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Effects of Incubator Humidity and Hen Age on Yolk Composition in Broiler Hatching Eggs from Young Breeders12
Effects of Incubator Humidity and Hen Age on Yolk Composition in Broiler Hatching Eggs from Young Breeders1,2 M. R. Burnham,* E. D. Peebles,*,3 C. W. Gardner,* J. Brake,‡ J. J. Bruzual,‡ and P. D. Gerard† *Department of Poultry Science, and †Experimental Statistics Unit, Mississippi State University, Mississippi State, Mississippi 39762; and ‡Department of Poultry Science, North Carolina State University, Raleigh, North Carolina 27695-7608 arachidonic acid concentrations were higher and myristic acid concentration was lower in eggs from the 26-wkold hens. Conversely, the highest yolk concentrations of linolenic and palmitoleic acids occurred in eggs from 30and 28-wk-old breeders, respectively. At 16, 17, 18, and 19 d of incubation, yolk oleic acid concentrations were significantly, but variably, affected by breeder age, whereas linoleic acid concentration was highest in 26-wkold breeders only at 19 d. Palmitic acid concentration at 17 d was lower in eggs incubated at 53% RH compared with 43 and 63% RH. Rate of yolk uptake from the yolk sac by embryos may be increased by incubating eggs at 53% RH, and the effects of changes in RH between 43 and 63% on yolk lipid content are influenced by breeder age.
(Key words: broiler breeder, embryo, incubation, relative humidity) 2001 Poultry Science 80:1444–1450
INTRODUCTION Hatchability (Lundy, 1969) and chick weight (Tullett and Burton, 1982; Burton and Tullett, 1985) are affected by the amount of moisture lost from the egg during incubation. Furthermore, egg water loss during incubation is influenced by the RH of the incubator (Lundy, 1969). Embryogenesis and posthatch development have been shown to be affected by interactions between breeder age (Shanawany, 1984) and incubator RH (Tullett, 1981; Tullett and Burton, 1982). Egg (Petersen, 1965; Shanawany, 1984) and yolk (Cunningham et al., 1960; O’Sullivan et al., 1991) weights increase as the hen ages. French and Tullett (1991) reported that hens progressing through lay produce larger eggs with larger yolks but with smaller
2001 Poultry Science Association, Inc. Received for publication November 27, 2000. Accepted for publication May 11, 2001. 1 This is Journal Article No. J-9763 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 or of similar ones not mentioned. 3 To whom correspondence should be addressed: dpeebles@ poultry.msstate.edu.
increases in the amount of albumen. In addition, eggs from young flocks, which have higher albumen qualities, respond positively to lowered incubation RH (Vick et al., 1993). Yolk fatty acid concentrations in fresh eggs are influenced by breeder hen age (Latour et al., 1998), and the fatty acid profile of a diet can affect the fatty acid profile of the yolk (Cruickshank, 1934; Sell et al., 1968; Sim et al., 1973; Hargis and Van Elswyk, 1993). Latour et al. (1996) showed that relative yolk sac weight (YSW) of embryos at 18 d of incubation was lower in eggs from breeder hens at 26 wk as compared to those at 36 wk of age. A reduced rate of lipid mobilization from the yolk into the membrane of the yolk sac of young breeders has been demonstrated (Noble et al., 1986), and Latour et al. (1996) have recently shown variable effects of broiler breeder hen age on several essential and nonessential yolk fatty acids. By monitoring the effects of breeder age and RH on yolk composition, optimal combinations of these two factors for the improvement of broiler embryo and chick
Abbreviation Key: YSW = yolk sac weight; YM = yolk moisture; YL = yolk lipid.
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ABSTRACT The effects of broiler breeder age (26, 28, and 30 wk) and incubator relative humidity (43, 53, and 63% RH) on yolk sac weight and composition in broiler hatching eggs between 16 and 19 d of incubation were evaluated. Percentage yolk sac weight was reduced in eggs from the youngest (26 wk) breeder hens and in eggs incubated at 53% RH. Percentage yolk moisture, in eggs from the youngest hens, was lowest at 16 d and was highest at 19 d, and percentage yolk lipid was highest at 16 and 17 d of incubation in eggs from 30-wk-old hens. Percentage yolk lipid content was higher at 63% RH compared with 53% RH in eggs from 26-wk-old breeders but was lower in eggs incubated at a 43% RH compared with 53 and 63% RH from 30-wk-old breeders. Yolk stearic and
INCUBATION HUMIDITY AND YOLK CONSTITUENTS
performance may be elucidated. This research was designed to determine yolk characteristics of broiler hatching eggs taken from young hens and subjected to various RH regimens.
MATERIALS AND METHODS Hatching Egg Supply
Incubation Machines used for incubation 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. These temperatures created the 43, 53, and 63% RH treatments, respectively. Machines were monitored twice daily for proper operation. At Day 16 of incubation, all eggs were candled for evidence of live embryos. Only eggs with viable embryos were transferred at 16 d of incubation to 30-wire pedigree hatching baskets and returned to the original incubator to complete incubation.
Yolk Sampling and Analysis Eggs used for yolk analyses were taken from the incubators at 16 (prior to transfer), 17, 18, and 19 d of incuba4
Arbor Acres Farm, Inc., Glastonbury, CT 06033. Butler Manufacturing Co., Ft. Atkinson, WI 53538.
5
tion. Four eggs in Trial 1 and 10 eggs in Trial 2 at each day of incubation, breeder age, and RH group were sampled for measurement of egg weight, YSW, yolk lipid (YL), yolk moisture (YM), and yolk fatty acid contents. Embryos were euthanized by cervical dislocation. Yolk sacs were carefully separated from their embryos as described by Peebles et al. (1998). The YSW was expressed as a percentage of egg weight prior to set. Percentage YM determinations and calculations were as described by Peebles et al. (1999) and were expressed as a percentage of yolk sample weight at necropsy. Dried samples were individually sealed in labeled plastic jars and stored at −20 C until further composition analyses. Yolk lipid extractions and fatty acid methylation and analysis were as described by Latour et al. (1998). Total YL content was expressed as a percentage of yolk sample weight and fatty acid concentrations were as percentages of total yolk fatty acids.
Statistical Analysis Each trial represented a replicate in time. A randomized complete block design was used with trials (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 interactions. 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). Least-squares means were compared in the event of significant effects. All data were analyzed using the mixed model procedure of SAS software (1996). Statements of significance were based on P ≤ 0.05 unless otherwise stated.
