet, dry matter basis) were used. Wool lambs fed 20 and 30 mg RAC had higher (P<0.05) total gain weight and lower feed conversion than 0 and 10 mg RAC. Wool lambs fed 20 mg RAC had the highest carcass weight, dressing, legs weight and longissimus area as compared to 0, 10 and 30 mg RAC. In hair lambs there were not effect of RAC on growth performance and carcass characteristics. It was concluded that addition of RAC to finishing diets offered the best growth performance and carcass traits in wool lambs as compared to hair lambs.

KeyWords:

• Carcass
• Growth
• Lamb
• Meat
• Ractopamine

Introduction

In a world that struggles with rising meat consumption, feed shortages, and environmental waste, improving the efficiency of animal production becomes critical. Anabolic and repartitioning agents remain the most effective and reliable means to alter the deposition of fat and lean in livestock (Sillence, 2004). However, the illegal use of clenbuterol a -agonist for animal feeding has caused considerable alarm, with cases of food poisoning in México (Estrada et al., 2008). While it is possible to eliminate the health risk of drug residues through carcasses screening, or approving access to short-acting compounds like ractopamine, it is much harder to remove the fear of drug residues among consumers. In December 2000, ractopamine became the first -agonist to be registered by the US Federal Drug Administration, for commercial use as a pig-feed additive (Mills, 2002). Ractopamine hydrochloride (RAC) has been extensively used in cattle (Walker et al., 2010) and swine (Leick et al., 2010) with beneficial effects on carcass and meat traits. Mexico (Diario Oficial de la Federación, 2002) and several other countries have authorized RAC in livestock feeding. The effects of RAC on sheep have been evaluated recently in hair lambs (Robles et al., 2009; Lopez et al., 2010) with beneficial effects on carcass characteristics. Daily recommendations of RAC for lambs are based on body weight (BW) (Robles et al., 2009; Lopez et al., 2010), which are not practiced under feedlot conditions due to variation in weight and feed intake. Also, these recommendations are based on trials using only hair lambs. An elevated sensitivity of wool lambs to RAC could be indicative of greater beta- adrenergic receptor affinity and higher number of receptor than hair lambs (Gilson et al., 1996) then we hypothesized that RAC effect might be different in wool and hair lambs. Therefore, the objective of this study was to determine the best dose level of RAC in diet for growth performance and carcass traits on wool and hair lambs.

Materials and methods

This experiment was conducted under the supervision of the Academic Committee of Colegio de Postgraduados, Campus Montecillo, according to experimental animal guidelines and procedures, enacted by the State of Mexico in México. Two experiments were conducted with different sheep breeds (wool and hair) each with four levels of RAC (0, 10, 20, and 30 mg/kg diet, dry matter basis). Forty eight lambs (31.3±5.8 kg BW), of which twenty were wool (Ramboullet x Suffolk), and twenty eight were hair (Tabasco) lambs. Ractopamine chlorhidrate (RAC; Optaflexx, Elanco Animal Health, Greenfield, IN, USA) was added in the mineral and vitamin premix, and its inclusion levels were calculated to offer 0, 10, 20, and 30 mg/kg diet [dry matter (DM) basis]. Diets were formulated using the NRC (1985) requirements, and ingredients included as follow (DM basis): corn grain (558 g/kg), sorghum grain (200 g/kg), soybean meal 44% crude protein (CP) (117 g/kg), molasses cane (50 g/kg), corn stover (45 g/kg), mineral and vitamin premix (30 g/kg). When RAC was included in the diet, corn grain was the feedstuff used to adjust the diet.

Each lamb was allocated in an individual pen. Lambs had free access to diets and water. Diets were offered twice a day (8:00 and 16:00 h). The adaptation periods to the diets were 15 d. The growth performance trial lasted 30 d. Feed offered and refused were daily recorded. Body weight of lambs was recorded at 0, 15 and 30 d. Thus, dry matter intake, average daily gain, and feed conversion were calculated. The DM of diets was determined by oven drying at 65°C to a constant weight. Samples were ground with a Wiley Mill fitted with a 1 mm screen (Arthur H. Thomas, Philadelphia, PA, USA) and then analyzed for DM, CP, ash (AOAC, 1997), and neutral detergent fibre (NDF) (Van Soest et al., 1991).

