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Effects of Incubational Humidity and Hen Age on Embryo Composition in Broiler Hatching Eggs from Young Breeders1,2
Effects of Incubational Humidity and Hen Age on Embryo Composition in Broiler Hatching Eggs from Young Breeders1,2 E. D. Peebles,*,3 M. R. Burnham,* C. W. Gardner,* J. Brake,‡ J. J. Bruzual,‡ and P. D. Gerard† *Department of Poultry Science, †Experimental Statistics Unit, Mississippi State University, Mississippi State, Mississippi 39762; and ‡Department of Poultry Science, North Carolina State University, Raleigh, North Carolina 27695 19 d of incubation in eggs from breeders at 26 wk when compared to those at 28 wk of age. The effects of RH on embryo crude protein and fat composition were not consistent and varied with breeder age and length of incubation. It was demonstrated that broiler breeder age affects embryogenesis and hatching chick BW. Furthermore, EM was influenced by breeder age, and changes in incubational RH between 43 and 63% affected embryogenesis without having associated effects on EM or consistent effects on embryo crude fat and protein content. Nevertheless, a depression in embryogenesis with a reduction in incubational RH to 43% may accentuate poor posthatch performance of chicks from young breeders.
(Key words: broiler breeder, embryo, incubation, relative humidity) 2001 Poultry Science 80:1299–1304
INTRODUCTION Increased embryo mortality (Noble et al., 1986) and decreased chick survival (McNaughton et al., 1978) are common in broiler hatching eggs from young breeders. Results of experiments by Smith and Bohren (1975) confirmed findings of Sunde and Bird (1959) showing that poor hatchability can be expected from very young pullets. Furthermore, significant increases in hatchability (Smith and Bohren, 1975) and significant decreases in the length of the incubation period (Crittenden and Bohren, 1962; Smith and Bohren, 1975) have been observed as pullets grow older. Bird age has been shown to affect internal egg (O’Sullivan et al., 1991; Benton and Brake, 1996; Latour et al., 1998) and eggshell quality (Peebles
2001 Poultry Science Association, Inc. Received for publication September 5, 2000. Accepted for publication May 11, 2001. 1 This is Journal Article No. J-9676 from the Mississippi Agricultural and Forestry Experiment Station supported by MIS-2985. 2 Use of trade names in this publication does not imply endorsement by Mississippi Agricultural and Forestry Experiment Station of these products nor of similar ones not mentioned. 3 To whom correspondence should be addressed: dpeebles@poultry. msstate.edu.
and Brake, 1987) characteristics. Latour et al. (1998) found altered fresh yolk fatty acid profiles, lower hatching BW, and greater relative yolk sac weights in chicks from young breeders. Rate of incubational egg water loss influences embryogenesis (Rahn and Ar, 1974) and subsequent hatchability (Lundy, 1969; Meir et al., 1984). Nevertheless, the rate of water loss from eggs during incubation can be regulated through changes in incubator RH (Peebles et al., 1987; Tullett, 1990). By monitoring the relationship between breeder age and incubational RH and its subsequent effects on embryo composition, we may elucidate more appropriate combinations of these two factors for the optimization of broiler embryo and chick performance. The potential influences of incubational RH on the body composition of embryos from young breeders of different ages have not been previously investigated. This research was, therefore, designed to determine the compositions of embryos in broiler hatching eggs subjected to various incubational humidities and from young broiler breeder flocks between 26 and 30 wk of age that
Abbreviation Key: DEW = percentage dry embryo weight; EM = percentage embryo moisture content; WEW = percentage wet embryo weight.
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ABSTRACT There is a paucity of information regarding the influence of incubational humidity on the characteristics of broiler embryos from young hens that often produce chicks of marginal quality. Therefore, the effects of broiler breeder age (26, 28, and 30 wk) in young broiler breeders and incubator humidity (43, 53, and 63% RH) on embryonic growth between 16 and 21 d of incubation, hatching chick weight, and embryo and chick body compositions were evaluated. Hatching broiler chick BW at 21 d was lower for 26-wk-old breeders compared to those at 28 and 30 wk, and the lowest RH decreased relative wet embryo weight. Embryonic growth, on wet and DM bases, was increased in eggs from the youngest hens. Embryo moisture content (EM) was lower at 16, 17, and
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are often reported to produce chicks of marginal quality (McNaughton et al., 1978; Wyatt et al., 1985).
MATERIALS AND METHODS Hatching Egg Supply
Incubation Machines used for incubation and hatching were Jamesway Model 252B incubators.5 All machines were operated at a dry bulb temperature of 37.5 ± 0.5 C and a wet bulb temperature of 26.7, 28.9, or 31.1 ± 0.5 C through 21 d of incubation. These wet bulb temperatures created the 43, 53, and 63% RH treatments, respectively. Machine operation was monitored by daily recordings of wet and dry bulb temperatures, with the use of wet and dry bulb thermometers, at 0900 and 1600 h. Temperatures were read without opening the incubator by inserting reference wet and dry bulb thermometers into access holes designed by the manufacturer. At the time of transfer, all eggs were candled for evidence of live embryos. Only eggs with viable embryos were transferred at 16 d of incubation to 30-egg wire pedigree hatching baskets and returned to the original incubator.
4
Arbor Acres Farm, Inc., Glastonbury, CT 06033. Butler Manufacturing Co., Ft. Atkinson, WI 53538.
5
Eggs used for embryo analyses were taken from the incubators at Days 16 (prior to transfer), 17, 18, and 19 of incubation. Hatched chicks were removed from the incubator at Day 21 for analysis. In each trial, 10 embryos at each day through Day 19 and 10 chicks at Day 21 at each week of breeder age and from each RH group were weighed. Of the 10 embryos and chicks sampled at the times and from the groups designated, four were used for determination of body moisture, protein, and lipid contents. Embryos and chicks were euthanized by cervical dislocation. Unhatched eggs were carefully opened, and embryos were separated from their yolk sacs, rinsed, and blotted dry before weighing. Wet embryo weights (WEW) at Days 16, 17, 18, and 19 of incubation were expressed as percentages of preset egg weight. Percentage embryo and chick moisture content (EM) determinations and calculations were as described by Peebles et al. (1999). Dry embryo weights (DEW) were expressed as percentages of preset egg weight. Body moisture content was expressed as a percentage of wet weight. Dry samples were individually sealed in labeled plastic bags and stored at −20 C for further composition analyses. Body crude protein and fat contents were determined as described by Latour et al. (1994). Body crude protein and fat contents were expressed as percentages of sample DM.
Statistical Design and Analyses Each trial represented a replicate in time. A randomized complete experiment design was used with replicates serving as blocks. A factorial arrangement was used to test for the main effects of breeder age, RH, and day of incubation and their interaction. The effects of only breeder age and RH were tested on 21 d chick BW. Angular transformations (arc sine of the square root of the proportion affected) were performed on all percentage data prior to analysis (Steel and Torrie, 1980). Leastsquares means were compared in the event of significant effects. All data were analyzed using the mixed procedure of SAS software (1996). Statements of significance were based on P ≤ 0.05 unless otherwise stated.
