336 EXTRA DIETARY CALCIUM studies showed that hatchability [lo] and embryo viability [ll] were si&icantly lower in fust-of-sequence eggs than in subsequent eggs within a laying sequence
Trang 1EFFECTS OF OVIPOSITION TIME,
Instituto Superior de Agronomia, 1399 Lisboa Codex, Portugal
Phone: (01) 3638161
F M : (01) 3635031
Primarv Audience: Breeder Production Managers Researchers
Eggshell quality as measured by egg
specific gravity (SG) has frequently been
associated with hatchability of eggs from
broiler breeder hens [l, 2,3,4,5,6] Research
indicates that a SG of 1.080 is the dividing
point between good and poor hatchability
breeder hens fed in the afternoon exhibit a
sig&cant improvement in eggshell quality as
measured by SG and eggshell weight [8, 91
Reis et al [6] also observed that coarse lime-
stone supplied in the afternoon slightly in- creased the SG of broiler breeder eggs, but markedly improved embryo viability
The literature also indicates that SG of broiler breeder eggs increases as time of laying becomes later in the day [l, 21, although hatch- ability of eggs laid in the afternoon is not significantly greater than that of eggs laid
during the morning [l] However, further
Trang 2336 EXTRA DIETARY CALCIUM
studies showed that hatchability [lo] and
embryo viability [ll] were si&icantly lower
in fust-of-sequence eggs than in subsequent
eggs within a laying sequence The fust egg of
a sequence is usually laid relatively early in
the day and the remainder laid later on each
following day; therefore, a high proportion of
eggs laid in the early morning of any given
day should be first-of-sequence eggs [12] In
addition, sequence length in feed-restricted
broiler breeder hens reaches a prime mean
length at 32 wk of age, then quickly shortens
with advancing hen age [13]; therefore, the
incidence of first-of-sequence eggs increases
with hen age
We conducted the present study to deter-
mine the effects of oviposition time, hen’s age,
and extra dietary calcium on egg weight (EW),
SG, EW loss during the first 18 days of in-
cubation, fertility, embryo viability, age of em-
bryonic death in fertile eggs, and hatchability
of eggs from feed-restricted broiler breeder
hens under commercial conditions Specific-
ally, we wished to ascertain whether the effect
of calcium supplementation varied with hen
age by affecting SG and with time of oviposi-
tion through interaction with time of calcium
absorption
SOURCE OF EGGS
The study was carried out over two pe-
riods, from November to December 1994 and
from March to April of the following year,
using eggs from one commercial flock of ap-
proximately 13,900 broiler breeder hens
(Cobb 500) at 46 and 65 wk of age Equal
numbers of birds were arbitrarily assigned to
each of two identical pens of one building at
effects of two treatments: no extra calcium
supplementation (NC) and extra calcium
supplementation (CS) Natural daylight was
supplemented with artificial light to give a
16 hr photoperiod (on 0790 hr, off 23:00 hr)
Daily low and high in-house air temperatures
ranged from 17 to 24°C and 16 to 24°C at ages
46 and 65 wk, respectively
All birds received a commercial broiler
breeder diet (16.50% CP, 2800 kcal ME,/kg,
formulated to meet or exceed National Re-
search Council [14] requirements, as pre-
viously described [6] Both sexes received the
same feed in separate sex feedings [15], as
diets used by the breeder hen appear to have
no detrimental effects on male performance
Hens received approximately 163 and 157 g
of feed per bird at 46 and 65 wk of age re- spectively, to maintain body weights recom-
mended by the primary breeder [16] The
hens had consumed their feed allowance by
approximately 11:OO hr each day A birds
consumed water ad libitum In the pen as- signed to CS treatment, coarse limestone
(4 g/bird daily) was scattered on the litter at
wood shavings (eucalyptus bark), so that white limestone particles were very visible; the birds rapidly consumed them The Limestone
supplement had particles ranging from 2 to
5 mm in diameter, with an average solubility of
described by Keshavarz et al [lq Extra di- etary calcium supplement was provided for
