The effect of different dietary electrolyte balances on eggshell quality

The effect of different dietary electrolyte
balances on eggshell quality in laying hens
S.S. GEZEN*, M. EREN and G. DENIZ
Department of Animal Nutrition and Nutritional Diseases, Faculty of Veterinary Medicine, University of Uludag, 16059-Gorukle, Bursa, Turkey.
* Corresponding author : e - mail : [email protected]
SUMMARY
RÉSUMÉ
This study was carried out to determine the effects of different dietary
electrolyte balances (DEB) on eggshell quality, egg weight, bone ash, litter
dry matter and on some blood parameters in laying hens.
A total of 216 Lohmann-Brown layer hens were used in this experiment,
and birds were randomly separated into 4 equal groups, each group containing 54 hens. The DEB of the control group was 170 mEq/kg, and in assay
groups, DEBs were adjusted to 80 mEq/kg (group 1) with NH4Cl, 256
mEq/kg (group 2) with NaHCO3 and to 330 mEq/kg (group 3) with
NaHCO3 and KHCO3. The experiment lasted 8 weeks. Hen day egg production, eggshell quality (shell ash, thickness, strength, cracked egg ratio),
egg weight, percentages of litter dry matter and bone ash, glucose and mineral concentrations and acid-base equilibrium related parameters (blood pH,
HCO3- concentrations, pCO2, pO2) were determined. Average egg weight
and final litter dry matter percentage were significantly higher in the group
2 than in the other groups (P < 0.001). In the group 2, eggshell thickness and
strength significantly increased compared to the group 1 (P < 0.05), and the
cracked egg ratio significantly decreased compared to the groups 1 and 3 (P
< 0.01). The tibia ash percentage was also significantly enhanced compared
to the control group (P < 0.05). Moreover, moderate (group 2) or high
(group 3) DEB induced significant decreases of chloride concentrations
during the 4 first weeks, and increases of HCO3- concentrations (P < 0.001).
Blood pH values were significantly higher in the group 3 than in the group
1 (P < 0.001). These results indicate that dietary alkaline supplementation
achieves a partial correction of the lay-induced metabolic acidosis, and that
negative effects on eggshell quality were observed when chloride excess
was associated with changes in electrolyte balance. Consequently, a moderate DEB (256 mEq/kg) can improve eggshell quality and acid-base equilibrium in laying hens.
Effets de différents apports alimentaires en électrolytes sur la qualité
des coquilles chez la poule pondeuse. Par S.S. GEZEN, M. EREN et G.
DENIZ.
Keywords : Dietary electrolyte balance - eggshell qualityblood gases- blood electrolytes.
L’objectif de cette étude est de déterminer l’influence de différents
apports alimentaires en électrolytes sur la qualité des coquilles, le poids des
œufs, le pourcentage de cendres osseuses et de matière sèche des œufs et sur
plusieurs paramètres sanguins. Au total, 216 poules pondeuses LohmannBrown ont été utilisées et réparties de façon aléatoire en 4 groupes égaux de
54 poules chacun. L’apport alimentaire en électrolytes a été de 170 mEq/kg
dans le groupe contrôle tandis que dans les groupes expérimentaux, les
apports ont été ajustés à 80 mEq/kg (groupe 1) par ajout de NH4Cl, à 256
mEq/kg (groupe 2) par NaHCO3 et à 330 mEq/kg (groupe 3) par NaHCO3
et KHCO3. L’expérience a duré 8 semaines. La production en œufs par
poule, leur poids, la qualité des coquilles (proportions minérales, épaisseur,
résistance, pourcentage d’œufs cassés), le taux de matière sèche dans les
œufs, et de minéraux dans les os, les concentrations plasmatiques de glucose et de minéraux ainsi que les paramètres sanguins reflétant l’équilibre
acido-basique (pH sanguin, concentrations en HCO3-, pCO2 et pO2) ont été
mesurés. Le poids moyen des œufs et la proportion de matière sèche ont été
significativement plus élevés dans le groupe 2 que dans les autres groupes