RESULTS There was a significant (P ≤ 0.0001) effect due to breeder age on chick BW at 21 d of incubation. Hatching chick BW was 36.7, 40.8, and 41.6 g (SEM = 0.57) at 26, 28, and 30 wk, respectively. Body weights of chicks at 28 and 30 wk were significantly greater than those at 26 wk. There was a significant (P ≤ 0.04) interaction of RH treatment by day of incubation for WEW (Table 1) and significant interactions of breeder age by day of incubation for WEW (P ≤ 0.03), DEW (P ≤ 0.0001), and EM (P ≤ 0.0001) (Table 2). Percentage WEW at 17, 18, and 19 d of incubation was higher in eggs incubated at 53 or 63% RH when compared to those incubated at 43% RH. Relative WEW at 16 d of
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Hatching eggs were produced from Arbor Acres4 feather-sexable yield females mated to Arbor Acres Yieldmaster males. Males and females were grown sexseparated in light-controlled facilities on an 8-h photoperiod. The feeding and BW programs were similar to that of Walsh and Brake (1997), and details of house management are described by Brake and Baughman (1989). At 20 wk (141 d) of age, the birds were moved to slat-litter breeding pens and photostimulated by a 14-h photoperiod. In each trial, eggs were collected from the donor flock at 26, 28, and 30 wk of age. Eggs were collected in the fall of 1996 in Trial 1 and the spring of 1997 in Trial 2. In Trial 1, 430, 774, and 866 eggs were set per RH treatment (incubator) at 26, 28, and 30 wk of age, respectively. In Trial 2, 348, 467, and 480 eggs were set per RH treatment at 26, 28, and 30 wk of age, respectively. Equal numbers of hatching eggs were collected daily, identified by date of collection and pen, and stored at 18 C and 70% RH until sorted into RH incubation treatments and set in incubators. Eggs from the various pens were randomly distributed equally among the various RH treatments (incubators) to eliminate any bias due to pen or length of egg storage. Eggs were stored for up to 6 d when set. At each week of breeder age, approximately 100 eggs per incubator were labeled, by pencil, with a number and weighed prior to set so that embryo BW at Days 16, 17, 18, and 19 of incubation could be calculated as a percentage of preset egg weight.
Embryo Sampling and Analyses
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INCUBATION HUMIDITY AND EMBRYOGENESIS TABLE 1. Percentage wet embryo weight at 16, 17, 18, and 19 d, in eggs incubated at 43, 53, and 63% RH1 Incubation RH (%)
Days of incubation
43
53
16 17 18 19
36.92 42.1b 47.7b 54.7b
36.7 44.1a 50.7a 56.8a
63
(%) 36.0 43.8a 49.9a 56.2a
a,b Means within day of incubation among RH with no common superscript differ significantly (P ≤ 0.05). 1 SEM based on pooled estimate of variance = 0.86. 2 n = 60.
incubation and DEW at 16, 17, and 19 d were greater in eggs laid by hens at 26 wk of age compared to those laid by hens at 28 or 30 wk. However, at 18 d, WEW from 28-wk-old hens was intermediate to those from hens at 26 and 30 wk, and DEW at 30 wk was intermediate to that at 26 and 28 wk. At 17 d, WEW at 26 and 28 wk was higher than that at 30 wk. At 19 d, WEW was greater at 26 wk compared to 30 wk, which in turn was greater than that at 28 wk. At 16, 17, and 19 d of incubation, EM was lower in eggs from breeder hens at 26 wk when compared to those at 28 wk of age. At 19 d, those at 30 wk were also higher than those at 26 wk, but at 16 d and 17 d, EM in eggs laid at 30 wk were intermediate to those laid at 26 and 28 wk. At 17 d of incubation, EM was also lower at 26 wk compared with 28 wk, but that at 30 wk was intermediate. There were significant interactions of breeder age by day of incubation by RH treatment for percentage embryo crude protein (P ≤ 0.03) and fat (P ≤ 0.002) contents. Differences among RH treatment within day of incubation and week of breeder age for embryo crude protein are provided in Table 3, and those for embryo crude fat are provided in Table 4. At 16 and 19 d of incubation, percentage crude protein of embryos from 28-wk-old breeders was higher when eggs were incubated at 63% rather than 43% RH, with eggs at 53% RH being intermediate. Conversely, at 18 d of incubation, embryos in eggs from breeders at 26 and 28 wk of age were higher in
DISCUSSION Egg size increases with flock age, and as described by Shanawany (1984), hatching chick weight is highly (P ≤ 0.01) correlated with egg size at setting. Wyatt et al. (1985) showed that broilers from large eggs were significantly heavier and had greater livability than broilers from small eggs. Perspectively, in this study, chick BW at 21 d was significantly lower from 26-wk-old breeders compared to those from breeders at 28 or 30 wk. Suarez et al. (1997) found in one experiment that hatch weight of broiler chicks increased in a curvilinear manner with increases in age of breeder hens between 29 and 47 wk and between 47 and 57 wk. Because increased breeder age from 29 wk to 41 or 47 wk has also been found to decrease incubation time (Suarez et al., 1997), hatched chicks from breeders at 28 and 30 wk in this study would be expected to have more time out of the shell to lose body moisture before being weighed. Wyatt et al. (1985) found that chicks weighed 5 to 12% less than other chicks that were removed from incubator trays 7 to 25 h earlier. Despite this potential effect, 21-d chick BW remained significantly lower at 26 wk compared to that at 28 and 30 wk. Tullett and Burton (1982) have suggested that fresh egg weight and rate of incubational weight loss account for approximately 87% of the varia-
TABLE 2. Percentage wet (WEW) and dry (DEW) weights and moisture contents (EM) of embryos at 16, 17, 18, and 19 d and moisture content of chicks at 21 d of incubation from broiler breeders 26, 28, and 30 wk of age Days of incubation 16 17 18 19 21
WEW1 (%) 26 wk 2,a
38.3 44.6a 50.6a 57.9a ...
28 wk b
35.9 43.7a 49.3ab 54.2c ...
DEW1 (%) 30 wk b
35.4 41.8b 48.4b 55.7b ...
26 wk 3,a
8.43 9.92a 11.09a 14.07a ...
EM1 (%)
28 wk
30 wk
26 wk
b
b
3,b
7.38 9.30b 11.56b 11.78b ...
7.52 9.00b 10.66ab 12.04b ...
78.3 77.7b 78.1 75.7b 75.9
28 wk a
79.4 78.7a 78.6 78.2a 76.2
30 wk 78.7ab 78.5ab 77.9 78.4a 75.8
a–c Means within day of incubation among breeder age with no common superscript differ significantly (P ≤ 0.05). 1 SEM based on pooled estimate of variance = 0.86, 0.201, and 0.28 for WEW, DEW, and EM, respectively. 2 n = 60. 3 n = 24.
