Evaluation of Tanzanian local chicken reared under intensive and semi-intensive systems: I. Growth performance and carcass characteristics

Y D Sanka and S H Mbaga¹

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

Abstract

The objective of this study was to determine the effect of rearing systems, sex and age at slaughter on growth performance and carcass traits of local chicken. A total of 96 local weaned chicks (two months old) were bought from farmers in Morogoro peri-urban and reared under two different rearing system viz. intensive and semi-intensive systems.  The birds were initially weighed and randomly assigned to each rearing system with equal number of males and females (48 birds per system). Two pens with deep litter were used to house the birds. Spacing for birds in both systems was 4birds/m².  However, birds under semi-intensive system had free access to grassy paddock (1 bird/10m²). All birds were offered the same diet with semi-intensive group receiving half of what was offered to the intensive group. Random sample of 24 males and 24 females in each rearing system were slaughtered at five and seven month.

Body weights at slaughter and body weight gain of birds from semi-intensive system were significantly lower than of those kept in intensive system. There was no difference in dressing percentage between the two rearing systems, the values being 65.2% and 65.7% for intensive and semi-intensive respectively. Dressing percent was higher (67.7%) at seven month than at five month of age (63.2%). The rearing systems significantly affected the breast percentage, being higher in semi-intensive (25.1%) compared to intensive system (23.3%).  Thigh percent was not influenced by rearing system or slaughter age, while drum stick percent was significantly lower at seven month old bird compared to five month old birds.  From the study, it is concluded that local chicken with modest supplementation and assuming availability of scavenging feed resources, semi-confinement system of chicken rearing could be more appropriate for the small holder poultry keepers. 

Keywords: age at slaughter, foraging, rearing system, scavenging, SFB

Introduction

Poultry, particularly chickens are the most widely kept and most numerous livestock species in the world (Perry et al 2002; Moreki et al 2010). Local chickens are widely distributed in rural and peri-urban areas where they play the important role of income generation, food production and social aspect (Mwalusanya et al 2001; Thornton et al 2002; Moreki et al 2010). In Tanzania, local chickens makeup over 70% of the total chicken population and supply most of the poultry meat and eggs for domestic market (MLFD 2012). Local chickens are reared under different production systems, mainly scavenging, semi-intensive system and to a lesser extent intensive systems. Free range system is dominant in most rural areas and has been practiced for many years in Africa (Sonaiya 1990 and Kitalyi 1998). Although requiring minimal resource input and considered secondary to other agricultural activities by farmers, this type of production has many limitations including diseases, predators and poor growth rate (Mwalusanya et al 2001; Mutayoba et al 2012). Furthermore, scavenging and semi-scavenging are characterized by low plane of nutrition that varies with season (Mwalusanya et al 2002; Goromela et al 2006) ultimately affecting the growth performance.

Presently, most research attempts on local chicken have been focused on increased production, disease management and marketing (Msofe et al 2002; Mwalusanya et al 2002; and Mlozi et al 2003).   However, there is an increase in demand of local chicken meat and eggs in Africa owing to their good taste compared to products from exotic commercial strains. In this regard, the increased demand, need to be matched with quality which to a larger extent will depend on the management systems to be adopted.  This study therefore investigates the effects of rearing systems and age at slaughter on growth performance and gross carcass characteristics.

Materials and Methods

Study area

The research was conducted at the Sokoine University of Agriculture, Department of Animal Science and Production poultry unit. The area is situated 6^o S and 37^o 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 ^oC and 35 ^oC during the hottest months (October to January) and 20 – 27 ^oC in the coolest months (April to August).

Experimental design and bird management

A flock of 96 local chickens at two months of age was used with 48 males and 48 female. 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. Initially the groups were arranged such that the mean body weight in each group was about 519 g. The birds under intensive system were raised on deep litter with a density of 4birds/m² in each pen. Temperature was 25±3°C and a relative humidity was 65-75% on average. All birds were group fed with a diet containing 19% CP and 2679KJ ME from 2^nd month to 5^th and or 7^th month of slaughter. On average 86 grams of feed was offered per day to each bird under intensive system.