8 consecutive days at both 46 and 65 wk of flock age Calcium distribution began 3 days
before the date of first egg collection for
experimental purposes (Table 1)
EGG COLLECTION AND HANDLING
At 46 and 65 wk of age eggs were collected for 5 and 4 days, respectively (Table l), at 2 hr
intervals beginning at 08:OO hr and ending
at 18:OO hr Eggs laid before 08:OO hr were
removed from the nests and were not used
in this experiment Eggs that were cracked, very dirty, misshapen, or of extreme size were culled From each pen and collection
time, a random sample of 150 hatching eggs
was obtained and eggs were then individually marked Eggs from each day’s production
reached the hatchery at 12:45, 16:45, and
weighed to the nearest 0.1 g, and SG was de-
termined in graded sodium chloride solutions kept at room temperature (about 20°C) and
ranging from 1.060 to 1.090, with an increment
of 0.005 units between successive solutions
The concentration in which the egg barely floated beneath the surface indicated egg
SG Eggs that did not float in any of the so-
lutions were assigned a SG of 1.095, and those
that floated in all solutions were assigned a
SG of 1.060 After SG measurement, the eggs were rinsed in warm tap water and dried in a stream of warm air at approximately 20°C
Trang 3NOVO et al
November 23
November 24
November 25
Field Report
337
TABLE 1 Egg collection and calcium supplementation for broiler breeders at two different periods (46 and
Eggs from each treatment and collection
time were then placed in setter trays
(150 eggshay)
INCUBATION AND HATCHING
Incubation was initiated at 2200 hr on the
day of egg collection in electronically con-
trolled single-stage incubators (Petersime
576) The ten experimental trays correspond-
ing to five different collection times and two
treatments were randomly placed in one
quadrant (front right) on the same trolley,
which was then filled with other eggs Quad-
rant and trolley positions were the same on all
9 collection days to reduce possible position
effects AU eggs were fumigated in the in-
cubator at incubation temperature on the
day of setting, using 20 g of potassium perman-
ganate and 30 mL formalin (400 g/L) per m3
incubator space with the ventilators closed for
20 min Eggs were automatically turned 90"
every hour and incubated at conventional
temperature and humidity conditions, as pre-
viously described by Roque and Soares [5]
The eggs were individually candled on the
18th day of incubation, using a hand candling
lamp Infertile eggs and eggs containing early
dead embryos were removed and broken out
for macroscopic examination The eggs with
apparently living embryos were individually
weighed to the nearest 0.1 g Weight loss was
calculated by difference and expressed in ab-
solute terms (g) and as a percentage of initial
fresh egg weight The eggs were quickly trans-
ferred to hatcher baskets, randomly distrib-
uted in the front part of the same trolley, and
placed in a hatcher (Petersime 192) operated
at conventional conditions, as outlined by Roque and Soares [5] Chicks and unhatched eggs were taken off at 21 days and 12 hr postincubation
Saleable hatched chicks and culls (un- marketable chicks) were recorded All eggs removed at candling, and unhatched eggs at the time of taking off the hatch, were broken out, examined macroscopically, and assigned
to one of the following categories: infertiles, early-dead germs (embryo deaths during 1 to
7 days of incubation), mid-dead germs (deaths during 8 to 18 days), late-dead germs (deaths after 18 days), pipped (beak penetrated eggshell but chick did not emerge), and rots (contaminated) From the data, percent hatchability (number of saleable chicks
hatched per all eggs set x 100) and percent
embryo viability (number of saleable chicks
hatched per number of fertile eggs set x 100)
were calculated A total of 7500 eggs were
used in the fust period (150 eggs per collection
time x 5 daily collection times x 5 days x 2 treatments), and 6000 eggs were used in the second period (4 days)
Data were statistically analyzed by analysis of variance [18,19,20]