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crude protein content when incubated at 43% rather than at 53% RH. The 63% RH resulted in embryo crude protein contents that were intermediate to the other two RH at 26 wk, whereas at 28 wk, like 53% RH, 63% RH led to a crude protein content that was also lower than that at 43% RH. At 30 wk and 21 d of incubation, 43 and 63% RH resulted in a greater percentage of embryo crude protein contents compared to 53% RH. Fat contents of embryos at 19 d of incubation in eggs from 26-wk-old breeders and at 16 d and 21 d in eggs from 28-wk-old breeders were higher when eggs were incubated at 63% RH compared to 43% RH, with 53% RH being intermediate. Conversely, at 19 d of incubation of eggs produced by 28-wk-old breeders, embryo fat was higher in the 43% RH group compared to the 53% RH group, which in turn were higher than those incubated at 63% RH.
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PEEBLES ET AL. TABLE 3. Percentage crude protein content of embryos at 16, 17, 18, and 19 d of incubation and of chicks at 21 d of incubation when incubated at 43, 53, and 63% RH from broiler breeders at 26, 28, and 30 wk of age1 16 d
17 d
18 d
19 d
21 d
Incubation RH (%)
Weeks of age
43
53
63
43
53
63
43
53
26 28 30
68.32 65.1b 63.4
70.1 68.3ab 71.0
65.6 76.0a 65.9
59.0 60.6 64.9
61.0 66.7 60.9
60.5 60.8 59.5
63.9a 63.2a 54.4
51.0b 47.9b 52.6
63
43
53
63
43
53
63
58.3ab 51.5b 55.8
44.4 41.0b 49.0
39.4 49.6ab 49.0
37.4 51.1a 42.9
39.8 40.2 42.0a
37.8 43.1 29.6b
38.7 36.0 38.4a
(%)
Means within day of incubation and breeder age among RH with no common superscript differ significantly (P ≤ 0.05). SEM based on pooled estimate of variance = 3.20. 2 n = 8. a,b 1
the last week of incubation. Impairment in the use of yolk lipids may contribute to lower water content of late-stage embryos from eggs laid by 26-wk-old breeders. Indeed, differences in the tissue hydration level of the embryos from these very young breeders may further be related to possible changes in their yolk fatty acid profiles (Latour et al., 1998). The impact of these differences would be increased by the fact that yolk absorption is markedly accelerated at the end of incubation. These results indicate that reduced hatchability and posthatch performance, which are common in young breeders, are largely due to imbalances in body moisture content in relation to total DM accumulation of embryos during the final week of incubation. Because of differences in particular internal egg and eggshell quality characteristics in eggs from young breeder flocks, Brake et al. (1997) has recommended that these eggs be allowed to remain at a warm temperature longer before being placed in a cooler or be allowed to remain in storage for a longer period before setting. These current data would indicate that measures taken to promote total water loss of eggs from young breeders prior to setting, as suggested by Brake et al. (1997), should be modified for very young flocks (at 26 wk of age or less), so that embryonic tissue water content during the latter stages of incubation is not compromised. The effects of changes in body moisture content on subsequent hatching success and posthatch performance in late stage embryos
TABLE 4. Percentage crude fat content of embryos at 16, 17, 18, and 19 d of incubation and of chicks at 21 d of incubation when incubated at 43, 53, and 63% RH from broiler breeders at 26, 28, and 30 wk of age1 16 d
17 d
18 d
19 d
21 d
Incubation RH (%)
Weeks of age
43
53
63
43
53
63
43
53
26 28 30
22.12 18.9b 18.1
19.9 21.2ab 18.5
21.5 22.4a 19.0
20.0 19.4 22.4
21.6 19.5 22.2
19.0 17.7 22.6
18.0 21.7 21.5
20.0 21.2 21.8
63
43
53
63
43
53
63
18.9 21.7 20.4
19.1b 22.6a 22.1
19.4ab 18.9b 22.8
22.7a 14.3c 20.9
20.0 14.9b 19.4
20.4 18.0ab 21.3
19.1 18.5a 20.7
(%)
a–c Means within day of incubation and breeder age among RH with no common superscript differ significantly (P ≤ 0.05). 1 SEM based on pooled estimate of variance = 3.29. 2 n = 8.
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tion in chick weight at 21 d, when chicks are normally removed from the hatcher. Shanawany (1984) found large increases in 18-d embryo weight with broiler breeder age between 28 and 36 wk upon comparing absolute 18-d embryo weights within specific egg weight classes. In contrast, WEW and DEW in the current study were higher between 16 and 19 d of incubation in eggs from 26-wk-old breeders compared to those at 28 and 30 wk, except at 17 and 18 d for WEW and at 18 d for DEW. At 17 and 18 d of incubation, WEW at 26 wk was significantly higher only when compared to 30 wk, and at 18 d of incubation, DEW at 26 wk was significantly higher only when compared to 28 wk. These results suggest that a positive relationship does not exist between breeder age and relative embryo weight in young breeders and that breeder age effects on WEW and DEW can change depending on the period of incubation at which embryos are weighed. Furthermore, it may be inferred from these data that during the last week of incubation, embryos are proportionally larger in relation to total egg mass at 26 wk than at 28 and 30 wk. This increased relative mass is largely due to an increase in relative DM, as evidenced by significant decreases in EM at 26 wk compared to 28 wk at 16 d and 17 d of incubation and compared to 28 and 30 wk at 19 d of incubation. Noble et al. (1986) concluded that the higher mortality of embryos from young parents was associated with inadequate yolk lipid assimilation and mobilization during
INCUBATION HUMIDITY AND EMBRYOGENESIS
significantly different from those incubated at 40% RH. Tullett and Burton (1982) presented data showing that the water content of the true chick is affected by water loss from the egg during incubation and accounts for differences in the weights of whole chicks at hatch from same-sized eggs. Relative humidity effects on hatching chick BW might have been significant if weights had been adjusted as a percentage of total egg weight. Incubation RH effects were noted for embryo crude protein and fat contents in the present study, but these effects were influenced by breeder age and day of incubation. There were no apparent consistent effects of RH on crude protein across breeder age and day of incubation. However, at 16 and 21 d of incubation at 28 wk, and at 19 d at 26 wk, crude fat content was significantly lower in embryos incubated at 43% RH compared to 63% RH. These results are further indicative of a decrease in yolk lipid utilization by the embryo, which would be a contributing factor to a decrease in WEW at the 43% RH. The results also suggest that RH is capable of affecting body crude protein and fat contents of embryos and that more extreme changes in incubational RH regimens may more consistently modify the compositions of embryos from young breeders. More extreme RH regimens may likewise be useful in determining if the depressing influences of a decrease in RH on WEW are related to changes in embryo crude protein and fat contents. In addition, within the RH and breeder age ranges investigated in this report, it has been shown that a reduction in RH to 43% decreased WEW without consistent effects on embryo body composition. Furthermore, decreases in the RH of incubators may need to be adjusted so that the body moisture contents of late-stage embryos from very young breeders are not compromised.