Birds under semi-intensive system were put in a separate pen (4 birds/m²), but with a free access to open grassy area (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 iron sheet fencing. For security reason semi-intensive birds were confined to indoor pens at night.

Data collection

All birds were weighed initially and thereafter, once per month. One half of the birds (n=48) with equal number of males (n=24) and females (n=24) 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 carcass was eviscerated and the warm carcass weighed. This was followed by removal and weighing of carcass parts mainly; the breast, thigh and drumstick. The dressing percent was expressed as percent of eviscerated carcass to the live body weight after fasting. The breast, thigh and drumstick weights were expressed as percent of dressed carcass weight.

Data analyses

Data were subjected to analysis of variance using a General Linear Model (GLM) procedure in SAS Software System (SAS 2006). Means were compared using t-test. The following statistical model was used to analyze the effects of rearing system sex and slaughter age on production and carcass parameters. Interaction were tested but were not significantly different.

Y_ijk = μ + R_i + S_j + A_k + b(x-∑𝑥∕𝑛)_ijk + e_ijk

Where,

Y_ijk       = an observation for a given variables.

μ          = overall mean

R_i           = effect of the i^th rearing system (i: 1=semi-intensive, 2=intensive)

S_j         = effect of the j^th sex (j: 1=male, 2=female)

A_k          = age at slaughter (k: 1=five month, 2=seven months)

b(x-∑𝑥∕𝑛)_ijk = initial weight as covariate

x          = initial weight of chicken

∑𝑥∕𝑛    = average initial weight

b          = regression coefficient

e_ijk        = residual random error

Results and Discussion

Growth Performance

Figure 1 show that the body weight of chicken reared under intensive system had greater response in body weight beginning week three than those under semi-intensive system. However, at week seven the difference was rather small; the group under intensive system appearing to slow down which could have resulted from inadequate feed intake. The continued growth under semi-intensive system could probably be associated with compensatory effects.

Figure 1: Effect of rearing system and age on live body weight.

On overall, the weight gain of chickens in the semi-intensive system was significantly (P<0.05) lower (9.84 g/d) than in the intensive system (11.95 g/d), the difference being about 21% (Table 1). The higher weight of birds kept in full confinement could be explained by higher feed intake, and probably better feed conversion efficiency due to lower energy expenditure for exercise. However, birds under semi-intensive system were more efficient in feed conversion ratio. Birds under partial confinement (semi-intensive) gained less despite the access to range, which provided enough green but, with limitation of energy. It should be noted that birds under semi-intensive system were given only half of the feed that were given to full confined group. These results are similar to those reported by Mutayoba et al (2012); Magala et al (2012); Dou et al (2009) and Castellini et al (2002) who reported growth rate and feed efficiency in scavenging, free-range and outdoor organic rearing respectively to be lower than in intensive rearing system.   The ADG ranged from 10.4 to 15.2 g/day in males and 8.4 g/day to 11.6 g/day in females. These results are closer to the average value of 10.81 g/d reported by Raach-Moujahed et al (2011) in  Tunisian local chicken, but higher than the value of 6.6 – 8.0g reported by Hassen et al (2006) in Ethiopia. The differences observed in these studies could be attributed to difference in genetic background of the stock used as well as type of management, including feeds.

As expected, body weight at slaughter increased progressively with age and at seven months old, both males and females were heavier compared to five month old birds (Table 1). Comparison between slaughter ages indicates that under intensive system, the difference in cumulative weight between males and females were about 4% (428.9 g for males and 446.8 g for females). This difference was much higher (10%) under semi-intensive system in favour of males (545.7g for males and 492.2 g for females).   

In this study there was a distinct difference in magnitude of decline in growth rate by sex and rearing system. Males under intensive system lost about 4 g between month five and month seven compared to males under semi-confinement (-1.5g). These observations connotes that males under semi-intensive had less stress compared to those under intensive system by having space to escape in case of presence of aggressive males. This probably gave them more access to feed and also explain the higher cumulative weight gain of males under semi-confinement.