The interaction between oviposition time and calcium supplementation was significant
only for embryo mortality up to 7 days and
contaminated eggs (Table 2); thus, it seems that the effect of oviposition time was basically the same for both treatments On the other
Trang 4338
VARIABLE
JAPR
EXTRA DIETARY CALCIUM
SOURCES OF VARIATION Treatment Breeder Oviposition T X A O X T O X A
0 Age (A) Time (0)
TABLE 2 Significance of different sources of variation in the preliminary analysis
Egg specific gravity
Egg weight at set, g
Fertility, %
Hatchability, %
NS
NS
* * * .** * t
* * ** I * * *.*
* * *
NS
* * *
EmbIyo viability, % NS
* P < .os; * *P < 01; ***P < 001
hand, the interaction between oviposition time
and age of the hen was signifcant not only
for early mortality and contaminated eggs but
also for egg weight loss, embryo viability,
and hatchability Interaction of hen age and
calcium treatment significantly affected all
traits except intermediate and late embryonic
mortality and contaminated eggs, which sug-
gests that the effect of calcium supplementa-
tion differs according to flock age
INFLUENCE OF OVIPOSITION TIME
The effects of oviposition time, expressed
as the linear regression coefficients of the vari-
ables analyzed on time of oviposition, are sum-
marized in Table 3, either within treatment or
age, or pooled, depending on interaction sig-
nificance These results clearly demonstrate
that regardless of hen age, EW decreases
(P < Ol) gradually as time of laying becomes
later in the day These data substantiate previ-
ous findings that eggs laid in the morning are
heavier than eggs laid during the later periods
of the day [12, 21, 22, 23, 241 Research in-
dicates that this variation in EW with time of
laying is related to the sequence of eggs in the
ovulatory cycle, but not directly related to the
time of oviposition [12] However, under usual
photoperiodic conditions, it is likely that early
morning ovipositions would include most of the first-of-sequence eggs [12], which are heavier than subsequent eggs [lo, 21,251 This probably occurs because an ovarian follicle destined to become the first egg in a clutch
resides as the largest follicle (F1) on the ovary
for about 16 hr longer than mature FI follicles
of subsequent eggs in the same sequence [26]
Such a long period of follicular growth is presumably associated with a greater yolk deposition, as it occurs in the ovary [27
Egg specific gravity increased signifi- cantly (P< 001) during the day at both ages, with a slightly higher increase in older hens (linear regression coefficients on time were
O.OOO4 and O.OOO5 at 46 and 65 wk of age, re- spectively) These findings are in general agreement with previous studies involving laying hens [22, 28, 29, 30, 311 and broiler breeder hens [l, 21, which showed that eggs laid in the afternoon have an average SG greater than eggs laid in the morning The reason for this variation is not clear This in- crease in SG may be due to a more adequate calcium carbonate supply directly from the feed administrated in the morning Eggshell calcification of eggs laid in the afternoon oc- curs in part when the hen has access to feed, whereas in eggs laid early in the morning the
Trang 5Field Report
NOVO et al
Embryo viability, 70 46 wk
65 wk
339
0.9247 0.0023 +0.0013 NS
* * *
0.8344 -0.0075f0.0018
aDo = Intercept
%,+sb = Linear regression coefficient f linear regression coefficient standard error
D ~ NO ~extra calcium supplementation =
= With extra calcium supplementation
'Pi.05; **P<.Ol; ***P<.OOl
calcium carbonate of the shell is formed at
night when the hen is not eating This hypoth-
esis is also supported by the work of Farmer et
fed at 16:OO hr had significantly better eggshell
quality (SG) than buds fed at 0530 hr
Flock age affected the relationship of ovi-
position time to egg weight loss during the first
18 days of incubation For hens 46 wk of age,
absolute and relative egg weight loss de-
creased significantly with later laying time
For hens at 65 wk of age no significant changes
for different laying times were observed when
weight loss was expressed in absolute terms;