ACKNOWLEDGMENTS This work was funded in part by a grant from the U.S. Poultry and Egg Association, Tucker, GA 30084-7303, and by the Mississippi Agricultural and Forestry Experiment Station, Mississippi State, MS 39762. The authors appreciate the expert technical assistance of Sharon Whitmarsh (Mississippi State University) and Susan Creech (North Carolina State University) and the secretarial assistance of Janice Orr (Mississippi State University).
REFERENCES Benton, C. E., and J. Brake, 1996. The effect of broiler breeder flock age and length of egg storage on egg albumen during early incubation. Poultry Sci. 75:1069–1075. Brake, J., and G. R. Baughman, 1989. Comparison of lighting regimes during growth on subsequent seasonal reproductive performance of broiler breeders. Poultry Sci. 68:79–85. Brake, J., T. J. Walsh, C. E. Benton, Jr., J. N. Petitte, R. Meijerhof, and G. Pen˜alva, 1997. Egg handling and storage. Poultry Sci. 76:144–151. Bruzual, J. J., S. D. Peak, J. Brake, and E. D. Peebles, 2000a. Effects of relative humidity during incubation on hatchability and body weight of broiler chicks from young breeder flocks. Poultry Sci. 79:827–830.
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may be accentuated by the lower relative levels of moisture in their tissues at that time in incubation (Peebles et al., 1999). Incubation RH must be properly controlled for proper embryo growth to proceed; Lundy (1969) and Robertson (1961a) reported 40 to 70% RH to produce satisfactory results. Vick et al. (1993) observed that an increase in hatchability and a decrease in early embryonic mortality in eggs subjected to a reduction in incubation RH from 58 to 50% was most evident when those eggs were taken from young breeder flocks. Robertson (1961a) reported that a high RH (75 to 80%) increased mortality and a lower RH (40 to 50%) lowered mortality at the end of incubating eggs laid by older hens. More recent work with young breeders by Bruzual et al. (2000a) has shown that the percentage late dead mortality increased significantly as RH increased from 53 to 63%, and hatching chick BW increased with increases in RH from 43 to 53% and from 53 to 63%. Studies on the subsequent effects of incubation RH on the posthatch broiler chick have shown that overall, optimal performance was achieved when hatching eggs from young hens were incubated at 53% rather than 43 or 63% RH (Bruzual et al., 2000b). Hatchability (Davis et al., 1988) and chick size (Swann and Brake, 1990a) are qualities that can be controlled by incubation egg moisture loss. Water loss is critical and influenced most when embryonic metabolism reaches a plateau (Swann and Brake, 1990b). Egg moisture loss is also inversely related to incubation RH (Robertson, 1961b). The specific incubation weight loss needed by eggs up until the time of internal pipping has been shown to be approximately 12% for commercial broiler strains under conditions of artificial incubation (Tullett, 1981; Peebles and Brake, 1986). Overall, chicks have been observed to hatch earlier when incubation RH was reduced from approximately 52 to 42% (Swann and Brake, 1990c). Percentage WEW between 17 and 19 d of incubation was lower in eggs incubated at the lowest RH (43%) than at the two higher RH (53 and 63%). Davis et al. (1988) reported that increased incubation RH (85 to 90%), which caused eggs to lose only 5.9% of their initial fresh egg mass by 20 d, did not lead to changes in wet or dry embryo mass or embryo moisture content during the final week of incubation. However, decreased incubation RH (0 to 10%), which caused eggs to lose 24% of their initial fresh egg mass by 19 d, resulted in decreased wet embryo mass at 20 and 21 d of incubation. Those embryos were observed to have undergone osmotic stress and dehydration. Individually, EM and DEW were not significantly affected by RH in the current investigation. However, the influence of a decrease in RH from 53 or 63% to 43% evidently promoted an overall decrease in WEW. It is suggested that combined small decreases in EM and DEW might have resulted in a significant decrease in relative WEW. Interestingly, the effects of RH on WEW did not carry over onto subsequent absolute 21-d chick BW. Robertson (1961b) also found that the absolute weights of 1-d-old chicks hatched from eggs incubated at 70% RH were not
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PEEBLES ET AL. Rahn, H., and A. Ar, 1974. The avian egg: Incubation time and water loss. Condor 76:147–152. Robertson, I. S., 1961a. Studies on the effect of humidity on the hatchability of hen’s eggs. I. The determination of optimum humidity for incubation. J. Agric. Sci. 57:185–194. Robertson, I. S., 1961b. Studies on the effect of humidity on the hatchability of hen’s eggs. II. A comparison of hatchability, weight loss and embryonic growth in eggs incubated at 40 and 70% RH. J. Agric. Sci. 57:195–198. SAS Institute, 1996. SAS/STAT威 Software: Changes and Enhancements Through Release 6.11. SAS Institute Inc., Cary, NC. Shanawany, M. M., 1984. The inter-relationship between egg weight, parental age and embryonic size. Br. Poult. Sci. 25:449–455. Smith, K., and B. B. Bohren, 1975. Age of pullet effects on hatch time, egg weight and hatchability. Poultry Sci. 54:959–963. Steel, R. G. D., and J. H. Torrie, 1980. Principles and Procedures of Statistics. A Biometrical Approach. 2nd ed. McGraw-Hill Book Co., New York, NY. Suarez, M. E., H. R. Wilson, F. B. Mather, C. J. Wilcox, and B. N. McPherson, 1997. Effects of strain and age of the broiler breeder female on incubation time and chick weight. Poultry Sci. 76:1029–1036. Sunde, M. L., and H. R. Bird, 1959. The effect of pullet maturity on fertility and hatchability of eggs. Poultry Sci. 38:272–279. Swann, G. S., and J. Brake, 1990a. Effect of dry-bulb temperature, relative humidity, and eggshell conductance during the first three days of incubation on egg weight loss and chick weight. Poultry Sci. 69:535–544. Swann, G. S., and J. Brake, 1990b. Effect of dry-bulb temperature, relative humidity, and eggshell conductance during Days 17 to 21 of incubation on egg weight loss and chick weight. Poultry Sci. 69:545–553. Swann, G. S., and J. Brake, 1990c. Effect of incubation dry-bulb and wet-bulb temperatures on time of hatch and chick weight at hatch. Poultry Sci. 69:887–897. Tullett, S. G., 1990. Science and art of incubation. Poultry Sci. 69:1–15. Tullett, S. G., 1981. Theoretical and practical aspects of eggshell porosity. Turkeys 29:24–28. Tullett, S. G., and F. G. Burton, 1982. Factors affecting the weight and water status of the chick at hatch. Br. Poult. Sci. 23:361–369. Vick, S. V., J. Brake, and T. J. Walsh, 1993. Relationship of incubation humidity and flock age to hatchability of broiler hatching eggs. Poultry Sci. 72:251–258. Walsh, T. J., and J. Brake, 1997. The effect of nutrient intake during rearing of broiler breeder females on subsequent fertility. Poultry Sci. 76:297–305. Wyatt, C. L., W. D. Weaver, Jr., and W. L. Beane, 1985. Influence of egg size, eggshell quality and posthatch holding time on broiler performance. Poultry Sci. 64:2049–2055.