RESULTS There were significant main effects due to breeder age (P ≤ 0.008), day of incubation (P ≤ 0.0001), and RH (P ≤ 0.001) for percentage YSW. Percentage YSW was higher in eggs from breeders at 28 and 30 wk compared with those at 26 wk. At 26, 28, and 30 wk, percentage YSW was 17.8, 18.6, and 18.5%, respectively (SEM = 0.19). Percentage YSW also decreased significantly with day of incubation between 16 and 19 d. Percentage YSW at 16, 17, 18, and 19 d, was 20.5, 19.7, 18.0, and 15.1%, respectively (SEM = 0.22). Furthermore, percentage YSW in eggs incubated at 53% RH was significantly smaller than that of eggs incubated at 43 and 63% RH. At 43, 53, and 63% RH, percentage YSW was 18.3, 17.8, and 18.8%, respectively (SEM = 0.19). There were significant breeder age by day of incubation interactions for percentage YM (P ≤ 0.0002) and percentage YL (P ≤ 0.02). Differences among breeder ages at each day of incubation are shown in Table 1. Percentage YM at 16 d of incubation was lower in eggs from 26-wk-old breeders compared with 28- and 30-wk-old breeders. At 19 d of incubation, percentage YM was higher in eggs from 26-wk-old breeders compared with that from 30-
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Hatching eggs were produced from Arbor Acres4 feather-sexable yield strain (FSY) females mated to Arbor Acres strain (Yield) males. Males and females were grown sex-separated in light-controlled facilities on an 8-h photoperiod. The feeding and BW programs were similar to those of Walsh and Brake (1997), and details of house management were as described by Brake and Baughman (1989). At 20 wk (141 d) of age, the birds were moved to slat-litter breeding pens and were photostimulated with 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 during the fall in Trial 1 and during the following spring 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, but equally, distributed 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 and weighed prior to set so that YSW at 16, 17, 18, and 19 d of incubation could be calculated as a percentage of egg weight obtained immediately prior to the initiation of incubation.
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BURNHAM ET AL. TABLE 1. Percentage yolk moisture and lipid content at 16, 17, 18, and 19 d of incubation in eggs from broiler breeders at 26, 28, and 30 wk of age 16 d
17 d
18 d
19 d
Week of age Yolk component
26
28
30
26
28
30
Yolk moisture1,3 Yolk lipid2,3
45.6b 20.4b
49.1a 22.5b
48.5a 25.3a
49.6 18.6b
49.5 19.3ab
49.1 21.3a
26
28
30
26
28
30
49.8 16.6
49.1 18.7
51.3 16.2
51.2a 16.7
49.1ab 18.1
47.2b 16.4
(%)
a,b Means within day of incubation among breeder ages with no common superscript differ significantly (P ≤ 0.05). 1 SEM based on pooled estimate of variance = 0.80. 2 SEM based on pooled estimate of variance = 0.97. 3 n = 42.
percentage myristic acid was highest at 16 d compared with that at 17, 18, and 19 d. There were significant (P ≤ 0.02) interactions of breeder age by day of incubation for yolk oleic and linoleic acid concentrations. Differences among breeder ages within day of incubation are shown in Table 5. Yolk oleic acid concentrations at 16, 17, 18, and 19 d of incubation were higher in eggs from 28-wk-old breeders compared with those from 26-wk-old breeders. Concentrations of oleic acid at 30 wk were also greater than those at 26 wk at 16 and 18 d of incubation. At 17 d, levels in eggs from 30wk-old hens were lower than those at 28 wk, whereas at 19 d, levels of oleic acid at 30 wk were intermediate to those at 26 and 28 wk. Yolk linoleic acid concentrations were significantly different among breeder ages only at 19 d of incubation. At that time, yolks from 26-wk-old hens had higher linoleic acid concentrations than those from 28-wk and 30-wk-old hens. There was a significant (P ≤ 0.04) day of incubation by RH interaction for yolk palmitic acid concentration. Differences among RH within day of incubation are provided in Table 6. Only at 17 d of incubation was there a significant effect due to RH. At that time, yolk palmitic acid concentration was lower in eggs incubated at 53% RH compared with those at 43 or 63% RH.
DISCUSSION As hens age, they lay larger eggs (Petersen, 1965; Shanawany, 1984; French and Tullett, 1991) with larger yolks
TABLE 2. Percentage yolk lipid content in eggs from broiler breeders at 26, 28, and 30 wk of age incubated at 43, 53, and 63% RH1,2 26 wk
28 wk
30 wk
Incubation RH (%) 43
53
63
43
18.7ab
17.9b
20.3a
18.9
53
63
43
53
63
19.3
16.6b
20.6a
19.9a
(%) 20.6
Means within breeder age among RH with no common superscript differ significantly (P ≤ 0.05). SEM based on pooled estimate of variance = 0.84. 2 n = 56. a,b 1
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wk-old breeders, with percentage YM at 28 wk being intermediate. Percentage YL content at 16 and 17 d of incubation was higher in eggs from 30-wk-old breeders compared with those from 26-wk breeders. At 16 d, percentage YL in eggs from breeders at 30 wk was also higher than that of eggs from breeders at 28 wk, but at 17 d, percentage YL from 28-wk-old breeders was intermediate to that observed at 26 and 30 wk. There was also a significant (P ≤ 0.03) breeder age by RH interaction for percentage YL. Differences among RH treatments at each breeder age are provided in Table 2. At 26 wk of breeder age, percentage YL was higher at 63% RH compared with that at 53% RH, with 43% RH being intermediate. In addition, at 30 wk, percentage YL was higher at 53 and 63% RH in comparison with 43% RH. There was a significant (P ≤ 0.0001) main effect due to breeder age for yolk concentrations of stearic, linolenic, arachidonic, palmitoleic, and myristic acids (Table 3). Percentage yolk stearic and arachidonic acids were higher at 26 wk compared with 28 or 30 wk. However, linolenic acid levels were higher at 30 wk compared with those at 26 and 28 wk, and yolk palmitoleic acid levels were higher at 28 wk compared with those at 26 and 30 wk. Myristic acid concentration was higher at 28 and 30 wk compared with that at 26 wk. There was a significant (P ≤ 0.0001) day of incubation main effect for concentrations of arachidonic and myristic acids in yolk (Table 4). Percentage yolk arachidonic acid was higher at 16 and 17 d of incubation compared with that at 18 and 19 d of incubation, and
INCUBATION HUMIDITY AND YOLK CONSTITUENTS TABLE 3. Yolk stearic, linolenic, arachidonic, palmitoleic, and myristic acid concentrations of eggs from broiler breeders at 26, 28, and 30 wk of age Week of age Acid
26
Stearic1,4 Linolenic2,4 Arachidonic3,4 Palmitoleic3,4 Myristic2,4
9.94a 0.01b 2.68a 3.22b 0.06b
28
30
(Percentage total fatty acids) 8.76b 0.08b 1.84b 3.89a 0.20a
9.27b 0.33a 1.77b 3.47b 0.18a
a,b Means among weeks of breeder age with no common superscript differ significantly (P ≤ 0.05). 1 SEM based on pooled estimate of variance = 0.198. 2 SEM based on pooled estimate of variance = 0.021. 3 SEM based on pooled estimate of variance = 0.100. 4 n = 168.
