Comparative study on some egg quality traits of exotic chickens in different production systems in East Shewa, Ethiopia

A total of 227 eggs were collected during summer 2013 from Isa Brown (IB), Bovan Brown (BB) and Potchefstroom Koekoek (PK) chickens for comparative study of internal and external egg quality traits under intensive and village production systems in East Shewa, Ethiopia. The data collected was analyzed using SPSS and significant differences in egg quality traits were compared using post hoc multiple comparisons. Average egg weight, Haugh Unit, shell thickness, yolk colour, albumen weight, yolk percent and yolk to albumin ratio of IB showed a significant difference (p<0.05) under intensive and village production systems. BB showed a statistical significant difference (p<0.05) for egg weight, yolk height, albumen height, yolk colour, Haugh Unit, shell thickness, yolk percent and albumen percent under intensive and village production systems. Further, average yolk height, yolk weight, yolk color, yolk percent and yolk to albumen ratio of PK revealed a significant difference under village and intensive production systems. The study revealed that even though the differences were observed in egg quality traits under intensive and extensive system, eggs produced from village were also found to be good quality.


INTRODUCTION
Worldwide, 80% of the total chicken populations are found in village poultry production system (Alabi et al., 2006), indicating the importance of village chicken production for the development rural economy. In Ethiopia, total poultry population at country level is estimated to be 50.38 million and with regard to breed, 96.9, 0.54 and 2.56% were reported to be indigenous, hybrid and exotic chickens, respectively (CSA, 2013). From the total population of chicken, 99% are raised under the traditional backyard system of management, while 1% is under intensive management system (Solomon, 2007). The poultry sector can be characterized into village or backyard, small scale and large scale commercial poultry production system (Dawit et al., 2008).
Embryo development is dependent on the egg quality traits such as egg weight, yolk and albumen weights, genetic line and age of the hen (Onagbesan et al., 2007), besides egg weight is one of the important phenotypic traits that influence egg quality and reproductive fitness of *Corresponding author. E-mail: tdesalew@gmail.com the chicken (Islam et al., 2001;Farooq et al., 2001). Eggshell thickness is an important trait for hatchability; in which hatchable egg thickness lies between 0.33 and 0.35 mm and few eggs with a shell thickness less than 0.27 mm will hatch (Khan et al., 2004). In addition, marketability of eggs entirely depends on eggshell thickness and strength, as poor eggshell quality results in millions of dollars of loss in USA (Roland, 1988). Even though, it is subjective and varies from country to country, yolk color remains to be key a factor for consumer acceptability (Okeudo et al., 2003). Further, the egg is probably the food item most frequently involved in outbreaks of foodborne infections with Salmonella species as ethiological agent (Gast et al., 2005;Gantois et al., 2009). Several factors affect penetration of the egg by Salmonella species, but the common factors includes the quality of eggshell, albumen and yolk (Messens et al., 2004).
With the aim of improving poultry productivity exotic chickens such as Isa Brown (IB), Bovan Brown (BB) and Potchefstroom Koekoek (PK) were distributed to smallholder farmers in Ada'a and Lume districts of East Shewa Zone, Ethiopia (Tadesse et al., 2013). In the layer reference for more than 30 years everywhere in the world, IB is the most efficient layer in the poultry industry producing many high quality eggs and adapts itself to all climates and environments (ISA, 2010). The PK was bred from crosses between the Black Australorp and the White Leghorn in South Africa and is one of the most promising breeds. It is also second to White Leghorn, Fayoumi in terms of hen-housed egg production per hen and hatchability, respectively (Grobbelaar et al., 2010).
Despite the benefits of quality eggs, common surveys and previous research works conducted by Tadelle et al. (2003), Moges et al. (2010) and Mengesha et al. (2011) indicated village poultry farmers have low awareness to sort eggs for different purposes such as for hatching, marketing and home consumption purposes. Hence a considerable portion of eggs will be lost because of indiscriminate use of eggs rather than sorting eggs for different purposes. The egg quality could be affected by the production system among others. Thus, comparison between eggs from village and intensive production system would help researchers to suggest possible intervention options to improve quality of eggs in different production systems. Thus, the present study was designed with the objective to compare egg quality traits of three exotic chickens under intensive and village poultry production systems in East Shewa Zone of Oromiya, Ethiopia.

Management of chickens
Under village production system, more than 90% of farmers provided separate housing for their chicken in Lume and Ada'a districts. Chickens scavenge feed materials such as kitchen wastes, insects, worms and agricultural leftovers. Maize and wheat were provided three times a day (morning, noon and evening) in addition to the normal scavenging by 95% farmers in both districts. Similarly, water was provided as free access by more than 96% of the farmers in both districts. Under intensive system, the housing management was based on semi-opened deep litter system, fed on commercial balanced ration and with standard feeder and watering facility in both private and government poultry farms sampled.

