Five hundred and forty eggs were allocated into three egg size treatments in a Complete Randomized Design (CRD). The
treatments were small (<44g), medium (45-54g) and large (>55g). Each egg was taken as an experimental unit and there
were three replicates per treatment and sixty (60) eggs per replicate. Ten eggs from each replicate were taken to
determine the shell thickness and egg yolk. The shell thickness was measured using a Vanier caliper. The egg yolk was
measured using a 0.01 g sensitivity level electronic scale. Eggs collected within eight days were taken to a sure hatch
machine for incubation. Dirty, cracked and irregular shaped eggs were not selected for incubation. A 0.01 g sensitivity
level electronic scale (RADWAG) was used to weigh the eggs. Eggs were fumigated with formalin potassium
permanganate in a ratio 1:2 for 15 minutes before they were placed in an incubator. The temperature and humidity were
set to 37.5°C and 82.5%, respectively for incubation and 37.0°C and 85% for hatching. The eggs that were less than
eight (8) days old were placed in an incubator. During the incubation period, the eggs were not turned for the first three
days. From the fourth day to the eighteenth day, egg turning was done three times a day. The eggs were candled on 7th
day of incubation period in a dark room with the eggs held before a light. The infertile eggs were determined by the
appearance of clear interior of the eggs and the fertile eggs were determined by presence of blood vessels. The numbers
of infertile eggs were recorded. At the 18th day, the eggs were removed from trays and placed into the hatching trays until
hatching time. The incubator was not disturbed for the last three (3) days of incubation. The chicks were removed from
the incubator on the morning of the 22nd day. The fertility rate and hatching percentage of eggs were calculated as
follows:
Fertility rate = Total number of fertile eggs ×100
Total number of incubated
Hatching percent = Total number of eggs hatched ×100
Total number of fertile eggs
Eggs that failed to hatch were broken to determine the developmental stage of an embryo. The embryo mortality
rate was measured by assessing at the developmental stage at which the un-hatched chick died using Hamburger and
Hamilton (1992) method. An incubator was opted for instead of natural hatching due to the fact that it would be difficult
to control the experiment since it would be difficult to get hens of the same age, size and behaviour. Above all, it would
not be practical to assume that the hens would brood at the same time. Data was recorded in excel spreadsheet and
averages were calculated. Data was tested for normal distribution. The analyses were done on transformed data. ANOVA
was used to separate the effects of egg size on shell thickness, egg yolk, egg fertility, hatching percentage and embryo
mortality. If significant, treatment effects were analysed and differences between treatments were tested by Duncan’s
new multiple-range test. The General Linear Models Procedure; SPSS (17.00) was used. Threshold for significance was p<
0.05.
RESULTS AND DISCUSSION
The results on shell thickness show that the small eggs had significantly thicker (P<0.5) shells than medium and large
eggs (Table 1). Increase in the egg size reduced the shell thickness by 8.3% and 25% comparatively to medium and small
eggs respectively. Therefore, the chances of egg cracking and as well allowing more foreign bodies to penetrate (infection)
an egg are higher and hence lower hatchability. This negative correlation between the shell thickness and egg size was
also reported by Suki and Park (2001). The egg yolk weight from large eggs was significantly (P<0.05) heavier than in
medium and small sized eggs by 11.3% and 25.4% respectively (Table 1). Suki and Park (2001) also reported the
proportion of egg yolk to be less in small eggs than in large ones.
Table 1 - Effect of egg size on egg shell thickness and egg yolk of Koekoek chickens
Shell thickness
Treatment (Egg size)
S.E
Egg yolk (g)
S.E
(mm)
0.45a
0.55b
0.60c
Large
Medium
Small
0.09
0.03
0.15
19.57a
17.36b
14.60c
0.81
0.40
0.24
abc Means within a row with no common superscript differ significantly p<0.05), S.E-standard error
Table 2 - Fertility rate and hatching percentage of different egg sizes
Fertility rate
(%)
91.10a
94.47a
88.60a
Hatching percent
S.E
S.E
Treatment (Egg size)
(%)
2.02
1.73
1.93
72.23a
75.67a
71.00a
3.19
2.40
3.86
Large
Medium
Small
abc Means within a row with no common superscript differ significantly p<0.05), S.E-standard error
279
Citation: Molapo S and Motselisi M (2020). The effect of egg size (weight) on the egg shell thickness, egg yolk and hatchability in Koekoek chickens. Online J. Anim.