Journal of Animal Science and Veterinary Medicine

Volume 2. Page 126-132
Published 31st July, 2017
ISSN: 2536-7099

Full Length Research

Effect of egg weight on external and internal egg quality traits of Isa Brown egg layer chickens in Nigeria

H. O. Ukwu1*, C. O. Ezihe2, S. K. Asaa1 and M. E. Anyogo1

1Department of Animal Breeding and Physiology, College of Animal Science, University of Agriculture Makurdi, P.M.B. 2373 Makurdi, Benue State, Nigeria.
2Department of Veterinary Physiology, Pharmacology and Biochemistry, University of Agriculture Makurdi, Benue state, Nigeria.

Received 28th April, 2017; Accepted 2nd May, 2017

*Correspondence: Dr. H. O. Ukwu, Department of Animal Breeding and Physiology, College of Animal Science, University of Agriculture Makurdi, P.M.B. 2373 Makurdi, Benue State, Nigeria. Email: ukwuhenry@gmail.com.

Copyright © 2017 Ukwu et al. This article remains permanently open access under the terms of the Creative Commons Attribution License 4.0, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

ABSTRACT

This study was designed to determine the effect of egg weight on internal and external egg quality characteristics of Isa brown egg layer chickens. A total number of 105 eggs collected within 24 hours of lay were used for the study. Eggs were numbered, weighed and classified into three egg weight groups: Light (less than 49.99 g), medium (50 to 55 g) and heavy (greater than 55 g) egg weight groups. Data were collected on internal egg quality characteristics (yolk height, albumen height, albumen length, albumen width, Haugh unit, yolk index, albumen index and yolk diameter) and external egg quality characteristics (egg length, egg width, oblong circumference, egg shell weight, egg shape index and egg shell thickness). Data were analyzed using Statistical Package for the Social Sciences (SPSS) version 20.0. Egg weight had significant (P < 0.05) effect on egg length, egg width, oblong circumference, eggshell weight, and eggshell thickness. Egg weight did not significantly (P > 0.05) affect Haugh Unit, yolk index, albumen index, and albumen length of the three egg weight groups. However, significant differences (P < 0.05) were observed among the light, medium and heavy egg weight groups in terms of yolk height, yolk diameter, and albumen height and albumen width. Positive correlations (P < 0.05) were observed between egg weight and egg length, egg width, oblong circumference, eggshell weight and eggshell thickness. Egg weight also correlated positively (P < 0.05) with yolk height, yolk diameter, albumen height and width.

Key words: Egg characteristics, chicken, correlation, Isa Brown, weight.

INTRODUCTION

The chicken egg, which is naturally designed for reproduction, is a veritable source of protein affordable to all classes of people whether rich or poor. In addition to protein, the chicken egg also contains carbohydrate, vitamins and other nutrients. Among the economically important traits in egg production enterprise are egg size, shell thickness and internal qualities of egg. The size of chicken egg, which is an important factor in marketing, is influenced by age, breed or strain of the chicken, as well as nutrition, and the colour varies from white to brown. Notably, consumers prefer jumbo size eggs to small-size eggs. Transportability of egg is dependent on its shell thickness since eggs with thin shells are liable to break on transit and hence constitute a great loss to the poultry farmer. Thus, the internal and external egg quality traits are of major importance to the egg industry worldwide (Ahmadi and Rahimi, 2011). Some researchers have studied the chicken egg quality from different perspectives. It has been reported that the quality of the chicken egg is influenced by genetic and non-genetic factors such as season, environment and feed intake (Ahmadi and Rahimi, 2011; Ojedapo, 2013; Burra, 2014). Egg quality traits had been reported to influence embryo development, hatchability, and growth performance of chicks (Khan et al., 2004; Onagbesan et al., 2007; Huwaida et al., 2015). Alabi et al. (2012) reported that medium-sized eggs could be considered for better hatchability, while large-sized eggs could be considered if growth performance is of primary importance. There are also reports on the relationship between egg size and egg quality characteristics (Abanikaanda et al., 2007; Olawumi and Ogunlade, 2008; Sarica et al., 2012). There is need to, further, investigate the influence of egg weight on its quality traits (internal and external), as such information could be useful in a selection programme to improve the quality of chicken egg as table egg, and for reproduction. This study, therefore, was designed to determine the effect of egg weight on internal and external egg quality traits of commercial Isa brown egg layer chickens.