however, weight loss as a percentage of fresh egg weight increased significantly for eggs laid later in the day The results obtained at 65 wk
of age are consistent with the findings of
Robinson et al [lo], who used eggs from broiler breeders 45 to 53 wk of age and ob-
served that eggs laid later in a sequence lost significantly more weight during the 7-day incubation period than did first-of-sequence eggs This relationship of weight loss to ovi- position time may not be attributable to differ- ences in shell quality, since SG increased through the day (Table 3), and previous studies showed that eggs with the highest SG
Trang 6340 EXTRA DIETARY CALCIUM
had the lowest weight loss [2,5] Present data
suggest that besides SG, other egg compo-
nents may also play an important role in water
loss during incubation The work of Meur and
Baumann [32] indicates viscous quality of
albumen during the initial stages of incubation
as one possibility
At both ages, oviposition time did not
sigruficantly influence fertility, intermediate
or late mortality, or percentage of pips In
their work with broiler breeders housed in
individual laying cages, Robinson et al [lo]
and Fasenko et al [ 111 had similar fmdings and
reported that fertility was not significantly
different between first-of-sequence and sub-
sequent eggs
At the younger age, oviposition time did
not significantly influence early embryonic
mortality, embryo viability, percentage of
contaminated eggs, or hatchability These
results are in general agreement with the
work of McDaniel et al [2], who suggested
that in eggs with SG higher than 1.080 there
appeared to be little relationship between
SG and hatchability In the present study,
younger hens produced eggs with a higher
average SG (1.084) (Table 4) In older hens,
on the other hand, there was a si&icant trend for hatchability and embryo viability
to decrease as oviposition occurred later in the day, mostly because of increased early embryonic mortality and mortality due to infections These results were unexpected, because previous studies [2, 3, 4, 5] have re- ported that thick-shelled eggs had better hatchability than thin-shelled eggs due to their greater fertility and lower embryonic mortal- ity, and that the SG of eggs from older hens increased with oviposition time Concerning the relationship between oviposition time and
embryonic mortality, Robinson et al [lo] re-
ported no significant difference for embryo viability between first (89.70%) and subse- quent (92.75%) eggs in a sequence, and
Fasenko et al [ l l ] found that viability was sig-
nificantly reduced in first-of-sequence eggs compared to subsequent eggs The data from the present research suggest that oviposition time (egg sequence position) affects viability
of fertile eggs in older flocks through higher early embryonic mortality, regardless of shell thickness
TABLE 4 Breeder age x treatment interaction effect on egg specific gravity, egg weight, survival, hatchability,
and embryo viability
B~~ = NO extra calcium supplementation
‘CS = With extra calcium supplementation
Means for the same combination effect and row with different suuescriuts differ at P < .OS
a x
Trang 7NOVO et al
Field Report
341
As Table 4 shows, average EW increased
with hen age (64.96 vs 67.34 g at 46 and
65 wk of age, respectively) Higher EW is
usually associated with an increase in yolk
deposition [33], as the largest preovulatory
follicle is heavier in older hens [34]
Average specific gravity of eggs was
greater for the eggs from younger hens (1.0840
vs 1.0799) Other studies with broiler breeder
hens [2,4,6] and with layer strain hens [35,36]
have also associated reductions in SG with
increased bird age Shell quality (SG and shell
thickness) declines as the hen ages chiefly be-
cause EW increases with no proportionate in-
crease in shell deposition [36,37l Dysfunction
of the shell gland may also be a contributing
factor [34]
Average weight loss during the first
18 days of incubation was slightly higher in
absolute terms in eggs from older hens (7.17
vs 6.99 gin treatment NC), but relative weight
loss decreased slightly with flock age (10.78
