Effect of the Line and Age of Female Broiler Breeder on Hatchability Performance of Eggs

ABSTRACT An experiment was conducted to assess how hatchability performance of eggs is affected by line and age of female broiler breeders. Response variables analyzed were hatchability, infertility, pipping (i.e., pipped shell but not emerged), embryonic mortality (1st, 2nd, and 3rd wk), and embryonic malposition. The trials involved a total of 2,880 fertile eggs from two broiler breeder lines (Ross 308 and Cobb 500) at two different ages (30 and 50 wk). A 2 x 2 factorial design was used, where the broiler breeder line and broiler breeder age were the main effects. The hatchability in the Ross 308 line was higher than the Cobb 500 line, but its infertility was higher than the Ross 308 line. Hatchability in interaction (50 wk age of the hen in the Cobb 500 line) was less, and their infertility was higher. Embryonic mortality, pipping, and embryonic malposition did not present differences for the interaction between factors. The results suggest that hatchability performance of eggs can be improved, if egg management and incubation procedures are adjusted to account for the interaction between broiler breeder line and broiler breeder age.


INTRODUCTION
The poultry industry wants fast-growing and uniform broilers (Bryant et al., 2021).However, the chick quality and hatchability are affected by some factors, such as broiler breeder age (Damaziak et al., 2021b), egg size (Luquetti et al., 2004), length of time eggs are stored (Tesarova et al., 2021), temperature (El-Shater et al., 2021), humidity (Abioja et al., 2021), controlled atmosphere (Damaziak et al., 2021a), and the orientation and position of the eggs (Ozlu et al., 2021b).There is a complex relationship between these factors.In the case of the reproductive female, her age is associated with a decrease in albumen height and viscosity, hatching time, and subsequent embryogenesis (Tona et al., 2002;Bouba et al., 2021;Ozlu et al., 2021b).The most obvious characteristic of eggs from young breeder females is low egg weight (Ozlu et al., 2021a).Because chick body weight is proportional to egg weight, small chicks are to be expected (Tesarova et al., 2021).Young breeder flocks are often reported to produce eggs with low hatching potential, extended incubation periods, and chicks of low quality (Tesarova et al., 2021), as judged by subsequent mortality and growth (Nangsuay et al., 2013).In addition, broiler breeder age affects internal egg and eggshell quality characteristics (Nasri et al., 2020).Young breeders lay eggs with thicker eggshells than those of older breeders; therefore, less oxygen is supplied to the embryos (Okur et al., 2022), which may explain their slower development, and the lack of hatching of the eggs (Damaziak et al., 2021b).Failure of eggs to hatch is determined by two factors: infertility and embryonic mortality

Effect of the Line and Age of Female Broiler Breeder on Hatchability Performance of Eggs
prior to, and during, incubation (Grochowska et al., 2019).Failure of an egg to hatch reduces reproductive efficiency and, therefore, is of economic interest to the poultry industry (Bryant et al., 2021).Thus, the objective of this study was to examine the effect of the line and age of female broiler breeders on hatchability, infertility, pipping (i.e., pipped shell but not emerged), embryonic mortality (1st, 2nd, and 3rd wk), and embryonic malposition.

Ethics Statement
All handling was performed in compliance with standard veterinary practice, and in accordance with Bioethics and Animal Welfare Commission of the Faculty of Veterinary Medicine and Zootechnics of the University of Colima.Evaluation act: No. 2, October 10, 2021.