TABLE 4. Yolk arachidonic and myristic acid concentrations of eggs from broiler breeders at 16, 17, 18, and 19 d of incubation1 Day of incubation Acid
16
Arachidonic2 Myristic2
2.32a 0.22a
17
18
19
(Percentage total fatty acids) 2.41a 0.14b
1.91b 0.13b
1.75b 0.09b
a,b Means among days of incubation with no common superscript differ significantly (P ≤ 0.05). 1 SEM based on pooled estimate of variance for arachidonic and myristic acids are 0.114 and 0.017, respectively. 2 n = 126.
during this time would consequently lead to greater differences in percentage YSW. Lower hatching rates (Romanoff, 1929, 1930) and poorer early chick performance (Tullett and Burton, 1982) are influenced by rate of incubational egg water loss. Furthermore, poorer hatching potentials (O’Sullivan et al., 1991) and posthatch performances (Wyatt et al., 1985) have been associated with eggs from young breeders. Tullett and Burton (1982) have also shown that hatchling mass is well correlated with initial egg mass and egg water loss during incubation. Ar (1991) has suggested that a 10% loss of total internal egg moisture is required to produce an air cell volume for adequate respiratory expansion during pipping. Because rate of water loss from eggs may be manipulated by altering incubational RH (Lundy, 1969), it is important to consider the effects of RH on yolk absorption and utilization by the embryo. A RH of 50% at an air temperature of 37.5 C is generally accepted as optimal for incubation of chicken eggs (Tullett, 1990). Recent studies have shown that better chick performance was achieved when hatching eggs from young hens were incubated at 53% RH rather than 43 or 63% RH (Bruzual et al., 2000). In the present study, percentage YSW between 16 and 19 d of incubation was lower in eggs incubated at 53% RH in comparison with those incubated at 43 or 63% RH. Whether or not posthatch performance of chicks from eggs incubated at a different RH is directly related to differences in embryonic yolk sac absorption rate can only be surmised. However, a higher rate of yolk absorption in late embryos at the 53% RH would be expected to promote posthatch performance as shown by Bruzual et al. (2000). Marshall and Cruickshank (1938) have established that percentage weight loss in small chicken eggs is more rapid than from larger eggs due to the relatively greater evaporative surface to volume of small eggs. The current results showed that percentage YM at 16 d of incubation was lower in eggs from 26-wk-old breeders compared with those from 28- and 30-wk-old breeders, suggesting that smaller eggs from 26-wk-old breeders are lower in YM early in the rapid yolk absorption phase compared with those from larger eggs laid by older breeders. However, by 19 d, when rate of yolk absorption had peaked, YM increased in the smaller eggs in relation to other yolk nutrients. This increase was evidenced by a significantly higher YM percentage in eggs from 26-wk-old breeders compared with 30-wk-old breeders at 19 d of incubation. Water concentration in the yolk is relatively low (42 to 65%) in comparison with that in the albumen (85 to 95%) (Southerland and Rahn, 1987), but moisture is maintained in the yolk in preference to the embryo when fluid reserves in the egg decrease just prior to hatch (Tullett and Burton, 1982). Yolk moisture in the smaller eggs, therefore, may be more highly conserved during this peak period of yolk absorption. A higher rate of yolk absorption may allow embryos from younger hens to maintain higher concentrations of tissue water. Declines in embryo moisture content with embryo age (Peebles et al., 1999) might then be slowed
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(Cunningham et al., 1960; O’Sullivan et al., 1991). However, percentage YSW of chicks from breeders at 51 wk of age have been reported to be smaller than those from broiler breeders at 36 and 64 wk (Latour et al., 1998). Current results indicated that percentage YSW of embryos between 16 and 19 d of incubation was lower in eggs from 26-wk-old breeders compared with those from 28-wk and 30-wk-old breeders. Likewise, Latour et al. (1996) found that 18-d embryos from breeders at 26 wk had a smaller percentage YSW when compared with breeders at 36 and 48 wk. The yolk sac is the main nutrient source for the developing embryo, as it absorbs yolk during the final week of incubation. It would appear that yolks of embryos from very young breeders (26 wk) may be absorbed at a higher rate between 16 and 19 d than those from hens that are slightly more mature (i.e., 28 and 30 wk). Subsequent declines in yolk absorption rate after 19 d in the 26-wk-old group may, likewise, eliminate or reverse comparative differences in residual percentage YSW of posthatch chicks from very young and more mature parents. Nevertheless, a relatively higher rate of yolk uptake during the final week of incubation by embryos from very young parents may stem from an effort to compensate for possible deficiencies in yolk nutrient content or inefficiencies in lipid transfer, nutrient utilization, and metabolism. Differences in rate of yolk absorption
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BURNHAM ET AL. TABLE 5. Yolk oleic and linoleic acid concentrations of eggs at 16, 17, 18, and 19 d of incubation from broiler breeders at 26, 28, and 30 wk of age1 16 d
17 d
18 d
19 d
Week of age Acid
26
28
30
26
28
30
Oleic2 Linoleic2
38.0b 12.1
42.6a 12.1
42.5a 12.0
39.7b 12.2
43.2a 12.0
26
28
30
26
28
30
42.6a 11.7
42.7b 13.5a
44.5a 11.8b
43.0ab 11.8b
(Percentage total fatty acids) 40.5b 12.4
40.1b 12.7
43.6a 12.5
a,b Means within day of incubation among weeks of breeder age with no common superscript differ significantly (P ≤ 0.05). 1 SEM based on pooled estimate of variance for oleic and linoleic acids are 0.60 and 0.34, respectively. 2 n = 42.
tion. In addition, percentage YL was lower in 28-wk-old breeders compared with 30-wk-old breeders at 16 d of incubation. The data from this study suggest that embryos in eggs from the younger birds in both scenarios are absorbing YL reserves at a relatively higher rate than their counterparts at 30 wk of age. Although percentage YL in this study was lower at 26 and 28 wk in comparison with that at 30 wk, it may be potentially greater relative to that in eggs from much more mature flocks (i.e., 41 wk of age). Results also indicated a reduction in percentage YL for those eggs incubated at 53% RH compared with those incubated at 63% RH and obtained from 26-wk-old breeders; we also noted a reduction in YL at 43% RH compared with the 53 and 63% RH in eggs from 30-wk-old breeders. These data further suggest that a lower RH, particularly in hens at 30 wk of age, may accentuate the rate of YL absorption. The impact of breeder age on the relationship between incubational RH and the utilization of yolk by developing embryos may be due to corresponding changes in egg weight. A companion article (Peebles et al., 2001) reported the effects of the same breeder ages and RH treatments used in this study on embryo body compositions. A significant breeder age by day of incubation by RH treatment interaction was found for embryo crude fat content. Fat contents of embryos at 19 d of incubation in eggs from 26-wk-old breeders and at 16 and 21 d in eggs from 28-wk-old breeders were higher
TABLE 6. Yolk palmitic acid concentrations of eggs at 16, 17, 18, and 19 d of incubation from broiler breeders at 26, 28, and 30 wk of age1,2 16 d
17 d
18 d
19 d
Incubation RH (%) 43
53
63
43
53
63
26.5
26.5
26.2
28.5a
26.6b
43
53
63
43
53
63
26.2
26.4
27.3
26.5
(Percentage total fatty acids) 27.9a
27.0
26.4
Means within day of incubation among RH, with no common superscript differ significantly (P ≤ 0.05). SEM based on pooled estimate of variance = 0.38. 2 n = 42. a,b 1
