Effect of Flock Age and Postemergent Holding in the Hatcher on

2005 Poultry Science Association, Inc.
Effect of Flock Age and Postemergent
Holding in the Hatcher on Broiler
Live Performance and FurtherProcessing Yield
N. S. Joseph and E. T. Moran, Jr.1
Department of Poultry Science, Auburn University, Auburn, Alabama 36849-5416
Primary Audience: Hatchery Managers, Live Production Supervisors, Processing Plant
Managers, Researchers
SUMMARY
Chicks held in an incubator or hatcher for an extended period of time prior to removal will
reduce body weight, yolk sac reserves, and immune function while increasing the risk of dehydration
and death. This experiment was conducted to compare the quality and subsequent performance
of early-emerging chicks that were held in the hatcher vs. those that emerged just prior to removal.
Eggs were obtained from young (32 wk) and prime age (41 wk) Ross × Ross 308 breeder flocks.
The mean incubation length of early-hatched chicks was 497 h compared with 509 h for latehatched chicks, resulting in an average postemergent duration of 15 h vs. 3 h in the hatcher,
respectively. Total chick yield was similar between young and prime flocks (82 and 83% of eggs
set, respectively), but proportionately, the prime flock produced more early-hatch chicks than the
young flock. Higher whole body weight and yolk sac weight at hatch were associated with late
emergence. Chick body weights after access to feed and water for 1 wk continued to be at a
disadvantage for birds from young hens, whereas early-hatched chicks were similar to late-hatched
chicks. Males and females responded similarly to flock age and hatch treatments. By 6 wk of age,
higher total feed conversion and carcass abdominal fat existed with broilers from prime compared
with those from young breeders, whereas yields of skinless boneless breast meat were similar.
Prolonged holding in the hatcher had no major effects on final live performance, carcass quality,
or breast meat yield.
Key words: broiler, flock age, hatch time, live performance, carcass yield
2005 J. Appl. Poult. Res. 14:512–520
DESCRIPTION OF PROBLEM
It is common practice to keep early-emerging chicks in the incubator or hatcher until nearly
all the chicks have hatched, as it is more efficient
to remove and process them all at once. However, chicks being held in the hatcher for an
extended period of time can lead to dehydration,
diminished yolk sac reserves, and increased ex1
cretion [1, 2] all of which can reduce body
weight [1, 3, 4, 5]. Chicks held in the hatcher
also have lower bursa and spleen weights [4, 5],
higher total plasma protein levels and heterophil:lymphocyte ratios [5], and higher mortality
before [6] and after placement [6, 7, 8].
Chicks from older flocks are more likely to
be affected because incubation length decreases
as hen age increases [9, 10, 11, 12, 13]. Wyatt
To whom correspondence should be addressed: [email protected].
JOSEPH AND MORAN: FLOCK AGE AND HATCH TIME
et al. [4] found that broiler chicks from an older
breeder flock began hatching 6 h sooner than
chicks from a younger flock. Because a greater
proportion of chicks originating from older
breeders will hatch earlier, they may be of poor
quality if held in the hatcher for the same length
of time as chicks from a younger breeder flock.
Prolonged holding in the hatcher can lower
chick quality; therefore, the practice of keeping
early-hatched chicks in the hatcher until latehatched chicks have emerged has been discouraged [1, 3, 4]. However, in the broiler industry,
the feasibility of changing a hatchery practice
is likely to depend on whether the quality of the
final product in the processing plant is affected
by prolonged holding in the hatcher. Therefore,
the objective of this experiment was to evaluate
the effect of flock age and prolonged holding
in the hatcher on chick quality, live performance,
and carcass characteristics of broiler chickens at
6 wk of age.
MATERIALS AND METHODS
The Auburn University Institutional Animal
Care and Use Committee approved the experimental protocol. Ross × Ross 308 eggs were
obtained from a single breeder complex. The
breeder flocks were 32 wk of age (young) and
41 wk of age (prime). Sixty eggs per flock age
were randomly chosen for measurement of egg
characteristics. Nine hundred eggs from each
flock were weighed by groups of 15 (equivalent
to 60 replicates) and set in a single-stage incubator [14]. At 18 d of incubation, those eggs
deemed infertile by candling were removed. The
remainder from each group was transferred to
hatch baskets (plastic perforated trays) and
placed in a hatcher [14]. The eggs were incubated at 37.0°C (and 54% RH) instead of 37.5°C
to extend the duration of the incubation period
[15] with the intention of widening the gap between early- and late-emerging chicks.