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Bruzual, J. J., S. D. Peak, J. Brake, and E. D. Peebles, 2000b. Effects of relative humidity during the last five days of incubation and breeding temperature on performance of broiler chicks from young broiler breeders. Poultry Sci. 79:1385– 1391. Crittenden, L. B., and B. B. Bohren, 1962. The effects of current egg production, time in production, age of pullet, and inbreeding on hatchability and hatching time. Poultry Sci. 41:428–433. Davis, T. A., S. S. Shen, and R. A. Ackerman, 1988. Embryonic osmoregulation: Consequences of high and low water loss during incubation of the chicken egg. J. Exp. Zool. 245:144–156. Latour, M. A., E. D. Peebles, C. R. Boyle, and J. D. Brake, 1994. The effects of dietary fat on growth performance, carcass composition, and feed efficiency in the broiler chick. Poultry Sci. 73:1362–1369. Latour, M. A., E. D. Peebles, S. M. Doyle, T. Pansky, T. W. Smith, and C. R. Boyle, 1998. Broiler breeder age and dietary fat influence the yolk fatty acid profiles of fresh eggs and newly hatched chicks. Poultry Sci. 77:47–53. Lundy, H., 1969. A review of the effects of temperature, humidity, turning and gaseous environment in the incubator on hatchability of hen’s eggs. Pages 143–176 in: The Fertility and Hatchability of the Hen’s Egg. T. C. Carter and B. M. Freeman, ed. Oliver and Boyd, Edinburgh, Scotland, UK. McNaughton, J. L., J. W. Deaton, F. N. Reece, and R. L. Haynes, 1978. Effect of age of parents and hatching egg weight on broiler chick mortality. Poultry Sci. 57:38–44. Meir, M., A. Nir, and A. Ar, 1984. Increasing hatchability of turkey eggs by matching incubator humidity to shell conductance of individual eggs. Poultry Sci. 63:1489–1496. Noble, R. C., F. Lonsdale, K. Conner, and D. Brown, 1986. Changes in the lipid metabolism of the chick embryo with parental age. Poultry Sci. 65:409–416. O’Sullivan, N. P., E. A. Dunnington, and P. B. Siegel, 1991. Relationships among age of dam, egg components, embryo lipid transfer, and hatchability of broiler breeder eggs. Poultry Sci. 70:2180–2185. Peebles, E. D., and J. Brake, 1986. The role of the cuticle in water vapor conductance by the eggshell of broiler breeders. Poultry Sci. 65:1034–1039. Peebles, E. D., and J. T. Brake, 1987. Eggshell quality and hatchability in broiler breeder eggs. Poultry Sci. 66:596–604. Peebles, E. D., J. Brake, and R. P. Gildersleeve, 1987. Effects of eggshell cuticle removal and incubation humidity on embryonic development and hatchability of broilers. Poultry Sci. 66:834–840. Peebles, E. D., L. Li, S. Miller, T. Pansky, S. Whitmarsh, M. A. Latour, and P. D. Gerard, 1999. Embryo and yolk compositional relationships in broiler hatching eggs during incubation. Poultry Sci. 78:1435–1442.
(Key words: broiler breeder, embryo, incubation, relative humidity) 2001 Poultry Science 80:1299–1304
INTRODUCTION Increased embryo mortality (Noble et al., 1986) and decreased chick survival (McNaughton et al., 1978) are common in broiler hatching eggs from young breeders. Results of experiments by Smith and Bohren (1975) confirmed findings of Sunde and Bird (1959) showing that poor hatchability can be expected from very young pullets. Furthermore, significant increases in hatchability (Smith and Bohren, 1975) and significant decreases in the length of the incubation period (Crittenden and Bohren, 1962; Smith and Bohren, 1975) have been observed as pullets grow older. Bird age has been shown to affect internal egg (O’Sullivan et al., 1991; Benton and Brake, 1996; Latour et al., 1998) and eggshell quality (Peebles
2001 Poultry Science Association, Inc. Received for publication September 5, 2000. Accepted for publication May 11, 2001. 1 This is Journal Article No. J-9676 from the Mississippi Agricultural and Forestry Experiment Station supported by MIS-2985. 2 Use of trade names in this publication does not imply endorsement by Mississippi Agricultural and Forestry Experiment Station of these products nor of similar ones not mentioned. 3 To whom correspondence should be addressed: dpeebles@poultry. msstate.edu.
and Brake, 1987) characteristics. Latour et al. (1998) found altered fresh yolk fatty acid profiles, lower hatching BW, and greater relative yolk sac weights in chicks from young breeders. Rate of incubational egg water loss influences embryogenesis (Rahn and Ar, 1974) and subsequent hatchability (Lundy, 1969; Meir et al., 1984). Nevertheless, the rate of water loss from eggs during incubation can be regulated through changes in incubator RH (Peebles et al., 1987; Tullett, 1990). By monitoring the relationship between breeder age and incubational RH and its subsequent effects on embryo composition, we may elucidate more appropriate combinations of these two factors for the optimization of broiler embryo and chick performance. The potential influences of incubational RH on the body composition of embryos from young breeders of different ages have not been previously investigated. This research was, therefore, designed to determine the compositions of embryos in broiler hatching eggs subjected to various incubational humidities and from young broiler breeder flocks between 26 and 30 wk of age that
Abbreviation Key: DEW = percentage dry embryo weight; EM = percentage embryo moisture content; WEW = percentage wet embryo weight.
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ABSTRACT There is a paucity of information regarding the influence of incubational humidity on the characteristics of broiler embryos from young hens that often produce chicks of marginal quality. Therefore, the effects of broiler breeder age (26, 28, and 30 wk) in young broiler breeders and incubator humidity (43, 53, and 63% RH) on embryonic growth between 16 and 21 d of incubation, hatching chick weight, and embryo and chick body compositions were evaluated. Hatching broiler chick BW at 21 d was lower for 26-wk-old breeders compared to those at 28 and 30 wk, and the lowest RH decreased relative wet embryo weight. Embryonic growth, on wet and DM bases, was increased in eggs from the youngest hens. Embryo moisture content (EM) was lower at 16, 17, and
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are often reported to produce chicks of marginal quality (McNaughton et al., 1978; Wyatt et al., 1985).