Egg sample collection and evaluation
From village production system, a total of 137 fresh eggs (57 from IB, 56 from BB and 24 from PK) were collected from adult laying hens from six Peasant Associations (PA's) (Momoshoki, Byobiskie and Jogogudedo) in Lume and (Denkaka, Kurkuradenbi and Godino) in Ada'a districts for egg quality evaluation. Further, under intensive production system a total of 90 freshly laid eggs from three breeds (30 from each) were collected from two privately owned farms for IB and BB and from a government owned intensive farm for PK. A total 227 eggs were collected from both production systems for evaluation of internal and external egg quality traits at Debre Zeit Agricultural Research Institute (DZARC) laboratory.

Data collection
External egg quality traits such as egg weight were measured using digital balance (g) and shell thickness (mm) using an electronic Digital Caliper (Mitutoyo, Japan). The shell thickness was measured at three different points in the equatorial shell and the calculated average of the three was taken as a trait. To determine the internal egg quality traits, eggs were broken onto a flat surface. The thick albumen height (AH) was measured at its widest part at a position half way between the yolk and the outer margin. Yolk height was measured using Tripod Micrometer (TSS, England). The yolks were carefully separated from the albumen. Albumen and yolk weight were determined by weighing with electronic sensitive balance (Sartorius, Germany) separately. The yolk colour was determined using the Roche Colour Fan (Printed in Switzerland); a standard colorimetric system ranged from 1 to 15. Individual Haugh Units (HU) were calculated from the two parameters; height of albumen (AH) and egg weight (EW) using the formula: HU=100log (AH-1.7 EW 0.37 + 7.6) Where HU=Haugh Unit, AH=Albumen height and EW=Egg weight (Haugh, 1937).
The albumen ratio (AR) and the yolk ratios (YR) were calculated as follows: Yolk percent= (weight of yolk/weight of whole egg) × 100 Albumen percent=(weight of albumen/weight of the whole egg) × 100.

Data management and analysis
The data were entered into Microsoft Excel spreadsheet and analyzed using SPSS (Version,17). To examine the significant differences among egg quality traits, post hoc multiple comparisons were done using means generated from one-way ANOVA.

Egg weight
It is one of the important phenotypic traits that influence  (Hocking et al., 2003). However, there was no significant difference for PK under intensive and village production systems; this could indicate that PK breed could perform comparatively under village production systems, as it is also an indigenous African chicken (Grobbelaar et al., 2010).

Shell thickness
The analysis for egg shell thickness revealed that (0.34, 0.31), (0.35, 0.33) and (0.29, 0.29) mm for IB, BB and PK under intensive and village production systems, respectively (Table 1). The average egg shell thickness of IB and BB under intensive production system was significantly higher (p<0.05) than under village production systems (P<0.05) and agreed with the reports of Tulin and Ahmet (2009) and Dorji (2013). However, the average egg shell thickness of PK did not differ significantly under intensive and village production system.

Yolk height
The analysis for yolk height (mm) revealed that (17.81, 17.35), (18.57, 18.11) and (17.59, 18.80) for IB, BB and PK under intensive and village production systems, respectively. Similar average yolk height was reported for IB under village production system by Tadesse et al. (2013). The average yolk height of BB was a significantly higher (p<0.05) in intensive than under village production system. However, the average yolk value of PK under village production system significantly higher (p<0.05) than intensive production system. In the present study, the yolk height recorded under intensive and village production was comparable to those reported in intensive system in northern Ethiopia by Niraj et al. (2014), but significantly higher than the report of Aberra et al. (2013) in different agro-ecology of Ethiopia for indigenous chickens under village production system.

Albumen height
The mean albumen heights were (6.17, 6.34), (9.51, 6.92) and (5.53, 5.54) g for IB, BB and PK under intensive and village production systems, respectively ( Table 2). The mean albumen height of BB under intensive system was significantly higher under village production system (p<0.05). However, albumen height of IB and PK breeds did not differ significantly in intensive and village production systems. Under village production system, comparable average albumen height was reported by Tadesse et al. (2013) for IB and PK breeds in East Shewa, Ethiopia. But, the present average albumen height recorded was significantly lower than the report of Niraj et al. (2014) under intensive management in northern Ethiopia.

