Contribution to a better definition of the production standards of the lamb Borrego do Nordeste Alentejano - PGI

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1 Contribution to a better definition of the production standards of the lamb Borrego do Nordeste Alentejano - PGI J. Santos-Silva 1 ; A. Esteves 2 ; N. Alexandre 2 ; S. Alves, 1 ; A.P. Portugal 1 ; I.A. Mendes 1; M. Silva Pereira 1 ; M. Vacas de Carvalho 2 & R.J.B. Bessa 1 1 Estação Zootécnica Nacional, Fonte-Boa, Vale de Santarém, Portugal 2 Natur-al-carnes, Parque de Leilões de Gado- EN 246, Portalegre, Portugal Abstract The objectives of this trial were to investigate the effects of: 1) the production system; 2) the increase of carcass weight from 12 to 15 kg; 3) the type of concentrate. In two consecutive years, a total of 336 lambs Borrego do Nordeste Alentejano PGI (BNA-PGI) were used. Two different management conditions were compared: in spring, when lambs were raised on pasture with their dams and supplemented with concentrate (120 lambs * 2 years); and in autumn when lambs were weaned and fed with concentrate afterwards (48 lambs * 2 years). Lambs were slaughtered at 28 or 33 kg live weight in order to obtain the target carcass weights. Three types of concentrate were compared: NATUR, a specific concentrate designed specially for BNA-PGI, vs. two commercial concentrates. Live weight was recorded every 14 days, from 60 days to slaughter. Carcasses were graded according to the UE grading schemes for lambs and carcass composition was estimated by partial dissection. Meat quality was evaluated by instrumental (colour and shear force) and sensorial methods. Fatty acid composition of intramuscular lipids of Longissimus thoracis muscle was determined. The quality of the BNA-PGI was totally independent of the type of concentrate. The increase of carcass weight had no negative effects on carcass or meat quality traits and did not compromise the requisites for certification as BNA-PGI. Shear force value was 40 % higher for lambs produced in confinement (autumn) than in pasture (spring). The panellists preferred meat from lighter lambs when raised in pasture (spring), and from heavier lambs when raised in confinement (autumn). The proportion of conjugated linoleic acid (C18:2 c9t11) was 2.65 fold higher and n-3/n-6 ratio was 2.55 higher in meat from lambs raised on pasture than from lambs raised in confinement. Keywords: lamb, carcass quality, meat quality, fatty acid, season Introduction The Borrego do Nordeste Alentejano (BNA-PGI) is a traditional product of the Northern Region of Alentejo in Portugal that is protected as a Geographical Indication. It represents an important income to the farmers of this region. In 2003, about carcasses (169 ton) of BNA-PGI were commercialised. The lambs are the product of Merino Branco (MB) ewes, a Portuguese breed for meat production, raised by the traditional production systems, where lambs are fed with natural pastures and local forages, supplemented with concentrates. Lambs must present slaughter ages from 90 to 120 days and carcass weights from 9 to 13 kg. They show high growth rates (> 300 g/day) in intensive production systems and produce carcasses up to 15 kg without excessive fat (Santos Silva & Vaz Portugal, 2000). The possibility of certificate carcasses up to 15 kg adds flexibility to the production systems and increases the sustainability of the production chain. To improve quality, some regulations of BNA-PGI could be altered increasing the safety and the homogeneity of the product. The definition of

