Evaluation of Tanzanian local chicken reared under intensive and semi-intensive systems: II. Meat quality attributes

Y D Sanka and S H Mbaga¹

Ministry of Livestock and Fisheries Development, P.O. Box 9152, Dar es Salaam, Tanzania
yeremiads@yahoo.com
¹Sokoine University of Agriculture, Department of Animal Science and Production, P.O. Box 3004, Morogoro, Tanzania

Abstract

The effect of rearing system and age at slaughter on meat tenderness, cooking loss and pH of male and female local chicken were assessed. The birds were randomly allotted to two rearing systems (intensive and semi-intensive systems). Each system was replicated four times with twelve birds each. In all the management systems, birds were given a diet containing 19% CP and 2679KJ ME with semi-intensive birds getting half of the amount given to intensive birds. At the end of the experiment, all 96 birds were slaughtered and carcass parts viz. breast, drumstick and thigh were separated. Pieces of meat from these parts were used for tenderness, cooking loss and pH evaluation.

There was no significant difference between intensive and semi-intensive systems on breast, thigh and drumstick meat tenderness. Chicken slaughtered at seventh month had higher shear force values than those slaughtered at fifth month. The cooking loss of male breast and thigh meat under intensive system were lower than that of birds under semi intensive system. Likewise, higher cooking losses were obtained for birds slaughtered at seven month than those at five month. Rearing system did not influence meat pH but, there was an increase in pH value of male thigh and drumstick meat with advanced slaughter age. It is concluded that the meat tenderness, cooking loss and pH values from both system were of acceptable standard, but the overall quality of meat is reduced with increased age at slaughter. To attain tender meat farmers should strive to improve management of their birds to reach slaughter weights at younger age.

Keywords: cooking loss, local chicken, meat tenderness, meat pH, production systems

Introduction

The poultry industry is going through a gradual but, definite change in product differentiation in response to consumer demands. However, some consumers still regard meat derived from local chicken as being tough. In Tanzania, chicken products are universally popular and in the coming years, the consumption of chicken meat will rise dramatically (FAO 2012). The trend is similar in many other Sub-Saharan Africa and Asia countries, where there has been a shift in demand for broiler meat in favor of local chicken meat. This preference is partly explained by their chewy texture, color and flavor of their meat (Guèye et al1997; Wattanachant et al 2005). Apart from taste, some consumers consider local chicken to contain less drug residue, since their management mimics that of organically farmed livestock. To ensure a sustainable continued growth and competitiveness of the local poultry meat industry, it is essential that local chicken meat quality and safety are maintained during production process.

Generally, quality of meat is judged by its tenderness, succulence, flavour and nutritive value. The quality is also influenced by strain, age at slaughter, the nutritional regime and rearing system (Sogunle et al 2010). Under scavenging mode of production, local chicken covers a great distance in search of feeds making the meat less tender (Guèye et al1997; Wattanachant et al 2004; Jaturasitha et al2008).Minimizing the distance covered by the birds and provision of supplementary feeds is expected to improve growth and quality of meat.Apart from other meat quality attributes, texture particularly tenderness, is an important selection criteria used by consumers when purchasing meat (Fanatico et al 2007). However, meat tenderness also depends on muscle type and some consumer discriminate meat cuts depending on their tenderness (Waskar et al 2009).The other factor influencing meat quality is the age at which the birds are slaughtered. Under traditional systems, often chickens are slaughtered many month post maturity, partly contributed by the slow growth rate. The result of which is increased toughness of meat (Northcutt et al 2001). It was the objective of this work to determine to what extent the quality of local chicken meat specifically; textural characteristics, water holding capacity and pH is affected by management system and slaughter age.

Materials and methods

Study site

The study was conducted at the Sokoine University of Agriculture, Department of Animal Science and Production Poultry Unit. The area is situated 6° S and 37° E and it is about 3 km south of Morogoro town. The area lies on the foot of the slopes of Uluguru Mountain at an elevation of about 500-600m above sea level. The annual rainfall ranges between 600 and 1000 mm per annum and the temperature ranges between 30°C and 35°C during the hottest months (October to January) and 20 – 27°C in the coolest months (April to August).