To differentiate early-emerging chicks from
late-emerging chicks, approximately every 4 h
beginning at 480 h of incubation (i.e., 20 d),
dry and saleable (healthy) chicks were feathersexed, marked, weighed, and placed back inside
the hatcher. Chicks hatching between 480 and
504 h were grouped into the early-hatch treatment. Beginning at 506 h of incubation, the procedure was repeated at approximately 4-h inter-
513
vals with the resulting chicks grouped into the
late-hatch treatment. To create separation between hatch treatments, chicks hatched from 504
to 506 h were not used for the trial. During
this process, the hatcher was opened frequently,
which likely affected incubation length by lowering the temperature and relative humidity inside the incubator. However with the incubator
used for this study, it could not be avoided. The
process was done swiftly (less than 2 min) each
time to minimize disturbance to the incubator environment.
At 512 h of incubation, all of the chicks were
removed, weighed once more, vaccinated for
Marek’s disease, and kept in the hatchery for 9
h before placement. The next day, sample chicks
from each treatment were euthanized with CO2
gas and then dissected to determine yolk sac
weight and yolk-free body weight. To assess
initial live performance and carcass characteristics 504 chicks were placed in 72 battery cages
(0.07 m2/chick) providing 9 replicate cages per
hatch time, flock age, and sex. Water and a common corn-soybean meal starter ration (3,070
kcal/kg of ME, 22.5% CP) were supplied ad
libitum under continuous lighting. Dissection of
a subsample of these chicks at 3 d of age (1
chick/replicate cage) allowed for determination
of yolk sac weight at 8 d of age (2 chicks/
replicate cage) and bone-in breast and liver
weights. Because the breast muscles (pectoralis
major and minor) were minimally developed at
1 d of age, inclusion of the frame (furculum, rib
cage, and keel) during dissection at 1, 3, and 8
d of age provided a more consistent measure of
breast weight.
To determine live performance and processing yield, 576 chicks were placed in 32 floor
pens (providing 4 replicate pens per hatch time,
flock age, and sex) for 6 wk. Initially, there were
18 chicks per pen, but at 8 d of age remaining
chicks from the battery cages were added to the
floor pens to provide 25 chicks per pen (0.16
m2/bird). Chicks were fed common corn-soybean meal rations throughout rearing. The starter
ration (3,070 kcal of ME/kg, 22.5% CP) was
fed from 0 to 16 d of age, the grower ration
(3,150 kcal of ME/kg, 20% CP) from 17 to 32
d of age, and the finisher ration (3,200 kcal of
ME/kg, 18.7% CP) from 33 to 42 d of age. Feed
consumption and individual body weights were
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514
TABLE 1. Characterization of broiler eggs originating from young and prime age breeder flocks1
Egg
weight (g)
Item
Shell
Yolk
Albumen
(% egg weight)
Without covariate
Young
Prime
SEM
P
Flock age
With covariate
Young
Prime
SEM
P
Flock age
Egg weight
53.6
60.0
0.48
8.7
8.6
0.09
28.5
31.9
0.30
62.8
59.5
0.31
***
NS
***
***
—
—
—
8.7
8.7
0.10
28.1
32.2
0.35
63.2
59.1
0.35
—
—
NS
NS
***
*
***
*
Flock age: Young = 32 wk of age, Prime = 41 wk of age. Values represent the least squares means of 60 eggs randomly
sampled from each source, analyzed with and without egg weight as a covariate.
*P ≤ 0.05; ***P ≤ 0.001; NS = P > 0.05.
1
determined when the rations were changed. Mortality was recorded daily. At 6 wk of age, birds
were cooped, held for 12 h, and then processed
in the poultry processing plant at the university.
