Poor egg shell quality accounts for major economic losses to commercial egg producers. There are numerous factors involved in egg shell formation and its subsequent quality. The macro factors include but are not limited to the source and level of calcium in the diet, phosphorus level in the diet and temporal intake of these minerals. The source and particle size of calcium used in laying hen diets are 2 factors that have received considerable attention in recent years.
The egg shell must be strong enough to resist the processes of lay, collection,
grading and transport reaching the final consumer intact. Egg shell defects
include cracks, deformities and irregular calcium deposition in addition to
invisible microbial contamination, resulting in economic losses. Modern layer
breeds have high egg production and low body weight in the 1st laying cycle.
Second-cycle layers produce large and extra large eggs and present a higher
percentage of thin egg shells due to disorders associated to calcium and vitamin
D3 metabolism. Laying birds have high calcium requirements for bone
maintenance and egg shell deposition which are supplied by adequate and available
calcium dietary sources (Pizzolante et al., 2009).
Phosphorus is an essential mineral for laying hens in the formation of egg shell
and metabolism (Wu et al., 2006). Studies on optimal
calcium levels in layer diets are economically important contributing to minimize
broken egg shell percentage, production costs and environmental impacts (Oliveira
et al., 2002). Calcium is used for bone formation, egg shell production
and blood clotting. It also affects the heard, muscles and nerves as well as
some of the bodys enzyme systems. Most of the bodys Ca is found
in the skeleton, calcium is comprised mainly of calcium phosphate with some
calcium carbonate. The shell deposition and shell quality are directly related
to the calcium level in the diet.
The main mechanism by which vitamin D facilitates calcification of bone and
formation of egg shell is believed to be a result of the effects of the physiologically
active form of vitamin D, 1.25-Dhydroxycholecalciferol (1.25 (OH) D) on intestinal
function. It is well established that in laying hens a vitamin D3
dependent Ca-binding protein is involved in the active transport of Ca across
the intestinal membrane and probably across the uterine membrane (Bolukbasi
et al., 2005). Dietary Phosphorus (P) levels influence Ca metabolism
in hens with the indication that growing birds respond to P deficiency by an
increase in intestinal 1.2-dihydroxy vitamin D3, Ca-Binding Protein
(CaBP) and intestinal Ca absorption. These reasches suggest that low blood P
stimulates the synthesis of 1,25-(OH)2D3 which is involved
in Ca homeostasis. The most active form of vitamin D, 1,25-(OH)2D
is responsible for increasing the absorption of intestinal Ca and phosphate,
mobilizing these ions from bone and increasing bone mineralization (Orban
et al., 1992).
The researchers conducted the present study to determine the effects of oviposition
time, hens age and extra dietary calcium on Egg Weight (EW), SG and EW
loss during the first 18 days of incubation, fertility, embryo viability, age
of embryonic death in fertile eggs and hatchability of eggs from feed-restricted
broiler breeder hens under commercial conditions (Novo et
al., 1997). Even though, the understanding of the importance of timing
of Ca intake in maintaining maximum shell quality in broiler breeders is incomplete,
it is unquestionable that shell quality is related to the ability of the hen
to absorb Ca from the intestine and to utilize skeletal Ca (Reis
and Fieo, 1995). It has long been known that vitamin D is needed for proper
absorption of calcium (Fritts and Waldroup, 2003). Calcium
and phosphorous are essential macro minerals with calcium forming a significant
component of the shell and phosphorous playing an important role in skeletal
calcium deposition and subsequent availability of calcium for egg shell formation
during the dark period.
However, the feeding of calcium levels before the requirement of the bird for
production has not been shown to improve shell quality. Indeed, feeding hens
high levels of calcium may interfere with the availability of other minerals
(NRC, 1994) and can have a negative impact on the ability
of the bird to utilise calcium, particularly if calcium levels in the diet are
subsequently decreased (Gerber, 2006). There are many
various factor effect on the egg weight and egg size. Methionine, linoleic acid
and supplemental fat are 3 factors that affect egg size (Safaa
et al., 2008; Keshavarz, 2003).
MATERIALS AND METHODS
About 200 and 40 Ross 308 broiler breeder hens were used in this experiment
which were 20 weeks of age and continued for 50 weeks periods. Birds were distributed
in 24 pens (1.00 m longx1.00 width) with housing 10 birds per pen plus a cockerel
each pen. Each cage was equipped with a cup drinker and a trough feeder place
in front of the cage. A completely randomized experimental design was applied
in 3x2 factorial arrangement that there were 4 experimental units for each of
the 6 treatment groups. Diets were formulated to meet the nutrient requirements
for Ross 308 broiler breeder (Table 1). All diets were isocaloric
|| Ingredient and calculated composition of experimental diet
There were six dietary treatments (one control and 5 experimental groups).
Six experimental dietary include different level of calcium, phosphorus and
vitamin D3 in each treat. Control diet (T3) containing
about 15% CP, 2750 kcal ME kg-1, (2.75, 0.37%) Ca, P and 3000 (IU)
Vitamin D3. In this experiment, use 2 levels of calcium, phosphorus
(2.56, 0.33%) and (3.13, 0.4%) 10% lower and 10% higher of Ross 308 requirements,
Vitamin D3 have 2 level 3000 and 3300 (IU) in the experimental diets. At the end of the 50 weeks feeding period, blood samples were obtained from the brachial veins of 4 hens per treatment, the plasma was separated by centrifugation blood for 10 min at 2000 x g and saved for determination of plasma Ca, P and Mg. The Ca, P and Mg were measured on auto analyzer by using commercial kits. At end of experiment, 2 hens slaughtered per each pen for tibia (Ca, P) analyze.
