Effect of translucency and eggshell colour on broiler breeder egg hatchability and hatch chick weight

I. INTRODUCTION

The eggshell functions as a resistance barrier protecting egg’s internal content from environmental hazards, allowing the proper embryo development during incubation. Egg quality parameters normally measured are specific gravity, vapor water conductance, weight, thickness, porosity, breaking strength, elastic modulus, static and dynamic stiffness, among others (McDaniel et al., 1979; King’ori, 2011; Liao et al., 2013). However, several of these quality measurements are destructive to the egg and require lengthy processes, whilst parameters such as shell translucency and colour don’t require destruction of the egg and may be easier to measure. Shell translucency is described as a mottled appearance spotted in different sizes and shapes observed when candling eggs (Baker and Curtiss, 1957), and its generation is suggested to be caused by moisture accumulation in the shell and uneven drying after the egg is laid, leaving opaque and translucent areas (Talbot and Tyler, 1974). Eggshell colour has been significantly related to eggshell quality parameters (Sekeroglu and Duman, 2011).The aim of this project was to describe the effects of eggshell translucency and colouration intensity (dark and light) on eggshell thickness, hatchability, and chick weight.

II. MATERIALS AND METHODS

A total of 4320 eggs from Ross 708 breeder hens between 50 and 55 weeks of age from a commercial hatchery were used. Eggs were collected over 4 consecutive days from different flocks each day (1080 eggs/d) and stored for 4 to 6 d at 15 °C and 70% relative humidity, prior sorting.

Pre-incubation and incubation measurements - Each day, 1080 eggs were categorized using the Zinpro® BlueBoxTM methodology, which consists of classifying each egg with one of three Translucency Scores (TS1 = low, TS2 = medium and TS3 = high). The 3-point scoring system takes into consideration the amount, size and coverage of spot patterns or mottling areas in the eggshell (Figure 1). After scoring, colouration lightness (L* value) was evaluated using an electronic colorimeter (Nix Colour Sensor Pro2), sorting the eggs as light or dark and placed in a total of twelve 90-egg-incubator-trays. Eggshell thickness was determined using a noninvasive ultrasound gauge (Eggshell Thickness Gauge by Egg Tester). The average egg weight per tray was the initial egg weight prior to incubation. Eggs were set in 4 identical single stage incubators (Nature Form, model NMC 1080) with capacity of 1080 eggs. Relative humidity and temperature were maintained constant during incubation (37.7 °C and 55% relative humidity) and eggs were turned every hour.

Figure 1 - Grades of eggshell Translucency Score. (A) TS1, (B) TS2, (C) TS3.

Egg transfer and post-hatch parameters - At d-18 of incubation, all eggs were candled to remove eggs that appeared to be infertile or with dead embryos. These eggs were then cracked to confirm the infertility and embryonic mortality by visual examination and counted for calculation of egg loss along with the cracked, contaminated, and exploded eggs. The fertile eggs placed in trays were weighed for the calculation of egg weight at transfer. Egg weight loss was calculated by the subtraction of transfer egg weight from the initial egg weight and then divided by the initial egg weight. Eggs were then transferred to hatching baskets and placed back into the same incubators at the same temperature and relative humidity. Hatchability was calculated based on the number of eggs hatched from the total of eggs set. Hatched chicks were weighed as an average of chicks per basket. Unhatched eggs were opened to visually confirm embryonic mortality and chicks that hatched but were weak and near death were culled and counted to calculate the unhatched+culls % based on the number of eggs set. Data of translucency and eggshell colour effects on initial and transferred egg weight, % water loss, % hatchability, % unhatched + culls, eggshell thickness, and chick weight was analyzed using the GLIMMIX procedure of SAS (V 9.4) and Tukey’s HSD test was performed to separate means. Significant difference was considered between the means when P < 0.05.

III. RESULTS

The effects of eggshell translucency and eggshell colour are summarized in Tables 1 and 2, respectively. An interaction between colour and translucency was observed only for eggshell thickness (P = 0.029), where eggs classified as light-colored and with TS1 had a thinner eggshell compared to those that were dark and had a TS3 egg.

Table 1 - Influence of translucency on initial egg weight, final egg weight, water loss %, egg loss %, hatchability, unhatched + culls %, chick weight and eggshell thickness.

Table 2 - Influence of eggshell colour on initial egg weight, final egg weight, water loss %, egg loss %, hatchability, unhatched + culls %, chick weight and eggshell thickness.

IV. DISCUSSION

According to Liao et al. (2013), the length of the mammillary layer and width of mammillary cones are positively correlated with eggshell thickness. Chousalkar et al. (2010) observed that translucent eggshells have changes primarily in their mammillary layer and cones, suggesting that the increased thickness of the whole shell of the highly translucent eggs is caused predominantly by increasing the width of the mammillary cones, which leads to a higher mammillary layer ultrastructure. In this study, the thinner eggshells had the highest hatchability. The differences could be attributed to better uniform shell over the entire egg, which causes a greater strength of the eggs as suggested by Yan et al. (2014), who found that eggs with thin and uniform shells are stronger than those with thick yet less uniform shells.

Research has suggested that loss of weight during incubation could be attributed to water vapor exchange that can be influenced by eggshell porosity (Sousa de Araujo et al., 2017) and thickness (Roque and Soares, 1994) as these authors found that thinner shells can lose more weight during incubation. This is contrary to our observations, as we found that eggs with thicker shells, but high translucency lost more weight during incubation than eggs with thin shells. Translucent eggs have been reported to have thinner inner membranes, indicating reduced toughness and elasticity, and less protection to the egg content and embryo (Wang et al., 2017), which also negatively affects the flow of gases through the shell. The translucency impacted the % egg losses to d-18 of incubation, showing 5.8% higher egg losses in TS3 compared to TS1 eggs, and causes of embryonic death in translucent eggs could be related to poor resistance to water loss, altered embryo respiration rate and higher susceptibility to bacterial contamination. The TS1 eggs had a 6.9% higher hatchability of eggs set and greater chick weight in comparison to eggs with a TS3, agreeing with Burin et al. (2023) that reported hatch of fertile eggs were significantly impacted by translucency (P < 0.0001) with hatchability for TS 1, 2 and 3 being 92.3%, 91.4% and 86.3%, respectively.

In this study, dark-colored eggs had 3.8% higher hatchability, which agrees with previous research (Baylan et al., 2017), whom also reported that darker eggshells from broiler breeders have been related to a higher maternal antibody content in the yolks. Dark-colored eggs also had a thicker eggshell in this study, and as shell pigmentation and the calcification process are interrelated, with a significant deposit of pigment causing an increase in calcium deposition in the eggshell (Lang and Wells, 1987), which may explain why darker-colored eggs are thicker. The interaction between colour and translucency is consistent with the effect of translucency and colour on thickness when evaluated independently. Our study suggests that thickness can be best estimated by considering both translucency and colour of the eggshell, although these factors could be influenced by variation between flocks due to factors such as different farm management, environmental challenges, age, nutrition and vaccinations.

V. CONCLUSION

In conclusion, high translucent eggs (TS3) had reduced hatchability and day-old chick weight in comparison to TS1 and TS2 whereas high translucent eggs had the thickest eggshells. Regarding the impact of colour lightness, greater values for thickness and hatchability were found in dark-colored eggs. The interaction of both translucency and colour lightness only impacted shell thickness. These results suggested that eggshell translucency and colouration lightness may be good noninvasive indicators of eggshell thickness, hatchability, and chick weight in breeder flocks.

Presented at the 35th Annual Australian Poultry Science Symposium 2024. For information on the latest and future editions, click here.