Experimental design and management of the experimental birds

A flock of 96 local chickens at two months old was used with 48 males and 48 females. Two rearing systems were evaluated viz. intensive (full confinement) and semi-intensive (partial confinement). A completely randomized experimental design was applied and males and females were allocated equally in the two rearing systems. The initial mean body weights in each group were about 519 g. The birds under intensive system were raised on deep litter. Density in each pen was 4birds/m². All birds were group fed with a diet containing 19% CP and 2679KJ ME from 2nd month to 5^th or 7^th month of slaughter. On average 86 g of feed per bird were offered to each bird in under intensive system.

Birds under semi-intensive system were raised outdoor allowing a space of 1 bird/10m². They were fed half of the amount allocated to birds under intensive system. Feed and water were provided outdoors using trough feeders and drinkers. Ground predators were excluded by fencing. For security reason, semi-intensive birds were confined to indoor pens at night.

All birds were weighed initially and thereafter, once per month. One half of the birds (n=48) with equal number of males and females in each rearing system were slaughtered for carcass evaluation at day 150 (approx. 5 month) and the remaining half slaughtered at day 210 (approx. 7 month). The birds were fasted for 12 hours, weighed individually and slaughtered by manual exsanguinations. The hot carcasses were divided into breast, thighs and drumsticks. The right part of the carcass was used for pH, cooking loss and tenderness evaluation.

pH measurements in meat muscle

A spear-end digital portable pH meter (Knick Portamess ® 910, Germany) was used to measure the pH of breast, thigh and drumstick of each individual bird at 45 minutes post-mortem. The pH meter was standardized by a two-point method against buffers of pH 4.0 and pH 7.0 standard solutions before measurement of each sample. In this regard, a total of 96 samples for each of the muscle part were used.

Cooking loss measurement

Forty five minutes post-slaughter, raw breast, thigh and drumstick muscle (20–30 g) from the right side of the carcass were cut, weighed and sealed in a plastic bag (30 microns) and cooked in a thermostatically controlled water bath (Fisher Scientific, Pittsburgh, PA) at 75°C for 45 minutes as described by Rizz et al (2007). Then, the samples cooled in running water for 15 minutes, dried with soft tissue and weighed. Cooking loss was calculated as percentage loss of weight during cooking relative to the weight of raw muscle (Petracci and Baéza 2009).

Tenderness (shear force value) measurement

Strips measuring about 1.0×1.0×2.5 cm parallel to the muscle fibres were prepared from breast, thigh and drumstick muscle portion and sheared vertically using Warner-Bratzler shear force device. The shear force values were recorded in Newtons (N).

Statistical data analysis

Data on shear force, cooking loss and pH were sorted by sex and analyzed using the General Linear Models (GLM) procedure of Statistical Analysis System (SAS 2006) software. Comparisons of means were analyzed using t-test. The model for shear force value, cooking loss and pH (pH45) analyses was as follows:

Y_ijk = μ + R_i + A_j+ (RA)_ij+ e_ijk

Where:
Y_ijk = the meat quality variables
μ = overall mean to all observations
R_i = effect of rearing system (full confinement or semi-scavenging)
A_j = the effect of slaughter age (5 months or 7 months)
(RA)_ik= the effect of interaction between rearing system and age
e_ijk = the residual random error.

Results and Discussions

Effect of rearing system and age at slaughter on meat tenderness

The mean levels of shear force values for meat muscle parts in the two rearing systems and at different ages at slaughter are presented in Table 1. The results shows that breast, thigh and drumstick meat from both male and female birds were not influenced (P>0.05) by the rearing system. The similarity of effects of rearing system on meat tenderness in the current study could be explained by reduced movements of semi-confined birds. This implies that under semi-confinement, birds have nearly equal movements to those under full confinement. The findings are in accordance with Fanatico et al (2005) and Dou et al (2009) who demonstrated that production system had no effect on tenderness of meat in the slow-growing broilers. Farmer et al (1997) also observed the same tendency for breast meat from birds reared under a lower stocking density, whilst Magala et al (2012) reported breast muscle tenderness in local Ugandan chicken not to be influenced by rearing system. However, these findings were contrary to those of Castellini et al (2002); Cheng et al (2008) and Pripwai et al (2014) who reportedproduction system to have an effect on the shear force values and higher values were generally obtained for breast and drumstick of chicken raised under free range system.

