2001 Poultry Science Association, Inc.

RELATIONSHIP BETWEEN BROILER BREEDER’S AGE AND EGG WEIGHT LOSS AND EMBRYONIC MORTALITY DURING INCUBATION IN LARGE-SCALE CONDITIONS K. TONA, F. BAMELIS, W. COUCKE, V. BRUGGEMAN, and E. DECUYPERE Katholieke Universiteit Leuven, Faculteit Landbouwkundige en Toegepaste, Biologische Wetenschappen, Onderzoekseenheid fysiologie der Huisdieren Labo of Statistiek and Proeftechniek, Kardinaal Mercierlaan 92 B-3001 Heverlee, Belgium Phone: 32-16-32-14-31 FAX: 32-16-32-19-94 e-mail: [email protected]

Primary Audience: Hatcherymen

SUMMARY The age of broiler breeders is an important parameter to be taken into account by the hatchery manager. Eggs produced by young or old breeders do not hatch as well as the eggs from the breeders of 40 to 42 wks of age. Field reports indicate that there are quadratic relationships between age of breeders and absolute egg weight loss during incubation, age of breeders and hatchability, and age of breeders and embryonic mortality. There is a trend of optimum relative egg weight loss on Day 18 of incubation for the highest hatchability. These results indicate that the eggs that incubate best are produced by the hens of 40 to 42 wk of age. It is suggested that the egg characteristics and the age of breeders have to be taken into account during incubation in order to design optimal incubation conditions and to improve hatchability. However, because the relative egg weight loss is not linked to the age of breeders, regulation of relative humidity during incubation to achieve optimum weight loss may take into account only the eggs characteristics. Key words: Egg weight loss, embryonic mortality, flock age 2001 J. Appl. Poult. Res. 10:221–227

DESCRIPTION OF PROBLEM Most of the energy needed for the embryonic development is taken from the fat stores of the yolk, and for every gram of fat burned an almost equal mass of metabolic water is generated. Therefore, the relative water content of the egg will increase during incubation unless water is lost [1]. Egg weight loss during incubation is almost entirely due to water diffusion through the shell. Christensen and McCorkle [2] pointed

out that incubation egg weight losses are a function of egg characteristics (shell structure, membrane structure, and initial egg weight) and interacting incubation conditions (temperature, humidity, and air velocity). Because temperature and air velocity requirements are set for development needs other than egg weight loss, humidity is regulated during incubation to minimize egg weight loss [3]. In its turn, egg weight loss affects hatchability and quality of 1-d-old chicks. The variation in chick weight at hatch is a function of egg weight loss [4].

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222 Fresh egg characteristics are closely linked with the age of laying breeder hen. Under commercial conditions, eggs are produced by flocks of different ages but incubated under standard incubation conditions. Eggs laid by young hens, however, differ in eggshell quality and albumen from those produced by old hens [5]. In general, the decline in hatchability of fertile eggs with increasing age of the breeders is caused by embryonic mortality. Because embryonic mortality and chick quality are believed to be related to weight loss during incubation, it is important 1) to know the relationships between the egg weight loss during the first 18 d of incubation with the age of the broiler breeder and hatchability and 2) to follow embryonic mortality as a function of the age of breeders and relative egg weight losses. To achieve predictable weight loss as a function of age of breeders, adjusting humidity during incubation may improve hatchability and chick quality. Therefore, the present study aimed to investigate the relationship between broiler breeder’s age on weight loss and embryonic mortality during incubation in large-scale conditions.

MATERIALS AND METHODS INCUBATION PROFILE Cobb broiler breeders, 27 to 60 wk of age, were reared under standard commercial husbandry practices, and their eggs were stored for an average of 6 d before setting in the incubators. Incubators (Petersime 576) and hatchers (192, Avibel n.v. Hatchery Company, Halle-Zoersel, Belgium) were used. During the first 18 d of incubation temperature was set at 37.6°C with 50% relative humidity; eggs were turned once each hour. From Day 18 of incubation until day of hatch, relative humidity and temperature changed as indicated in Table 1. EGG WEIGHING One hundred twenty-six trays of 150 eggs were followed during 28 incubation batches. For each setting, three trolleys were chosen at random and were followed during the whole incubation period. The 16 trays at the front of each trolley were labeled from 1 (top) to 16 (bottom). A tray of 150 eggs was considered as the mea-

TABLE 1. Temperature and relative humidity program from Day 18 of incubation to hatching INCUBATION LENGTH (d:h) 18:00 18:06 18:12 19:00 20:00 20:06 20:21 20:22 20:23

TEMPERATURE (°C)

RELATIVE HUMIDITY (%)