and 10.67% at 46 and 65 wk of age, respec-
tively), probably because of the associated
increase in egg weight These data support the
suggestion of Reis et al [6] that the same in-
cubator humidity might be recommended for
eggs from broiler breeder hens from 46 to
64 wk of age
Fertility, embryo viability, and hatchabil-
ity declined significantly ( P < Ol) with hen
age, phenomena that are well documented in
the literature [6, 11, 38, 39, 401 The present
study’s very high level of early embryonic mor-
tality for eggs from hens 65 wk of age was
unexpected, since lower levels have been re-
ported at similar broiler breeder ages [6, 391
However, embryonic viability per 100 eggs set
(fertility x viability) reported in the present
investigation (91.98 and 72.11% at 46 and
65 wk of age, respectively) is consistent with
findings on eggs from flocks of similar ages
[6, 391 The discrepancy in the relative im-
portance of early embryonic mortality and
infertility may result from difficulties in dis-
tinguishing between infertile blastodiscs and
very early dead blastoderms by macroscopic
examination
EFFECTS O F CALCIUM SUPPLEMEN-
TATION
As shown in Table 4, the effects of extra
calcium fed in the afternoon varied mark-
edly with flock age: there was a significant
treatment x age interaction for most traits
analyzed At 46 wk of age, none of the de- pendent variables were significantly (P < Ol) affected by calcium supplementation, with the exception of SG, which increased slightly
In contrast, at 65 wk of age, calcium supplementation significantly affected all response variables but SG and relative egg weight loss It could be anticipated that cal- cium supplementation would have a higher effect on SG of eggs from the same birds at
an older age, but that was not the case, as was also found by Reis et al [6] Presumably thin- shelled eggs from aged birds are associated with a disorder of vitamin D metabolism, pos- sibly associated with reduced synthesis of
1,25-dihydroxycholecalciferol by the kidney [34,41] and also related to a decreasing ability
to absorb calcium from the intestine and to mobilize skeletal calcium [42] In agreement with Reis et al [6], our results suggest that extra dietary calcium does not increase SG but still improves hatchability This improvement
is probably attributable to both increased fer-
tility and decreased early embryonic mortality
Early embryonic mortality and pipped
eggs were significantly (P c .01) reduced when older hens received extra calcium Therefore,
a significant improvement in embryo viability (5.88%) also occurred in eggs from broiler breeders receiving supplemental calcium at
65 wk of age Results from this experiment supported the previous finding [6] that coarse limestone fed in the afternoon caused an im- provement in embryo viability; however, the improvement observed in this experiment was due to lower early embryonic mortality and pipped eggs In contrast, Reis et al [6] attrib- uted the higher viability to a reduction in con- taminated eggs (the suspected contaminant was Pseudomonas spp)
Calcium supplementation was associated with a slight increase of fresh egg weight in older hens, in agreement with the results
obtained by Bootwalla et al [8] with broiler
breeders, but in contrast to those of Reis et al
[6] with broiler breeders, and Muir et al [43]
and Watkins et al [44] with laying hens In
older hens, extra dietary calcium was also associated with a slight increase of absolute weight loss during incubation, but not with weight loss as a percentage of egg weight at set (Table 4)
Trang 8342
JAPR
EXTRA DIETARY CALCIUM
At 65 wk of age, the feeding of coarse
limestone scattered on the litter in the
afternoon was associated with a significant
(P < 01) improvement in fertility (93.08 vs
96.37%) This improvement could be due to a
stimulus to heavy males to be sexually active
Spreading of coarse limestone increased the
birds’ activity, which may have led to more females being mated The increased fertility and reduction in embryonic mortality associ- ated with calcium supplementation resulted