The results of the present study have similarly indicated that birds slaughtered at seven month had higher shear force values than those slaughtered at five month, implying that the meat was less tender (Table 1). The difference in tenderness values between age are explained by differences in thickness of sarcolemma muscle fibre whereby, young birds are expected to have thinner sarcolemma fiber rendering its meat to be more tender (Bals 2009). Age of the animal may be important because myoglobin, the primary muscle pigment, tends to increase with age in chicken (Lyon et al 2004).  However, Baéza et al (2012) reported contrasting finding whereby age at slaughter did not influence shear force value of cooked meat from a heavy broiler line raised for 63 days with slaughter age at 35 days, 42days, 49 days, 56 days and 63 days. An interaction effect between ages at slaughter within system on male breast tenderness was significant but, all in all birds slaughtered at older age regardless of the system had less tender meat.

Effect of rearing systems and age at slaughter on meat cooking loss

Results presented in Table 2 shows that cooking loss of male breast and thigh meat from birds reared under intensive system was lower than that of semi-intensive reared birds. However, the percentage cooking loss of breast and leg meat observed in the current study are much less than value of 29.81% and 33.69% for Thai indigenous chicken breeds raised indoor for 14 weeks as reported by Pripwai et al (2014). The difference could be attributed to breed effects. These results in the current study agrees with those of Castellini et al (2002) and Fanatico et al (2007) who observed that outdoor (free range) reared birds have lower cooking loss than birds reared indoors. To the contrary, Magala et al (2012) found no difference in cooking loss of Ugandan local chicken meat raised under three rearing system. To the consumer, cooking losses is important in carcass and further-processed meat product, since less cooking loss result to increased juiciness and tenderness of meat (Dabes 2001 and Wang et al 2009).

Table 2 summarizes the effects of slaughter age on cooking loss. Cooking losses were higher in both male and female slaughtered at seven month than those slaughtered at younger age (five months). Likewise, there was an increase in cooking loss in all parts (breast, thigh and drumstick) with age. Similar trend was observed by Baéza et al (2012) in a modern heavy broiler line. As expected, there were a parallel relation between cooking loss and tenderness although, cooking loss did not vary much between parts (Table 1 and 2). Furthermore, significant interactions were also observed between rearing system and age at slaughter on cooking losses percentage in male breast and thigh meat. The implication of this finding is that one should choose an appropriate age to slaughter local chicken so as to optimize meat quality especially, tenderness.

Effect of rearing systems and age at slaughter on meat pH

Rearing system did not influence meat pH at 45 minutes post-slaughter although the general trend was for pH to be slightly lower in cuts from semi-intensive system (Table 3). In contrast, Culioli et al (1990), Castellini et al (2002), Alvarado et al(2005), Wattanachant (2008) and Hanyani (2012) reported high meat pH in chickens raised under free-ranging systems. Similarly, Husaket al (2008) observed higher pH values in broiler meat raised organically compared to those under conversional production system. Such results are expected, and the difference from current study could be explained by the limited movement of birds under semi-intensive system. It was further revealed that thigh and drumstick meat tended to exhibit higher pH than the breast. These differences are probably attributed to higher muscle activities in leg muscles than breast muscles.

Conversely, Jaturasitha et al (2008) reported pH value of 5.77 at the age of 112 days in Thai native chicken, the value to a large extent being influenced by the nature of rearing. Nonetheless, the pH values obtained in the current study at 45 minutes post-slaughter are within the range of 6.16 to 6.31 for 15 minutes and 1 hour post-slaughter respectively reported by Raach-Moujahed and Haddad (2013). Normally, living muscle has a pH value of 7. The pH drops relatively quickly thereafter, post slaughter. At a pH of 5.4 to 6.2 the meat is normally considered to be of high quality (Vacaru-Opris and Col, 2000 cited by Bals, 2009; Owens et al 2000; Woelfel et al 2002).

With regard to age effects, there was no sex difference in pH values for birds slaughtered at five or seven month of age. Nonetheless, the effect of slaughter age on pH was inconsistent although males exhibited slightly higher pH values for drumstick and thigh respectively, at seven month than at five months (Table 3), implying that, males were probably more active than females. In contrast, Baéza et al (2012) reported major changes in breast meat between the age of 35 and 49, with an increase in muscle pH at 15 minutes and 24 hours post-mortem in heavy broiler line. Similar observation was made by Ponte et al (2008c). According Husak et al (2008) higher meat pH is more effective for retaining desirable colour and moisture absorption properties. But, higher pH is also related to poor shelf life since it provides conducive environment for bacterial growth (Owen et al 2000; Woelfel et al 2002).Significant interaction were also observed between rearing system and age at slaughter on meat pH of male thigh and drumstick meat muscles. This has been mainly influenced by effect of age at slaughter.