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with increased uptake of yolk-derived water by the embryo. Higher percentage YM at 19 d of incubation in small eggs from very young breeders would compensate for an increased relative rate of water loss and protect the embryo from dehydration. An excess amount of moisture inside the yolk during the last half of incubation, on the other hand, has been found to have no effect on embryonic growth (Thomas et al., 1988). Water is a metabolic byproduct of lipid oxidation (Ar and Rahn, 1980), and increased YL utilization may allow for increased availability of metabolic water; however, embryo body fat and moisture contents have been found to be negatively correlated by the end of incubation (Peebles et al., 1999). Nevertheless, rate of YL uptake and selective fatty acid oxidation may permit embryos partial control of body moisture levels. Embryos from very young flocks (25 wk of age) have been reported by Noble et al. (1986) to have larger relative amounts of residual total YL in their yolk sacs at 19 d of incubation when compared with older flocks (41 wk of age). That finding suggests that embryos from more mature flocks utilize more YL than those from very young flocks. Embryos in eggs from young hens have also been noted to have difficulty metabolizing YL into energy (Noble et al., 1986), and YL transfer from the yolk sac to the embryo may be less efficient in eggs from young breeders (Shanawany, 1984). Current results indicated decreased percentage YL in the eggs of 26-wk-old breeders compared with 30-wk-old breeders at 16 and 17 d of incuba-
INCUBATION HUMIDITY AND YOLK CONSTITUENTS
arachidonic acid was being absorbed at a slower rate only. Because yolk sac membrane ∆-9 desaturase activity converts stearic acid to oleic acid (Noble and Shand, 1985; Noble and Cocchi, 1990), perhaps higher stearic and lower oleic acid concentrations in the yolks of eggs from 26wk-old breeders compared with those at 30 wk may also be due to decreased ∆-9 desaturase activity in the very young hens relative to the slightly older birds. Nevertheless, the significant effects of breeder age on yolk oleic and arachidonic acid concentrations point to breeder age effects on yolk sac membrane desaturase activity. At Day 17, yolk palmitic acid concentration was lower at 53% RH compared with that at 43 or 63% RH. Also, percentage YSW was lower at 53% RH compared with 43 and 63% RH, and percentage YL was lower at 53% RH compared with 63% RH in eggs from 26-wk-old hens. In related work by Peebles et al. (2001), relative wet embryo weight was higher in eggs incubated at 53% RH compared with 43% RH between 17 and 19 d of incubation. Peebles et al. (1999) previously noted that as the embryo absorbed YL during the second week of incubation, an associated decrease in yolk palmitic acid occurred. It was suggested that the utilization of yolk palmitic acid with embryonic growth during that time may be necessary for increased embryo DM synthesis. Yolk palmitic acid concentration was also found by Peebles et al. (1999) to be positively correlated with percentage embryo moisture content at 9 and 12 d of incubation; however, Peebles et al. (2001) reported no influence of RH on embryo moisture content. Taken together, these data suggest that embryonic growth rate, in terms of DM accumulation, was maximized at a 53% RH and was concomitant with increased total yolk and yolk palmitic acid utilization in eggs from young broiler breeders.
ACKNOWLEDGMENTS This work was funded in part by a grant from the US 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 Ar, A., 1991. Roles of water in avian eggs. In: Egg Incubation: Its Effects on Embryonic Development in Birds and Reptiles. D. C. Deeming, and M. J. W. Ferguson, ed. Cambridge University Press, Cambridge, U.K. Ar, A. and H. Rahn, 1980. Water in the avian egg: Overall budget of incubation. Am. Zool. 20:373–384. Brake, J., and G. R. Baughman, 1989. Comparison of lighting regimens during growth on subsequent seasonal reproductive performance of broiler breeders. Poultry Sci. 68:79–85. Bruzual, J. J., S. D. Peak, J. Brake, and E. D. Peebles, 2000. 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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when eggs were incubated at 63% RH compared with 43% RH. Water and fat contents of embryos have been shown to exhibit inverse functional relationships between 15 and 21 d of incubation (Peebles et al., 1999). However, decreased water loss from eggs at the highest RH (63%) may decrease the need for yolk-derived water and may subsequently decrease associated YL uptake and its deposition in embryonic tissues. Lipid oxidation and the production of metabolic water, likewise, may be impeded. Nevertheless, relative wet embryo body weight was higher at 63% RH compared with 43% RH (Peebles et al., 2001), indicating that a slower uptake of YL at the highest RH did not retard overall growth of the embryo. Water production through metabolic oxidation differs for individual fatty acids (Lehninger, 1979), and embryos appear to preferentially absorb certain fatty acids. Yolk fatty acid profiles, therefore, would be expected to change with breeder age and incubation RH as well as with day of incubation. Latour et al. (1998) provided data showing that broiler breeder age influences the YL contents of fresh eggs and the utilization of YL by developing embryos. More specifically, fresh egg yolks from 36-wk-old breeders exhibit higher levels of palmitoleic acid when compared with the levels observed in fresh egg yolks of 51-wk or 64-wk-old breeders. Those levels also decrease significantly by 21 d of incubation only in eggs from 36wk-old hens. Furthermore, at 36 wk of breeder age, the concentrations of oleic and arachidonic acid are higher in yolks from hatched chicks than in fresh eggs. Current results showed that breeder age by day of incubation interactions occurred for percentage YL and several yolk fatty acids. However, there were notable consistent associated changes between percentage YL and a few fatty acids in response to breeder age. When comparing 26- and 30-wk-old breeders, decreased percentages of YL at 16 and 17 d of incubation in the younger age group were associated with decreased yolk linolenic and myristic and increased stearic and arachidonic acids between 16 and 19 d. Decreased yolk oleic acid at 16 and 18 d of incubation was also found in the 26-wk-old group compared with those at 30 wk. These results suggest that the uptake of linolenic, myristic, and oleic acids by embryos from the younger hens was greater in proportion to other fatty acids in conjunction with an increase in percentage YL utilization. Conversely, stearic and arachidonic acids were relatively spared in the yolks of younger hens. Arachidonic acid is synthesized from linoleic acid and is essential for chick growth. Linoleic acid concentration, therefore, would be expected to decrease in association with increased yolk arachidonic acid concentrations. Whether or not increased arachidonic acid concentrations in the yolk were due to a lower rate of absorption or from increased production from linoleic acid through elevated ∆6-desaturase activity in the yolk sac membrane is uncertain (Noble and Shand, 1985; Noble and Cocchi, 1990). However, the lack of any change in linoleic acid concentration between 16 and 18 d and an elevation at 19 suggest that