After immersion in chilled ice water for 3 h,
carcasses were drained, and abdominal fat pads
were removed. Breast fillet and tenders were
removed 24 h postmortem by experienced personnel using stationary cones. Our statistical
analysis is described in the References and Notes
section [16].
RESULTS AND DISCUSSION
Egg Characterization and Hatchability
The prime flock had a heavier mean egg
weight than the young flock (Table 1). With or
without taking egg weight into account, eggs
from the prime flock had proportionately more
yolk at the expense of albumen than eggs from
the young flock, which was consistent with other
reports [12, 18, 19]. Shell weight was equivalent
for both flock ages. After incubation, it was
found that both flocks had similar levels of fertility, and overall hatchability was not affected by
flock age (Table 2).
The mean incubation length for the earlyhatch treatment was 497 h vs. 509 h for the latehatch treatment, a difference of 12 h. The
early-hatched chicks were in the hatcher for up
to 32 h postemergence, with a mean holding
time of 15 h. The late-hatch treatment was held
for up to 6 h postemergence in the hatcher, with
a mean holding time of only 3 h. The number
of early-hatched vs. late-hatched chicks was also
affected by flock age (Table 2). Eggs from the
prime flock produced a greater number of earlyhatched chicks compared with the young flock,
whereas the opposite occurred during the latehatch period. These results agreed with previous
observations that hatch time decreased as flock
age increased [9, 10, 11, 13].
The relationship between flock age and incubation length is poorly understood. It is not a
function of egg weight because when egg weight
is held constant, incubation length will still decrease with increasing flock age [1, 8, 20, 21].
Incubation length may relate to shell conductance and the rate of embryonic development.
Older hens produce thin-shelled eggs [22, 23,
24]. Thin eggshells increase the rate of water
loss [25] and eggshell conductance (the ability
to respire) [26] compared with thick eggshells.
Studies have also shown that embryos from older
flocks are further developed at 2 d of incubation
[27], have a faster rate of yolk lipid uptake [28,
29], and have greater intestinal development
[30] than those from younger flocks. Christensen
et al. [26] suggested that greater conductance
and advanced development could place added
pressure on the embryo at the plateau stage of
incubation, increasing the already high demand
JOSEPH AND MORAN: FLOCK AGE AND HATCH TIME
515
TABLE 2. Hatchability of broiler eggs from young and prime age breeder flocks1
Source
Flock age
Young
Prime
SEM
P
Hatchability (% eggs set)2
Saleable chicks3 (n)
Fertility
(% eggs set)
All chicks
Saleable chicks
Early
Late
98
98
0.6
NS
82
83
1.4
NS
80
82
1.4
NS
334
376
2.0
***
220
203
1.5
***
Flock age: Young = 32 wk of age, Prime = 41 wk of age. Values represent the least squares means of 60 replicate trays
of 15 eggs at the start of experimentation.
2
Number of eggs set: 900 per flock age.
3
Chicks emerged either before 504 h (Early) or after 506 h (Late) of incubation. Chicks that emerged between 504 and 506
h of incubation were not included in the data set.
***P ≤ 0.001; NS = P > 0.05.
1
for carbohydrate metabolism. The embryo then
must either emerge early or perish. Indeed, more
deaths late in incubation of chickens [31], higher
pipping mortality of turkeys [26], and an overall
decline in hatchability have been reported with
increasing flock age [26, 31, 32, 33, 34].
Chick Weight and Quality
Chick quality was assessed as BW upon final
removal from the hatcher, 1-wk BW gain, and
carcass characteristics at 1, 3, and 8 d of age.
Flock age affected the BW at emergence and
upon removal from the hatcher, which followed
differences observed in egg weight (Table 3). A
loss of approximately 1 g of BW occurred between emergence and removal, which in other
studies has been attributed to dehydration [1, 2].