The weights of the birds were recorded at beginning and end of the experimental
period. During the experimental period, daily feed intake per bird egg weight,
hatchability, egg production, egg shell losses, broken egg, total egg shell
losses percentage and mortality were recorded. Feed conversion was calculated
from feed intake to egg weight production. Statistical analyses was performed
by the statistical package SPSS (1999) for windows, version
10.0. Multiple comparisons of the data were done by using the Duncans
test after One-Way Analysis of Variance (one-way ANOVA).
RESULTS AND DISCUSSION
According to the results of the study shown in Tables 2-4,
the effects of different levels of Ca, P and vitamin D3 on variants,
including Ca, P and Mg contents of blood plasma, P and ashes of bone, percentage
of hairline fracture, soft and broken eggs, total losses and the egg weight
were not significant.
|| Effect of dietary Ca, P and vitamin D3 on Ca,
P and Mg level of plasma and tibia
|a, bMeans within column with no common superscript
|| Effect of dietary Ca, P and vitamin D3 on egg
|a, bMean within column no common superscript
Considering (Table 2), the influences of Ca, P and vitamin
D3 on Ca contents of bone ashes were not noticeable whereas there
was a significant interaction among them in this regard (p<0.05). Concentrations
of Ca, P and Mg are shown in Table 2 and as it is seen, there
was no difference among them.
For these, parameters were not influenced by hatching time, they could not
be proper indicators for various levels of Ca and P which was in agreement with
previous observation by Orban et al. (1992).
No clear differences in quality of egg shell could be detected between different
levels of Ca, P and vitamin D3 (Table 3). Finding
of other studies suggested that qualitative improvement of egg shell is related
to the weight (Gerber, 2006). The effects of Ca, P and
vitamin D3 on the egg weight and production, dietary conversion coefficient
and hatching are shown in (Table 4).
||Effect of dietary Ca, P and vitamin D3 on performance
FCR hatchability (%)
|a , bMeans Within column with no common superscript
As it is deduced from these results, the average of egg weight was not affected
by experimental factors. According to assays carried out by Safaa
et al. (2008) and Keshavarz (2003), the egg
weight was influenced by dietary protein, choline, folic acid and vitamin B12
and different amounts of Ca, P and vitamin D3 couldn't significantly
affect the egg weight which is in consistent with the findings (Table
4). Data shown in Table 4 revealed that the effects of
different concentrations of Ca and P on production percent were significant
(p<0.05) and increasing Ca and P caused a loss in egg production. By reduction
of P and Ca concentrations, production percent was increased drastically (p<0.01).
Also it can be observed that vitamin D3 increments resulted in higher
production percent (p<0.05). It is clear from Table 4 that
the interaction between Ca, P and vitamin D3 levels was fully marked
(p<0.05) and decreasing P and Ca, in combination with increasing vitamin
D3 increased production percent severely. However, it was already
suggested that addition of Ca caused the egg production to increase (Oliveira
et al., 2002; Pizzolante et al., 2009).
It is observed that Ca and P concentrations of 10% lower than in control were
appropriate levels and that the incorporation of higher values of Ca and P (i.e.,
2.56 and 0.33%, respectively) suffered from an oversupply that limited the availability
of other nutrients (NRC, 1994). The Table
4 also implies that increasing vitamin D3 from 3000-3300 I.U.
added up to an increase of 82.163-83.808% proving that addition of vitamin D3
causes improvement of releasing Ca and P which is similar to the findings of
Oliveira et al. (2002) and Pizzolante
et al. (2009). It is shown in the Table 4 that
the influences of Ca and P on hatching were not significant and this outcome
was in contrast with those of Novo et al. (1997)
who reported that the hatchability of fertile eggs was declined by decreasing
P amounts and it might owe to lack of any P deficiency among the levels tested
here. Furthermore, the researchers observed that an increase of 3000-3300 I.U.
in concentration of vitamin D3 increased the hatching rate from 91.69,94.72%
The rationale behind such an increase could be the increase in Ca content of
blood (Table 4), as has been noted earlier (Orban
et al., 1992; Fritts and Waldroup, 2003).
In the case of feed conversion coefficient, considerable effects of P and vitamin
D3 were again found (Table 4). Considering that
there was a direct relationship between feed conversion coefficient and egg
production and weight, one can said that the feed conversion coefficient is
well-correlated with egg production an weight. From Table 4,
it is obvious that Ca and P of 10% lower than in control have been optimal and
reasonable choices, evidenced by diminished feed conversion coefficient after
using higher amounts of Ca and P. Indeed, it is indicated that the increase
of 3000-3300 I.U. in the amount of vitamin D3 had a positive effect
on practical variables (Table 4). The combined results suggest
that high levels of Ca and P had no dramatic influence on egg shell quality
or they were far more than required, resulting in blocking other dietary nutrients
and making them out of reach and thus, leading to a diminution in feeding efficiency.
In other words, consisting of standard levels, the control treatment was an
overdose of Ca and P and by a 10% reduction in concentration of these nutrients,
strong effects on performance variables could be observed. Additionally, increase
of vitamin D3 improved this effect drastically (p<0.05).