MATERIALS AND METHODS Hatching Egg Supply
Incubation Machines used for incubation and hatching were Jamesway Model 252B incubators.5 All machines were operated at a dry bulb temperature of 37.5 ± 0.5 C and a wet bulb temperature of 26.7, 28.9, or 31.1 ± 0.5 C through 21 d of incubation. These wet bulb temperatures created the 43, 53, and 63% RH treatments, respectively. Machine operation was monitored by daily recordings of wet and dry bulb temperatures, with the use of wet and dry bulb thermometers, at 0900 and 1600 h. Temperatures were read without opening the incubator by inserting reference wet and dry bulb thermometers into access holes designed by the manufacturer. At the time of transfer, all eggs were candled for evidence of live embryos. Only eggs with viable embryos were transferred at 16 d of incubation to 30-egg wire pedigree hatching baskets and returned to the original incubator.
4
Arbor Acres Farm, Inc., Glastonbury, CT 06033. Butler Manufacturing Co., Ft. Atkinson, WI 53538.
5
Eggs used for embryo analyses were taken from the incubators at Days 16 (prior to transfer), 17, 18, and 19 of incubation. Hatched chicks were removed from the incubator at Day 21 for analysis. In each trial, 10 embryos at each day through Day 19 and 10 chicks at Day 21 at each week of breeder age and from each RH group were weighed. Of the 10 embryos and chicks sampled at the times and from the groups designated, four were used for determination of body moisture, protein, and lipid contents. Embryos and chicks were euthanized by cervical dislocation. Unhatched eggs were carefully opened, and embryos were separated from their yolk sacs, rinsed, and blotted dry before weighing. Wet embryo weights (WEW) at Days 16, 17, 18, and 19 of incubation were expressed as percentages of preset egg weight. Percentage embryo and chick moisture content (EM) determinations and calculations were as described by Peebles et al. (1999). Dry embryo weights (DEW) were expressed as percentages of preset egg weight. Body moisture content was expressed as a percentage of wet weight. Dry samples were individually sealed in labeled plastic bags and stored at −20 C for further composition analyses. Body crude protein and fat contents were determined as described by Latour et al. (1994). Body crude protein and fat contents were expressed as percentages of sample DM.
Statistical Design and Analyses Each trial represented a replicate in time. A randomized complete experiment design was used with replicates serving as blocks. A factorial arrangement was used to test for the main effects of breeder age, RH, and day of incubation and their interaction. The effects of only breeder age and RH were tested on 21 d chick BW. Angular transformations (arc sine of the square root of the proportion affected) were performed on all percentage data prior to analysis (Steel and Torrie, 1980). Leastsquares means were compared in the event of significant effects. All data were analyzed using the mixed procedure of SAS software (1996). Statements of significance were based on P ≤ 0.05 unless otherwise stated.
RESULTS There was a significant (P ≤ 0.0001) effect due to breeder age on chick BW at 21 d of incubation. Hatching chick BW was 36.7, 40.8, and 41.6 g (SEM = 0.57) at 26, 28, and 30 wk, respectively. Body weights of chicks at 28 and 30 wk were significantly greater than those at 26 wk. There was a significant (P ≤ 0.04) interaction of RH treatment by day of incubation for WEW (Table 1) and significant interactions of breeder age by day of incubation for WEW (P ≤ 0.03), DEW (P ≤ 0.0001), and EM (P ≤ 0.0001) (Table 2). Percentage WEW at 17, 18, and 19 d of incubation was higher in eggs incubated at 53 or 63% RH when compared to those incubated at 43% RH. Relative WEW at 16 d of
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Hatching eggs were produced from Arbor Acres4 feather-sexable yield females mated to Arbor Acres Yieldmaster males. Males and females were grown sexseparated in light-controlled facilities on an 8-h photoperiod. The feeding and BW programs were similar to that of Walsh and Brake (1997), and details of house management are described by Brake and Baughman (1989). At 20 wk (141 d) of age, the birds were moved to slat-litter breeding pens and photostimulated by a 14-h photoperiod. In each trial, eggs were collected from the donor flock at 26, 28, and 30 wk of age. Eggs were collected in the fall of 1996 in Trial 1 and the spring of 1997 in Trial 2. In Trial 1, 430, 774, and 866 eggs were set per RH treatment (incubator) at 26, 28, and 30 wk of age, respectively. In Trial 2, 348, 467, and 480 eggs were set per RH treatment at 26, 28, and 30 wk of age, respectively. Equal numbers of hatching eggs were collected daily, identified by date of collection and pen, and stored at 18 C and 70% RH until sorted into RH incubation treatments and set in incubators. Eggs from the various pens were randomly distributed equally among the various RH treatments (incubators) to eliminate any bias due to pen or length of egg storage. Eggs were stored for up to 6 d when set. At each week of breeder age, approximately 100 eggs per incubator were labeled, by pencil, with a number and weighed prior to set so that embryo BW at Days 16, 17, 18, and 19 of incubation could be calculated as a percentage of preset egg weight.
Embryo Sampling and Analyses
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INCUBATION HUMIDITY AND EMBRYOGENESIS TABLE 1. Percentage wet embryo weight at 16, 17, 18, and 19 d, in eggs incubated at 43, 53, and 63% RH1 Incubation RH (%)
Days of incubation
43
53
16 17 18 19
36.92 42.1b 47.7b 54.7b
36.7 44.1a 50.7a 56.8a
63
(%) 36.0 43.8a 49.9a 56.2a
a,b Means within day of incubation among RH with no common superscript differ significantly (P ≤ 0.05). 1 SEM based on pooled estimate of variance = 0.86. 2 n = 60.
