Physical egg quality characteristics of free-range local chickens in Morogoro municipality, Tanzania

H E Nonga, F F Kajuna, H A Ngowi and E D Karimuribo

Department of Veterinary Medicine and Public Health, Sokoine University of Agriculture, Box 3021, Morogoro, Tanzania
hezron@suanet.ac.tz   ;   nongahezron@yahoo.co.uk

Abstract

Physical quality characteristics of free range local chicken (FRLC) eggs were determined in Morogoro municipality between January and February 2007. Ching’wekwe, N’zenzegere and Morogoro medium were the FRLC ecotypes common in Morogoro municipality of which their eggs were assessed. Ninety and 60 eggs samples were collected from backyard farms and central market respectively. Up to 88% of the farmers reported to store the eggs at room temperature for up to 12 days. All the egg sellers at markets stored the eggs at room temperature for up to two weeks.

Mean values for egg traits were 40.8g, 4.9g, 0.4mm, 21.9g, 3.9mm, 13.6g, 0.76cm, 2.5cm, 31.6% and 67.7 for egg weight, shell weight, shell thickness, albumen weight, albumen height, yolk weight, yolk height, yolk width, yolk index and Haugh unit, respectively. The mean egg weight for eggs from the farms were significantly (p<0.05) higher than those from the market. An overall prevalence of egg defects recorded was 44.7%. A significantly (p<0.05) higher number of defected eggs was observed in eggs from the farm (51.1%) than those from the market (35.0%). The defects recorded include rough shell (6.0%), cracked shell (15.3%), ruptured viteline membrane (5.3%), pungent smell (4.7), mottled yolk (7.3%), meat spots (2.7%), blood spots (4.7%), brown spots (2.0%), flabby yolk (4.7%), embryonated (2.0%), watery albumen (8.0%) and cloudy albumen (1.3%). Most of the eggs examined (79.3%) had dirty shells which were stained with faeces, leaking albumen, feather particles, soils and litter materials.

This survey provides a preliminary baseline data on physical egg quality characteristics of FRLC in Morogoro urban and periurban areas. Further studies are recommended on quality characteristics using specified FRLC eco-types from different regions of the country to better conclude on their quality.

Keywords: eggs, free range local chickens, quality characteristics, Tanzania

Introduction

The population of free-range local chicken (FRLC) in Tanzania as per 1998 National livestock census comprises of 26,385,506 birds (MAFS 2002). Like many other developing countries; chicken production in Tanzania largely depends on FRLC constituting up to 94% of the total poultry population (MAFS 2002). More than 80% of local chickens are kept under free-range system in rural areas with an average flock size of 23-30 birds (Msoffe 2003). The local chicken sector constitutes a significant contribution to human livelihood and contributes significantly to food security of poor households in most African countries (Mlozi et al 2003; Gondwe 2004). It is an important agricultural activity of almost all rural communities in Africa, providing scarce animal protein in the form of meat and eggs as well as being a reliable source of petty cash, savings, investment, insurance and serve in traditional medicine (Mlozi et al 2003). The importance of FRLC in the national economy of developing countries and its role in improving the nutritional status and income of many smallholder farmers and landless communities has been very significant (FAO 1997; Mwalusanya et al 2001).

The importance of FRLC does not end only to rural communities but rather the entire population in Tanzania. In fact, the big market for FRLC meat and eggs is in urban areas where consumers from such urban markets are hotels, restaurants and some affluent city dwellers (Mlozi et al 2003). Recently, there are trends in consumers’ general preference for products of chickens kept in free-range conditions. In most African urban areas, FRLC eggs and meat are more expensive than the intensively reared poultry because the former are considered as tastier, free of antibiotics, hormones and other harmful chemicals. Furthermore, there are no cultural or religious taboos relating to consumption of eggs and chicken meat like those for pig meat (Tadelle 2003). Therefore, this may be the reason for eggs and meat of FRLC in Tanzania to fetch higher market and prices compared to commercial layer chicken eggs. For example, eggs from a local hen sell at five times higher price than the eggs from exotic strain. Currently, FRLC production in Tanzania is increasing largely due to increased demand for eggs and chicken meat of which more people venture into the chicken projects (Mwalusanya 2001).

