Effect of production system on the growth rate, carcass characteristics and carcass composition of Dorper lambs

J J E Cloete*, L C Hoffman, B Claasen** and S W P Cloete***

Department of Animal Sciences, Faculty of Agriculture and Forestry Sciences, University of Stellenbosch, Private Bag X1, Matieland 7602, South Africa
jasperc@elsenburg.com
* Elsenburg Agricultural Training Institute, Private Bag X1, Elsenburg 7607, South Africa
** Department of Animal Science, Faculty of Agriculture and Natural Resources, University of Namibia, Private Bag 13301, Windhoek, Namibia
*** Institute for Animal Production: Elsenburg, Private Bag X1, Elsenburg 7607, South Africa

Abstract

An investigation on the effect of production system on growth rate, carcass characteristics and carcass composition of Dorper lambs was carried out under South African conditions.  The study involved sixty lambs which were divided into two production/feeding groups (feedlot (FL) vs. free-range (FR)) at weaning.  Each group consisted of 10 lambs from three gender classes (ewes, rams and castrates).  The FL-lambs were fed a commercial pelleted ration while the FR-group grazed natural pastures.  The production system x gender interaction indicated that male lambs (castrates and rams) grew twice as fast as ewes under FL-conditions.

Gender groups were less pronounced in FR-lambs.  FL-lambs produced heavier carcasses, higher dressing percentages and greater carcass fatness levels than FR-lambs.  Ram lambs attained heavier slaughter weights and produced heavier carcasses than ewe lambs with castrates being intermediate.  Production system did not have an effect on intramuscular lipid concentration, barring a tendency in the Biceps femoris muscle. It was concluded that the FL-diets were generally associated with better lamb growth rates, greater carcass fatness and an improved dressing percentage.  Although animal performance was generally improved in the more intensive FL-system, it was also concluded that discerning consumers will likely prefer the more natural (and therefore more ethically acceptable) FR-meat.    

Keywords: Feedlot, free-range, lamb meat

Introduction

Consumer attitudes and behavioural changes/choices are based on both personal experience and information acquired through various media (Richardson 1994).  In today’s era of information overload, consumers are not only concerned about the kind of food they consume (Jimenez-Colmenero et al 2001) but also about the treatment the animal received ante-mortem.  Issanchou (1996) summarised the hypothesis set forth by Van Trijp (1995) that animal welfare issues would gain importance as far as consumer preferences in the future are concerned.  Concluding remarks by Verberke and Viaene (2000) supported this hypothesis when they assessed the relative importance attached by consumers to product safety and animal welfare.  Although their results indicated that animal welfare issues were ranked among the less important fresh meat attributes, Verberke and Viaene (2000) stated that since it is associated with consumption decisions that were unfavourable for beef and pork in the past, it should be considered important.  Animal production systems should therefore be geared towards meeting emerging consumer decisions while remaining competitive on major target markets.  Although health and food safety concerns are paramount to animal welfare issues, the latter should enjoy equal attention. It is the prerogative of every affected country, including South Africa, to ensure that animal welfare issues are addressed.     

The increased emphasis on animal welfare creates the perfect market for free-range animal production.  Free-range animal production emanates from a philosophy that involves holistically “working with natural systems rather than seeking to dominate them”, as may be the case with more intensive farming systems (McEachern and Tregear 2000).  The free-range system is often viewed as a superior system for the environment, soil, livestock and humans who work in it and utilize its products (Raven 2000).  Free-range products are thus perceived as natural food products without chemicals and growth hormones (Davies et al 1995) that are produced in favourable environments pertaining to animal health and welfare (McEachern and Willock, 2004).  On the other hand, it is accepted that feedlot lambs generally produce heavier carcasses than free-range lambs (Díaz et al 2002; Priolo et al 2002). Feedlot diets also yield carcasses of greater fatness than free-range carcasses (Díaz et al 2002; Murphy et al 1994; Crouse et al 1981). 