in an 8.2% improvement in hatchability for eggs from older hens, whereas no improve- ment was observed in eggs from younger birds
1 Egg weight decreased, specific gravity increased, and fertility was unaffected as time of
laying became later during the day
2 In contrast to younger (46 wk) birds, at the older age (65 wk) hatchability and embryo
viability declined during in eggs laid later in the day
3 Fertility, embryo viability, and hatchability declined with hen age In older hens, early
embryonic mortality was a greater source of overall loss in hatchability than was infertility
4 The most significant effects of extra dietary calcium supplementation were observed at
65 wk of age: egg weight, fertility, embryo viability, and hatchability were improved
1 McDaniel, G.R and D.A Roland, 1977 The influ-
ence of time of oviposition and eggshell quality on hatch-
ability of e from broiler breeder hens Poultry Sci
56:1354 ( A b 7
2 McDaniel, G.R, D.A Roland, Sr., and M.A Cole-
man, 1979 The effect of e shell qualityon hatchability
and embryonic mortality &try Sci 5810-13
3 McDaniel, G.R, J Brake, and M.K Ekman, 1981
Factors affecting broiler breeder performance 4 The
interrelationship of some reproductive traits Poultry Sci
60:1792-1797
4 Bennett, C.D., 1992 The influenceof shell thickness
on hatchability in commercial broiler breeder flocks
J Appl Poultry Res 1:61-65
quali and broiler breeder age on hatchability #%:$
Sci 721838-1845
6 Reis, LH., P Feio, LT Gama, and M.C %ares,
1995 Extra dietary calcium su lement and broiler
breeders J Appl Poultry Res 4:$?&282
7 North, M.O and D.B Bell, 1990 Commercial
Chicken Production Manual 4th Edition Van Nostrand
Reinhold, New York, NY
8 Bootwalla, S.M., R H Harms, and H.R Wilson,
1982 Effect of feeding time and sup lementation with
calcium/phosphorus pellets on the pe A r m a nce of broiler
breeders Poultry Sci 61:1421 (Abs)
9 Farmer, M., D.A Roland, Sr., and M.K Ethan,
1983 Calcium metabolism in broiler breeder hens 2 The
influence of the time of feedine on calcium status of the
5 Roque, L and M.C Soares, 1994 Effects of e
digestive system and eggshell Gauality in broiler breeders
Poultry Sci 62465471
10 Robinson, F.E, RT Hardin, N.A Robinson, and
BJ Williams, 1991 The influence of egg sequence posi-
tion on fertility, embryo viability, and embryo weight in
broiler breeders Poultry Sci 70760-765
11 Fasenko, G.M., RT Hardin, F.E Robinson, and
J.L Wilson, 1992 Relationship of hen age and egg se-
quence position with fertility, hatchability, viability, and preincubation embryonic development in broiler breed- ers Poultry Sci 71:1374-1383
12 Choi, J.H., R.D Miles, AS Arafa, and R.H
Harms, 1981 The influence of oviposition time on egg weight, shell quality, and blood phosphorus Poultry Sci
60824-828
13 Robinson, F.E, RT Hardin, and A.R Robblee,
1990 Reproductive senescence in domestic fowl: Effects
on egg production, sequence length, and inter-sequence pause length Br PoultIy Sci 31:871-879
1 4 National Research Council, 1994 Nutrient
Requirements of Domestic Animals Nutrient Require- ments of Poultry 9th Rev Edition Natl Acad Sci., Washington, DC
15 McDaniel, G.R, 1985 Feed males and females
separately World Poultry-Misset 2(1):12-13
16 Laughlln, K., 1994 Cobb 500 Breeder Manage-
ment Guide T h e Cobb Breeding Co Ltd., East Hanningfield, Chelmsford, UK
17 Keshavan, K., M.L Scott, and J Blanchard, 1993
The effect of solubility and particle size of calcium sources
on shell quali and bone mineralization J Appl Poultry Res 2259-267
18 Data were analyzed by analysis of covariance with the General Linear Models procedure (PROC GLM) of SAS 1191 Hatchability, embryo viability and sources of mortality =re coded as 0 or 1 and analyzed accordingly,
as indicated by Hawey [20] In a preliminary analysis the linear model included the effects of calcium supplemen- tation and breeder age as discrete independent variables
and time of oviposition as a linear covariate, with 3 two-
way interactions between these factors If an interaction was not statistically significant (P =- .OS) for a given re- sponse variable, it was dropped and the reduced model
run in order to obtain least-squares means and estimates