2 specific formulae to produce BNA-PGI would allow a better control of the feeds, reducing variability of carcass composition and eventually the production costs, contributing to improve the image of the product, increase the market value and the farmer s profitability. Material and methods Three hundred and thirty six MB lambs BNA-PGI were used in 4 trials, conducted in 2 years. Two production systems were defined: in spring, when the lambs were raised in the pasture with the dams and supplemented with concentrate after 60 days of age; in autumn when lambs were weaned with 60 days, and fed in confinement with concentrate ad libitum and hay. Three types of concentrate were tested: two commercial (A and B) and one formulated specially to BNA-PGI (NATUR). Two slaughter weights were considered to obtain carcasses of 12 and 15 kg. In autumn, lambs were assigned to 6 groups of 8 lambs each, according to type of concentrate (A, B, NATUR) and carcass weight (12 and 15 kg), totalising 96 lambs in the 2 years. To study carcass composition and meat quality traits, 24 carcasses were used in each year. In spring, the trials were conducted in 2 private producers of BNA-PGI. In each farm, 60 lambs were assigned to 6 groups of 10 lambs, corresponding to the type of concentrate (A, B, NATUR) and carcass weight (12 and 15 kg), totalising 120 lambs per year. To study carcass composition and meat quality traits, 48 carcasses were used in each year. Live weight was controlled every 14 days. The lambs were slaughtered at Sousel slaughterhouse after a fasting period of 18 hours. The carcasses assigned to be studied, were transported to EZN abattoir and graded according to UE grading schemes (EEC, 1992). At the 7 th day, the left halves of the carcasses were divided in 8 joints (Calheiros & Neves, 1968) and the chumps and shoulders were dissected to estimate carcass composition (Santos Silva & Simões, 1999). The left loins were vacuum packed and frozen at 20ºC for shear force determination (Santos-Silva et al., 2002a). Colour of muscle Longissimus thoracis was measured in the L*, a* and b* system after 1 hour of blooming, using a Minolta CR-300 chromometer. Samples of Longissimus thoracis muscle were minced and frozen at 80ºC until lipid extraction, by the Soxlet method (AOAC, 1990; method ), and fatty acid determination. The fatty acid methyl esters were prepared according to Rule et al. (1997) and resolved in a gas chromatograph Varian 3800GC, using a Omegawax capillary column (Supelco, 30m length and 0.25 mm of internal diameter). The right loins and chops were collected and frozen at 20ºC until the organoleptic evaluation of meat. A panel of 50 consumers of BNA-PGI were used to evaluate the effects of the type of concentrate and carcass weight in meat quality. Frozen right joints (loins and ribs) were cut transversally in chops with 1 cm of thickness. Samples were grouped according to the 6 treatments of this trial (A-12 kg, A-15 kg, B-12 kg, B-15 kg, NATUR-12 kg, NATUR- 15 kg). Twenty-fours hours before the sessions, chops were thawed at 0ºC, salted, grilled and served in hot plates. Each panellist was presented simultaneously with 3 or 2 chops, to compare meat from the 3 concentrates or the 2 carcass weights respectively. Each panellist was asked to evaluate the likeness between samples and to grade them according to tenderness, taste, juiciness and overall acceptability. Data were studied using the Proc Mixed of SAS (2004), considering the fixed effects of production system, concentrate, carcass weight and their interactions, and using the year as aleatory block. Results and discussion Lambs growth and carcass and meat quality

3 In table 1 are presented the results for lambs growth, carcass composition and meat quality traits. Table 1. Effects of production system (PS), type of concentrate (C) and carcass weight (CW) on average daily weight gain (ADG), carcass composition and meat quality traits PS C CW Significance Aut Spr A B Natur PS C CW C*CW S*CW ADG (g) ns ns * CCW (kg) ns ns *** ** DP (%) ns ns *** HP (%) ns ns ns ** KKCF (%) *** ns * M (%) ns ns ns SF (%) ns ns ns DisF (%) ns ns ns MB *** ns ** IF/SF ns ns * L* ns ns ns a* ns ns ns b* ns ns ns SF (kg) *** ns ns Aut - autumn; Spr spring; CCW cold carcass weight; DP dressing percentage; HP higher price joints (leg, chump, loin and chops); KKCF kidney knob and channel fat; M muscle; SF subcutaneous fat; DisF dissectable fat (subcutaneous + intramuscular fat); MB muscle/bone; IF/SF - intramuscular fat / subcutaneous fat; L* a* b* - colour parameters; SF shear force; * - P<0.05; **- P<0.01; *** - P<0.001; ns not significant Generally, the carcasses with 12 kg were graded as class 3 of 1st quality. With 15 kg, most of the carcasses were graded as R and O for conformation and 2 and 3 for fattening. As the specifications of BNA-PGI include only carcasses graded as 2 or 3, the effects studied had no implication in the certification process. The lambs showed high growth performances (> 300g), in accordance to the results obtained in other trials (Santos Silva e Portugal, 2000; Santos-Silva et al., 2002a). Differences in carcass composition parameters were very narrow and probably have no implication in commercial value. Carcasses presented high proportion of muscle and low fat content independently of the production system and carcass weight. The effects studied have not affected meat colour, and values are similar to those reported by Santos Silva et al. (2002a). Lambs produced in spring showed lower shear force values, indicating a higher tenderness of meat. This was an interesting and unexpected result because the lamb s performances, carcass composition, management before and during slaughter and in storage (Sañudo et al., 1998) were similar. Consumer s panel have not depreciated meat of lambs fed with NATUR and preferred meat from lighter carcasses when lambs were raised in pasture (spring) and from heavier carcasses when lambs were raised in confinement (autumn).