37.4 37.3 37.2 37.1 37 36.9 36.9 36.9 36.9

55 55 55 55 55 55 54 52 50

surement unit per incubation setting for weight recording. The weights of Trays 1, 6, 10, and 16 containing 150 eggs each and weights of the same empty trays were recorded on Days 0 and 18 of incubation. The weights of the empty trays were subtracted from those of the full trays to obtain the weights of 150 eggs at setting (W0) and on Day 18 of incubation (W18). These data were used to calculate the absolute egg weight loss and the relative egg weight loss related to the egg weight of Day 0 and expressed on a per egg basis. Absolute egg weight loss = W0 − W18; relative weight loss = 100 × (W0 − W18)/W0, where W0 = weight at setting, and W18 = weight on Day 18 of incubation. On Day 18 of incubation, after the weighing, the eggs were candled, and those with evidence of living embryos were recorded and transferred to the hatcher. The remaining candled eggs were broken for macroscopic analysis to distinguish the fertile from the infertile eggs. At the end of each incubation, the hatched chicks and dead embryos were recorded, and the numbers were used to calculate the hatchability and embryonic mortality in relation to fertile eggs. EMBRYONIC MORTALITY Thirty-six thousand eggs were followed during 30 incubation settings (600 to 1,800 eggs per setting). The eggs were incubated under conditions described above. On Day 18 of incubation, the eggs were candled, and those with evidence of living embryos were recorded and transferred to the hatcher. The remaining eggs were candled and then broken for macroscopic

TONA ET AL.: EGG WEIGHT AND HATCHABILITY analysis to distinguish the eggs containing dead embryos from the infertile eggs. Dead embryos were recorded and classified as early dead embryos, those estimated to have died during less than 8 d of incubation; and medium dead embryos, those estimated to have died from Day 8 to 17 of incubation. At the end of incubation, hatched chicks were recorded, and the eggs with embryos that failed to hatch were broken and classified as late dead in shell (estimated to have died from Day 18 and later during incubation) and pipped embryos. The dead embryos for which the heads over right wing, between thighs, or not at the blunt end, or beaks were away from the air cell, or legs were over the head were counted and recorded as malpositioned embryos. These data were used to calculate mortality, i.e., the number of the total dead embryos (early, medium, and late dead embryos), and the per-

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centage of malpositioned embryos in relation to the number of fertile eggs. We also used these data to calculate the percentages of early, medium, and late dead embryos in relation to the number of total dead embryos. ALIVE IN SHELL Because incubation was stopped on Day 21 and 6 h, all embryos that did not hatch on time were counted. The embryos that were not classified as malpositioned and were alive in the shell were recorded as alive in shell. These data were used to calculate the percentage of alive in shell in relation to the number of fertile eggs.

RESULTS AND DISCUSSION EGG WEIGHT LOSS AND HATCHABILITY For 150 eggs, the average absolute weight loss varied from 0.930 to 1.220 kg (6.2 to 8.11

FIGURE 1. Relationship between the age of breeders and the average egg weight and absolute egg weight loss per egg.

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FIGURE 2. Relative egg weight loss in relation to the age of breeders.

FIGURE 3. Relationship between age of breeders and hatchability.

g/egg) and the percentage of weight loss varied respectively from 10.30 to 11.40%. Figure 1 shows that as the age of the hens increased, the egg weight and absolute egg weight loss increased concomitantly (P < 0.001). There were quadratic relationships between the age of the hens and 1) egg weight at setting and 2) absolute egg weight loss at Day 18 of incubation. However, the egg weight at setting increased more rapidly than the absolute egg weight loss at Day 18 of incubation. y = −0.0058x2 + 0.2319x + 9.4923 (r = 0.98), where y = egg weight at setting, and x = age; y = −0.0057x2 + 0.1805x + 6.1951 (r = 0.78), where y = absolute egg weight loss and x = age. There was no significant relationship between the relative egg weight loss and the age of the hens (Figure 2). Hatchability varied from 69.34 to 90.89% with an average of 84.53 ± 0.483%. The highest hatchabilities were obtained when the breeders were 42 wk of age (Figure 3). There was a significant quadratic relationship between the hatchability and the age of breeders; y = −0.0288x2 + 2.1615x + 45.886 (r = 0.82), where y = hatchability and x = age. Hatchability was not significantly linked with the relative egg weight loss. However, there was a tendency for middle weight losses to be associated with hatchability (Figure 4). The best hatchability was obtained when the relative egg

weight loss ranged 10.90 to 11.10% on Day 18 of incubation. High relative egg weight loss affected the hatchability less than low values of relative weight loss. Like hatchability, embryonic mortality was not significantly linked to the relative egg weight loss. EMBRYONIC MORTALITY There was a highly significant quadratic relationship between the age of breeders and abso-

FIGURE 4. Hatchability distribution according to the relative egg weight loss.