(P < 0.001). Dans ce groupe, l’épaisseur et la résistance de la coquille ont
été augmentées par rapport au groupe 1 (P < 0.05) et le pourcentage d’œufs
cassés réduit comparé aux groupes 1 et 3 (P < 0.01). La proportion de
cendres issues du tibia a également été augmentée par rapport au groupe
contrôle (P < 0.05). De plus, une balance électrolytique alimentaire modérée (groupe 2) ou élevée (groupe 3) a significativement diminué les concentrations plasmatiques en chlorures pendant les 4 premières semaines et a
augmenté celles des HCO3- (P < 0.001). Le pH sanguin a été plus élevé dans
le groupe 3 que dans le groupe 1 (P < 0.001). Ces résultats montrent qu’une
supplémentation en sels alcalins assure une correction partielle de l’acidose
métabolique due à la ponte et que des effets négatifs sur la qualité des
coquilles sont observés lorsque l’excès de chlorures est associé à une modification de la balance en électrolytes. Par conséquent, une balance alimentaire électrolytique modérée (256 mEq/kg) peut améliorer la qualité des
coquilles et l’équilibre acido-basique chez la poule pondeuse.
Mots-clés : Balance électrolytique alimentaire - qualité
des coquilles des œufs - gaz sanguins - électrolyte.
Introduction
“Electrolytes” are compounds, which are dissolved and
dissociated into positively and negatively ions in a suitable
medium. This term, commonly used in animal nutrition primarily refers to sodium (Na+), potassium (K+) and chloride
(Cl-) [23]. Dietary Electrolyte Balance (DEB) is often described by simple formulas expressed as mEq/kg of diet such
[Na+] + [K+] - [Cl-] [37] or ([Na+] + [K+] ) / [Cl-] [17]. These
monovalent minerals are essential for synthesis of tissue proteins, maintenance of intracellular and extracellular homeostasis and electric potential of cell membranes, enzymatic
reactions, osmotic pressure and acid-base balance [9]. When
Revue Méd. Vét., 2005, 156, 10, 491-497
layers are caged in, acid-base equilibrium can be affected :
increase of Na+ and K+ concentrations can induce metabolic
alkalosis, whereas increases of Cl- concentrations can promote acidosis. Although birds have minimum requirements
for the monovalent minerals Na+, K+ and Cl- provided by
natural ingredients and electrolyte salts, the proper dietary
balance should not only maintain acid-base homeostasis but
also achieve optimal growth performance.
Several researches [5, 11, 29, 42] reported that excessive
dietary Cl- depressed blood pH and related parameters and
caused the decrease of eggshell quality. MONGIN [36]
demonstrated that two H+ are generated for each molecule of
492
CaCO3 synthesized in the shell gland, leading to acidosis
until the 22nd hour after ovulation. In view of the adverse
effect of acidogenic compounds on eggshell calcification, it
has been suggested that alkaline salts could be useful as dietary supplements to improve eggshell quality. In a study on
acid-base balance conducted by COHEN et al. [16], alterations of the dietary sodium / chloride ratio, regardless of the
total quantities of these two ions in the diet, could produce
metabolic acidosis or alkalosis.
According to SOUVEUR and MONGIN [42], no effect on
shell weight or surface was obtained when electrolyte
balance evaluated by [Na+] + [K+] - [Cl-] was comprised between 160-360 mEq/kg. On the contrary, HAMILTON and
THOMPSON [21] reported no significant alteration of eggshell quality when electrolyte balance was lower than 330
mEq/kg or higher than 620 mEq/kg, but they observed the
reduction of the rate of lay and of feed intake. Furthermore,
in their experiment, a low electrolyte balance depressed
blood pH, HCO3- concentrations and shell quality.
Consequently, we postulate that laying hens need dietary
supplementation by alkaline salts through continuous provision of NaHCO3 or KHCO3 into diets, for compensating layinduced metabolic acidosis, and maintaining eggshell quality.