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BURNHAM ET AL. 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. Peebles, E. D., T. Pansky, S. M. Doyle, C. R. Boyle, T. W. Smith, M. A. Latour, and P. D. Gerard, 1998. Effects of dietary fat and eggshell cuticle removal on egg water loss and embryo growth in broiler hatching eggs. Poultry Sci. 77:1522–1530. Petersen, C., 1965. Factors influencing eggshell quality. A review. World’s Poult. Sci. J. 21:110–138. Romanoff, A. L., 1929. Effects of humidity on the growth, calcium metabolism, and mortality of the chick embryo. J. Exp. Zool. 54:343–348. Romanoff, A. L., 1930. Biochemistry and biophysics of the developing hen’s eggs. I. Influence of humidity. Cornell Univ. Agr. Exp. Stn. Mem. 132:59. SAS Institute Inc., 1996. SAS威 User’s Guide: Basics. Version 6 ed. SAS Institute Inc., Cary, NC. Sell, J. L., S. H. Choo, and P. A. Kondra, 1968. Fatty acid composition of egg yolk and adipose tissue as influenced by dietary fat and strain of hen. Poultry Sci. 47:1296–1302. Shanawany, M. M., 1984. Inter-relationship between egg weight, parental age and embryonic development. Br. Poult. Sci. 25:449–455. Sim, J. S., D. B. Bragg, and G. C. Hodson, 1973. Effect of dietary animal tallow and vegetable oil on fatty acid composition of egg yolk, adipose tissue and liver of laying hens. Poultry Sci. 52:51–57. Southerland, P. R., and H. Rahn, 1987. On the composition of bird eggs. Condor 89:48–65. Steel, R. G. D., and J. H. Torrie, 1980. Principles and Procedures of Statistics. A Biometric Approach. 2nd ed. McGraw-Hill, New York, NY. Thomas, A. D., S. S. Sheldon, 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. Tullett, S. G., 1981. Theoretical and practical aspects of eggshell porosity. Turkeys 29:24–28. Tullett, S. G., 1990. Science and the art of incubation. Poultry Sci. 69:1–15. 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. B., T. J. Walsh, and J. Brake, 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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Burton, F. G., and S. G. Tullett, 1985. The effects of egg weight and shell porosity on the growth and water balance of the chicken embryo. Comp. Biochem. Physiol. 81A:377–385. Cruickshank, E. M., 1934. Studies of fat metabolism in the fowl. The composition of the egg fat and depot fat of the fowl as affected by the ingestion of large amounts of different fat. Biochem. J. 28:965–977. Cunningham, F. E., O. J. Cotterill, and E. M. Funk, 1960. The effect of season and age of bird on the chemical composition of egg white. Poultry Sci. 39:300–308. French, N. A., and S. G. Tullett, 1991. Variation in the eggs of various poultry species. Pages 59–77 in: Avian Incubation. Butterworth and Heinemann, London, U.K. Hargis, P. S., and M. Van Elswyk, 1993. Manipulating the fatty acid composition of poultry meat and eggs for the health conscious consumer. World’s Poult. Sci. J. 49:251–264. Latour, M. A., E. D. Peebles, C. R. Boyle, S. M. Doyle, T. Pansky, and J. D. Brake, 1996. Effects of breeder hen age and dietary fat on embryonic and neonatal broiler serum lipids and glucose. Poultry Sci. 75:695–701. 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. Lehninger, A. L., 1979. Oxidation of fatty acids. Pages 543– 558 in: Biochemistry. 2nd ed. Worth Publishing Inc., New York, NY. Lundy, H., 1969. A review of the effects of temperature, humidity, turning, and gaseous environment in the incubator on the 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, U.K. Marshall, W., and D. B. Cruickshank, 1938. The function of the cuticle in relation to the porosity of eggs. J. Agric. Sci. 28:24–42. Noble, R. C., and M. Cocchi, 1990. Lipid metabolism and the neonatal chicken. Prod. Lipid Res. 29:107–140. Noble, R. C., F. Lonsdale, K. Conner, and D. Brown, 1986. Changes in lipid metabolism of the chick embryo with parent age. Poultry Sci. 65:409–416. Noble, R. C., and J. H. Shand, 1985. Unsaturated fatty acid compositional changes and desaturation during the embryonic development of the chicken. Lipids 20:278–282. 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., M. R. Burnham, C. W. Gardner, J. Brake, J. J. Bruzual, and P. D. Gerard, 2001. Effects of incubational humidity and hen age on embryo composition in broiler hatching eggs from young breeders. Poultry Sci. 80:1299–1304.
(Key words: broiler breeder, embryo, incubation, relative humidity) 2001 Poultry Science 80:1444–1450
INTRODUCTION Hatchability (Lundy, 1969) and chick weight (Tullett and Burton, 1982; Burton and Tullett, 1985) are affected by the amount of moisture lost from the egg during incubation. Furthermore, egg water loss during incubation is influenced by the RH of the incubator (Lundy, 1969). Embryogenesis and posthatch development have been shown to be affected by interactions between breeder age (Shanawany, 1984) and incubator RH (Tullett, 1981; Tullett and Burton, 1982). Egg (Petersen, 1965; Shanawany, 1984) and yolk (Cunningham et al., 1960; O’Sullivan et al., 1991) weights increase as the hen ages. French and Tullett (1991) reported that hens progressing through lay produce larger eggs with larger yolks but with smaller
2001 Poultry Science Association, Inc. Received for publication November 27, 2000. Accepted for publication May 11, 2001. 1 This is Journal Article No. J-9763 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 or of similar ones not mentioned. 3 To whom correspondence should be addressed: dpeebles@ poultry.msstate.edu.
increases in the amount of albumen. In addition, eggs from young flocks, which have higher albumen qualities, respond positively to lowered incubation RH (Vick et al., 1993). Yolk fatty acid concentrations in fresh eggs are influenced by breeder hen age (Latour et al., 1998), and the fatty acid profile of a diet can affect the fatty acid profile of the yolk (Cruickshank, 1934; Sell et al., 1968; Sim et al., 1973; Hargis and Van Elswyk, 1993). Latour et al. (1996) showed that relative yolk sac weight (YSW) of embryos at 18 d of incubation was lower in eggs from breeder hens at 26 wk as compared to those at 36 wk of age. A reduced rate of lipid mobilization from the yolk into the membrane of the yolk sac of young breeders has been demonstrated (Noble et al., 1986), and Latour et al. (1996) have recently shown variable effects of broiler breeder hen age on several essential and nonessential yolk fatty acids. By monitoring the effects of breeder age and RH on yolk composition, optimal combinations of these two factors for the improvement of broiler embryo and chick
Abbreviation Key: YSW = yolk sac weight; YM = yolk moisture; YL = yolk lipid.
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ABSTRACT The effects of broiler breeder age (26, 28, and 30 wk) and incubator relative humidity (43, 53, and 63% RH) on yolk sac weight and composition in broiler hatching eggs between 16 and 19 d of incubation were evaluated. Percentage yolk sac weight was reduced in eggs from the youngest (26 wk) breeder hens and in eggs incubated at 53% RH. Percentage yolk moisture, in eggs from the youngest hens, was lowest at 16 d and was highest at 19 d, and percentage yolk lipid was highest at 16 and 17 d of incubation in eggs from 30-wk-old hens. Percentage yolk lipid content was higher at 63% RH compared with 53% RH in eggs from 26-wk-old breeders but was lower in eggs incubated at a 43% RH compared with 53 and 63% RH from 30-wk-old breeders. Yolk stearic and
INCUBATION HUMIDITY AND YOLK CONSTITUENTS
performance may be elucidated. This research was designed to determine yolk characteristics of broiler hatching eggs taken from young hens and subjected to various RH regimens.
MATERIALS AND METHODS Hatching Egg Supply
Incubation Machines used for incubation 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. These temperatures created the 43, 53, and 63% RH treatments, respectively. Machines were monitored twice daily for proper operation. At Day 16 of incubation, all eggs were candled for evidence of live embryos. Only eggs with viable embryos were transferred at 16 d of incubation to 30-wire pedigree hatching baskets and returned to the original incubator to complete incubation.
Yolk Sampling and Analysis Eggs used for yolk analyses were taken from the incubators at 16 (prior to transfer), 17, 18, and 19 d of incuba4
Arbor Acres Farm, Inc., Glastonbury, CT 06033. Butler Manufacturing Co., Ft. Atkinson, WI 53538.
5
tion. Four eggs in Trial 1 and 10 eggs in Trial 2 at each day of incubation, breeder age, and RH group were sampled for measurement of egg weight, YSW, yolk lipid (YL), yolk moisture (YM), and yolk fatty acid contents. Embryos were euthanized by cervical dislocation. Yolk sacs were carefully separated from their embryos as described by Peebles et al. (1998). The YSW was expressed as a percentage of egg weight prior to set. Percentage YM determinations and calculations were as described by Peebles et al. (1999) and were expressed as a percentage of yolk sample weight at necropsy. Dried samples were individually sealed in labeled plastic jars and stored at −20 C until further composition analyses. Yolk lipid extractions and fatty acid methylation and analysis were as described by Latour et al. (1998). Total YL content was expressed as a percentage of yolk sample weight and fatty acid concentrations were as percentages of total yolk fatty acids.