Eggs And Incubation Conditions
An experiment was carried out over a period of 21d, using 2,880 fertile eggs from two commercial broiler breeder lines (Ross 308 and Cobb 500) in the tropical zone of two age groups (30 and 50 wks of age).As the two broiler breeder lines were obtained from different broiler breeder flocks, the effects of age that were analyzed reflect the joint effect of flock age and housing conditions.Nevertheless, the temperature (14ºC to 18ºC for the younger and older lines) and feeding (2,850 kcal ME/kg, 16.60% CP, 3.12% calcium ion, and 0.37% phosphorus ion) were identical in the two poultry farms.
The incubation was performed in a commercial hatchery.The eggs were pre-warmed in the incubator for 10h at around 30ºC and 65% relative humidity, just before the incubation period, which took place in one electronically controlled, single-stage incubator (HatchTech; Gildetrom 25.3905 TB., Veenendaal, Netherlands), with a capacity of 4,800 eggs in trays holding 150 eggs.All eggs were fumigated in the incubator on the day of setting.Incubation conditions were 37.7ºC dry bulb temperature and 29.3ºC wet bulb temperature, until eggs were turned at an angle of 45º at a frequency of 24 times/d.The incubator has temperature sensors (±0.1ºF), humidity sensors [±0.1% relative humidity (RH)], and CO 2 sensors (±100ppm).The air circulation was horizontal and laminar, through perforated radiators, to provide pressure differences, better air distribution, and a uniform flow through each egg, from top to bottom and from front to back.Before hatching, the eggs were individually marked with indelible ink and weighed to the nearest 0.1g.The eggs with apparently living embryos (18d of incubation) were transferred to hatching baskets.All chicks were removed at 514h post incubation, individually weighed to the nearest 0.1g, and humidity losses were quantified.The eggs that failed to hatch were broken out and examined macroscopically to determine the infertile eggs and dead embryos.From the data, hatchability, infertility, pipping, embryonic mortality, and embryonic malposition were calculated.

Statistical Analyses
We processed the data using software SPSS (IBM SPSS Statistics, v. 22.O, Armonk, NY.IBM Corp).The experimental design was completely randomized.Broiler breeder line and broiler breeder age were the main effects in the 2 x 2 factorial design with four replicates (n = 1,440 egg/factor).The comparison between groups (broiler breeder line and broiler breeder age) was assessed by Analysis of Variance.A multiple comparison test of Tukey was performed when the effect of group was found to be significant (p<0.05).Angular transformations (arc sine of the square root of the proportion affected) were performed on all percentage data prior to the analysis.

RESULTS
The effect of the line and age of female broiler breeder on hatchability performance of eggs are shown in Table 1.The hatchability in the Ross 308 line was higher than the Cobb 500 line, but its infertility was higher than the Ross 308 line.Hatchability in interaction (50 wk age of the hen in the Cobb 500 line) was less, and its infertility was higher.Embryonic mortality, pipping, and embryonic malposition did not present differences in the interaction between factors.

DISCUSSION
Eggs from youngest hens have been shown to have low hatchability and tend to be more susceptible to dehydration than eggs from older breeders (Bruzual et al., 2000;Archer et al., 2009;Damaziak et al., 2021b).It is not clear to what extent the changes in the hatchability of fertile eggs in relation to flock age are caused by associated changes in egg weight or breeder line (Vieira et al., 2005).Therefore, it is important to know the extent to which changes in hatchability are due to age of the hen (Bouba et al., 2021), the breeder line (Ozlu et al., 2021a), or a combination of the two factors (Table 1).

Effect of the Line and Age of Female Broiler Breeder on Hatchability Performance of Eggs
The eggshell provides the incubation environment that causes the embryo to develop and perform gas exchange (Shafey, 2002).Its quality is an important factor to the poultry industry, due to reproductive and economic implications (Luquetti et al., 2004).The youngest hens lay eggs with thicker eggshells than those of older breeders, and, therefore, less oxygen is supplied to the embryos (Okur et al., 2022).The eggshell thickness decreases with advancing breeder age, because the egg size increases more quickly than the shell weight (Shafey, 2002), and because there is an increase in egg size, rather than calcium deposition in the eggshell (Kismiati et al., 2018).Hen age also affects the proportion of yolk and albumen (Grochowska et al., 2019).However, in the study, although the weight of the egg varied with the age of female breeder, no significant differences were observed in embryonic mortality, pipping, and embryonic malposition.These results can be partly attributed to the different breeder lines, which is also related to shell quality.The interaction between the age of the hen and the breeder line did not show significance in pipping and embryonic malposition.In addition, their values are within the values reported in the literature (Grochowska et al., 2019;Damaziak et al., 2021b).The embryonic mortality observed during the 1st wk suggests adjustments in the handling and storage time of the egg prior to incubation (Table 1); the breeder line is what makes the difference in the main incubation variable.In this work, it was shown that the interaction of the two main factors (the age and the line) are the ones that influence hatchability, so those in charge of hatcheries must emphasize these factors to improve hatchability and chicken quality.

CONCLUSION
The findings of this study revealed that embryonic mortality, infertility, pipping, and embryonic malposition are not dependent on breeder age.The results suggest that the hatchability performance of eggs can be improved, if egg management and incubation procedures are adjusted to account for the interaction between broiler breeder line and broiler breeder age.