Conclusions

• It is concluded that rearing system had little influence on meat quality in terms of tenderness and pH at 45 minutes post slaughter and slaughtering birds at five month yielded more tender meat with lower cooking loss. Furthermore, the meat tenderness, cooking loss and pH values from both systems were of acceptable standard, but the overall quality of meat is reduced with increased age at slaughter. Therefore, poultry farmers should raise their local chicken for meat production for at about five month; which has been observed to have recommendable weight for slaughter and higher quality meat.

Acknowledgements

This work was supported by the Government of the United Republic of Tanzania under the Ministry of Livestock and Fisheries Development. Appreciation is extended to laboratory technicians and assistant poultry attendants of the department of animal science and production at Sokoine University of Agriculture, for their tireless assistance in data collection.

References

Alvarado C Z, Wenger E and O’keefe S F 2005 Consumer perception of meat quality and shelf-life in commercially raised broilers compared to organic free ranged broilers. Journal of Poultry Science 84:129.

Baeza E, Arnould C, Jlali M, Chartrin P, Gigaud V, Mercerand F, Durand C, Méteau K, Le Bihan-Duval E and Berri C 2012 Influence of increasing slaughter age of chickens on meat quality, welfare, and technical and economic results. Journal of Animal Science 90:2003-2013. Retrieved on March 27, 2014 from http://www.journalofanimalscience.org/content/90/6/2003

Bals C 2009 Quality of Poultry meat and factors that define it. University of Oradea, Faculty of Environmental Protection, 26 Gen. Magheru St. 410048 Oradea.

Castellini C, Mugnai C and Bosco A D 2002 Effect of organic production system on broiler carcass and meat quality. Meat Science, 60:219-225.

Cheng F Y, Huang C W, Wan T C, Liu Y T, Lin L C and Lou Chyr C Y 2008 Effects of Free-range Farming on Carcass and Meat Qualities of Black-feathered Taiwan Native Chicken Asian-Australian Journal of Animal Science. 21 (8): 1201 – 1206.

Culiolo J, Touraille C, Bordes P and Giraud J P 1990 Carcass and meat quality in fowls given the “farm production label”. Archiv fuer Gefluegelkunde 53, 237-245.

Dabes A C  2001 Propriedades da carne fresca. Revista Nacional da Carne, Săo Paulo, 25: 32-40.

Dou T C, Shi S R, Sun J and Wang K H 2009 Growth rate, carcass traits and meat quality of slow-growing chicken grown according to three raising systems. Animal Science Papers and Reports, 27 (4): 361-369.

Fanatico A C, Pillai P B, Cavitt L C, Owens C M and Emmert J L 2005 Evaluation of slow-growing broiler genotypes grown with and without outdoor access: Growth performance and carcass yield. Poultry Science, 84, 1321-1327.

Fanatico A C, Pillai P B, Emmert L J and Owens C M 2007 Meat quality of slow- and fast- growing chicken genotypes fed low-nutrient or standard diets and raised indoors or with outdoor access. Journal Poultry Science 86, 2245-2255

FAO 2012 Scoping Study on Value Chain Initiatives and Studies in Tanzania. Study Undertaken by Match Maker Associates Limited. Final Report, April 2012.

Farmer L J, Perry G C, Lewis P D, Nute G R, Piggott J R and Patterson R L S 1997 Responses of two genotypes of chicken to the diets and stocking densities of conventional UK and label rouge production systems. II. Sensory attributes. Meat Science 47, 77-93.

Guèye E F, Dieng A and Dieng S 1997 Meat Quality of Indigenous and Commercial Chickens in Senegal. Proceedings of INFPD Workshop. M’Bour, Senegal.

Hanyani C T 2012 Effect of Full and Semi-Scavenging Rearing Systems on Crop Contents and the Quality of Meat from Village Chickens during the Spring Season of Eastern Cape, South Africa. Msc Thesis, Fort Harare University, South Africa.