MATERIALS AND METHODS

Experimental location

The research was conducted at the University of Agriculture Makurdi, Benue state. The state is located within the lower river Benue trough in the middle belt region of Nigeria. Its geographical coordinates are Longitude 7° 47ˈ and 10° 0ˈ East and Latitude 6° 25ˈ and 8° 8ˈ North. The area is characterized by a period of dry season between October to March and a period of rainy season from April to September. Annual rainfall ranges from 973 to 1324 mm.

Experimental birds and data collection

The eggs used in this study were collected from Isa brown strain, kept on deep litter system at a reputable farm located in Makurdi, Benue state, Nigeria. The birds were six months in lay and fed ad libitum on layers mash containing 16.0% crude protein. One hundred and five (105) eggs were collected on the same day, i.e. within 24 hours of lay. The eggs were weighed and further grouped into light weight (< 49.9 g), medium weight (50 to 55 g) and heavy weight (> 55 g) groups. Egg weight was measured using a sensitive digital weighing balance (Mettler Toledo, PL203 CE) with accuracy of 0.001 g. Egg length and egg width were taken using a vernier caliper. Oblong circumference of each egg was taken using the measuring tape. The eggshell weight was taken after breaking the egg, and the content poured into a separate container. The eggshells were dried at room temperature and thereafter weighed using a digital electronic weighing balance (Mettler Toledo, PL203 CE). Eggshell thickness (in mm) was measured using a micrometer screw gauge. Three measurements were taken at the broad end, middle and tapering end of the egg, and thereafter the average was taken as the eggshell thickness. Yolk height and yolk diameter for each egg were measured using vernier caliper. Albumen height, albumen width and albumen length were also measured with vernier caliper. Haugh unit, yolk index, albumen index and egg shape index were calculated using the equations below.

Haugh unit (HU) = 100 log10 [H – 1.7w0.37+ 7.6]

Where H= albumen height (in mm) and W= egg weight (in g).

Yolk index (%) =(yolk height)/(yolk diameter) x100

Albumen index (%) =(albumen height)/(albumen length+ albumen width/2) x100

Egg shape index (%) =(egg width)/(egg length) x100

Statistical analysis

Data collected from the study were subjected to one-way Analysis of Variance and Pearson’s product moment correlation using Statistical Package for the Social Sciences (SPSS, 2011) version 20.0. The following model was used for ANOVA.

Yij= µ+Wi+eij

Where; Yij = jth observation in the ith egg weight group, µ = population mean, Wi = effect of the ith egg weight (i=1, 2, 3); light, medium and heavy egg weight groups and eij = error term with the usual properties.

RESULTS AND DISCUSSION

The descriptive statistics of external egg quality traits and internal egg quality characteristics in different egg weight groups were shown in Tables 1 and 2 respectively. The effect of egg weight on external egg quality traits were shown in Table 3, while the effects of egg weight on internal egg quality traits were shown in Table 4. The phenotypic correlations among egg weight and external egg quality traits were shown in Table 5, while correlations among egg weight and internal egg quality traits were shown in Table 6.


Tables 1



Tables 2



Tables 3



Tables 4



Tables 5



Tables 6


Effect of egg weight on external egg quality traits

Egg length

The egg length of light, medium and heavy egg weight groups were significantly (P < 0.05) different. Numerically, heavy weight egg group had highest egg length (5.25 cm) while light weight egg groups had the least egg length (4.94 cm). It could be observed from this study that egg length increased with egg weight. The mean egg lengths observed in this study were slightly lower than the value (5.63 cm) reported by Abanikannda et al. (2007) for eggs from Harco heavy breed layers.

Egg width

The egg width of light, medium and heavy egg weight groups were significantly (P < 0.05) different. Numerically, the heavy egg weight group had the highest egg width (3.99 cm) while light weight egg had the lowest egg weight (3.73 cm). The result suggests that egg width increased with egg weight. The mean egg widths observed in this study were also slightly lower than the value (4.25 cm) reported by Abanikannda et al. (2007) for eggs from Harco heavy breed layers.

Oblong circumference

The oblong circumference of the egg weight groups were significantly different (P< 0.05), with numerical values of 14.62, 15.06 and 15.53 cm for light, medium and heavy weight groups respectively. The heavy weight egg group had the highest mean oblong circumference (15.53 cm) while the light weight egg group had the lowest mean oblong circumference (14.62 cm). Oblong circumference increased with egg weight as observed in this study. The mean oblong circumference values obtained in this study were lower than the value (16.39 cm) reported by Esonu et al. (2004) for Shikka brown layers 10 months in lay. This could be an indication that age of the birds has an influence on the oblong circumference of the eggs.