Because of this expansion of FRLC production industry and market, a need for good quality food from the chicken is important. This is aimed at safeguarding the public and market improvement for the products. Moreover, quality determines the acceptability of the eggs to potential customers who are interested with good quality food. Proper attention to production, storage, distribution and point-of-sale phases are of vital importance in maintaining egg quality. It is clear that the egg quality and their stability during storage are largely determined by their physical structure and chemical composition (Seidler 2003). The value physical factors most generally appreciated in eggs are shell appearance and strength, egg size, weight and physical appearances of internal structures (Seidler 2003; Roberts 2004). The internal physical quality factors include appearance of albumen and yolk, Haugh unit and yolk index (Tharrington et al 1999; Zaman et al 2005). Moreover, these egg quality traits have significant and direct effects on the prices especially when the eggs are graded (Seidler 2003).

Several studies that have been conducted aimed at improving management and productivity of FRLC in Tanzania (Mwalusanya et al 2001; Msoffe et al 2002). No studies have been carried out to characterize, evaluate and understand the quality of eggs produced from FRLC production systems in Tanzania. Scarcity of studies on quality of eggs makes it difficult to establish quality standards, grades and possibly expand FRLC egg market to export level. This may also be difficult to provide tangible advice to farmers on the appropriate requirements for good quality egg production. The current study aimed to determine physical egg quality characteristics of FRLC eggs produced in Morogoro Municipality in Tanzania. This baseline information established will be useful to the producers, sellers and livestock officials on how to improve the FRLC egg so as to safeguard the public health and can fetch good markets.

Materials and methods 

Study areas

The study was conducted in Morogoro municipality from January to April 2007. The municipality is situated at the latitude 5.7 to 10^oS and longitude 35.6 to 39.5^oE, with an elevation of 500 to 600m above sea level and is about 200 km west of Dar es Salaam. Although selection of Morogoro municipality, as study area, was based on convenience of accessibility from the laboratory (due to limited funding of the project), it generally represents smallholder local chicken farming in urban and periurban areas of Tanzania.   

The samples were collected from the purposively selected households with FRLC and willingness of farmers to participate in the study. A pre-survey was done to identify households keeping FRLC which were at the laying stage. The study farms were from different suburbs of Morogoro urban and periurban areas namely Kididimo, Mkundi, Forest hill, Mazimbu, Kilakala, Miembeni, Kihonda, Mafiga, Misufini and Sabasaba. In addition, some FRLC eggs were obtained from sellers at Morogoro central market who were willing to participate in the study. Eggs from the market were included for the quality comparison with the freshly laid eggs from households. The egg sellers at the market receive FRLC eggs for sale from villages nearby the municipality.

Sampling of eggs

Ninety eggs were obtained from 30 different households and 60 eggs from 10 egg sellers at the Morogoro central market. During the visit information on chicken strain (ecotype), age, management, feeding, period the eggs were laid, uses of eggs and storage conditions were recorded. The eggs were selected using random sampling and on average three eggs were sampled from each study household. Only freshly laid eggs (not more than 24 hours from oviposition time) were considered for study. The same egg selection approach was used from the egg sellers at the market where six eggs were bought from each selected seller. All the egg samples were labeled accordingly and stored in cool box with ice pack at 4^oC during field sampling. The samples were subsequently transported to the laboratory at the Faculty of Veterinary Medicine, Sokoine University of Agriculture, for physical quality characteristic analysis on the same day of sampling.

Egg quality assessment

Egg quality traits were measured following standard procedures as described by Monira et al (2003) and Fayeye et al (2005). Briefly, the external egg quality traits investigated were, egg weight (g), shell colour, shell texture, shell cleanness and shell soundness. The shell colour was assessed by naked eyes while shell texture was examined through palpation. Egg weight was determined using an electronic weight scale. The shell micro cracks were assessed using egg candler. Similarly, internal egg parameters which were measured include, shell weight (g), shell thickness (mm), general appearances of internal egg parts, smell, albumen weight (g), albumen height (mm), yolk height (cm), yolk width (cm), yolk weight (g), yolk index (%) and Haugh unit.