Numerous investigations report differences in lamb growth rate, carcass composition and carcass fatness levels due to feeding system (Díaz et al 2002; Santos-Silva et al 2002).  Free-range diets are generally associated with slower lamb growth rates compared to faster growth rates achieved with feedlot diets (Notter et al 1991).   Nonetheless, free-range diets allow skeletal and muscle tissue growth without excess fattening.   

Sex hormones also influence the growth pattern of lambs.  It is known that intact males grow faster and reach a heavier slaughter weight than castrates and ewes.  Intact males also produce leaner carcasses than castrates and ewes (Field 1971; Crouse et al 1981; Seideman et al 1982; Arnold and Meyer 1988).  The fast growth rate of ram lambs is attributed to their ability to utilize feed more efficiently (Notter et al 1991). Carcasses from ram lambs are commonly heavier than carcasses from castrates and ewes (Dransfield et al 1990), although ewe lambs usually display higher dressing percentages than rams and castrates (Vergara et al 1999) when slaughtered at the same age.  It is generally accepted that fat deposition is influenced by the energy concentration of a diet. Feedlot diets enable ram lambs to fully exhibit their superiority in growth potential over castrates and ewes (Field 1971).  However, the growth advantage of rams over castrates is less pronounced when nutritional levels are reduced or when diets are of poorer quality (Crouse et al 1981).     

Studies on the proximate chemical composition of meat indicate that muscle moisture content decreases when fat content increases, as is the case with feedlot diets and resultant fatter carcasses (French et al 2001).  However, other investigations did not find muscle moisture differences between different production systems (Schroeder et al 1980).  According to Theriez and Tissier (1981), muscle protein content decreases as muscle fat percentage increases.  Animals on feedlot diets have higher fat concentrations than animals on free-range diets (Schroeder et al 1980; Diaz et al 2002).  Gender studies also indicate that muscles of castrates and ewe lambs have a higher concentration of intramuscular fat than those of ram contemporaries.  It seems that production system does not have an appreciable effect on muscle ash (mineral) content (Theriez and Tissier 1981). 

Against this background, there is little doubt that modern, discerning consumers would be more inclined towards free-range production for their meat consumption.  Although there is international literature on the effect of free-range and feedlot feeding on lamb growth, studies on African sheep breeds are scarce. The Dorper sheep is an early maturing breed selected for adaptability under South Africa’s harsher conditions (Milne 2000; Schoeman 2000).  In this experiment, Dorper lambs of the same age were finished off intensively in a feedlot or under more natural free-range conditions and slaughtered after a pre-determined period.  Therefore the aim of this study was to determine the effect of system (free-range or feedlot) on growth rate, carcass characteristics and meat chemical composition.  The effect of gender on growth performance and carcass characteristics was studied simultaneously. 

Materials and methods

Dorper lambs born between May and June 2005 at the Nortier Research Farm were used for this study. The farm is situated at 32º 02’South and 18º 20’East, and is approximately 10 km north from Lamberts Bay in the Western Cape.  The annual long-term precipitation at the site amounts to 221mm, of which 76% are expected between April and September. Every second ram lamb that was born was castrated by means of a rubber ring. The lambs were weaned in September 2005.  Sixty lambs, weighing 36.3 ± 3.2 kg on average (20 ewes, 20 castrates and 20 ram lambs), were selected from the larger population (n = 336) to minimize variation in starting weight.  The mean weaning age of these animals were 121 ± 5 days.  These lambs were randomly divided on stratified body weight basis within gender groups to one of two production systems (feedlot – FL or free-range – FR).  Each group consisted of 10 ewes, 10 castrates and 10 rams.  Lambs in each production system were kept together during the trial period. 

The vegetation at the Nortier Research farm is a combination of Strandveld and Sandveld (Cloete and De Villiers 1987).  Free-range lambs were observed feeding primarily on Exomis microphyla, Atriplex mumelarianum, Felicia bergeriana and Manochlamys albicans.  Pasture was abundant and did not limit growth.  Feedlot lambs were fed a commercial pelleted diet (Table 1).  Both groups had ad libitum access to water.  