The trend in body weight shows that under both systems, birds could be slaughtered at the age of five month and above when birds have attained body weight of more than one kilogram.  This implies that if scavenging feed resources are adequate, semi-confinement system of rearing with modest supplementation could thus be more economical for the small holder poultry keepers. Kitalyi (1998) support the contention that free-ranging chicken should be given supplementary feeds depending on seasonal availability of common feed resources. When such feeds are adequate performance of such birds can be improved and the feed costs will always be lower than if birds are fully confined. However, if birds are left to roam freely, the distance moved by the birds in search of feed can have negative effects on growth and ultimately affect slaughter age and meat quality. Nonetheless, body weights at five month old in this experiment are within the range of weights reported for some of the Tanzania ecotypes. For example, Lwelamira et al (2008b) reported body weights of 1295-2318 g for Kuchi ecotype and 1070-2040 g for Medium ecotype under intensive system and 870-1567 g for Kuchi ecotype and 817-1419 g for Medium ecotype under extensive system at the age of 20 weeks.  Comparable results were also reported in growth parameters by Hassan et al (2006) in indigenous chickens under intensive management conditions in Northwest Ethiopia.

Carcass traits

The effects of rearing system, sex and age on carcass traits are shown in table 2 and figure 2. There was no significant difference between dressing percent in the two rearing systems, the value being 65.2% and 65.7% for birds under intensive and semi-intensive system respectively.  The results conform to those reported by Dou et al (2009), Cheng et al (2008), Fanatico et al (2005) and Raach-Moujahed and Haddad (2013). Raach-Moujahed and Haddad (2013) reported a mean dressing percent of 68.6 percent for Tunisia local chicken raised for 112 days with outdoor access.  Likewise, there was no significant difference in dressing percent between males and females within slaughter age, the average values being 66.2 and 64.7 percent for males and females respectively. However, birds slaughtered at seven month had significantly higher carcass percent (67.7) than those at five month (63.2%) (Figure 2). The higher dressing percent in 7 month birds is expected since, as birds increase in weight there is proportionate increase in muscle and other tissues except bones which at 5^th month are most likely to have approached peak growth.

Figure 2. Effect of age on carcass traits percentage of local chicken.

Differences were also observed for breast percent between rearing system and slaughter age. Semi intensively reared birds had significant higher breast percent (24.9) compared to intensively reared birds (23.6%).  This observation is similar to that reported by Cheng et al (2008) and Castellini et al (2002) who found that breast meat content of carcass increased when birds had access to outdoor production system. This can be explained that the lower stocking density and increased physical activity could reduce the abdominal fat and increase the percentage of breast meat (Lewis et al 1997). But, the findings are contrary to those of Wattanachatt (2008) who reported high percentage of breast muscle from village chickens reared under full feed supplements compared to those under extensive system. Likewise, older birds at 7 month had higher value for breast compared to those at 5 month. Similarly Baéza et al (2012) reported higher meat yield of breast in broiler chicken slaughtered at different ages.

Percent drumstick was only influenced by sex and age at slaughter, with higher values in males compared to females and lower value at 7 month (14.5%) compared to a value of 16.2% at five month. These observations imply that slaughter age is most critical in determining dressing percent and weights of carcass components.  The only component that was not affected by slaughter age was the proportion of the thigh. Thus, in deciding as to when birds are to be slaughtered a compromise must be reached taking into account the management system to be adopted. 

Conclusions

• It is concluded that rearing system has a significant influence on slaughter weight, weight gain and breast percent. Similarly, slaughter age influenced most of the carcass traits except thigh percent. Furthermore, birds under semi-intensive system consumed relatively less supplementary feed and resulted to better feed conversion efficiency. This implies that, with modest supplementation and assuming availability of scavenging feed resources, semi-confinement system of chicken rearing could be more economical for the small holder poultry keepers.

Acknowledgements

The authors would like to thank the Ministry of Livestock and Fisheries Development for the financial support. 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 support in data collection.

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Received 25 May 2014; Accepted 1 June 2014; Published 1 July 2014

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