incubation and DEW at 16, 17, and 19 d were greater in eggs laid by hens at 26 wk of age compared to those laid by hens at 28 or 30 wk. However, at 18 d, WEW from 28-wk-old hens was intermediate to those from hens at 26 and 30 wk, and DEW at 30 wk was intermediate to that at 26 and 28 wk. At 17 d, WEW at 26 and 28 wk was higher than that at 30 wk. At 19 d, WEW was greater at 26 wk compared to 30 wk, which in turn was greater than that at 28 wk. At 16, 17, and 19 d of incubation, EM was lower in eggs from breeder hens at 26 wk when compared to those at 28 wk of age. At 19 d, those at 30 wk were also higher than those at 26 wk, but at 16 d and 17 d, EM in eggs laid at 30 wk were intermediate to those laid at 26 and 28 wk. At 17 d of incubation, EM was also lower at 26 wk compared with 28 wk, but that at 30 wk was intermediate. There were significant interactions of breeder age by day of incubation by RH treatment for percentage embryo crude protein (P ≤ 0.03) and fat (P ≤ 0.002) contents. Differences among RH treatment within day of incubation and week of breeder age for embryo crude protein are provided in Table 3, and those for embryo crude fat are provided in Table 4. At 16 and 19 d of incubation, percentage crude protein of embryos from 28-wk-old breeders was higher when eggs were incubated at 63% rather than 43% RH, with eggs at 53% RH being intermediate. Conversely, at 18 d of incubation, embryos in eggs from breeders at 26 and 28 wk of age were higher in
DISCUSSION Egg size increases with flock age, and as described by Shanawany (1984), hatching chick weight is highly (P ≤ 0.01) correlated with egg size at setting. Wyatt et al. (1985) showed that broilers from large eggs were significantly heavier and had greater livability than broilers from small eggs. Perspectively, in this study, chick BW at 21 d was significantly lower from 26-wk-old breeders compared to those from breeders at 28 or 30 wk. Suarez et al. (1997) found in one experiment that hatch weight of broiler chicks increased in a curvilinear manner with increases in age of breeder hens between 29 and 47 wk and between 47 and 57 wk. Because increased breeder age from 29 wk to 41 or 47 wk has also been found to decrease incubation time (Suarez et al., 1997), hatched chicks from breeders at 28 and 30 wk in this study would be expected to have more time out of the shell to lose body moisture before being weighed. Wyatt et al. (1985) found that chicks weighed 5 to 12% less than other chicks that were removed from incubator trays 7 to 25 h earlier. Despite this potential effect, 21-d chick BW remained significantly lower at 26 wk compared to that at 28 and 30 wk. Tullett and Burton (1982) have suggested that fresh egg weight and rate of incubational weight loss account for approximately 87% of the varia-
TABLE 2. Percentage wet (WEW) and dry (DEW) weights and moisture contents (EM) of embryos at 16, 17, 18, and 19 d and moisture content of chicks at 21 d of incubation from broiler breeders 26, 28, and 30 wk of age Days of incubation 16 17 18 19 21
WEW1 (%) 26 wk 2,a
38.3 44.6a 50.6a 57.9a ...
28 wk b
35.9 43.7a 49.3ab 54.2c ...
DEW1 (%) 30 wk b
35.4 41.8b 48.4b 55.7b ...
26 wk 3,a
8.43 9.92a 11.09a 14.07a ...
EM1 (%)
28 wk
30 wk
26 wk
b
b
3,b
7.38 9.30b 11.56b 11.78b ...
7.52 9.00b 10.66ab 12.04b ...
78.3 77.7b 78.1 75.7b 75.9
28 wk a
79.4 78.7a 78.6 78.2a 76.2
30 wk 78.7ab 78.5ab 77.9 78.4a 75.8
a–c Means within day of incubation among breeder age with no common superscript differ significantly (P ≤ 0.05). 1 SEM based on pooled estimate of variance = 0.86, 0.201, and 0.28 for WEW, DEW, and EM, respectively. 2 n = 60. 3 n = 24.
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crude protein content when incubated at 43% rather than at 53% RH. The 63% RH resulted in embryo crude protein contents that were intermediate to the other two RH at 26 wk, whereas at 28 wk, like 53% RH, 63% RH led to a crude protein content that was also lower than that at 43% RH. At 30 wk and 21 d of incubation, 43 and 63% RH resulted in a greater percentage of embryo crude protein contents compared to 53% RH. Fat contents of embryos at 19 d of incubation in eggs from 26-wk-old breeders and at 16 d and 21 d in eggs from 28-wk-old breeders were higher when eggs were incubated at 63% RH compared to 43% RH, with 53% RH being intermediate. Conversely, at 19 d of incubation of eggs produced by 28-wk-old breeders, embryo fat was higher in the 43% RH group compared to the 53% RH group, which in turn were higher than those incubated at 63% RH.
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PEEBLES ET AL. TABLE 3. Percentage crude protein content of embryos at 16, 17, 18, and 19 d of incubation and of chicks at 21 d of incubation when incubated at 43, 53, and 63% RH from broiler breeders at 26, 28, and 30 wk of age1 16 d
17 d
18 d
19 d
21 d
Incubation RH (%)
Weeks of age
43
53
63
43
53
63
43
53
26 28 30
68.32 65.1b 63.4
70.1 68.3ab 71.0
65.6 76.0a 65.9
59.0 60.6 64.9
61.0 66.7 60.9
60.5 60.8 59.5
63.9a 63.2a 54.4
51.0b 47.9b 52.6
63
43
53
63
43
53
63
58.3ab 51.5b 55.8
44.4 41.0b 49.0
39.4 49.6ab 49.0
37.4 51.1a 42.9
39.8 40.2 42.0a
37.8 43.1 29.6b
38.7 36.0 38.4a
(%)
Means within day of incubation and breeder age among RH with no common superscript differ significantly (P ≤ 0.05). SEM based on pooled estimate of variance = 3.20. 2 n = 8. a,b 1
the last week of incubation. Impairment in the use of yolk lipids may contribute to lower water content of late-stage embryos from eggs laid by 26-wk-old breeders. Indeed, differences in the tissue hydration level of the embryos from these very young breeders may further be related to possible changes in their yolk fatty acid profiles (Latour et al., 1998). The impact of these differences would be increased by the fact that yolk absorption is markedly accelerated at the end of incubation. These results indicate that reduced hatchability and posthatch performance, which are common in young breeders, are largely due to imbalances in body moisture content in relation to total DM accumulation of embryos during the final week of incubation. Because of differences in particular internal egg and eggshell quality characteristics in eggs from young breeder flocks, Brake et al. (1997) has recommended that these eggs be allowed to remain at a warm temperature longer before being placed in a cooler or be allowed to remain in storage for a longer period before setting. These current data would indicate that measures taken to promote total water loss of eggs from young breeders prior to setting, as suggested by Brake et al. (1997), should be modified for very young flocks (at 26 wk of age or less), so that embryonic tissue water content during the latter stages of incubation is not compromised. The effects of changes in body moisture content on subsequent hatching success and posthatch performance in late stage embryos
TABLE 4. Percentage crude fat content of embryos at 16, 17, 18, and 19 d of incubation and of chicks at 21 d of incubation when incubated at 43, 53, and 63% RH from broiler breeders at 26, 28, and 30 wk of age1 16 d
17 d
18 d
19 d
21 d
Incubation RH (%)
Weeks of age
43
53
63
43
53
63
43
53
26 28 30
22.12 18.9b 18.1
19.9 21.2ab 18.5
21.5 22.4a 19.0
20.0 19.4 22.4
21.6 19.5 22.2
19.0 17.7 22.6
18.0 21.7 21.5
20.0 21.2 21.8
63
43
53
63
43
53
63
18.9 21.7 20.4
19.1b 22.6a 22.1
19.4ab 18.9b 22.8
22.7a 14.3c 20.9
20.0 14.9b 19.4
20.4 18.0ab 21.3
19.1 18.5a 20.7
(%)
a–c Means within day of incubation and breeder age among RH with no common superscript differ significantly (P ≤ 0.05). 1 SEM based on pooled estimate of variance = 3.29. 2 n = 8.