So, experiments were conducted to study the effects of different electrolyte balance (80, 170, 250, 330 mEq/kg) on the
eggshell quality and on some blood parameters.
Materials and Methods
HENS AND MANAGEMENT
Two hundred sixteen beak-trimmed Lohmann Brown 47
week old hens were used. They were reared in cages
(60x45x40 cm3) under conventional conditions with access
to feed and water ad libitum and with a constant 16 hour
lighting daily. The experiment was carried out between the
August 23th and October 11th (8 weeks). During this time,
the interior temperature was recorded twice a day. The daily
average temperature varied from 27°C during the first 28 day
period (period 1) to 22.5°C during the second 28 day period
(period 2) with a maximum of 30°C and a minimum of 15°C.
Relative air humidity was 70% throughout the experiment.
TREATMENTS AND EXPERIMENTAL PROTOCOL
Hens housed in cages were randomly assigned into four
equal main groups (n = 54) as one control and three assay
groups. A practical layer diet was provided during the experiment. All diets were in the meal form and based on corn
and soybean meal. The diets were formulated to be isonitrogenous (163.6 g kg-1) and isocaloric (2600 Kcal kg-1) as fed
basis.
Treatment groups were formed according to dietary electrolyte balance (DEB). DEB was calculated in mEq according to MONGIN’s formula : DEB = [Na+]+[K+]-[Cl-] [37].
Sodium, potassium and chloride were added to diet as
GEZEN (S.S.) AND COLLABORATORS
NaHCO3, KHCO3, NH4Cl and NaCl (Table I). Basal diet
(DEB = 170 mEq/kg) was given to control birds, whereas
assay groups received using alkaline supplementation (group
1 : DEB = 80 mEq/kg with 0.48% NH4Cl ; group 2 : DEB =
256 mEq/kg with 0.70% NaHCO3 and group 3 : DEB = 330
mEq/kg with 1.04% NaHCO3 and 0.35% KHCO3).
CHEMICAL ANALYSIS AND MEASUREMENT OF
EGGSHELL QUALITY
Prior feeding, laboratory assays were conducted on each
diets for sodium, potassium and chloride. The sodium and
potassium were determined by flame spectrophotometer [2].
The chloride in feed was determined by titration [31]. Using
these determined values, NaHCO3, KHCO3, NH4Cl quantities were adjusted to provide the wanted DEB according to
assay groups. Analyses of the drinking water revealed very
low quantities of sodium, potassium and chloride. Therefore,
the intake of those elements via the drinking water was not
considered in the calculations. Experimental diets were chemically analysed according to the AOAC methods [1].
Metabolisable energy of feed ingredients was calculated
based on equation of HARTEL [22].
Hen day egg production, cracked eggs were recorded
daily. During the two day periods, eggs from each treatment
group were taken to determine eggshell quality parameters.
All eggs were visually checked for cracks and breakage
under artificial lighting. The exterior shell quality evaluations were based on shell thickness, breaking strength and
shell ash. The eggshell breaking strength was measured
using a cantilever system by applying increased pressure to
the broad pole of the shell [8]. The shell thickness was measured with a micrometer gauge (mitutoya®) on three part of
shell from the equator of each egg. The shell ash was determined after drying at room temperature for 3 days.
Ten hens were randomly sampled (at night) from each
treatment group and 0.5 ml blood sample were collected by
anterior heart puncture into heparinized (Lithium heparin)
syringes. Samples were gently mixed and acid-base traits
were measured within 30 min by a Blood Gas Analyzer
(Chiron, Chiron Diagnostics, Mod 865) calibrated for chicken blood. Immediately after measurement of acid-base
parameters, blood samples were centrifuged for 15 min at
1500xg and plasmas were stored at -20°C prior to analyses
of ion concentrations. Plasmas were analysed with a spectrophotometer (Novaspec® II, Mod 4040) using commercial
kits (Teco diagnostics). The acid-base balance (pH, pCO2,
pO2 and HCO3-), plasma concentrations of ions and glucose
were measured on 51 week old hens, then only plasma ion
concentrations were determined on 55 week old birds.