Lambs weights were recorded individually at the beginning of every week.  After a five week trial period, average daily gain (ADG) was calculated for each lamb.  For this purpose, live weight was regressed on weighing date (in weeks) for each lamb. The regression coefficient was divided by seven to obtain the average daily gain to account for the fact that weekly weights were recorded.  

Previous research at the experimental site indicated that purebred Dorper lambs were weaned at ~31 kg at ~100 days (Cloete et al 2007).  Better pasture conditions and an older weaning age of 121 days in the present study resulted in a higher average weaning weight of ~36 kg in the present study, which could be considered close to a fasted slaughter weight of ~40 kg used for Dorper lambs by Snyman and Olivier (2002).  However, it is also known that the Dorper lambs used by Cloete et al (2007) attained a slaughter weight of 42.1 kg with acceptable fat measurements of 0.22 cm at the 13^th rib and 0.27 cm between the 3^rd and 4^th lumbar vertebrae.  Based on these results as well as on the average growth rate to weaning, it was estimated that the FR- lambs in the present study would reach a weight of 42-43 kg and fat cover of 0.2-0.3 cm after an additional growth period of 5-6 weeks to an average (± s.d.) slaughter age of 159 ± 7 days at the experimental site.  This would allow for sufficient time for a valid comparison between the FR- and FL-treatments.  After five weeks, 15 lambs from each of the two production groups (each group represented by five lambs from each gender class) were randomly selected, weighed and transported approximately 250 km to the abattoir.  The last weight recorded on the farm before the lambs were transported was regarded as the slaughter weight.  Upon arrival at the abattoir, all lambs were grouped together in lairage overnight.  The next morning, the lambs were electrically stunned and slaughtered using standard South African methods.  Most of the carcasses were classified as A2 according to the South African classification system (Government Notice No. 1748, 26 June 1992).  An A2 lamb has no permanent incisors and has a lean fat cover (1.0-4.0 mm subcutaneous fat depth measured at the ninth rib, 50 mm from the midline). The remaining 30 lambs in the investigation were slaughtered six weeks after feeding commenced. They underwent exactly the same procedures outlined above. The two slaughter dates were prompted purely by logistic considerations, as it was impossible to process all 30 lambs at once.   

The abdominal fat was removed from each carcass and weighed.  After 48 hours of refrigeration at 4^ºC, individual cold carcass weights were recorded and expressed relative to the slaughter weight to derive dressing percentage.  Longissimus dorsi (LD) muscles, excised from between the 8^th to 11^th ribs from both sides of each carcass, were transported to the laboratory for further analyses.  The LD muscles from the right side of the carcass were used for subcutaneous fat thickness measurements.  A dial clipper was positioned 1.5 cm from the midline and 1.5 cm from the edge of the last rib to determine the subcutaneous fat thickness.  Measurements taken from the midline were recorded as subcutaneous fat 1 and measurements from the edge were recorded as subcutaneous fat 2.   The LD muscle samples were vacuum-sealed and stored at -20^ºC until required for chemical meat quality analysis.  Biceps femoris (BF) muscles were excised from the right hind leg of each carcass.  Connective tissue and all visible fat were trimmed of all the muscles before being minced, vacuum-sealed and stored at -20ºC until required for chemical analysis. The kidney fat from each carcass was removed, weighed, vacuum-sealed and stored at -20^ºC for later use. 

Raw, finely minced, thawed LD and BF muscle samples were used for proximate composition analysis, which is described in terms of percentages moisture, protein, lipid and ash.  Total moisture was determined according to procedures prescribed by the AOAC (2002).  Weighed muscle samples were dried in an oven for 24 hours at 100ºC and the moisture percentage calculated.  The moisture free muscle previously used to determine muscle moisture content was used for the determination of ash content according to the methodology outlined by the AOAC (2002).  The muscle samples were ashed in an oven at 500ºC for 6 hours and the ash percentage calculated.  The total lipid concentration was determined by extracting lipids with chloroform: methanol (2:1 v/v) solution as described by Lee et al (1996).  The total crude protein fraction (N x 6.25) was determined by the Dumas combustion method (method 968.06; AOAC 1997) using the Leco FP 528 on the same samples (fat-free) used for lipid content determination.  Thawed, homogenized meat samples were used to extract myoglobin according to the method described by Krzywicki (1982).  Duplicate minced samples of approximately five grams of meat were weighed and placed in 50 ml polypropylene centrifuge tubes.  Twenty-five milliliters of ice-cold phosphate buffer was added to each tube and the sample homogenized for 40-45 seconds at a low speed.  Samples were then held on ice (4ºC) for one hour.  Samples were then centrifuged at 9000 RPM for 45 min at 4 ⁰C.  Thereafter, the supernatant was filtered through Whatman no.1 filter paper.  Individual absorbencies were then taken at 525 and 700 nm.  Myoglobin concentration was calculated as: Myoglobin (mg/ml) = ((A x 525) x (A x 700)) x 2.303 x 6, where A represented the weight of the muscle sample.   