Eggshell weight

The eggshell weights of light, medium and heavy weight groups were significantly (P < 0.05) different and were observed to be 4.51, 5.29 and 5.56 g respectively. Eggshell weight increased as the egg weight increased as revealed in this study. Mean eggshell weight recorded in this study were lower than the values (6.36, 7.6, and 7.81 g) reported by John-Jaja et al. (2016) for Bovan Nera black layer chickens at 25, 51 and 72 weeks of age respectively.

Egg shape index

The egg shape indices of light, medium and heavy weight groups were not significantly (P > 0.05) different. The medium egg weight group had the highest egg shape index (76.36%) while the heavy weight group had the lowest egg shape index (75.98%), but were statistically insignificant. Mean egg shape indices observed in this study were comparable to the values reported by Sarica et al. (2012) for white (75.58±0.11%) and brown (76.71±0.09%) egg layer that were within the range 28 to 72 weeks of age. Egg shape indices obtained in this study showed that the eggs had normal shape.

Eggshell thickness

Mean eggshell thickness of light, medium and heavy egg weight groups were significantly (P < 0.05) different. However, the light egg weight group had the lowest egg shell thickness (0.32 mm) while, both the medium and heavy egg weight groups had the highest egg shell thickness (0.36 mm) each. The mean egg shell thickness observed in this study was in agreement with the finding of Sarica et al. (2012) who reported mean egg shell thickness of 0.349 and 0.355 mm for brown and white egg layers respectively. In addition, comparable eggshell thickness value (0.34 mm) was also reported by Tadesse et al. (2015) for Isa brown egg layers.

Effect of egg weight on internal egg quality traits

Haugh unit (HU)

The mean Haugh unit of the different egg weight groups were not significantly (P>0.05) affected by egg weight, although eggs from heavy weight group had numerically better Haugh unit than eggs in light and medium weight groups. The mean Haugh unit values for light, medium and heavy egg weight groups were 69.98, 69.40 and 71.49 respectively. The Haugh unit values obtained in this study were lower than the value (85.34) reported by Tadesse et al. (2015) for Isa brown egg layers on intensive system.

Yolk index

Yolk indices for light, medium and heavy egg groups were 39.55, 39.24 and 41.45% respectively. Eggs from the three egg weight groups did not differ significantly (P > 0.05) in their yolk indices, although eggs in heavy weight group had better yolk index (41.45) than eggs in the other groups. The yolk indices observed in this study were higher than the yolk index (38.0%) reported by Esonu et al. (2004) for Shikka brown layers already in 10 months of lay. However, mean yolk indices recorded in this study were lower than the values reported by Sarica et al. (2012) for white (44.65%) and brown (44.74%) egg layer within the range of 28 to 72 week of age.

Albumen index

Mean albumen indices were 7.11, 6.87 and 7.65% for light, medium and heavy egg weight groups respectively. Albumen indices among the different egg weight groups did not differ significantly (P> 0.05). However, the heavy egg weight group still had a better albumen index (7.65) than eggs in the other groups. Mean albumen indices observed in this study were lower than the values reported by Sarica et al. (2012) for white (9.95%) and brown (8.08%) egg layers within the range of 28 to 72 weeks of age.

Yolk height

Yolk height of the three egg weight groups were significantly (P < 0.05) different, with eggs in the heavy egg weight group having the highest value of 1.48 cm. The change in yolk height observed among the egg weight groups in this study showed that yolk height increased as egg weight increased. This is in line with the findings of Sekeroglu and Altuntas (2009) who observed a positive change in yolk height among medium, large, extra- large and jumbo size eggs. However, mean yolk height values observed in this study were lower than the value (1.78 cm) reported by Tadesse et al. (2015) for Isa brown layers. The values were also lower than the values reported by Sarica et al. (2012) for white (1.87 cm) and brown (1.85 cm) egg layer within age range of 28 to 72 weeks.

Yolk diameter

Yolk diameter of the different egg weight groups differ significantly (P<0.05). The heavy and the medium egg weight group had the highest numerical values of 3.60 and 3.58 cm of yolk diameter respectively, while the light egg weight group had the least value of 3.46 cm. It could be observed from this study that yolk diameter increased as egg weight increased. This result was in agreement with the report of Alkan et al. (2015) who reported that yolk width (diameter) increased as the egg weight increased.