At the end of the trial, ten hens were killed in each group
to determine bone ash and their left legs and carinas were
used to test the boiling/extraction method [3], in which the
bones are placed in boiling water to loosen the flesh only,
chilled, stripped of adhering flesh with care to leave the cartilage caps on the bones, extracted for 24 hour each with
ethanol and anhydrous ether, dried, weighed, ashed for 24
hour at 600°C and re-weighed.
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EFFECT OF DIETARY ELECTROLYTE BALANCES ON EGGSHELL QUALITY IN LAYING HENS
493
* Vitamin Premix supplied the following per kg diet : Retinol 10 000 IU, cholecalciferol 2 000 IU, tocopherol
15 mg, Vitamin K3 2 mg, thiamin 1 mg, riboflavin 6 mg, pyridoxine 2 mg, cyanocobalamin 0.015 mg, folic
acid 1 mg, Calcium c- pantotenate 8 mg, D - Biotin 0.05 mg, niacin 33 mg
** Trace Mineral Premix supplied the following per kg diet : Manganese 100 mg, iron 25 mg, zinc 6 mg, copper 5 mg, iodine 0.5 mg, cobalt 0.1 mg, selenium 0.2mg
*** BHT : Butylated hydroxytoluene, as antioxidant
**** Calculated
***** Electrolyte balance calculated as Na+K-Cl in mEq/kg
TABLE I. — Ingredients and chemical composition of the experimental diets (as fed).
The litter moisture was determined at 47th and 55th week
of age by taking random specimens from each pen followed
by oven drying at 105°C for 6 hour.
STATISTICAL ANALYSIS
The data from the entire experimental period were pooled
and analyzed by analysis of variance. Differences between
treatment means and also between main treatment categories
were tested according to Tukey’s test [46]. Hen day egg production among the groups were analysed by the Chi-Square
test procedure [44]. All analyses were performed using
SPSS® computer software 10.00 (SPSS Inc., Chicago, USA,
1999). Differences were considered significant when P
values were less than 0.05.
Revue Méd. Vét., 2005, 156, 10, 491-497
Results
For the total experimental period, hen day egg production
was not statistically different between groups (Table II).
There was no significant difference in eggshell ash during
the experiment (Table III). By contrast, eggshell strength and
thickness (Table III) were reduced in group 1 (DEB = 80
mEq/kg), but only differences between group 1 and group 2
(DEB = 256 mEq/kg) were statistically significant for the
total experimental period (P < 0.05). Besides, the ratio of
cracked eggs was significantly lowered in the group 2 (group
2 vs. group 1 and group 2 vs. group 3 (DEB = 330mEq/kg):
P < 0.01) (Table III). In the same way, significant increases
of egg weight (Table III) were noticed in this group as soon
as hens were 49 week old (P < 0.01 in comparison with all
the other groups), until they were 55 week old (P < 0.001
494
GEZEN (S.S.) AND COLLABORATORS
TABLE II. — The Effects of Different Dietary Electrolyte Balances (DEB) on the Mean Hen Day Egg
Production of Laying Hens.
Differences are not significant.
group 2 vs group control and group 2 vs. group 1). For the
total experimental period, the egg weight was significantly
enhanced in the group 2 compared to control group and to
the other assay groups (P < 0.001). At the end of experiment,
the percentages of carina ash were similar in all groups while
the tibia ash percentage was significantly increased in the
group 2 in comparison to the control group (P < 0.05).
Furthermore, a marked increase of litter dry matter percentage (Table III) was observed in the group 2 (DEB = 256
mEq/kg) at the end of the experiment (P < 0.001 in comparison to the control group and the 2 other assay groups).
No variation of plasma ion concentrations (sodium, potassium, calcium) were noticed according to dietary electrolyte
balances over the 2 experimental periods except for chloride
concentrations in the first period (Table IV). Layer hens
receiving high dietary electrolyte correction (groups 2 and 3)
presented markedly lowered chloride concentrations compared to the control group and to the group 1 (P < 0.001).