Once the growth performance trial (30-day period) was concluded the BW was immediately recorded before slaughter. Hot carcass weight was recorded at slaughter. Chilled carcass weight (4ºC) was recorded 24 h after slaughter. The carcass length, leg length, leg perimeter, and leg weight (four legs) were measured. Dorsal fat at the12th rib was measured by using a caliper. For the 12^th rib, the Longissimus (LD) muscle area was measured using the cross-sectional method described by Rust et al. (1970). Samples of LD were taken at the 12^th and 13^th rib. The samples were sat on ice and transported to the laboratory to be vacuum-packed and frozen at -20ºC until analysis; then, samples were thawed at 4ºC for 24 h to determine tenderness, unfrozen samples of LD were broiled for 60 sec at 90ºC and 1 cm² was cut parallel to the muscle fibre orientation. On this sample, a shear force was measured using a Texturometer (TAXT2, Stable Microsystems Corp, NY, USA) equipped with Warner-Brazler shear blades with a crosshead speed of 50 mm/min (Bratzler, 1949). The pH was measured using a pH meter (Fisher Accument, Pittsburgh, PA, USA). Colour readings were taken in L* (white and black spectrum), a* (red and green spectrum), and b* (yellow and blue spectrum) colour space (Wulf and Wise, 1999) using a colourimeter (Minolta Chroma Meter CR-200, Minolta Corp., Ramsey, NJ), light source pulsed Xenon arc lamp and 50-mm-diameter aperture. The pH and colourimeter measurements on meat case-stored samples were taken on d 7 after storage (AMSA, 1991). Water-holding capacity (WHC) was determined by the gravimetric method proposed by Honikel (1998). Water activity was carried out with Aqualab equipment CX-1 (Ann Arbor, MI, USA). Data were analyzed as a completely randomized design of treatments (RAC level: 0, 10, 20 and 30 mg/kg diet). The BW changes, average daily gain (ADG), dry matter intake (DMI) and feed conversion (FC) were analyzed using the Mixed procedure of SAS (1999). The model included treatments RAC level, and period (0, 15 and 30 d). Lamb was considered as a random component in the model. The repeated measure was analyzed within lamb. The covariance structure that resulted in the lowest Akaike’s information was first-order autoregressive. Since interactions of treatment x period were not significant, ADG, DMI, and FC data were averaged (30 d). Carcass and LD data were analyzed without the repeated measure using the same model. Orthogonal polynomials (linear, quadratic and cubic) were used to test effects of RAC level in the diet on lambs. Differences were accepted and discussed when P≤0.05.

Results

Experimental diets averaged (per kg as DM basis) 139 g crude protein, 260 g neutral detergent fibre (NDG), and 65 g ash. Chemical composition of diets was similar. Wool lambs showed cubic effects (P<0.05) of RAC level on total gain and feed conversion, being 20 and 30 mg RAC which offered the highest total gains and the lowest feed conversion values (Table 1) as compared to 0 and 10 mg RAC. In wool lambs, hot and chilled carcass weights and dressing were affected quadratically (P<0.05) by RAC level, being lambs fed 20 mg RAC which showed the highest values. In wool lambs, dorsal fat and hindquarters were not affected by RAC (Table 2), but lambs fed 20 mg RAC had heavier legs, skin, offal, gastrointestinal tract and gastrointestinal content, as well as higher values of Longissimus dorsi area than lambs fed 0, 10 or 30 mg RAC (quadratic effect of RAC level at P<0.05). In wool lambs, there not RAC effect on shear force, pH, water activity, waterholding capacity, meat colour, and blood and head weight.

In hair lambs, growth and carcass performance were not affected by RAC levels (Table 3). In hair lambs, there were no differences in carcass, LD traits and organ characteristics for the different RAC doses (Table 4).

Discussion

According to the DMI and final BW showed in Table 1, wool lambs fed diets with 10, 20 and 30 mg/kg DM, received 0.31, 0.62 and 0.108 mg RAC/kg BW, and hair lambs received 0.39, 0.78, and 0.123 mg RAC/kg BW, respectively. The daily RAC doses used in this experiment are in agreement with doses (0.35, 0.70, and 105 mg/kg BW) evaluated by Lopez et al. (2010). These authors found that final weight, total weight gain, ADG, carcass weight, dressing percentage, and longissimus muscle area of hair lambs, increased linearly as levels of RAC increased. These results are partially in agreed with the results found in wool lambs in the present study.