Yolk weight
As presented in Table 2, there was no significant statistical difference in yolk weight for IB and BB; this is in agreement with the report of Tulin and Ahmet (2009) for eggs collected under village production system. The mean yolk weight recorded in the present study was comparable to the report of Tadesse et al. (2013), but significantly lower than the report of Niraj et al. (2014) under intensive management for Rohde Island Red breed. Further, in the current study, the average yolk weight of PK recorded under village was significantly higher (p<0.05) than intensive production system; this might suggest the capability of PK to perform well for better yolk weight at village level (Grobbelaar et al., 2010).

Yolk color
In the present study, the yolk color of eggs collected from IB, BB and PK under village production system had a deep yellow colour (~8 to 12) than that of collected under intensive system (~6 to 10) (Table 2), indicating yolk colour is a function of feed not breeds (Demeke, 2004). Village chicken roaming near the backyard could get enough the xanthophyl (plant pigment) content of the diet consumed, which determines the yolk colour (Silversides and Scott 2006). Green grass during scavenging might be responsible for carotenoid deposits in the yolk, which improves the yolk color. Ethiopian consumers have a strong preference for eggs with deep yellow yolk colour. Very small sized eggs from the scavenging local chicken with deep yellow yolk colour fetch much higher prices compared to larger eggs of improved strains with pale yolk (Tadelle et al., 2003).

Albumen weight
Albumen weight had more closely associated with egg weight than yolk weight (Harms and Hussein, 1993).The analysis for albumen weight (g) revealed that (37.23, 33.19), (35.98, 34.54) and (26.07, 25.14) for IB, BB and PK under intensive and village production system, respectively (Table 2). In the current study, the average albumen weight of IB under intensive system was significantly higher than under village production system (P<0.05). However, albumen weight of BB and PK did not differ under intensive and village production system. The current albumen weight recorded under village and intensive system for IB and BB was higher than the report of Niraj et al. (2014) in Ethiopia and comparable with the report of Kabir et al. (2014) in Nigeria under intensive management.

Haugh Unit
The Haugh Unit (HU) is calculated from the height of the inner thick albumen and the weight of an egg and it is considered to be a typical measure of albumen quality (Haugh, 1937). In the present study, the average HU value were (85.34, 77.56), (87.45, 79.26) and (78.38, 77.26) for IB, BB and PK under intensive and village production system, respectively (Table 2). It is generally accepted that the higher the HU value, the better the quality of the eggs. Study has shown in UK that there is consumer resistant to purchase eggs which have HU's below 60 and the minimum acceptable level of 70 HU on regular documented tests (TSS, 1999). The average HU of IB and BB under intensive production was significantly higher than that in under village production system (p<0.05). The average HU recorded for IB and BB in the current study was significantly higher than the report of Niraj et al. (2014) under intensive management for Rohde Island Red and Bovans white breeds in northern Ethiopia. The current finding disagreed with Tulin and Ahmet (2009) and Dorji (2013), who reported no significant difference in HU for eggs collected from village and intensive production systems.

Albumen and yolk percent
The results of albumen and yolk percent are presented in  (Table 2). In the present study, the yolk percent of IB, BB and PK under village production system was significantly higher than under intensive system (p<0.05) and this was in agreement with the finding of Dorji (2013). As presented in Table 2, the albumen percent were (56.48, 56.28), (56.85, 57.05) and (54.66, 53.07) for IB, BB and PK under intensive and village production systems, respectively. In the current study, the albumen percent of IB, BB, and PK did not differ significantly under intensive and village production system and this was disagreed with the comparative egg quality study of Dorji (2013) in under intensive and village production systems.

Yolk to albumen ratio
The yolk albumen ratio in the present study revealed that (0.45, 0.50), (0.43, 0.47) and (0.56, 0.64) for IB, BB and PK under intensive and village production systems, respectively ( Table 2). The yolk to albumen ratio of IB and PK under village production system was a significantly higher than under intensive production system (p<0.05), while the yolk : albumen ratio of BB did not differ significantly. It was reported that there was a small positive relationship between egg weight and yolk albumen ratio was found (Harms and Hussein, 1993). Higher yolk to albumen ratio is an attribute to differences more in proportion of albumen than in proportion of yolk (Suk and Park, 2001). However, the yolk albumen ratio of IB in both production systems in the present study was significantly higher than the report Suk and Park (2001) and Harms and Hussein (1993) under intensive management.

Conclusion
In the current study, even though the differences were observed in egg quality traits under intensive and extensive system, eggs collected from the village were also found to be good quality, which are normally perceived as inferior quality by consumers. This could indicate the efforts of farmers to apply improved management in housing, feeding and health management provided by agricultural extension works in the study areas.