The growth and slaughter data of the animals was tested for normality and homogeneity of variances before being subjected to analyses.  The basic analysis involved a 2 (production system: FL vs. FR) x 3 (gender: ewe vs. castrate vs. ram) factorial experimental design.  As slaughter date (5 vs. 6 weeks of feeding) was not part of the initial experimental outlay, it was not included in the statistical analysis as such.  To account for this effect, data were corrected prior to analysis to reflect the differences stemming from the slightly longer growth period.  An additional analysis involving the inclusion of slaughter age as a linear covariate was also conducted.  Growth differences between the treatment groups were estimated with the Proc GLM procedure of SAS (1999).  Preliminary analyses on all traits involved the full model, i.e. the effects of production system and gender, as well as the two-factor interaction between these effects.  The final model used to assess growth differences included all effects listed.  Interaction effects were removed from the final analyses on live weights, carcass traits and chemical composition, because results indicated that these effects were not significant (P > 0.05).  Carcass weight was included as a linear covariate in additional analyses involving indications of fatness, as will be pointed out later.  The contribution of either a main effect or an interaction to a response variable was defined as the sum of squares accounted for by a specific main or interaction effect divided by the corrected total sum of squares.  This value was multiplied by 100 to express the contribution as a percentage.  

Results and Discussion

The two-way interaction between gender and production system on lamb average daily gain (ADG) is presented in Table 2.  Production system did not affect lamb ADG but interacted (P < 0.05) with gender.  The interaction contributed to most of the variation accounted for by the model (18.2 %), compared to gender (12.9 %) and production system (2.4 %).  The average growth of male lambs (castrates and rams) was more than double that of ewes in the FL-production system (P < 0.05).  Much smaller gender differences were observed in the FR-system.  It is generally accepted that male lambs grow faster than ewes because they utilize feed more efficiently (Seideman et al 1982).  Moreover, feedlot diets are associated with faster growth rates (Crouse et al 1981; Arnold and Meyer 1988; Santos-Silva et al 2002) and should enable male lambs to fully exhibit their superiority in growth over ewe lambs (Bradford and Spurlock 1964; Crouse et al 1981; Seideman et al 1982; Arnold and Meyer, 1988; Notter et al 1991).  The growth advantage of male lambs is attributed to the presence of testicular hormones, particularly testosterone (Scanbacher et al 1980).  Although the growth pattern of the respective gender groups under FL-conditions observed in this study concurs with previously reported results, a difference of this magnitude was not expected.  In the FR-production system, the growth of ram lambs was clearly compromised in comparison with the FL-system.  The contention that ram lambs may not show clear growth advantages over castrates on pasture (Purchas 1978), is supported by the lack of a growth rate difference with castrate FR-lambs in the present study.  Furthermore, results seem to indicate that FR-feeding may have been sufficient to sustain ewe lamb growth.  The slow growth rate of FL-ewes can be attributed to insufficient feed intake as a result of them being dominated during feeding times by the heavier and more aggressive male lambs that were also frequently observed mounting them.  It could be argued that these unwanted behavioural patterns should be foreseen, and the ewes finished in a separate pen.  However, this was not the case and the results in Table 2 are as obtained.  It is interesting to note that Salim et al (2003) observed that ewe and doe growth performance may be optimized with concentrate supplementation on pasture, a system that was not considered in the present experiment. 