Chick carcass characteristics are presented
in Table 4. At 1 d of age young flock chicks
had reduced yolk-free BW and fewer yolk sac
reserves than prime flock chicks, which was expected given their small egg sizes and yolk
weights [35]. At 3 d of age, young flock chicks
still had a lower BW, but yolk sac weights were
similar to those of prime flock chicks. At 1 d of
age, holding time in the hatcher did not affect
yolk-free body weight, but early-hatched chicks
had smaller yolk sac reserves than chicks that
hatched late. By 3 d of age, yolk sac weights
were similar and early-hatched chicks weighed
more than late-hatched chicks. Males and females had similar yolk-free body and yolk sac
weights at 1 d of age (36 ± 0.4 g and 3.7 ± 0.15
g for BW and yolk sac weight, respectively)
and at 3 d of age (59 ± 0.6 g and 1.3 ± 0.06
g, respectively).
Some studies have found that males are
heavier than females at hatch [36, 37, 38],
whereas others, including this study, have found
no sex differences in BW [2, 19, 39, 40, 41, 42].
TABLE 3. Weight of chicks originating from young and prime age breeder flocks at emergence and the subsequent
loss with removal from hatcher1
BW at emergence (g)
BW at removal (g)
Source
Early
Late
Early
Late
Weight loss of
early-hatched chicks2
Flock age
Young
Prime
SEM
P
41.3
44.9
0.33
***
41.7
44.9
0.39
***
40.3
43.6
0.32
***
41.7
44.9
0.39
***
1.06
1.30
0.068
*
Flock age: Young = 32 wk of age, Prime = 41 wk of age. Body weight once chicks emerged from shell, upon removal
from the hatcher, and their difference. Values represent the least squares means of chicks originating from 60 replicate
groups of 15 eggs.
2
Weight loss was calculated for early-hatched chicks only because a measurable weight loss among late-hatched chicks was
not detected.
*P ≤ 0.05; ***P ≤ 0.001.
1
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516
TABLE 4. The effect of early vs. late emergence on yolk-free body and yolk sac weights of broiler chicks from
young and prime age breeder flocks1
1 d of age
Source
Body (g)
3 d of age
Yolk sac (g)
Body (g)
Yolk sac (g)
Flock age
Young
Prime
34.3
37.5
3.3
4.2
56.1
62.2
1.4
1.2
Hatch time
Early
Late
SEM
35.9
36.0
0.47
3.4
4.1
0.17
60.0
58.3
0.60
1.3
1.3
0.09
33.6c
35.1bc
3.0
3.5
55.9c
56.2c
1.3
1.5
38.2a
36.9ab
0.66
3.7
4.8
0.24
64.1a
60.3b
0.85
1.3
1.2
0.12
***
NS
*
***
**
NS
***
*
*
NS
NS
NS
Flock age
Young
Early hatch
Late hatch
Prime
Early hatch
Late hatch
SEM
P
Flock age
Hatch time
Flock age × hatch time
a–c
Means within a column and main effect with no common superscript differ significantly.
Flock age: Young = 32 wk of age, Prime = 41 wk of age. Values represent the least squares means of 7 and 9 replicates
at 1 and 3 d of age, respectively.
*P ≤ 0.05; **P ≤ 0.01; ***P ≤ 0.001; NS = P > 0.05.
1
Female chicks tend to emerge sooner than male
chicks [3, 19, 37], suggesting that females may
weigh the same as males at emergence but then
lose weight when held in the hatcher, thereby
weighing less than males upon removal. Therefore, discrepancies in published reports regarding the sexual dimorphism of BW may be a
reflection of the amount of time the chicks were
held in the hatcher before they were weighed.
Flock age and hatch time affected BW at 1
and 3 d posthatch. At 1 d, young flock chicks
weighed less and prime flock chicks weighed
more with early emergence, whereas both were
of intermediate BW with late emergence. Three
days later, chicks from the prime flock that
emerged early were still heavier followed by
those that emerged late. Chicks from the young
flock weighed less, regardless of hatch time.
Growth and carcass characteristics were
studied at 8 d of age to determine if there were
any differences in BW, bone-in breast weight,
and liver weight (Table 5). Prime flock chicks
gained more weight than those from the young
flock, whereas breast and liver weights were
similar. In the present study, holding in the
hatcher did not affect BW at 8 d of age because
early-hatched chicks gained more weight from
1 to 8 d than those emerging late. This finding
was consistent with the findings of Hager and
Beane [1]. Early-hatched chicks had a greater
breast weight and a lower liver weight than latehatched chicks, but as a proportion of BW, neither differed by hatch treatment. Sex differences
in BW were observed at 8 d of age. There was
no difference in breast weight, but females had
a slightly higher liver weight than males. Flock
age and hatch time did not affect BW, breast
weight, or liver weight at 8 d of age.