Statistical Analysis Each trial represented a replicate in time. A randomized complete block design was used with trials (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 interactions. 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). Least-squares means were compared in the event of significant effects. All data were analyzed using the mixed model procedure of SAS software (1996). Statements of significance were based on P ≤ 0.05 unless otherwise stated.
RESULTS There were significant main effects due to breeder age (P ≤ 0.008), day of incubation (P ≤ 0.0001), and RH (P ≤ 0.001) for percentage YSW. Percentage YSW was higher in eggs from breeders at 28 and 30 wk compared with those at 26 wk. At 26, 28, and 30 wk, percentage YSW was 17.8, 18.6, and 18.5%, respectively (SEM = 0.19). Percentage YSW also decreased significantly with day of incubation between 16 and 19 d. Percentage YSW at 16, 17, 18, and 19 d, was 20.5, 19.7, 18.0, and 15.1%, respectively (SEM = 0.22). Furthermore, percentage YSW in eggs incubated at 53% RH was significantly smaller than that of eggs incubated at 43 and 63% RH. At 43, 53, and 63% RH, percentage YSW was 18.3, 17.8, and 18.8%, respectively (SEM = 0.19). There were significant breeder age by day of incubation interactions for percentage YM (P ≤ 0.0002) and percentage YL (P ≤ 0.02). Differences among breeder ages at each day of incubation are shown in Table 1. Percentage YM at 16 d of incubation was lower in eggs from 26-wk-old breeders compared with 28- and 30-wk-old breeders. At 19 d of incubation, percentage YM was higher in eggs from 26-wk-old breeders compared with that from 30-
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Hatching eggs were produced from Arbor Acres4 feather-sexable yield strain (FSY) females mated to Arbor Acres strain (Yield) males. Males and females were grown sex-separated in light-controlled facilities on an 8-h photoperiod. The feeding and BW programs were similar to those of Walsh and Brake (1997), and details of house management were as described by Brake and Baughman (1989). At 20 wk (141 d) of age, the birds were moved to slat-litter breeding pens and were photostimulated with 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 during the fall in Trial 1 and during the following spring 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, but equally, distributed 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 and weighed prior to set so that YSW at 16, 17, 18, and 19 d of incubation could be calculated as a percentage of egg weight obtained immediately prior to the initiation of incubation.
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BURNHAM ET AL. TABLE 1. Percentage yolk moisture and lipid content at 16, 17, 18, and 19 d of incubation in eggs from broiler breeders at 26, 28, and 30 wk of age 16 d
17 d
18 d
19 d
Week of age Yolk component
26
28
30
26
28
30
Yolk moisture1,3 Yolk lipid2,3
45.6b 20.4b
49.1a 22.5b
48.5a 25.3a
49.6 18.6b
49.5 19.3ab
49.1 21.3a
26
28
30
26
28
30
49.8 16.6
49.1 18.7
51.3 16.2
51.2a 16.7
49.1ab 18.1
47.2b 16.4
(%)
a,b Means within day of incubation among breeder ages with no common superscript differ significantly (P ≤ 0.05). 1 SEM based on pooled estimate of variance = 0.80. 2 SEM based on pooled estimate of variance = 0.97. 3 n = 42.
percentage myristic acid was highest at 16 d compared with that at 17, 18, and 19 d. There were significant (P ≤ 0.02) interactions of breeder age by day of incubation for yolk oleic and linoleic acid concentrations. Differences among breeder ages within day of incubation are shown in Table 5. Yolk oleic acid concentrations at 16, 17, 18, and 19 d of incubation were higher in eggs from 28-wk-old breeders compared with those from 26-wk-old breeders. Concentrations of oleic acid at 30 wk were also greater than those at 26 wk at 16 and 18 d of incubation. At 17 d, levels in eggs from 30wk-old hens were lower than those at 28 wk, whereas at 19 d, levels of oleic acid at 30 wk were intermediate to those at 26 and 28 wk. Yolk linoleic acid concentrations were significantly different among breeder ages only at 19 d of incubation. At that time, yolks from 26-wk-old hens had higher linoleic acid concentrations than those from 28-wk and 30-wk-old hens. There was a significant (P ≤ 0.04) day of incubation by RH interaction for yolk palmitic acid concentration. Differences among RH within day of incubation are provided in Table 6. Only at 17 d of incubation was there a significant effect due to RH. At that time, yolk palmitic acid concentration was lower in eggs incubated at 53% RH compared with those at 43 or 63% RH.
DISCUSSION As hens age, they lay larger eggs (Petersen, 1965; Shanawany, 1984; French and Tullett, 1991) with larger yolks
TABLE 2. Percentage yolk lipid content in eggs from broiler breeders at 26, 28, and 30 wk of age incubated at 43, 53, and 63% RH1,2 26 wk
28 wk
30 wk
Incubation RH (%) 43
53
63
43
18.7ab
17.9b
20.3a
18.9
53
63
43
53
63
19.3
16.6b
20.6a
19.9a
(%) 20.6
Means within breeder age among RH with no common superscript differ significantly (P ≤ 0.05). SEM based on pooled estimate of variance = 0.84. 2 n = 56. a,b 1
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wk-old breeders, with percentage YM at 28 wk being intermediate. Percentage YL content at 16 and 17 d of incubation was higher in eggs from 30-wk-old breeders compared with those from 26-wk breeders. At 16 d, percentage YL in eggs from breeders at 30 wk was also higher than that of eggs from breeders at 28 wk, but at 17 d, percentage YL from 28-wk-old breeders was intermediate to that observed at 26 and 30 wk. There was also a significant (P ≤ 0.03) breeder age by RH interaction for percentage YL. Differences among RH treatments at each breeder age are provided in Table 2. At 26 wk of breeder age, percentage YL was higher at 63% RH compared with that at 53% RH, with 43% RH being intermediate. In addition, at 30 wk, percentage YL was higher at 53 and 63% RH in comparison with 43% RH. There was a significant (P ≤ 0.0001) main effect due to breeder age for yolk concentrations of stearic, linolenic, arachidonic, palmitoleic, and myristic acids (Table 3). Percentage yolk stearic and arachidonic acids were higher at 26 wk compared with 28 or 30 wk. However, linolenic acid levels were higher at 30 wk compared with those at 26 and 28 wk, and yolk palmitoleic acid levels were higher at 28 wk compared with those at 26 and 30 wk. Myristic acid concentration was higher at 28 and 30 wk compared with that at 26 wk. There was a significant (P ≤ 0.0001) day of incubation main effect for concentrations of arachidonic and myristic acids in yolk (Table 4). Percentage yolk arachidonic acid was higher at 16 and 17 d of incubation compared with that at 18 and 19 d of incubation, and
INCUBATION HUMIDITY AND YOLK CONSTITUENTS TABLE 3. Yolk stearic, linolenic, arachidonic, palmitoleic, and myristic acid concentrations of eggs from broiler breeders at 26, 28, and 30 wk of age Week of age Acid
26
Stearic1,4 Linolenic2,4 Arachidonic3,4 Palmitoleic3,4 Myristic2,4
9.94a 0.01b 2.68a 3.22b 0.06b
28
30
(Percentage total fatty acids) 8.76b 0.08b 1.84b 3.89a 0.20a
9.27b 0.33a 1.77b 3.47b 0.18a
a,b Means among weeks of breeder age with no common superscript differ significantly (P ≤ 0.05). 1 SEM based on pooled estimate of variance = 0.198. 2 SEM based on pooled estimate of variance = 0.021. 3 SEM based on pooled estimate of variance = 0.100. 4 n = 168.
