Background and Objective: The egg grading and size classification system used for commercial chicken breeds and hybrids is proposed for Philippine native chickens. In this regard, this study aimed to compare the egg characteristics of native breeds to egg-type, meat-type, dual-purpose and fancy-type breeds. Materials and Methods: A total of 315 eggs from 14 chicken breeds was used in this study. The size, shape, internal and external egg quality characteristics were analyzed. Egg parameters were analyzed by least square procedures to account for the effects of breed, size, grade classification and hen age. Results: Egg weight was highly correlated (p<0.01) with yolk weight (r = 0.72), albumen weight (r = 0.90) and shell weight (r = 0.71) but not related (p>0.05) to Haugh Unit. According to the size classification system the eggs were 4.1% jumbo, 7.3% extra-large, 20.3% large, 21.9% medium, 39.7% small and 6.7% peewee. Egg distribution by grade classification based on Haugh Unit was 13.3% Grade AA, 40.6% Grade A, 43.2% Grade B and 2.9% Grade C. Conclusion: Philippine native chickens (Banabang Kalabaw, Joloano, Paraoakan and Palawan Lasak), Black Silkies and White Silkies eggs were classified as small, while White Rock eggs were classified as medium. Black Australorp, Barred Plymouth Rock, New Hampshire, Rhode Island Red and Taiwan Yellow eggs were classified as large. Nagoya and White Leghorn eggs were classified as extra-large. The Philippine native chickens, Barred Plymouth Rock, New Hampshire, Taiwan Yellow and White Leghorn eggs were classified as Grade A. Eggs from White Rock, Black Silkies, White Silkies, Black Australorp, Nagoya and Rhode Island Red were classified as Grade B.
O.L. Bondoc, R.C. Santiago, A.R. Bustos, A.O. Ebron and A.R. Ramos, 2021. Grading and Size Classification of Chicken Eggs Produced by Native, Egg-Type, Meat-Type, Dual-Purpose and Fancy-Type Breeds Under Philippine Conditions. International Journal of Poultry Science, 20: 87-97.
Chicken eggs are the most commonly consumed protein-rich food in the Philippines, with a per capita consumption of 5.78 kg in 20181. Based on the 2015 Philippine Dietary Survey, chicken eggs ranked 7th among the 30 commonly consumed food items in the Philippines. Egg intake ranked 6th in urban areas but only 9th in rural areas. Egg consumption also ranked 5th and 12th among the rich and poorest households respectively2. Chicken egg production in 2018 was 533.91 thousand metric tons, i.e., 84.02% were produced by commercial layer farms and 15.98% from native chickens and their upgrades in backyard farms3.
Unfortunately, eggs produced by local breeds in rural households are not subjected to the standard egg grading and size classification system used by some commercial layer farms. In the grading process, for example, eggs are examined for interior quality (condition of the white and yolk and size of the air cell) and exterior quality (cleanliness and soundness of the shell) at the time when eggs are packed. Eggs are then sorted according to weight (size) based on the average weight per dozen4. A similar egg grading and size classification systems is thus proposed for native chickens. However, basic information on egg characteristics will be required not only to promote the proper management and improvement of native chickens5,6 but also to understand their implications on human health and nutrition in rural areas.
In this regard, this study evaluated the size, shape, internal and external quality of chicken eggs which were classified using the standard egg grading (based on albumen quality or Haugh Unit) and size classification system. The egg characteristics from four native chicken breeds (Banabang Kalabaw, Joloano, Paraoakan and Palawan Lasak) were compared with other adapted egg-type, meat-type, dual-purpose and fancy-type breeds in the Philippines. The results of the study were also compared with selected reports containing both egg weight and Haugh Unit values of indigenous breeds and commercial hybrids of some countries in Asia, Africa and Europe.
MATERIALS AND METHODS
This study was conducted in compliance with the requirements of the Institutional Animal Care and Use Committee of the University of the Philippines Los Baños in collaboration with the National Swine and Poultry Research and Development Center (NSPRDC), Bureau of Animal Industry (BAI), Department of Agriculture.
Data Collection: A total of 315 eggs were randomly collected from 14 chicken breeds (Gallus gallus domesticus L.) consisting of 4 Philippine native chickens (Banabang Kalabaw, Joloano, Paraoakan and Palawan Lasak), 1 egg-type (White Leghorn), 1 meat-type (White rock), 6 dual-purpose (Black Australorp, Barred Plymouth Rock, Nagoya, New Hampshire, Rhode Island Red and Taiwan Yellow) and 2 fancy-type breeds (Black Silkies and White Silkies). The birds were housed by breed, fed the same diet and raised in similar semi-intensive farm conditions at the NSPRDC, BAI-DA in Tiaong, Quezon. The chicken laying mash were analyzed at the government-accredited Optimal Laboratories, Inc., Lipa City, Batangas and found to contain 17.31% crude protein, 5.41% crude fat, 1.81% crude fiber, 10.24% moisture, 14.88% ash, 4.14% calcium and 0.82% phosphorus using the Semi-micro Kjeldahl distillation, Soxhlet extraction, Weende method, oven drying, ashing at 600°C, Titrimetric and Colorimetric-UV-Vis method respectively.
Newly laid eggs from May 10, 2019 to January 31, 2020 were measured for their size and shape (egg weight, short and long circumference and short-long circumference ratio), internal egg quality (yolk weight, albumen weight, percent yolk, percent albumen, yolk-albumen ratio, yolk color, albumen height, Haugh Unit) and external egg quality (shell weight, percent shell, shell thickness at the tip, middle and bottom portions and average shell thickness).