Each egg was later carefully broken opened to release the albumen and yolk taking care not to rupture the viteline membrane. The yolk and albumen were then carefully separated and placed in separate Petri dishes, which had initially been weighed. The difference in the weight of each Petri dish after and before the introduction of the yolk and albumen was taken as the weight of the yolk and albumen respectively. The yolk and albumen heights were determined using a tripod micrometer. Yolk index was calculated as a ratio of the yolk height to its width as follows:

Any abnormality or defects observed in the albumen and yolk were recorded. Shell weight (shell membrane inclusive) was obtained by weighing on the electronic scale. The thickness of each shell was determined using a micrometer screw gauge. Accuracy of shell thickness was ensured by measuring shell sample at the broad end, middle portion and narrow end of the shell. Individual Haugh unit (Haugh 1937) score was calculated using the egg weight and albumen height as follows:

HU = 100 log (H+7.6-1.7W^0.37)

Where,

Hu = Haugh unit,

H  = observed height of the albumen in millimeter,

W = weight of egg in grams.

Results  

Management of chicken and uses of eggs

Most (95%) of the FRLC ecotypes were mixture of Ching’wekwe, N’zenzegere and Morogoro medium. It was difficult to real establish each egg laid by which specific ecotype since one farmer could have more that one ecotypes in the same flock. It was also difficult to establish the real age of laying chickens since most farmers had no records of their birds. The FRLC were housed in backyard and allowed to scavenge freely during day around homestead. The farmers provided water, table and kitchen remains to their chicken. Occasionally, the chickens were provided with cereals as supplementary feed. No disease preventive measures were recorded to be done in the investigated flocks. Most of the eggs sampled (82%) from the farmers were those reported to be laid between 24 to 36 hours. Up to 88% of the farmers interviewed reported that the eggs were left in the laying nest under room temperature for up to 12 days before were sold. However, majority of the farmers (70%) said that the eggs were incubated to hatch chicks and only a few (30%) were released for sale and sometimes used for home consumption. All the eggs at market place were stored at room temperature in trays. The maximum period egg sellers sold the eggs before all were bought was reported to be two weeks.

Egg quality traits of indigenous chickens

Mean values for external and internal traits of the eggs are presented in Table 1. Up to 65.3% of the eggs had white shell and 34.7% had brown colour. There was a significant difference (p<0.05) in weight between eggs from the farm (48.5±5.1 gm) and market (32±4.7 gm). However, the eggs from the farm and market were found not to be significantly different (p>0.05) in Haugh unit (67.49±3.4 vs 67.96±3.01) and yolk index percentage (34.1±1 vs 28.5±4).

Different types of egg defects which were detected are shown in Table 2.

The overall defects prevalence in the assessed eggs was 44.7%. A significantly (p<0.05) higher number of defected eggs was observed in eggs from the farm (51.1%) than those from the market (35.0%). Most of the eggs examined (79.3%) had dirty shells which were stained with faeces, leaking albumen, feather particles, soils and litter materials.

Discussion 

The results of the current study give variable information on the physical quality characteristics of local chicken eggs. In this context; local chicken egg quality is described on basis of being used as food for human consumption.  The physical appearance of an egg makes the first impression upon the consumer. If the product does not meet perceived expectations, consumer confidence diminishes. Therefore external and internal characteristic of eggs are prerequisite for safety, soundness and wholesomeness of the eggs.

The mean egg weights in the present study are higher than values of 38.0, 38.5 and 39.9 reported for Sudanese indigenous chicken ecotypes (Mohammed et al 2005). They are comparable to the previous studies in Tanzania which reported 41.4g and 41.6g (Minga et al 1989; Msoffe et al 2002) but different from 44.1g reported by Mwalusanya et al (2001). FRLC eggs are mostly small in size with small weight when compared to eggs from commercial layer chickens. Most of the FRLC in Africa produces eggs which weigh from 35 to 45g (Katule 1990; Yakubu et al 2008). Egg weight is largely affected by environmental factors, feeding, chicken ecotype, age, genetic make up and parental average body weight (Msoffe et al 2002; Yakubu et al 2008). The difference in weight recorded in eggs from the farm and market may be contributed by poor storage and laying duration. Eggs from the farms probably were freshly laid compared to the eggs from the market. Studies by Silversides and Scott (2001); Jones and Musgrove (2005) and Dauda et al (2006) described that prolonged poor storage of eggs under room temperature decreases the egg weight.