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lute embryonic mortality during incubation (P < 0.001); y = 0.013x2 − 1.05x + 24.62 (r = 0.88), where y = absolute mortality, and x = age. According to this relationship, the lowest mortality was supposed to be obtained when the hens were 40 wk of age, which corresponded to the age for the highest hatchability. Figure 5 shows that mortality was decreased for breeders from 27 to 40 wk of age than for those older than 40 wk. STAGE OF EMBRYONIC MORTALITY The rate of embryonic mortality was not constant throughout the whole incubation period. The highest embryonic mortalities were observed from 1 to 7 d of incubation (40%) and from Day 18 to the end of incubation (41%). There was a significant but poor quadratic relationship between early embryo mortality and the age of parent flock (P < 0.01) during incubation (Figure 6); y = 0.0362x2 − 2.868x + 92.807 (r = 0.52), where y = early mortality (1 to 7 d),and x = age. MALPOSITIONED EMBRYOS For embryos that died between Day 18 and the end of incubation, an average of 83.53% were malpositioned. Figure 7 shows that the incidence of malpositioning decreased for the

FIGURE 5. Relationship between absolute embryonic mortality and age of breeders.

FIGURE 6. Relationship between early embryonic mortality and age of breeders.

young breeders until 42 wk of age and increased thereafter with age of breeders. The significant quadratic relationship (P < 0.001) between the percentage of malpositioned embryos and the age was y = 0.007x2 − 0.5714x + 13.572 (r = 0.70), where y = malposition, and x = age.

FIGURE 7. Relationship between percentage of malpositioned embryos and age of breeders.

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FIGURE 8. Percentage of embryos alive in shell in relation to the age of breeders.

ALIVE IN SHELL On average, 0.505% ± 0.186 of the embryos alive in shell did not hatch after 21 d and 6 h of incubation. The percentage of alive in shell was not significantly related to the age of breeders. However, the incidence of alive in shell tended to increase when breeders were older than 45 to 50 wk (Figure 8). This study confirms the quadratic relationship between the age of the breeders and the egg weight and hatchability reported by Peebles and Brake [6]. The quadratic relationship between ages of the breeders and absolute egg weight loss at Day 18 of incubation indicates that as the age of the hen increased, the egg weight and egg susceptibility to losing weight increased. Although the water conductance of the whole egg increases with the egg weight, the rate of water loss per gram egg weight decreases for larger eggs [7, 8]. This observation may explain the nonsignificant relationship between the relative egg weight loss and age; this nonsignificance may be due to the fact that the egg size and the shell surface area do not increase at the same rate. Moreover, eggshell quality as linked to the hen’s age [5, 9] may also influence the absolute and relative weight loss. As shown by Meir and Ar [10], Meir et al. [11], Rahn et al. [1], Tullet [3], Taylor [12], and Christensen

JAPR: Research Report and McCorkle [2], there is an optimum water loss, under or above which eggs do not hatch well. This phenomenon may be related to the dehydration state of the embryo during the last days of incubation, making the hatching process difficult in the case of excessive water loss, or the embryo may drown in its amniotic fluid. Moreover, dehydration of the membranes may affect O2 and CO2 permeability and critical gas exchange during last days of incubation. As with egg production,the embryonic development is linked to the hen’s age [13], which may explain the variations between the embryonic mortality according to the age of breeders. Because the flock was kept in closed building under controlled environmental conditions throughout the production period, seasonal effects could be buffered even if they were not completely canceled. In fact, the lower embryonic mortality as well as the higher hatchability observed around 40 wk of age is in line with the observation of Kirks et al. [14], who pointed out that maximum hatchability is observed around 44 wk of age. According to Bains [5], the albumen quality follows a similar pattern to the shell thickness, and optimum quality is found in eggs laid at the peak of production (around 35 wk of age). Hence, if the eggs of optimum quality are the best for incubation, the highest hatchability would be obtained around 35 wk of age. The lower hatchability as well as the higher embryonic mortality of the eggs from breeders less than 40 wk of age may be due to the smaller egg size. Because the eggs from young breeders are small and because embryonic metabolism, such as lipid utilization and respiration, increases with embryonic growth [15], there may be insufficient nutrients and pores, which could affect the embryo development and its hatching process. In addition, as pointed out by Mcloughlin and Gous [15], the lower porosity combined with the thicker shell membrane cuticle and more viscous albumen may not allow the optimum respiration rate of the embryos from eggs of young breeders. As for the older flock, the lower hatchability may be due to the fact that the larger eggs do not allow an optimum rate of ventilation. The combined effects of lower ventilation rate and high heat production of larger eggs at the end of incubation [16] may result in increased embryo temperature and,

TONA ET AL.: EGG WEIGHT AND HATCHABILITY hence, an increase of embryonic mortality. The hypothesis and logical relationships as stated above do not exclude, however, that the physio-

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logical effects of breeder age per se may affect embryogenesis and hence the pattern of mortality and rate of development.