Starting and final weights of animals on the FL- and FR-production systems did not differ (P > 0.10 – Table 3). However, both production system and gender had significant (P < 0.05) effects on cold carcass weights of Dorper lambs.  Gender contributed more to the variation accounted for by the model (33.2 %) compared to production system (14.0 %).  With regard to production system, FL-lambs produced 10% heavier carcasses than FR-lambs (Table 3).  McClure et al (1994) also found that lambs finished on forage had lighter carcasses than concentrate fed lambs.  The observed slaughter weight of 42.7 kg in FR-lambs of the Dorper breed is consistent with a fasted slaughter weight of ~40 kg (Snyman and Olivier 2002) and a slaughter weight of 42.1 kg recorded at the same locality in an earlier study (Cloete et al 2007). 

Production system had a significant (P < 0.05) effect on the dressing percentage of lambs and contributed to 30.1 % of the variation accounted for by the model.  On the other hand, gender did not have any significant (P > 0.05) effect on dressing percentage and contributed only 0.1 % to the variation accounted for by the model.  Díaz et al (2002) similarly reported higher dressing values for feedlot lambs than for lambs raised under free-range conditions.  Part of the difference in dressing percentage between FL- and FR-lambs possibly stems from a smaller alimentary tract in the animals fed concentrates. Herbage consuming FR-lambs have larger alimentary tracts, thus weighing more (Owens et al 1993). Slaughter weight was also suggested to play a role in the higher dressing percentage of FL-lambs compared to FR-lambs (Díaz et al 2002).  This effect could not be confirmed in the present study, since no significant differences in slaughter weight were found between FL- and FR-lambs (Table 3).  Contrary to the present results, Santos-Silva et al (2002) found that FL- and FR-lambs showed similar dressing percentages.   

The effect of production system was significant (P < 0.05) for all measures of fatness considered (Table 3). The contribution of this factor to the variation accounted for by the model was 8.8 % for abdominal fat (P < 0.05), 15.5 % for kidney fat (P < 0.01), 14.6 % for subcutaneous fat 1 (P < 0.01) and 10.2 % for subcutaneous fat 2 (P < 0.05).  In contrast, the effect of gender was not significant, with respective contributions of 7.1 % (P = 0.11), 5.0 % (P = 0.18), 2.0 % (P = 0.53) and 6.3 % (P = 0.14).  According to these results, FL-lambs had greater levels of fat deposition than FR-lambs. Crouse and Field (1978) also observed greater fat deposition in lambs fed a high energy diet whilst Diaz et al (2002) observed a higher subcutaneous fat cover in FL-lambs compared to those raised under FR-conditions.  Lower levels of fat deposition in FR-lambs may be due to changes in the metabolism caused by physical activity during foraging.  Physical activity leads to greater muscular development at the cost of fat deposition.  Furthermore, an increase in carcass weight (Table 3) is also marked by an increase in carcass fatness.  It could thus be expected that the heavier carcasses of FL-lambs had greater fatness levels than FR-carcasses.  This argument was supported by the effect of production becoming non significant in analyses where carcass weight was included as a linear covariate.  Respective percentages of the variation accounted for by production system in these analyses were 0.3 % for abdominal (P = 0.61), 3.0 % for kidney fat (P = 0.09), 3.4 % for subcutaneous fat 1 (P = 0.12) and 1.9 % for subcutaneous fat 2 (P = 0.24).   

Male lambs (rams and castrates) were heavier at slaughter and produced heavier carcasses than ewes (P < 0.05; Table 4), with rams also outperforming castrates.  A comparable study suggested that carcasses of entire males are heavier than those of castrates and ewes (Dransfield et al 1990).  McClure et al (1994) also found that ram lambs produced heavier carcasses than ewe lambs in a study that did not include castrates.  