The egg shell quality is a good indicator of external egg quality. Most of the eggs had white shell. The mean shell weights and thickness obtained in the present study are comparable to that reported in Nigeria and Egypt (El-Safty et al 2006; Yakubu et al 2008) and higher than that reported by Ershad (2005) in Bangladesh. This might be due to the good shell weight and thickness of eggs obtained from local chicken ecotypes in Morogoro (Ching’wekwe, N’zenzegere and Morogoro medium). The differences might be due to the differences in rearing systems. The main chemical component of egg shell is calcium which may have different levels in feed. Because of the differences in rearing system, the uptake of calcium may also be different.

Shell quality particularly shell thickness, is an important bioeconomic trait that primarily breeder of egg laying flock incorporate in their breeding programmes to reduce egg shell breakages. However, of the eggs assessed, a higher percentage had dirty shells probably because of dirty laying nests and lack of farmer’s awareness on egg cleanliness. Dirtiness of egg shell may predispose the internal egg parts to infections. Indeed, the 15.3% recorded egg shells with cracks’ could have had contributed to egg dirtying through stains and warrants for condemnation which may be a loss to farmers. The nine percent rough corrugated shell observed in the study may be contributed by many factors like poor nutrition and diseases like Newcastle disease and infectious bronchitis (Jordan and Pattison 1996). 

The mean albumen weight recorded in the current study is in agreement with those reported by Fayeye et al (2005) and Yakubu et al (2008) but the albumen height was slightly low. The Haugh unit (67.7) and yolk index (31.6%) in the present study were also lower than the Nigerian local chickens (Fayeye et al 2005; Yakubu et al 2008). The differences in values of internal physical egg characteristics may be ascribed by the eco-type of chicken, age, storage conditions and type of feed scavenged by the chickens (Jones and Musgrove 2005; Zaman et al 2005). Indeed the results from questionnaire survey showed that most farmers and egg sellers reported to keep the eggs for up to two weeks under room temperature. This could also account for our observation of no difference in Haugh unit and yolk index percentage of eggs recorded from the farm and market. Generally, the albumen has a major influence on overall interior egg quality. Thinning of the albumen is a sign of quality loss. When an egg contains a large proportion of thick white are regarded as being of high quality as it will have higher Haugh unit. Albumen is normally sensitive to diseases, nutrition, poor storage and may easily be affected compared to yolk. Albumen weight had been reported to be more closely associated with egg weight than yolk weight (Harms and Hussein 1993). On the other hand, the flabby yolk, watery albumen and ruptured viteline membrane defects which were observed might had been caused by poor and prolonged storage of eggs.  However the few eggs which had cloudy albumen and pungent rot smell indicated potential rot probably due to bacteria or fungus (Roberts 2004).

The study also recorded blood spots, meat spots and brown spots in yolk albumen. Seidler (2003) and Smith and Musgrove (2008) described blood spots as natural factors which are caused by rapture of small blood vessels while the egg is being formed. Genetic factors, old aged birds, stress during ovulation, vitamin deficiency and diseases are the other possible causes of the defects (Jordan and Pattison 1996; Seidler 2003). Laying hens, if infected with Salmonella, may produce eggs with blood spots that could contain this pathogen (Schlosser et al 1999). Therefore, blood spots are undesirable findings in eggs intended for human consumption.

The present survey provides a preliminary baseline data on physical egg quality characteristics of local scavenging chickens in Morogoro urban and periurban areas. However, we recommend that further studies on quality characteristics should be conducted using specified different local scavenging chicken eco-types from different regions of the country to better conclude on their quality.

Acknowledgements 

The authors highly acknowledge the financial support from Tanzania Higher Education Student Loan Board. The support and cooperation we received from the local chicken farmers and egg sellers in Morogoro municipality is highly appreciated. Technical support rendered by Mr. Kitime A, Mkuchu P and Chambo F in the course of the work is highly acknowledged.

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Received 9 April 2010; Accepted 26 September 2010; Published 9 December 2010

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