of regression coefficients on time of oviposition The latter were obtained either as pooled coefficients or
within age or treatment, according to the significance of the interactions
Trang 9NOVO et al
Field Report
343
Results for total eggs were based on data from 13,500
eggs; results for fertile eggs, on 13,145 eggs
19 SAS Institute, 1985 SAS Users Guide: Statistics
Version 5 Edition SAS Institute, Inc., Cary, NC
20 Harvey, W.R, 1982 hast-squares analysis of
discrete data J Anim Sci 54:1067-1071
21 Atwood, H., 1929 Observations concernin the
time factor in egg production Poultry Sci 8:137-148
22 Roland, D.A., Sr and R H Harms, 1974 Specific
gravity of e in relation to egg weight and time of
oviposition F oultry Sci 53:1494-1498
23 Arafa, AS., R H Harms, J.H Choi, R D Miles,
and RB Christmas, 1979 Some characteristics of eggs
from different strains of hens as affected by time of
oviposition Poultry Sci 581009 (Abs)
24 Arafa, AS., R H Harms, R D Miles, RB Christ-
mas, and J.H Choi, 1982 Quality characteristics of eggs
from different strains of hens as related to time of ovi-
position Poultry Sci 61:842-847
25 Bennion, N.L and D.C Warren, 1933 Some fac-
tors affecting egg size in the domestic fowl Poultry Sci
26 Scott, H.M and D.C Warren, 1936 Influence of
ovulation rateon the tendencyof the fowl toproduceeggs
in clutches Poultry Sci 15:381-389
27 Warren, D.C and RM Conrad, 1939 Growth of
the hens ovum J Agric Res 58875-893
12362-367
28 Roland, D.A., Sr., D.R Sloan, and R H Harms,
1973 Calcium metabolism in the laying hen 6 Shell
guality in relation to time of oviposition Poultry Sci
2506-510
29.Roland,D.A.,Sr.,B.L Damron,andRH.Harms,
1977 Specific gravity of eggs as influenced by dietary
calcium and time of oviposition Poultry Sci 56717-719
30 Washburn, K.W and P.L Potts, 1975 Effect of
strain and production age on the relationship of ovi-
osition time to various shell strength characteristics
Foultry Sci 54:1348 (Abs)
31 Cipera, J.D., 1976 Effect of oviposition time
and storage conditions on the specific gravities of eggs
Poultry Sci 55:1132-1134
32 Meuer, H.J and R Bauman, 1988 Oxygen pres-
sure in intra- and extra-embryonic blood vessels of early
chick embryos Resp Physiol 71:331-342
33 Bahr J.M and S.S Palmer 1989 The influence
of a-'ng o n ovarian function Crit Rev Poultry Biol
2 : l O ~ l l O
34 Joyner, CJ., M.J Peddie, and T.G Taylor, 1987
The effect of age on egg production in the domestic hen
a m p Endocrinol 65:331-336
35 Hamilton, RM.G., 1978 Observations on the
changes in physical characteristics that influence eggshell
y l i t y in ten strains of White Leghorns Poultry Sci
7 1192-1197
36 Roland, D.A., Sr., 1979 Factors influencing shell quality of aging hens Poultry Sci 58: 774-777
37 Roland, D.A., Sr., D.R Sloan, and R H Harms,
1975 The ability of hens to maintain calcium deposition
in the egg shell and egg yolk as the hen ages Poultry Sci
54:172&1723
38 Tomhave, AE, 1956 Influence of age of New
Hampshire female breeders upon hatchability of eggs
Poultry Sci 35:236-237
39 Kirk, S, G.C Emmans, R McDonald, and D
b o t , 1980 Factors affecting the hatchability of eggs
from broiler breeders Br Poultry Sci 21:37-53
40 Reis, M.L.H and M.C Soares, 1993 The effect of
candling on the hatchability of eggs from broiler breeder hens J Appl Poultry Res 2142-146
41 Abe, E, H Horikawa, T Masumara, M Sugahar,
M Kubota, and T Suda, 1982 Disorders of cholecalcif- erol metabolism in old egg-laying hens J Nutr 112436-
446
42 Tulleti, S.G., 1987 Eggshell formation and quality
Pages 123-146 in: Egg Quality - Current Problems and Recent Advances RG Wells and C.G Belyavin, eds
Butterworths, London, U K
43 Muir, P.V., P.C Hanls, and R.W Gerry, 1976 The
comparative value of five calcium sources for laying hens
Poultry Sci 55:1046-1051
44 Watkins, RM., B.C Dihvorth, and EJ Day, 1977
Effect of calcium supplement particle size and source
on the performance of laying chickens Poultry Sci
561641-1647
ACKNOWLEDGEMENT
The authors express their appreciation to Valouro Group, Portugal for providingboth facilities and financial support for this study