Dressing percentage and fat deposition were not affected by gender in the initial analyses without carcass weight as covariate (P > 0.10).  However, when means for the different indications for fatness were adjusted for carcass weight, it became clear that entire males had less fat deposition than ewes or castrates (Table 4).  They also had a thinner subcutaneous fat cover at site 2 than ewes and castrates.  This finding is not surprising, as it is generally accepted that ram lambs produce leaner carcasses than castrates and ewes at similar carcass weights (Crouse et al 1981; Seideman et al 1982; Arnold and Meyer 1988; Cloete et al 2007)      

The effect of production system on chemical meat quality characteristics of the BF and LD muscles is presented in Table 5.  Significant (P < 0.05) differences due to production system were observed for both the moisture and protein concentrations of both the BF and LD muscles between FR- and FL-lambs.  For both muscles, the average muscle moisture concentration of FR-lambs was higher than that of FL-lambs.  Although the intramuscular fat concentrations of both muscles did not differ between feeding systems, the FL-systems had higher fat concentrations in absolute terms, especially as pertaining to the BF where there was a tendency towards significance (P = 0.094). It could be argued that this difference might have become more pronounced and been similar to those reported by Kemp et al (1976) if the feedlot period was extended.  Summers et al (1978) also found that the average moisture concentration was higher in unweaned, pasture raised lambs compared to weaned, concentrate fed lambs.  Similar studies involving cattle show that steers fed concentrates ad libitum had lower LD moisture concentrations than steers fed either only grass as compared to grass supplemented with concentrates (French et al 2001).  Theriez and Tissier (1981) found that moisture and protein concentrations decreased when the fat concentration of lamb increased.  Schoeder et al (1980), on the other hand, found no difference in moisture concentrations between forage- and grain-finished beef.  The protein percentage of both the BF and LD muscles of FL-lambs was higher than that of FR-lambs.  These findings do not accord with those by Theriez and Tissier (1981) that muscle protein content decreases when fat content increases.  On the other hand, Rowe et al (1999) found that muscle protein was not affected by production system. Production system did not affect (P > 0.05) ash percentages or muscle myoglobin concentrations.

The effect of gender on the chemical meat quality characteristics of the BF and LD muscles is presented in Table 6.  Significant (P < 0.05) gender differences were found for the moisture concentration of both muscles.  Muscles of ram lambs had a higher moisture concentration than muscles from castrates and ewes.  It is well known that ram lambs produce carcasses with lower levels of fat deposition than castrates and ewes (Crouse et al 1981; Seideman et al 1982; Arnold and Meyer 1988), as was also observed for the LD muscle in the present investigation (Table 4).  In this investigation, the lower lipid concentration of meat from the LD muscle of ram lambs relative to castrates was related to an increased moisture concentration.  LD muscles of castrate lambs contained more (P < 0.05) intramuscular lipid than those of rams, ewes being intermediate and not different from the other sexes. Gender had no effect on the myoglobin concentration of both the BF and LD muscles. 

Conclusion

• The study agreed with published research results, indicating that feedlot lambs were generally fatter with a higher dressing percentage and carcass weight than free range lambs.  Despite generally heavier fat depots and a generally thicker subcutaneous fat cover, only a tendency towards an increased intramuscular lipid concentration was found for the Biceps femoris muscle of feedlot lambs.  The combination of leaner meat (as reflected by smaller fat depots and less subcutaneous fat) with a free range-production environment perceived by consumers to be beneficial to animal welfare, weighs heavily in favour of the latter system.  This lack of serious adverse effects on growth and slaughter traits of Dorper lambs under free range-conditions needs to be confirmed for lambs subjected to earlier weaning as well as a longer finishing phase in future studies.

Acknowledgements

The technical assistance of the technicians of the the Nortier Research Farm is appreciated, as is the financial contribution of the National Research Foundation of South Africa. 

References

AOAC 1997 Official Methods of Analysis.  15^th ed.  Arlington,VA.  USA:  Association Official Analytic Chemistry. 

AOAC 2002 Official methods of analysis (17^th edition). Arlington, Virginia, USA:  Association Official Analytic Chemistry. Ash of Animal Feed.  AOAC Official method 942.05. 