CONCLUSIONS AND APPLICATIONS 1. The highest quality of eggs for incubation eggs were produced by hens that were 40 to 42 wk of age. 2. Eggs laid by young, medium, or old breeders may be incubated under different conditions in order to improve hatchability. 3. Egg characteristics and the age of breeders may be taken into account during incubation in order to provide optimal incubation conditions and to improve hatchability. However, because the relative egg weight loss is not linked to the age of breeders, relative humidity regulation during incubation to achieve optimum weight may take into account only the eggs characteristics.

REFERENCES AND NOTES 1. Rahn, H., A. Ar, and C.V. Paganelli, 1979. How bird eggs breathe. Sci. Am. 240:208–217.

12. Taylor, G., 1999. High-yield breeds require special incubation. World’s Poult. Sci. J. 3(15):27–29.

2. Christensen, V.L., and F.M. McCorkle, 1982. Turkey egg weight loss and embryonic mortality during incubation. Poult. Sci. 61:1209–1213.

13. Decuypere, E., E.J. Nouwen, E.R. Ku¨hn, and G.H. Michels, 1979. Iodohormones in the serum of chick embryo and post hatching chickens as influenced by incubation temperature. Relationship with the hatching process and thermogenesis. Annu. Biol. Anim. Biophys. 19:171–181.

3. Tullett, S.G., 1981. Theoretical and practical aspects of eggshell porosity. Turkeys 29:24–28. 4. Tullett, S.G., and F.C. Burton, 1986. The recent reawakening of interest in bird physiology particular eggs, eggshell and embryonic respiration. Wiss. Zeitschr. Humboldt-Univ. Berlin Math. Nat. Res. 35:273–284. 5. Bains, B.S., 1994. Internal egg quality influence on fertility and hatchability. World Poult. Sci. J. 10(11):35–37. 6. Peebles, E.D., and J. Brake, 1987. Eggshell quality and hatchability in broiler breeder eggs. Poult. Sci. 66:596–604. 7. Ar, A., C.V. Paganelli, R.B. Reeves, D.G. Greene, and H. Rahn, 1974. The avian egg: Water vapor conductance, shell thickness, and functional pore area. The Condor 76:153–158. 8. Paganelli, C.V., A. Olszowka, and A. Ar, 1974. The avian egg: surface area, volume, and density. Condor 76:319–325. 9. Christensen, V.L., W.E. Donaldson, and J.P. McMurtry, 1996. Physiological differences in late embryons from turkey breeders at different ages. Poult. Sci. 75:172–178. 10. Meir, M., and A. Ar, 1987. Improving turkey poult quality by correcting incubator humidity to match eggshell conductance. Br. Poult. Sci. 28:337–342. 11. Meir, M., A. Nir, and A. Ar, 1984. Increasing hatchability of turkey eggs by matching incubator humidity to shell conductance of individual eggs. Poult. Sci. 63:1489–1496.

14. Kirks, S., G.C. Emmans, R. McDonald, and D. Arnot, 1980. Factors affecting the hatchability of eggs from broiler breeder. Br. Poult. Sci. 21:37–53. 15. Mcloughlin, L., and R.M. Gous, 1999. The effect of egg size on pre- and post-natal growth of broiler chickens. World’s Poult. Sci. J. 15(8):34–38. 16. Deeming, D.C., 1996. Large eggs: an incubation challenge. Poult. Int. 35(14):50–54. 17. A SAS generalized linear model with a logit was used to analyze the data. In relation to the age of breeders and absolute and relative weight losses, we analyzed the proportions of hatched chicks and the relationship between hatchability and relative egg weight loss. The proportions of total dead embryos, early and late dead embryos, malpositioned and alive in shell, taking into account fertile eggs, were analyzed in relation to the age of breeders. A probability value of 0.05 indicated significance. The graphs were fitted in Excel for Windows using the average data according to the age.

ACKNOWLEDGMENTS K. Tona thanks Avibel (Watermolen 9, Halle-Zoersel, Belgium) for financial and material assistance. V. Bruggeman was a postdoctoral fellow from the Fund for Scientific research Flanders, Belgium. F. Bamelis was granted by the Vlaams Instituut voor de bevordering van het Wetenschappelijk—Technologisch onderzoek in de inudstrie (IWT).