The egg weight, yolk color, albumen height and Haugh Unit were measured using the Orka Egg Analyzer (ORKA Food Technology LLC, Utah, USA). The Haugh Unit7 was calculated as:
100 log10 (H-1.7 W0.37+7.6)
where, H = height of the albumen and W = egg weight. The grade classification system8 to describe albumen and their corresponding Haugh Unit was as follows: Grade AA (72 or more), Grade A (60-71), Grade B (31-59) and Grade C (30 or less). Yolk was separated from the albumen using a yolk separator. Yolk and albumen weight were measured separately using digital weighing scale. Percentages of egg components (yolk, albumen and shell) as well as the ratio to egg weight were determined using the following equation:
Yolk-albumen ratio was computed as:
The proportion and weight of shell including the shell membrane and shell thickness (without the membrane) at the tip, middle and butt portions were recorded using the Tactix® Digital Caliper (Meridian International Co., Ltd, Shanghai, China). The short and long circumference were recorded using the common measuring tape and used to compute long-short circumference ratio, whose value when more than 1.00 implies a more elongated shape.
The modified size classification system prescribed by the Philippine National Standard9 was used-Jumbo (>70 g), Extra-large (65-69 g), Large (60-64 g), Medium (55-59 g), Small (45-54 g) and Peewee (<45 g). Eggs were not grouped based on shell color. The number and distribution of chicken eggs by size and grade classification is shown in Table 1 and 2 respectively.
Statistical analysis: Pearson product–moment correlation coefficients among size and shape with internal and external quality of chicken eggs were determined using CORR procedure of SAS10.
The general least squares procedures for unbalanced data were used to examine the principal sources of variation affecting each size, shape, internal and external quality trait. The following linear “Fixed effects” model was used to determine, using an F-test10,
yijklm = μ+Breedi+Sizej+Gradek+Agel+eijklm
where, yijklm is the dependent variable (size, shape and egg quality traits), μ is overall mean, Breedi is the fixed effect of the ith breed, Sizej is the fixed effect of the jth size classification (jumbo, extra-large, large, medium and small), Gradek is the fixed effect of the kth grade classification (AA, A, B and C), Agel is the lth covariate effect of hen age (weeks) and eijklm is error term assumed to be normally distributed with variance of errors as constant across observations.
The least square means and standard error for each egg characteristic were used to compare different breeds while adjusted for the effects of hen age. To account for data outliers and skewed distribution within a breed, the median of egg weight and Haugh Unit values was used to compare different breeds according to the size classification and egg grading systems. Duncan’s Multiple Range test (DMRT) was also used to compare treatment means. Statistical significance was set at p<0.05.
RESULTS AND DISCUSSION
Correlations of egg weight, Haugh Unit and hen age with egg characteristics:Table 3 shows that egg weight was highly correlated (p<0.01) with yolk weight (r = 0.72), albumen weight (r = 0.90) and shell weight (r = 0.71). Egg weight, however, was negatively correlated with percent yolk (r = -0.32), percent shell (r = - 0.18) and yolk-albumen ratio (r = -0.44). Egg weight was also highly correlated (p<0.01) with size in terms of its short circumference (r = 0.88) and long circumference (r = 0.92). Egg weight was weakly correlated with yolk color (r = 0.16) and average shell thickness (r = 0.23). The results of this study were in agreement with Johnston and Gous11 who reported that the proportion of yolk is negatively correlated with egg size and that larger eggs contain greater absolute amounts of the three components than smaller eggs but relatively less yolk and more albumen. In the analysis of eggs from different weight categories, shell percentage was also reported to be lowest in larger eggs12.
The Haugh Unit which is a measure of the viscosity of the thick albumen due to the high ovomucin content13 and thus may reflect the freshness of an egg14, was highly correlated with albumen height (r = 0.91) but not correlated (p>0.05) with albumen weight. The Haugh Unit was negatively correlated (p<0.01) with yolk weight (r = -0.22), percent yolk (r = -0.29), percent albumen (r = -0.19), yolk color (r = -0.16) and age of the laying hen (r = -0.15). The latter was in agreement with Silversides and Scott15 who showed that albumen quality declines with bird age. On the contrary, Zita et al.16 reported that the Haugh Units in different chicken genotypes increased with hen age from 20 weeks to 60 weeks. The Haugh Unit in this study was not related (p>0.05) to egg weight and shape, shell weight and shell thickness.
Hen age was significantly (p<0.01) correlated with egg weight (r = 0.21), yolk weight (r = 0.34), albumen weight (r = 0.17), percent yolk (r = 0.15), yolk color (r = 0.15) and percent shell (r = -0.12) but not correlated (p>0.05) with egg shape, percent albumen, yolk–albumen ratio, albumen height, shell weight and shell thickness (Table 3). This was in agreement with Johnston and Gous11 who showed that the percent yolk increases as the hen ages. Furthermore, Sahan et al.17 reported that yolk percentage as well as egg weight, yolk and albumen weight and yolk-albumen ratio also increased as hen age increased but the albumen percentage decreased.
Breed comparisons in terms of egg size and shape, internal and external egg quality:Table 4 shows that breed had significant effects on all measures of egg size, shape, internal and external quality. By comparison, similar significant effects of hen breed18, strain16, purebred and hybrid chickens19 were already reported on the proportional content of yolk and albumen in the chicken egg. Eggshell quality was likewise reported to be affected by the hen strain12. While yolk color is largely affected by feed, mainly by the presence of xanthophyll carotenoids (luthein and zeaxanthin), this study showed that yolk color was also affected by breed. This was similar to the results of Lordelo et al.18 who reported that yolk color was markedly lighter in eggs laid by native chicken breeds in Portugal than the Hybrid group. They also showed that commercial hens produced eggs that were heavier and more rounded in shape but with lower Haugh Units than eggs from the indigenous chicken breeds.