The RAC levels evaluated in our experiment showed a quadratic effect in most of the traits evaluated only for wool lambs. Optimal response in terms of growth performance and carcass traits was observed at the 20 mg RAC/kg diet. The basis for this quadratic effect to the RAC level is not certain, but similarly Walker and Drouillard (2010) found that lowmedium, but not high RAC doses, increased growth of gram-negative bacteria in the rumen which affected positively rumen fermentation. More research is needed to support the effects of RAC on rumen microorganisms and fermentation.

The different response of wool and hair lambs to RAC has not been evaluated in lambs. Inconsistent with the present research, Gruber et al. (2007) did not observe an interaction of various biological cattle types and RAC supplementation. Reason for inconsistencies between studies is unclear, but could involve direct (e.g., tissue specific) and indirect (e.g., endocrine) changes associated with fat and muscle metabolism (Gilson et al., 1996). Although, both alpha and beta-adrenergic receptors are present in ovine adipose tissue (Watt et al., 1991), variations in the sensitivity and responsiveness of individual adipose depots to cathecholamines stimulation have been demonstrated in lambs. Ractompamine is similar in structure to natural cathecholamines (Mills, 2002). Variations in the sensitivity of RAC on specific lamb breed could be due to differences of adiposities characteristics and basal lipolysis (Zamiri and Izadifard, 1995). Thus, the elevated sensitivity of wool lambs to RAC could be indicative of greater beta- adrenergic receptor affinity and higher number of receptor than hair lambs (Gilson et al., 1996).

In agreement with our results, the benefits of feeding RAC to lamb on live and carcass traits have been found in finishing lambs (Robles et al., 2009; Lopez et al., 2010) as a result of repartitioning accretion of protein relative to fat (Bryant et al., 2010). The mechanism by which RAC increases longissimus area in our experiment could be interconnected with its ability to alter the metabolic profile of the individual fibres (Gonzalez et al., 2009). In agreement with these researchers, in the current study, RAC supplementation did not affect the colour characteristics in the longissimus.

Conclusions

Given these results, it is concluded that RAC at 20 mg/kg diet may have an important effect on growth performance and carcass traits in wool lambs. Effective use of RAC for managing growth of finishing lambs requires a more thorough understanding of how various kinds of lambs respond to its inclusion in finishing diets. Larger-scale commercial studies would assist in making broader inferences concerning responses of various breed lambs to RAC supplementation.

Table 1. Growth performance and carcass dressing of wool lambs fed ractopamine chlorhidrate.

	Ractopamine, mg/kg DM
	0	10	20	30	SEM
Growth performance
Initial body weight, kg	34.9	40.7	40.0	34.9	4.8
Final body weight^°, kg	45.0^b	50.8^a	51.4^a	46.4^b	4.4
Total gain^#, kg	10.1^b	10.1^b	11.4^a	11.5^a	1.1
Average daily gain, kg	0.337	0.337	0.380	0.383	0.09
Dry matter intake, kg	1.58	1.59	1.61	1.68	0.15
Feed conversion^Footnote#Footnote§	4.7^a	4.7^a	4.2^b	4.4^b	0.35
Carcass performance
Hot carcass weight^°, kg	20.1^b	23.2^a	25.4^a	22.6^a	3.2
Chilled carcass weight^°, kg	19.4^b	22.0^a	24.0^a	21.5^a	3.2
Hot carcass dressing^°, %	44.7^b	45.7^b	49.4^a	48.7^a	3.8
Chilled carcass dressing^°, %	43.1^b	43.3^b	46.7^a	46.3^a	3.5

DM, dry matter.

°Quadratic effect (P<0.01) of RAC level

^#cubic effect (P<0.01) of RAC level

^§feed conversion = dry matter intake/average daily gain.

^a,bMeans in the same row with different superscripts differ (P≤0.05).

Table 2. Carcass and Longissimus dorsi traits, and organs weight in wool lambs fed ractopamine chlorhidrate.