Arnold A M and Meyer H H 1988 Effects of gender, time of castration, genotype and feeding regime on lamb growth and carcass fatness.  Journal of Animal Science, 66:2468-2475. http://jas.fass.org/content/66/10/2468  

Bradford G E and Spurlock G M 1964 Effect of castrating lambs on growth and body composition.  Journal Animal Production, 6:291-299.  

Cloete J J E, Cloete S W P, Olivier J J and Hoffman L C 2007 Terminal crossbreeding of Dorper ewes to Ile de France, Merino Landsheep and SA Mutton Merino sires: Ewe production and lamb performance.  Small Ruminant Research, 69:28-35. 

Cloete S W P and De Villiers T T 1987 Production parameters for a commercial Dorper flock on extensive pastures.  South African Journal of Animal Science, 27:121-127.  

Crouse J D, Busboom J R, Field R  A and Ferrell C L 1981 The effects of breed, diet, sex, location and slaughter weight on lamb growth, carcass composition and meat flavour.  Journal of Animal Science, 53:376-381. http://jas.fass.org/content/53/2/376  

Crouse J D and Field R A 1978 Effect of dietary energy intake on carcass composition and palatability of different weight carcasses from ewe and ram lambs.  Journal of Animal Science, 47:1207-1218. http://jas.fass.org/content/47/6/1207  

Davies A, Titterington A J and Cochrane C 1995 “Who buys organic food?”  A profile of the purchasers of organic food in Northern Ireland.  British Food Journal, 97:17-23. 

Díaz M T, Velasco S, Caneque V, Lauzurica S, de Huidobro F R, Perez C, Gonzalez J and Manzanares C 2002 The use of concentrate or pasture for fattening lambs and its effect on carcass and meat quality.  Small Ruminant Research, 43: 257-268. 

Dransfield E, Nute G R, Hogg B W and Walters B R 1990 Carcass and eating quality of ram, castrated ram and ewe lambs.  Animal Production, 50:291-299. 

Field R A 1971 Effect of castration on meat quality and quantity.  Journal of Animal Science, 32:849. http://jas.fass.org/content/32/5/849.full.pdf+html  

French P, O’Riordan E G, Monahan F J, Caffrey P J, Mooney M T, Troy D J and Moloney AP 2001 The eating quality of steers fed grass and/or concentrates.  Meat Science, 57:379-386. 

Issanchou I 1996 Consumer expectations and perceptions of meat and meat product quality.  Review article.  Meat Science, 43:S5-S19. 

Jimenez-Colmenero F, Carballo J and Cofrades S 2001 Healthier meat and meat products: their role as functional foods, Review.  Meat Science, 59:5-13. 

Kemp J D, Johnson A E, Stewart D F, Ely D G and Fox J D 1976 Effect of dietary protein, slaughter weight and sex on carcass composition, organoleptic properties and cooking losses of lamb.  Journal of Animal Science, 42:575-583. http://jas.fass.org/content/42/3/575  

Krzywicki K 1982 The determination of haem pigment in meat.  Meat Science, 7:29-36. 

Lee C M, Trevino B and Chaiyawat M 1996 A simple and rapid solvent extraction method for determining total lipids in fish tissue.  Journal Association Official Analytic Chemistry, 79:2. 

McClure K A, Van Keuren R W and Althouse P G 1994 Performance and carcass characteristics of weaned lambs either grazed on orchard grass, ryegrass or alfalfa or fed all concentrate diets in feedlots.  Journal of Animal Science, 72:3230-3237. http://jas.fass.org/content/72/12/3230  

McEachern M G and Tregear A 2000 Farm Animal Welfare in the UK: A Comparison of Assurance Schemes.  Farm Manager, 10:11.  University of Reading. 

McEachern M G and Willock J 2004 Producers and consumers of organic meat: A focus on attitudes and motivations.  British Food Journal, 106:534-552. 

Milne C 2000 The history of Dorper sheep.  Small Ruminant Research, 36:99-102. 