TABLE 4. Yolk arachidonic and myristic acid concentrations of eggs from broiler breeders at 16, 17, 18, and 19 d of incubation1 Day of incubation Acid
16
Arachidonic2 Myristic2
2.32a 0.22a
17
18
19
(Percentage total fatty acids) 2.41a 0.14b
1.91b 0.13b
1.75b 0.09b
a,b Means among days of incubation with no common superscript differ significantly (P ≤ 0.05). 1 SEM based on pooled estimate of variance for arachidonic and myristic acids are 0.114 and 0.017, respectively. 2 n = 126.
during this time would consequently lead to greater differences in percentage YSW. Lower hatching rates (Romanoff, 1929, 1930) and poorer early chick performance (Tullett and Burton, 1982) are influenced by rate of incubational egg water loss. Furthermore, poorer hatching potentials (O’Sullivan et al., 1991) and posthatch performances (Wyatt et al., 1985) have been associated with eggs from young breeders. Tullett and Burton (1982) have also shown that hatchling mass is well correlated with initial egg mass and egg water loss during incubation. Ar (1991) has suggested that a 10% loss of total internal egg moisture is required to produce an air cell volume for adequate respiratory expansion during pipping. Because rate of water loss from eggs may be manipulated by altering incubational RH (Lundy, 1969), it is important to consider the effects of RH on yolk absorption and utilization by the embryo. A RH of 50% at an air temperature of 37.5 C is generally accepted as optimal for incubation of chicken eggs (Tullett, 1990). Recent studies have shown that better chick performance was achieved when hatching eggs from young hens were incubated at 53% RH rather than 43 or 63% RH (Bruzual et al., 2000). In the present study, percentage YSW between 16 and 19 d of incubation was lower in eggs incubated at 53% RH in comparison with those incubated at 43 or 63% RH. Whether or not posthatch performance of chicks from eggs incubated at a different RH is directly related to differences in embryonic yolk sac absorption rate can only be surmised. However, a higher rate of yolk absorption in late embryos at the 53% RH would be expected to promote posthatch performance as shown by Bruzual et al. (2000). Marshall and Cruickshank (1938) have established that percentage weight loss in small chicken eggs is more rapid than from larger eggs due to the relatively greater evaporative surface to volume of small eggs. The current results showed that percentage YM at 16 d of incubation was lower in eggs from 26-wk-old breeders compared with those from 28- and 30-wk-old breeders, suggesting that smaller eggs from 26-wk-old breeders are lower in YM early in the rapid yolk absorption phase compared with those from larger eggs laid by older breeders. However, by 19 d, when rate of yolk absorption had peaked, YM increased in the smaller eggs in relation to other yolk nutrients. This increase was evidenced by a significantly higher YM percentage in eggs from 26-wk-old breeders compared with 30-wk-old breeders at 19 d of incubation. Water concentration in the yolk is relatively low (42 to 65%) in comparison with that in the albumen (85 to 95%) (Southerland and Rahn, 1987), but moisture is maintained in the yolk in preference to the embryo when fluid reserves in the egg decrease just prior to hatch (Tullett and Burton, 1982). Yolk moisture in the smaller eggs, therefore, may be more highly conserved during this peak period of yolk absorption. A higher rate of yolk absorption may allow embryos from younger hens to maintain higher concentrations of tissue water. Declines in embryo moisture content with embryo age (Peebles et al., 1999) might then be slowed
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(Cunningham et al., 1960; O’Sullivan et al., 1991). However, percentage YSW of chicks from breeders at 51 wk of age have been reported to be smaller than those from broiler breeders at 36 and 64 wk (Latour et al., 1998). Current results indicated that percentage YSW of embryos between 16 and 19 d of incubation was lower in eggs from 26-wk-old breeders compared with those from 28-wk and 30-wk-old breeders. Likewise, Latour et al. (1996) found that 18-d embryos from breeders at 26 wk had a smaller percentage YSW when compared with breeders at 36 and 48 wk. The yolk sac is the main nutrient source for the developing embryo, as it absorbs yolk during the final week of incubation. It would appear that yolks of embryos from very young breeders (26 wk) may be absorbed at a higher rate between 16 and 19 d than those from hens that are slightly more mature (i.e., 28 and 30 wk). Subsequent declines in yolk absorption rate after 19 d in the 26-wk-old group may, likewise, eliminate or reverse comparative differences in residual percentage YSW of posthatch chicks from very young and more mature parents. Nevertheless, a relatively higher rate of yolk uptake during the final week of incubation by embryos from very young parents may stem from an effort to compensate for possible deficiencies in yolk nutrient content or inefficiencies in lipid transfer, nutrient utilization, and metabolism. Differences in rate of yolk absorption
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BURNHAM ET AL. TABLE 5. Yolk oleic and linoleic acid concentrations of eggs at 16, 17, 18, and 19 d of incubation from broiler breeders at 26, 28, and 30 wk of age1 16 d
17 d
18 d
19 d
Week of age Acid
26
28
30
26
28
30
Oleic2 Linoleic2
38.0b 12.1
42.6a 12.1
42.5a 12.0
39.7b 12.2
43.2a 12.0
26
28
30
26
28
30
42.6a 11.7
42.7b 13.5a
44.5a 11.8b
43.0ab 11.8b
(Percentage total fatty acids) 40.5b 12.4
40.1b 12.7
43.6a 12.5
a,b Means within day of incubation among weeks of breeder age with no common superscript differ significantly (P ≤ 0.05). 1 SEM based on pooled estimate of variance for oleic and linoleic acids are 0.60 and 0.34, respectively. 2 n = 42.