Live Performance
Flock age effects on BW observed at hatch
and again at 8 d of age had dissipated by 16 d
of age (data not shown). By 6 wk of age, birds
from the prime flock were of similar BW to
birds of the young flock but had a higher feed
conversion (Table 6). Mortality during rearing
was not affected by flock age. Total live performance, including final BW, feed conversion, and
JOSEPH AND MORAN: FLOCK AGE AND HATCH TIME
517
TABLE 5. Effect of early vs. late emergence on initial live performance and body characteristics of broiler chicks
from young and prime age breeder flocks1
Breast2
Body weight (g)
Source
8 d of age
Gain
Weight (g)
Liver
(% BW)
Weight (g)
(% BW)
Flock age
Young
Prime
156
173
117
130
20
22
12.6
12.7
8.9
8.9
5.4
5.4
Hatch time
Early
Late
166
163
125
121
21
20
12.8
12.5
8.5
9.3
5.3
5.4
Sex
Male
Female
SEM
167
162
1.5
125
121
1.5
21
21
0.2
12.6
12.7
0.12
8.9
8.9
0.12
5.3
5.5
0.07
***
NS
*
***
*
NS
NS
***
NS
NS
NS
NS
NS
***
NS
NS
NS
*
P
Flock age
Hatch time
Sex
Flock age: Young = 32 wk of age, Prime = 41 wk of age. Body weight values represent the least squares means of 9
replicate pens each having 7 chicks. Breast and liver values represent the least squares means of 2 chicks each from 9
replicate pens. No significant interactions (P > 0.05) were detected among main effects.
2
Breast was removed with the rib cage (bone-in).
*P ≤ 0.05; ***P ≤ 0.001; NS = P > 0.05.
1
mortality, was similar for hatch treatments. This
finding was consistent with the findings of Hager
and Beane [1], Williams et al. [3], and Wyatt et
al. [4], who found that holding early-hatched
chicks in the hatcher for up to 32, 36, and 48
h, respectively, had no effect on posthatch BW
when compared with the BW of late-hatched
chicks. In these studies, advantages in BW occurred only when early-emerging chicks were
promptly removed from the hatcher and placed
TABLE 6. Effect of early vs. late emergence on total live performance of 6-wk old broilers from young and prime
age breeder flocks1
Body weight (g)
Source
Total
Final
Gain
Flock age
Young
Prime
2,429
2,462
Hatch time
Early
Late
Sex
Male
Female
SEM
P
Flock age
Hatch time
Sex
2
Feed conversion
Mortality (%)
2,390
2,419
1.79
1.84
8.0
5.6
2,443
2,448
2,402
2,407
1.82
1.82
8.0
5.6
2,634
2,257
19.3
2,593
2,216
19.3
1.76
1.87
0.016
8.7
4.9
2.02
NS
NS
***
NS
NS
***
*
NS
***
NS
NS
NS
Flock age: Young = 32 wk of age, Prime = 41 wk of age. Values are the least squares means of 4 replicate pens each with
25 chicks at the start of experimentation. No significant interactions (P > 0.05) were detected among main effects.
2
Feed conversion (kg of feed/kg of gain) values were corrected for mortality.
*P ≤ 0.05; ***P ≤ 0.001; NS = P > 0.05.