	Ractopamine, mg/kg DM
	0	10	20	30	SEM
Carcass traits
Dorsal fat at 12^th rib, mm	4.0	4.2	4.0	4.2	0.31
Hindquarters perimeters, cm	60.0	60.2	60.2	60.1	3.1
Hindquarters width, cm	31.1	30.4	30.4	30.3	2.0
Legs weight^°, kg	10.0^b	10.8^b	12.0^a	10.2^b	0.82
Longissimus dorsi
Area^°, mm^2	11.4^b	11.8^b	12.9^a	11.6^b	1.0
Shear force, kg/cm^2	1.9	2.2	2.0	2.0	0.33
pH	5.73	5.70	5.69	5.71	0.09
Water activity	0.96	0.96	0.97	0.97	0.06
Water-holding capacity, mL	35.9	35.9	37.2	36.8	3.1
Colour^#
^L*	35.1	36.8	36.0	37.4	4.0
^a*	19.1	18.5	19.3	18.4	1.8
^b*	6.7	6.2	7.0	6.8	0.81
Organs
Blood, kg	2.0	1.8	1.9	1.9	0.31
Head, kg	2.0	1.9	2.1	2.0	0.30
Skin^°, kg	4.5^b	4.5^b	5.2^a	4.9^a	0.39
Offal^°, kg	6.0^ab	6.1^ab	6.4^a	5.9^b	0.41
Gastrointestinal tract^°, kg	4.0^b	4.1^b	4.4^a	4.0^b	0.33
Gastrointestinal content, kg	3.5	3.3	3.5	3.3	0.29

°Quadratic effect (P<0.01) of RAC level

^#the Hunter

L* values are a measure of lightness (a higher value indicates a lighter colour) the Hunter

a* values are a measure of redness (a higher value indicates a redder colour); the Hunter

b* values are a measure of yellowness (a higher value indicates a more yellow colour).

^a,bMeans in the same row with different superscripts differ (P≤0.05).

Table 3. Growth performance and carcass dressing of hair lambs fed ractopamine chlorhidrate.

	Ractopamine, mg/kg DM
	0	10	20	30	SEM
Growth performance
Initial body weight, kg	26.9	25.1	24.4	23.6	6.1
Final body weight, kg	36.6	35.1	34.5	34.1	6.3
Total gain, kg	9.7	10.0	10.1	10.5	1.4
Average daily gain, kg	0.323	0.333	0.337	0.350	0.10
Dry matter intake, kg	1.41	1.24	1.35	1.40	0.17
Feed conversion^°	4.4	4.1	4.0	4.0	0.37
Carcass performance
Hot carcass weight, kg	17.9	17.6	17.5	17.1	3.5
Chilled carcass weight , kg	17.3	16.8	16.9	16.6	3.6
Hot carcass dressing, %	49.0	50.0	49.6	50.3	3.9
Chilled carcass dressing, %	47.2	47.9	47.9	48.7	3.6

°Feed conversion = dry matter intake/average daily gain.

Table 4. Carcass and Longissimus dorsi traits, and organs weight in hair lambs fed ractopamine chlorhidrate.

	Ractopamine, mg/kg DM
	0	10	20	30	SEM
Carcass traits
Dorsal fat at 12^th rib, mm	3.0	3.1	3.1	3.2	0.32
Hindquarters perimeters, cm	57.2	57.2	57.1	57.1	3.3
Hindquarters width, cm	28.1	28.1	28.1	28.0	2.1
Legs weight, kg	8.5	8.3	8.1	8.0	0.84
Longissimus dorsi
Area, mm^2	10.4	10.0	10.6	9.9	1.1
Shear force, kg/cm^2	2.0	1.7	1.8	1.9	0.35
pH	5.74	5.69	5.72	5.72	0.10
Water activity	0.97	0.97	0.97	0.97	0.07
Water-holding capacity, mL	35.9	36.5	36.4	36.6	3.2
Colour^°
^L*	34.3	37.7	36.6	36.7	3.1
^a*	18.6	19.3	18.6	19.3	0.81
^b*	6.9	7.1	7.1	6.8	0.83
Organs
Blood, kg	1.4	1.3	1.3	1.3	0.32
Head, kg	1.9	1.7	1.6	1.6	0.31
Skin, kg	2.8	2.8	2.7	2.8	0.40
Offal, kg	6.0	6.1	6.1	5.9	0.42
Gastrointestinal tract, kg	4.4	4.5	4.5	4.2	0.35
Gastrointestinal content, kg	2.7	2.6	2.6	2.6	0.31

°The Hunter

L* values are a measure of lightness (a higher value indicates a lighter colour); the Hunter

a* values are a measure of redness (a higher value indicates a redder colour); the Hunter

b* values are a measure of yellowness (a higher value indicates a more yellow colour).

Acknowledgments

This research was supported by the program Line 7, Safety, Food Quality and Biosafety, Colegio de Postgraduados en Ciencias Agrícolas, Texcoco, México.