Increases of electrolyte into diets have also induced elevation of pH values (Table IV) : the highest value (7.50 ± 0.02)
was obtained in the group 3 (DEB = 330 mEq/kg) whereas
the lowest value (7.36 ± 0.02) was observed in the group 1
(DEB = 80 mEq/kg). Parallel changes in the HCO3- concentrations were also evidenced (Table IV) : they were dramatically increased in the groups 2 and 3 (P < 0.001). By
contrast, no difference of pCO2, pO2 and glucose concentrations between groups was encountered.
Discussion
The present study was undertaken to investigate the effects
of different dietary electrolyte balances (DEB) on eggshell
quality, egg weight, bone ash and on some blood parameters
of laying hens.
Egg weight and eggshell thickness and strength were markedly increased in the group 2 (DEB = 256 mEq/kg) while
the cracked egg ratio was decreased for the total duration of
the experiment, suggesting an improvement of egg quality
by the dietary alkaline supplementation. However, a doseeffect relationship was not observed, because in the group 3
receiving the greatest DEB (330 mEq/kg), egg traits were
comparable to those of the control group (DEB = 170
mEq/kg). CHEN and BALNAVE [11] reported an optimal
activity of carbonic anhydrase that plays an important role in
eggshell formation in slightly alkaline medium. Moreover,
an excessive chloride intake limited calcium transport to
shell gland and reduced bicarbonate concentrations in shell
gland lumen [11, 41]. Consequently, our findings, i.e. that
low and high DEB negatively affected the eggshell quality,
are consistent with these observations. Previous studies [13,
48] have also showed that excess of dietary sodium (>
0.35%) could lower eggshell quality, but DIKICIOGLU [19]
reported that different DEB did not modify shell ash. Several
studies reported that eggshell quality (thickness and
strength) was affected by low and high electrolyte balances
(given by the formula : [Na+] + [K+] - [Cl-]) [7, 21, 24, 38,
48], while other reports only related negative effects of high
dietary chloride quantities [20, 25, 27, 42]. In our study, high
DEB associated with constant chloride content (group 3 vs.
group 2) or low DEB associated with various Cl- quantities
(control group vs. group 1) did not significantly modify the
eggshell quality. But significant differences for egg thickness and strength were evidenced between the groups 1
(DEB = 80 mEq/kg) and 2 (DEB = 256 mEq/kg), showing
that diminution of the eggshell quality was obtained with
high chloride levels coupled to changes in dietary electrolyte
balances.
When the ratio ([Na+] + [K+] / [Cl-]) in the diet was ranged
from 4.46 to 6.47, JUNQUEIRA et al [28] observed a reduction of the egg weight. In our study, the group 3 presented the
highest ratio (5.13) and in this group, the egg weight was
comparable to the control group, but was significantly lowered than in the group 2. On the contrary, LOTT [33] and
AUSTIC [5] demonstrated a reduction of the egg weight
when the dietary chloride content increased. In the same
way, the lowest egg weight values were recorded in the
group 1, which low DEB (80 mEq/kg). In addition, BALNAVE and MUHEEREZA [8] and CHOCT et al [12] obtained the highest egg weight when hens were respectively fed
with diets including 1.00% NaHCO3 or with DEB equal to
182 mEq/kg.
As calcium necessary for eggshell formation is stemming
from medullar bones (tibia, femur etc...) [15, 32], the measurement of bone ash percentages inform about the intensity of
calcium mobilisation in the different groups. The tibia ash
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EFFECT OF DIETARY ELECTROLYTE BALANCES ON EGGSHELL QUALITY IN LAYING HENS
495
a,b : Means within rows with no common superscripts are significantly different. *P<0.05, **P<0.01, *** P<0.001 NS : Not Significant, Results
are expressed as means ± Standard errors
TABLE III. — The Effects of Different Dietary Electrolyte Balances (DEB) on Egg Qualities (Shell Ash, Strength, Thickness, Cracked Egg
Ratio, Egg Weight), Bone Ash Percentages and on Litter Dry Matter in Laying Hens.
percentage was significantly affected in the group 2, suggesting that calcium mobilisation from bones was higher when
dietary electrolyte balance was moderately corrected. The
litter dry matter percentage was only significantly enhanced
in the group 2. This finding is in agreement with previous
reports that mentioned decreases of this parameter in layer
hens fed with diets containing high quantities of electrolytes
[14, 35, 40] or supplementation by NH4Cl [43].