Albumen height

Significant (P < 0.05) differences were observed in the albumen height of the different egg weight groups. The heavy egg weight group had the highest albumen height (5.34mm). The change in albumen height observed among the egg weight groups in this study showed that albumen height increased as the egg weight increased. This result is in agreement with the findings of Seleroglu and Altuntas (2009) who observed a positive change in albumen height among medium, large, extra-large and jumbo size eggs. However, mean albumen heights recorded in this study were lower than values (6.34 mm) reported by Tadesse et al. (2015) for Isa brown egg layers and Sarica et al. (2012) for white (8.24 cm) and brown (7.22 cm) egg layers.

Albumen length

Albumen length of the different egg weight groups did not differ significantly (P > 0.05), although eggs in the heavy weight groups had longer albumen length (7.68 cm) than other egg weight groups. Although there was no significant effect of egg weight on albumen length, it could be observed from this study that albumen length numerically increased as egg weight increased. This result agreed with the report of Alkan et al. (2015) who reported that albumen length increased with egg weight.

Correlation between egg weight and external egg quality traits

The correlations between egg weight and egg length, egg width, oblong circumference, egg shell weight were highly positive and significant (P < 0.01), while moderate positive and significant (P < 0.01) correlation was found between egg weight and shell thickness. This implies that as egg weight increases, egg length, egg width, oblong circumference, eggshell weight and shell thickness also increase. The positive correlations observed in this study, between egg weight and egg length, egg width, eggshell weight, and egg shape index were in agreement with the results of Alkan et al. (2015). However, moderate positive correlation observed in this study, between egg weight and shell thickness (0.395) disagreed with the result (-0.425) reported by Alkan et al. (2015). In addition, the association among the external egg measurements varied from positive to negative. The relationship between egg length and oblong circumference was highly positive (0.88) and significant (P < 0.01), which is an indication that egg length increases with oblong circumference. Moderate correlation was found between egg length and egg width, and eggshell weight, while low positive association was found between egg length and shell thickness (P < 0.01). However, low negative correlation was found between egg length and egg shape index (P < 0.01), which suggests that egg shape index decreases as egg length increases. Positive correlations were also observed between egg width and oblong circumference, eggshell weight, egg shape index, and shell thickness (P < 0.01). Low to moderate positive correlations were observed between oblong circumference and egg shell weight and shell thickness, while highly positive correlation was observed between egg shell weight and shell thickness.

Correlation between egg weight and internal egg quality traits

Positive correlations were found between egg weight and albumin index, yolk height, yolk diameter, albumin height (P < 0.01) and albumin length (P < 0.05), which implies that increase in egg weight results to corresponding increase in albumen index, yolk height, yolk diameter, albumen height and albumen length. However, non-significant (P > 0.05), low and positive correlations were observed between egg weight and Haugh unit, yolk index and albumin index. The low to moderate positive correlations observed in this study, between egg weight and Haugh unit, albumin index, yolk height, yolk diameter, albumin height, and albumin length were in agreement with the findings of Alkan et al. (2015). In addition, correlations among internal egg quality parameters varied from positive to negative. Haugh unit was positively associated with yolk index, albumin index, yolk height and albumin height, but negatively associated with yolk diameter, and albumin length (P < 0.01). Yolk index was positively associated with albumin index, yolk height, and albumin height, but negatively associated with yolk diameter, and albumin length (P < 0.01). Albumin index showed positive association with yolk height, and albumin height, but negative association with yolk diameter, and albumin length (P < 0.01). Yolk height showed positive association with albumin height, but negative association with albumin length (P < 0.01). Yolk diameter had positive association with albumin length (P < 0.01). Albumin height was found to have negative association with albumin length (P < 0.01).

CONCLUSION

It could be observed from this study that the weight of the chicken egg had positive influence on the egg length, egg width, oblong circumference and eggshell weight. Egg weight also had positive influence on yolk height, yolk diameter and albumen height. Egg weight had positive association with egg length, egg width, oblong circumference, egg shell weight, shell thickness, yolk height, yolk diameter, albumen height and albumen length. The relationships between egg weight and egg shape index, yolk index and Haugh unit were insignificant. This information could be very important in designing a selection programme for the improvement of egg quality traits of Isa brown egg layers.

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