tion. In addition, percentage YL was lower in 28-wk-old breeders compared with 30-wk-old breeders at 16 d of incubation. The data from this study suggest that embryos in eggs from the younger birds in both scenarios are absorbing YL reserves at a relatively higher rate than their counterparts at 30 wk of age. Although percentage YL in this study was lower at 26 and 28 wk in comparison with that at 30 wk, it may be potentially greater relative to that in eggs from much more mature flocks (i.e., 41 wk of age). Results also indicated a reduction in percentage YL for those eggs incubated at 53% RH compared with those incubated at 63% RH and obtained from 26-wk-old breeders; we also noted a reduction in YL at 43% RH compared with the 53 and 63% RH in eggs from 30-wk-old breeders. These data further suggest that a lower RH, particularly in hens at 30 wk of age, may accentuate the rate of YL absorption. The impact of breeder age on the relationship between incubational RH and the utilization of yolk by developing embryos may be due to corresponding changes in egg weight. A companion article (Peebles et al., 2001) reported the effects of the same breeder ages and RH treatments used in this study on embryo body compositions. A significant breeder age by day of incubation by RH treatment interaction was found for embryo crude fat content. Fat contents of embryos at 19 d of incubation in eggs from 26-wk-old breeders and at 16 and 21 d in eggs from 28-wk-old breeders were higher
TABLE 6. Yolk palmitic acid concentrations of eggs at 16, 17, 18, and 19 d of incubation from broiler breeders at 26, 28, and 30 wk of age1,2 16 d
17 d
18 d
19 d
Incubation RH (%) 43
53
63
43
53
63
26.5
26.5
26.2
28.5a
26.6b
43
53
63
43
53
63
26.2
26.4
27.3
26.5
(Percentage total fatty acids) 27.9a
27.0
26.4
Means within day of incubation among RH, with no common superscript differ significantly (P ≤ 0.05). SEM based on pooled estimate of variance = 0.38. 2 n = 42. a,b 1
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with increased uptake of yolk-derived water by the embryo. Higher percentage YM at 19 d of incubation in small eggs from very young breeders would compensate for an increased relative rate of water loss and protect the embryo from dehydration. An excess amount of moisture inside the yolk during the last half of incubation, on the other hand, has been found to have no effect on embryonic growth (Thomas et al., 1988). Water is a metabolic byproduct of lipid oxidation (Ar and Rahn, 1980), and increased YL utilization may allow for increased availability of metabolic water; however, embryo body fat and moisture contents have been found to be negatively correlated by the end of incubation (Peebles et al., 1999). Nevertheless, rate of YL uptake and selective fatty acid oxidation may permit embryos partial control of body moisture levels. Embryos from very young flocks (25 wk of age) have been reported by Noble et al. (1986) to have larger relative amounts of residual total YL in their yolk sacs at 19 d of incubation when compared with older flocks (41 wk of age). That finding suggests that embryos from more mature flocks utilize more YL than those from very young flocks. Embryos in eggs from young hens have also been noted to have difficulty metabolizing YL into energy (Noble et al., 1986), and YL transfer from the yolk sac to the embryo may be less efficient in eggs from young breeders (Shanawany, 1984). Current results indicated decreased percentage YL in the eggs of 26-wk-old breeders compared with 30-wk-old breeders at 16 and 17 d of incuba-
INCUBATION HUMIDITY AND YOLK CONSTITUENTS
arachidonic acid was being absorbed at a slower rate only. Because yolk sac membrane ∆-9 desaturase activity converts stearic acid to oleic acid (Noble and Shand, 1985; Noble and Cocchi, 1990), perhaps higher stearic and lower oleic acid concentrations in the yolks of eggs from 26wk-old breeders compared with those at 30 wk may also be due to decreased ∆-9 desaturase activity in the very young hens relative to the slightly older birds. Nevertheless, the significant effects of breeder age on yolk oleic and arachidonic acid concentrations point to breeder age effects on yolk sac membrane desaturase activity. At Day 17, yolk palmitic acid concentration was lower at 53% RH compared with that at 43 or 63% RH. Also, percentage YSW was lower at 53% RH compared with 43 and 63% RH, and percentage YL was lower at 53% RH compared with 63% RH in eggs from 26-wk-old hens. In related work by Peebles et al. (2001), relative wet embryo weight was higher in eggs incubated at 53% RH compared with 43% RH between 17 and 19 d of incubation. Peebles et al. (1999) previously noted that as the embryo absorbed YL during the second week of incubation, an associated decrease in yolk palmitic acid occurred. It was suggested that the utilization of yolk palmitic acid with embryonic growth during that time may be necessary for increased embryo DM synthesis. Yolk palmitic acid concentration was also found by Peebles et al. (1999) to be positively correlated with percentage embryo moisture content at 9 and 12 d of incubation; however, Peebles et al. (2001) reported no influence of RH on embryo moisture content. Taken together, these data suggest that embryonic growth rate, in terms of DM accumulation, was maximized at a 53% RH and was concomitant with increased total yolk and yolk palmitic acid utilization in eggs from young broiler breeders.
ACKNOWLEDGMENTS This work was funded in part by a grant from the US 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 Ar, A., 1991. Roles of water in avian eggs. In: Egg Incubation: Its Effects on Embryonic Development in Birds and Reptiles. D. C. Deeming, and M. J. W. Ferguson, ed. Cambridge University Press, Cambridge, U.K. Ar, A. and H. Rahn, 1980. Water in the avian egg: Overall budget of incubation. Am. Zool. 20:373–384. Brake, J., and G. R. Baughman, 1989. Comparison of lighting regimens during growth on subsequent seasonal reproductive performance of broiler breeders. Poultry Sci. 68:79–85. Bruzual, J. J., S. D. Peak, J. Brake, and E. D. Peebles, 2000. 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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when eggs were incubated at 63% RH compared with 43% RH. Water and fat contents of embryos have been shown to exhibit inverse functional relationships between 15 and 21 d of incubation (Peebles et al., 1999). However, decreased water loss from eggs at the highest RH (63%) may decrease the need for yolk-derived water and may subsequently decrease associated YL uptake and its deposition in embryonic tissues. Lipid oxidation and the production of metabolic water, likewise, may be impeded. Nevertheless, relative wet embryo body weight was higher at 63% RH compared with 43% RH (Peebles et al., 2001), indicating that a slower uptake of YL at the highest RH did not retard overall growth of the embryo. Water production through metabolic oxidation differs for individual fatty acids (Lehninger, 1979), and embryos appear to preferentially absorb certain fatty acids. Yolk fatty acid profiles, therefore, would be expected to change with breeder age and incubation RH as well as with day of incubation. Latour et al. (1998) provided data showing that broiler breeder age influences the YL contents of fresh eggs and the utilization of YL by developing embryos. More specifically, fresh egg yolks from 36-wk-old breeders exhibit higher levels of palmitoleic acid when compared with the levels observed in fresh egg yolks of 51-wk or 64-wk-old breeders. Those levels also decrease significantly by 21 d of incubation only in eggs from 36wk-old hens. Furthermore, at 36 wk of breeder age, the concentrations of oleic and arachidonic acid are higher in yolks from hatched chicks than in fresh eggs. Current results showed that breeder age by day of incubation interactions occurred for percentage YL and several yolk fatty acids. However, there were notable consistent associated changes between percentage YL and a few fatty acids in response to breeder age. When comparing 26- and 30-wk-old breeders, decreased percentages of YL at 16 and 17 d of incubation in the younger age group were associated with decreased yolk linolenic and myristic and increased stearic and arachidonic acids between 16 and 19 d. Decreased yolk oleic acid at 16 and 18 d of incubation was also found in the 26-wk-old group compared with those at 30 wk. These results suggest that the uptake of linolenic, myristic, and oleic acids by embryos from the younger hens was greater in proportion to other fatty acids in conjunction with an increase in percentage YL utilization. Conversely, stearic and arachidonic acids were relatively spared in the yolks of younger hens. Arachidonic acid is synthesized from linoleic acid and is essential for chick growth. Linoleic acid concentration, therefore, would be expected to decrease in association with increased yolk arachidonic acid concentrations. Whether or not increased arachidonic acid concentrations in the yolk were due to a lower rate of absorption or from increased production from linoleic acid through elevated ∆6-desaturase activity in the yolk sac membrane is uncertain (Noble and Shand, 1985; Noble and Cocchi, 1990). However, the lack of any change in linoleic acid concentration between 16 and 18 d and an elevation at 19 suggest that
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