4 Fatty acid composition of intramuscular fat In table 2 is presented the fatty acid composition of intramuscular fat. Table 2 Effects of production system (PS), type of concentrate (C) and carcass weight (CW) in Intramuscular fat content and fatty acid composition of muscle Longissimus thoracis adjusted to the proportion of intramuscular fat PS C CW (kg) Significance Aut Spr A B Natur PS C CW GI (%MS) *** ns ns C14: *** ns ns C15: *** ns ns C16: * ns ns C16: *** ns ns C17: *** ns ns C18: *** ns ns C18:1 c *** ns ns C18:2 n ** ns ns C18:3 n *** ns ns C18:2 c9t *** ns ns C20:2 n *** ns ns C20:3 n * ns ns C20:4 n *** ns ns C20:5 n *** ns ns C22:4 n *** ns ns C22:5 n *** ns ns C22:6 n *** ns ns hh ** ns ns n-6/n *** ns ns Aut - autumn; Spr spring; hh hipocholesteremic fatty acids (C18:0+C18:1 c9 + PUFA n-6 e+ PUFA n-3) / hipercholesteremic fatty acids (C14:0+C16:0); * - P<0.05; **- P<0.01; *** - P<0.001; ns not significant The production system was the main effect associated with the differences in the fatty acids composition of intramuscular fat. In accordance to other reports (Rowe et al., 1999; Sañudo et al., 2000; Santos Silva et al., 2002b), lambs raised on pasture showed a 2.5 fold higher proportion of n-3 fatty acids, reflecting the high content in linolenic acid of the grass lipids (Raes et al., 2004). The lambs raised in confinement had higher proportion of n-6 fatty acids, but the differences between production systems were not so expressive as for n-3 fatty acids. The ratio between n-6/n-3 fatty acids was 2.6 fold lower for lambs raised in spring, what is advantageous considering the recommendations of the nutritional advisers (Department of Health, 1994). The rumenic acid (C18:2 c9t11) is the main conjugated isomer of linoleic acid in ruminants fat that may have an important role in the prevention of some types of cancer (Pariza et al., 2001). The proportion of the C18:2 c9t11 was 2.65 higher in lambs raised on pasture than in those raised in

5 confinement. Other authors have reported high levels of C18:2 c9t11 in ruminants fed with diets rich in C18:3 n-3 (Raes et al., 2004, Bessa et al., 2005). The ratio between hipocolesteric and hipercolesteremic fatty acids was used as and indicator of the effect of fatty acid composition in cholesterol metabolism (Santos-Silva et al., 2002b). The higher value was observed for lambs raised in confinement, which is opposite to the results reported by Santos-Silva et al. (2002). In that trial the authors obtained hh values of 1.84 in lambs raised in confinement and fed with concentrate and 2.04 in lambs fed raised on pastured with their dams and supplemented with concentrate. The difference in the results is probably related to the higher number of n-6 isomers that were quantified in the present trial. References AOAC, Association of Official Analitycal Chemists. Fat (crude or ether extract in meat ), Official methods of analysis. Washington DC, USA Bessa R.J.B., P. V. Portugal, I. A. Mendes & J. Santos-Silva, Effect of lipid supplementation on growth performance, carcass and meat quality and fatty acid composition of intramuscular lipids of lambs fed dehydrated lucerne or concentrate. Livestock Production Science (accepted for publication) Calheiros, F. & A. Neves Rendimentos ponderais no borrego Merino Precoce. carcaça e 5º quarto. Sep. Boletim Pecuário ano XXXVI: Department of Health, Nutritional Aspects of Cardiovascular Disease. Report on Health and Social Subjects Nº46. HMSO, London EEC, Council Regulation (EEC) nº 2137/1992, concerning the Community Scale for the classification of carcasses of ovine animals. Official Journal L.214, 30/07/92,1-5 Pariza, M.W., Y. Park & M.E. Cook, The biologically active isomers of conjugated linoleic acid. Progress in Lipids Research, 40, Raes, K., S. de Smet & D. Demeyer, D., Effect of dietary fatty acids on incorporation of long chain polyunsaturated fatty acids and conjugated linoleic acid in lamb, beef and pork meat: a review. Animal Feed Science and Technology 113: Rowe, A., F.A.F. Macedo, J.V. Visentainer, N.E. Sousa & M. Matsushita, Muscle composition and fatty acid profile in lambs fattened in drylot or pasture. Meat Science, 51: Santos-Silva J. & A.V. Portugal, Influência do peso da carcaça na qualidade das carcaças de borregos das raças Serra da Estrela e Merino Branco produzidos em sistemas intensivos de produção. Revista Portuguesa de Zootecnia, ano VII, nº 1: Santos-Silva, J., R.J.B. Bessa & I. Mendes, 2002a. 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, Santos-Silva, J., R.J.B. Bessa & F. Santos-Silva, 2002b. The effect of genotype, feeding system and slaughter weight on the quality of light lambs. 2. Fatty acid composition of meat. Livestock Production Science, 77, Santos-Silva, J. & J. Simões, Predição da composição da carcaça de borregos da raça Merino Branco. Revista Portuguesa de Zootecnia, VI(1), Sañudo, C., M. Enser, M.M. Campo, G.R. Nute, G. Maria, I. Sierra & J.D. Wood, Fatty acid composition and sensory characteristics of lamb carcasses from Britain and Spain. Meat Science, 54: Sañudo C., A. Sanchez & M. Afonso, Small ruminant production systems and factors affecting lamb meat quality. Meat Science, 49, Suppl. 1:S29-S64 SAS Institute Inc, SAS/STAT 9.1User s Guide, Cary, NC, USA.