Revue Méd. Vét., 2005, 156, 10, 491-497
In our study, the higher DEBs (256 and 330 mEq/kg) have
induced significant increases of blood pH and HCO3concentrations. These observations are in agreement with
previous studies [18, 21, 27, 29], which reported variations
of these 2 parameters according to the dietary electrolyte
supplementation. SUCHY et al [45] reported that pCO2, pH
and HCO3- concentrations were respectively comprised between 4.59 and 7.89 mm Hg, between 7.28 and 7.44 pH units,
and between 21.29 and 25.69 mmol/L in laying hens, and
496
GEZEN (S.S.) AND COLLABORATORS
a,b
: Means within rows with no common superscripts are significantly different. *** P<0.001. NS : Not Significant. P1 : Period 1 : 47 week 51 week old layer hens. P2 : Period 2 : 52 week - 56 week old layer hens. Results are expressed as means ± Standard errors.
TABLE IV. — The Effects of Different Dietary Electrolyte Balances (DEB) on Mineral Concentrations and on Acid-Base Equilibrium and
Glucose Concentrations in Laying Hens.
that after the 35th week of age, pCO2 and HCO3- concentrations increased. In complement, HUGHES [24] specified
that blood pH values above 7.6 and below 7.0 could induce
death in hens.
Several studies have shown that pH, pCO2 and HCO3concentrations were significantly reduced when the DEB
was low, whereas elevations of HCO3- concentrations and of
blood pH were observed when Na+ was added to diets [5, 16,
17, 32]. JUNQUEIRA et al [28] obtained significant
increases of blood pH in laying hens when the dietary electrolyte supplementation given by the ratio ([Na+] + [K+]) /
[Cl-] was within 4.46 - 6.47. Using two different dietary electrolyte supplementations (164 and 254 mEq/kg) with
NaHCO3 or with NH4Cl, VELDKAM et al [47] showed that
the electrolyte supplementations decreased pCO2 but increased HCO3- concentrations. Taken together, the high dietary
chloride supplementation negatively affected blood pH,
HCO3- concentrations and pCO2 leading to alteration of eggshell quality. During eggshell formation, the carbonate production by the shell gland leads to proton (H+) releases and
decreases of the uterus and blood pH, and calcification is
inhibited when the blood concentrations of protons are
increased [6, 10].
Whatever the group, plasma glucose and plasma anion
concentrations were within normal ranges [4]. Despite DEB
corrections, plasma anion concentrations were similar between groups whereas chloride concentrations were lowered
during the first experimental period in the hens of the groups
2 and 3 receiving diets in which the ratios anions / chloride
were low. This biochemical alteration reflected the relation
between the diet electrolyte balances and the blood electrolyte concentrations and was comparable to previous studies
[30, 34]. In agreement with our study, JOHNSON and
KARUNAJEEVA [26] did not found any modification of
calcium, sodium and potassium plasma concentrations even
when hens received a high DEB (553 mEq/kg).
In conclusion, our study has not only confirmed that a high
dietary balance could correct acid-base equilibrium by
increasing blood pH values and HCO3- concentrations, and
also shown that moderate DEB (256 mEq/kg) improved eggshell quality (thickness, strength and decreases of cracked
egg ratio). Consequently, during establishments of layer hen
diets, minimum requirements for each mineral given by
NRC [39] should be provided in a first attempt, then after the
dietary electrolyte balance should be adjusted.
Acknowledgement
This project was kindly supported by the Research Fund of
Uludag University (Prj no: 2001-19).
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