1
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TABLE 7. Effect of early vs. late emergence on carcass and breast meat yield of 6-wk old broilers from young
and prime age breeder flocks1
Carcass without abdominal fat2
Weight
(g)
Carcass
weight (%)
Fillets4
Weight
(g)
Tenders4
Source
Weight
(g)
Flock age
Young
Prime
1,635
1,658
67.0
67.1
37
41
2.21
2.41
377
380
23.1
23.1
85
86
5.24
5.24
Hatch time
Early
Late
1,645
1,648
67.1
67.0
39
38
2.34
2.28
377
380
23.2
23.1
85
86
5.24
5.24
Sex
Male
Female
SEM
1,768
1,525
0.6
66.8
67.3
0.04
38
39
15.5
2.13
2.49
0.036
404
354
5.8
22.9
23.4
0.12
90
81
1.5
5.10
5.38
0.052
NS
NS
NS
NS
NS
***
***
NS
***
**
NS
NS
NS
NS
***
NS
NS
**
NS
NS
**
NS
NS
**
P
Flock age
Hatch time
Sex
Live weight
(%)
Abdominal fat3
Carcass
weight (%)
Weight
(g)
Carcass
weight (%)
Flock age: Young = 32 wk of age, Prime = 41 wk of age. Values represent the least squares means of 4 replicate pens
each with ca. 22 carcasses. No significant interactions (P > 0.05) were detected among main effects.
2
Carcass without neck and giblets after 4 h of ice-water chilling and removal of abdominal fat, expressed on an absolute
basis and relative to full-fed live body weight.
3
Depot fat removed from the abdominal cavity expressed on an absolute basis and relative to the chilled carcass.
4
Fillets and tenders correspond to the pectoralis major and minor, respectively, and are expressed on an absolute basis and
relative to the chilled carcass.
**P ≤ 0.01; ***P ≤ 0.001; NS = P > 0.05.
1
in brooder pens. Although in the present study
all of the early-hatched chicks were kept in the
hatcher until hatch pull, and, therefore, the effects of hatch time and holding time could not
be separated, this study is very applicable because this practice is common in industry. Sex
differences in live performance were evident;
males gained more weight than females and had
lower feed conversion.
Carcass Yield and Further Processing
Chickens originating from prime breeders
had more abdominal fat than young breeders
with similar carcass weights (Table 7). Chicks
from older breeders have more body fat at hatch
[43], which is likely influenced by yolk size.
However, we did not expect to observe an effect
at 6 wk of age. In one study, differences in
broiler fat retention with breeder age were not
observed after 7 d of age [44]. Breast fillet and
tender yields were not affected by flock age.
Carcass weight was not affected by hatch treatments. Abdominal fat pad weights and breast
fillet and tender yields were the same for early
and late-hatched chicks. Female carcasses
weighed less than male carcasses and, consequently, had more depot fat as a percentage of
carcass weight. Carcasses from males had more
breast meat than females.
CONCLUSIONS AND APPLICATIONS
1. A greater proportion of chicks from the prime flock (41 wk) emerged earlier from their eggs
than from the young flock (32 wk).
2. After emergence, chicks being held in the hatcher up to 32 h reduced their BW and yolk sac
reserves more than when held up to 6 h.
3. Despite losses from extended holding of early-emerging chicks in the hatcher, total live performance was similar to that of late-emerging chicks.
JOSEPH AND MORAN: FLOCK AGE AND HATCH TIME
519
4. Although live BW at 6 wk of age was similar for flock age, broilers from the prime flock had
higher feed conversion during rearing and more abdominal fat than those from a young flock.
5. Yields of chilled carcass and breast meat were similar, regardless of chick source.
6. Males responded similarly to females with respect to hatchability and chick quality at hatch.
At 6 wk of age, carcass and breast meat yields were higher for males than females.
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results, data from these 2 hatch baskets were eliminated from the
data set. The data (excluding egg characterization analysis) were
analyzed by 3-way analysis of variance using the GLM procedure
in SAS [17]. To separate differences attributed to the egg versus
those of the dam, egg characteristics were analyzed with egg weight
as the covariate using the GLM procedure in SAS [17]. Hatch data
were transformed to arc sine values before analysis. Differences
between treatment means were separated using the Tukey’s honestly
significant difference test. Significance was based on testing at P ≤
0.05. For flock age and hatch time, differences between males and
females were not found and, therefore, will not be discussed further.
17. SAS Institute Inc. 2001. The SAS System for Windows,
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The authors thank Aviagen Incorporated for donation of eggs in
kind as well as Derek Emmerson and Valerie Carney for their guidance. Also, assistance from Svetlana Blake, Jin Fung Chen, Jaume
Galobart Cots, Angel Juarez Zarate, and graduate students at the
Poultry Science Unit was greatly appreciated.