Murphy T A, Loerch S C, McClure K E and Solomon M B 1994 Effects of restricted feeding on growth performance and carcass composition of lambs subjected to different nutritional treatments.  Journal of Animal Science, 72:3131-3137. http://jas.fass.org/content/72/12/3138  

Notter D R, Kelly R F and McClaugherty F S 1991 Effects of ewe breed and management system on efficiency of lamb growth production: II. Lamb growth, survival and carcass characteristics.  Journal of Animal Science, 69:22-33. http://jas.fass.org/content/69/1/22  

Owens F N, Dubeski P and Hanson C F 1993 Factors that alter the growth and development of ruminants.  Journal of Animal Science, 71:3138-3150. http://jas.fass.org/content/71/11/3138  

Priolo A, Micol D, Agabrie J, Prache S and Dransfield E 2002 The effect of grass or concentrate feeding system on lamb carcass and meat quality.  Meat Science, 62:179-185. 

Purchas A W 1978 Some effects of nutrition and castration on meat production from male Suffolk cross (Border Leicester-Romney cross) lambs.  New Zeeland Journal Agricultural Research, 22:375-383. 

Raven H 2000 (2001 in text) New voice for Scotland’s organic farmers.  The Scottish Farmer, ABC Bussiness Publication Ltd, Glasgow, 8 April. 

Richardson N J 1994 UK consumer perceptions of meat.  Proceedings Nutritional Society, 53:281-287. 

Rowe A, Macedo F A F, Visentainer J V, Souza N E and Matsushita M 1999 Muscle composition and fatty acid profile in lambs fattened in drylot or pasture.  Meat Science, 51:283-288. 

Salim H M, Shahjalal M, Tareque A M M and Akter N 2003 Intake and growth performance of female goats and sheep given concentrate supplement under grazing condition.  Pakistan Journal of Biological Science, 6:1304-1309. 

Santos-Silva J, Mendes L A and Bessa R J B 2002 The effect of genotype, feeding system and slaughter weight on the quality of light lambs 1. Growth, carcass composition and meat quality.  Livestock Production Science, 76:17-25. 

SAS 1999 SAS/STAT User’s Guide, Version 8, 1^st printing, Volume 2.  SAS Institute, Inc, SAS Campus Drive, Cary, North Carolina 27513.    

Schanbacher B D, Crouse D J and Ferrel LC 1980 Testosterone influences on growth, performance and carcass characteristics and composition of market young lambs.  Journal of Animal Science, 51:685-691. 

Schoeman S J 2000 A comparative assessment of Dorper sheep in different production environments and systems.  Small Ruminant Research, 36:137-146. 

Schroeder J W, Cramer D A, Bowling R A and Cook C W 1980 Palatability, shelf-life and chemical differences between forage- and grain- finished beef. Journal of Animal Science, 50:852-859. http://jas.fass.org/content/50/5/852  

Seideman S C, Cross H R, Oltjen R R and Scanbacher B D 1982 Utilization of intact male for red meat production.  Journal of Animal Science, 55:826-840. http://jas.fass.org/content/55/4/826  

Snyman M A and Olivier W J 2002 Productive performance of hair and wool type Dorper sheep under extensive conditions. Small Ruminant Research, 45:17-23. 

Summers R L, Kemp J D, Elly D G and Fox J D 1978 Effects of weaning, feeding system and sex of lamb on lamb characteristics and palatability. Journal of Animal Science, 47:622-629. http://jas.fass.org/content/47/3/622  

Theriez M and Tissier M 1981 The chemical composition of intensively fed lambs.  Animal Production 32:29-37. 

Van Trijp H 1995 Variety Seeking in Product Choice Behaviour: Theory with Application in the Food Domain, Ph.D. Dissertationd, Wageningen Agricultural University, the Netherlands. 

Verberke W A J and Viaene J 2000 Ethical challenges for livestock Production: Meeting consumer concerns about meat safety and animal welfare.  Journal Agricultural Environmental Ethics, 12:141-151. 

Vergara H, Molina A and Gallego L 1999 Influence of sex and slaughter weight on carcass and meat quality in light and medium weight lambs produced in intensive systems.  Meat Science, 52:221-226.

Received 26 December 2011; Accepted 14 April 2012; Published 1 June 2012

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