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tion in chick weight at 21 d, when chicks are normally removed from the hatcher. Shanawany (1984) found large increases in 18-d embryo weight with broiler breeder age between 28 and 36 wk upon comparing absolute 18-d embryo weights within specific egg weight classes. In contrast, WEW and DEW in the current study were higher between 16 and 19 d of incubation in eggs from 26-wk-old breeders compared to those at 28 and 30 wk, except at 17 and 18 d for WEW and at 18 d for DEW. At 17 and 18 d of incubation, WEW at 26 wk was significantly higher only when compared to 30 wk, and at 18 d of incubation, DEW at 26 wk was significantly higher only when compared to 28 wk. These results suggest that a positive relationship does not exist between breeder age and relative embryo weight in young breeders and that breeder age effects on WEW and DEW can change depending on the period of incubation at which embryos are weighed. Furthermore, it may be inferred from these data that during the last week of incubation, embryos are proportionally larger in relation to total egg mass at 26 wk than at 28 and 30 wk. This increased relative mass is largely due to an increase in relative DM, as evidenced by significant decreases in EM at 26 wk compared to 28 wk at 16 d and 17 d of incubation and compared to 28 and 30 wk at 19 d of incubation. Noble et al. (1986) concluded that the higher mortality of embryos from young parents was associated with inadequate yolk lipid assimilation and mobilization during
INCUBATION HUMIDITY AND EMBRYOGENESIS
significantly different from those incubated at 40% RH. Tullett and Burton (1982) presented data showing that the water content of the true chick is affected by water loss from the egg during incubation and accounts for differences in the weights of whole chicks at hatch from same-sized eggs. Relative humidity effects on hatching chick BW might have been significant if weights had been adjusted as a percentage of total egg weight. Incubation RH effects were noted for embryo crude protein and fat contents in the present study, but these effects were influenced by breeder age and day of incubation. There were no apparent consistent effects of RH on crude protein across breeder age and day of incubation. However, at 16 and 21 d of incubation at 28 wk, and at 19 d at 26 wk, crude fat content was significantly lower in embryos incubated at 43% RH compared to 63% RH. These results are further indicative of a decrease in yolk lipid utilization by the embryo, which would be a contributing factor to a decrease in WEW at the 43% RH. The results also suggest that RH is capable of affecting body crude protein and fat contents of embryos and that more extreme changes in incubational RH regimens may more consistently modify the compositions of embryos from young breeders. More extreme RH regimens may likewise be useful in determining if the depressing influences of a decrease in RH on WEW are related to changes in embryo crude protein and fat contents. In addition, within the RH and breeder age ranges investigated in this report, it has been shown that a reduction in RH to 43% decreased WEW without consistent effects on embryo body composition. Furthermore, decreases in the RH of incubators may need to be adjusted so that the body moisture contents of late-stage embryos from very young breeders are not compromised.
ACKNOWLEDGMENTS This work was funded in part by a grant from the U.S. Poultry and Egg Association, Tucker, GA 30084-7303, and by the Mississippi Agricultural and Forestry Experiment Station, Mississippi State, MS 39762. The authors appreciate the expert technical assistance of Sharon Whitmarsh (Mississippi State University) and Susan Creech (North Carolina State University) and the secretarial assistance of Janice Orr (Mississippi State University).
REFERENCES Benton, C. E., and J. Brake, 1996. The effect of broiler breeder flock age and length of egg storage on egg albumen during early incubation. Poultry Sci. 75:1069–1075. Brake, J., and G. R. Baughman, 1989. Comparison of lighting regimes during growth on subsequent seasonal reproductive performance of broiler breeders. Poultry Sci. 68:79–85. Brake, J., T. J. Walsh, C. E. Benton, Jr., J. N. Petitte, R. Meijerhof, and G. Pen˜alva, 1997. Egg handling and storage. Poultry Sci. 76:144–151. Bruzual, J. J., S. D. Peak, J. Brake, and E. D. Peebles, 2000a. Effects of relative humidity during incubation on hatchability and body weight of broiler chicks from young breeder flocks. Poultry Sci. 79:827–830.
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may be accentuated by the lower relative levels of moisture in their tissues at that time in incubation (Peebles et al., 1999). Incubation RH must be properly controlled for proper embryo growth to proceed; Lundy (1969) and Robertson (1961a) reported 40 to 70% RH to produce satisfactory results. Vick et al. (1993) observed that an increase in hatchability and a decrease in early embryonic mortality in eggs subjected to a reduction in incubation RH from 58 to 50% was most evident when those eggs were taken from young breeder flocks. Robertson (1961a) reported that a high RH (75 to 80%) increased mortality and a lower RH (40 to 50%) lowered mortality at the end of incubating eggs laid by older hens. More recent work with young breeders by Bruzual et al. (2000a) has shown that the percentage late dead mortality increased significantly as RH increased from 53 to 63%, and hatching chick BW increased with increases in RH from 43 to 53% and from 53 to 63%. Studies on the subsequent effects of incubation RH on the posthatch broiler chick have shown that overall, optimal performance was achieved when hatching eggs from young hens were incubated at 53% rather than 43 or 63% RH (Bruzual et al., 2000b). Hatchability (Davis et al., 1988) and chick size (Swann and Brake, 1990a) are qualities that can be controlled by incubation egg moisture loss. Water loss is critical and influenced most when embryonic metabolism reaches a plateau (Swann and Brake, 1990b). Egg moisture loss is also inversely related to incubation RH (Robertson, 1961b). The specific incubation weight loss needed by eggs up until the time of internal pipping has been shown to be approximately 12% for commercial broiler strains under conditions of artificial incubation (Tullett, 1981; Peebles and Brake, 1986). Overall, chicks have been observed to hatch earlier when incubation RH was reduced from approximately 52 to 42% (Swann and Brake, 1990c). Percentage WEW between 17 and 19 d of incubation was lower in eggs incubated at the lowest RH (43%) than at the two higher RH (53 and 63%). Davis et al. (1988) reported that increased incubation RH (85 to 90%), which caused eggs to lose only 5.9% of their initial fresh egg mass by 20 d, did not lead to changes in wet or dry embryo mass or embryo moisture content during the final week of incubation. However, decreased incubation RH (0 to 10%), which caused eggs to lose 24% of their initial fresh egg mass by 19 d, resulted in decreased wet embryo mass at 20 and 21 d of incubation. Those embryos were observed to have undergone osmotic stress and dehydration. Individually, EM and DEW were not significantly affected by RH in the current investigation. However, the influence of a decrease in RH from 53 or 63% to 43% evidently promoted an overall decrease in WEW. It is suggested that combined small decreases in EM and DEW might have resulted in a significant decrease in relative WEW. Interestingly, the effects of RH on WEW did not carry over onto subsequent absolute 21-d chick BW. Robertson (1961b) also found that the absolute weights of 1-d-old chicks hatched from eggs incubated at 70% RH were not
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