Husak R L, Sebranek J G, Bregendahl K 2008 A Survey of Commercially Available Broilers Marketed as Organic, Free-Range, and Conventional Broilers for Cooked Meat Yields, Meat Composition, and Relative Value. Journal Poultry Science 87, 2367–2376

Jaturasitha S, Kayan A and Wicke M 2008 Carcass and Meat characteristics between Thai Village chickens compared with improved layer breeds and their crossbred. Poultry Science, 51(3): 283- 294.

Lyon B G, Smith D P, Lyon C E, Savage E M 2004 Effect of diet and feed withdrawal on sensory descriptive and instrumental profiles of broiler breast fillets. Poultry Science 83: 275-281.

Magala H, Kugonza D R, Kwizera H and Kyarisiima C C 2012 Influence of Management System on Growth and Carcass Characteristics of Ugandan Local Chickens. Journal of Animal Science Advance Vol. 2(6): 557-567.

Northcutt J K, Buhr R J, Young L L , Lyon C E, and Ware G O 2001 Influence of age and post chill carcass aging duration on chicken breast fillet quality. Poultry Science. 80:808–812.

Owens C M, Hirschler E M, McKee S R, Martinez-Dawson R and SamsA R 2000 The characterization and incidence of pale, soft, exudative turkey meat in a commercial plant. Poultry Science 79:553–558.

Petracci M and Baéza E 2009 Harmonization of methodology of assessment of poultry meat quality features. Working paper of WPSA Working Group 5 Poultry Meat July 2009.

Ponte P I P, Prates A M, Crespo J P, Crespo D G, Mourao M A, Alves S P, Bessa R J B, Chaveiro-Soares M A, Ferreira L M A and Fontes C M G A 2008  Restricting the intake of a cereal-based feed in free-range-pastured poultry:Effect on performance and meat quality. Poultry Science 87, 2032-2042

Pripwai N, PattanawongW,Punyatong M andTeltathum T 2014 Carcass Characteristics and Meat Quality of Thai Inheritance Chickens. Journal of Agricultural Science; 6 (2):182. http://dx.doi.org/10.5539/jas.v6n2p182

Raach-Moujahed A and Haddad B 2013 Performance, Livability, Carcass Yield and Meat Quality of Tunisian Local Poultry and Fast-Growing Genotype (Arbor Acres) Fed Standard Diet and Raised Outdoor Access. Journal of Animal Production Advance Vol. 3(3): 75-85.

Rizz C, Marangon A, and Chiericat G M 2007 Effect of Genotype on Slaughtering Performance and Meat Physical and Sensory Characteristics of Organic Laying Chicken. Poultry Science, 86:128–135.

Sogunle O M, Egbeyale L T, Alajo O A, Adeleye O O, Fafiolu A O, Onunkwor O B C, Adegbite J A, and Fanimo A O 2010 Comparison of Meat Composition and Sensory Values of Two Different Strains of Broiler Chickens. Archivos de zootecnia. vol. 59, no. 226, p. 314.

SAS 2006 Statistical Analysis Software. The SAS system for Windows (Release 9.1).SAS Institute, Cary, NC, USA.

Wang K H, Shi S R, Dou T C and Sun H J 2009 Effect of a free-range raising system on growth performance, carcass yield, and meat quality of slow-growing chicken. Poultry Science. 88:2219-2223.

Waskar V S, Devangare A A, Gosavi P P, Ravikanth K, Maini S, Rekhe D S 2009 Meat quality Attributes of broilers supplemented with Herbal Toxin Binder product. Veterinary World, 2(7): 274-277.

Wattanachant S, Benjakul S, Ledward D A 2004 Composition, colour, and texture of Thai indigenous and broiler chicken muscles. Poultry Science, 83: 123–128.

Wattanachant S, Benjakul S and Ledward D A 2005 Microstructure and thermal characteristics of Thai indigenous and broiler chicken muscles. Poultry Science 84:328–336.

Wattanachant S 2008 Factors affecting the quality characteristics of Thai indigenous chicken meat. Journal of Science and Technology, 15 (4): 317-332.

Woelfel R L, Owens C M, Hirschler E M, Martinez-Dawson R and Sams A R 2002 The characterization and incidence of pale, soft, and exudative broiler meat in a commercial processing plant. Poultry Science, 81: 579–584.

Received 23 June 2014; Accepted 7 July 2014; Published 5 September 2014

Go to top