Embryonic malpositions in broiler chickens and bobwhite quail
Wilson, H R
Embryonic Malpositions in Broiler Chickens and Bobwhite Quail1
Primary Audience: Hatchery Managers, Hatching Egg Producers, Researchers, Primary Breeders
One of the factors contributing to failure of avian embryos to hatch is the positioning of the embryo at the end of incubation in such a manner that emergence from the egg is inhibited. Abnormal positions, or ma(positions, may also be associated with other problems without directly affecting the ability of the chick to hatch. The effect of strain, breeder age, and gender of embryo on incidence of malpositions before hatching was determined in broiler embryos. The effect of strain, breeder age, pre-incubation egg storage, setting orientation, and turning during incubation on incidence of malpositions before hatching was determined in bobwhite quail embryos. Although there were variations among strains and between genders for incidence of malpositions, they were not statistically significant. Differences among settings and evaluators were as great as strain effects. No significant strain or breeder age effect on malposition incidence was found in quail. Long-term pre-incubation storage increased the incidence of quail embryos with head between the thighs, possibly related to delayed embryonic development. Setting quail eggs with the small end up resulted in 75% of the embryos with head in the small end of the egg. Eggs set normally but not turned had increased incidences of head in small end, beak away from air cell, and head over wing embryonic malpositions. Therefore, in these studies, the incidence of malpositions was affected by pre-incubation egg storage, egg orientation, and turning, whereas it was not affected by strain, embryo gender, and breeder age.
Key words: chicken, embryo, hatchability, malposition, quail
DESCRIPTION OF PROBLEM
The avian embryo progresses through a series of positions throughout incubation and ends in a normal position for hatching. Just prior to the beginning of the hatching process, embryos of chickens and most domestic species move into a normal position within the egg, characterized by the long axis of the body being aligned with the long axis of the egg. The head is curled forward and to the right with the beak tucked under the right wing and the tip of the beak pointed toward the air cell in the large end of the egg . The legs are flexed and tucked against the abdominal wall with the abdomen (including the internalized yolk) between the thighs . Early orientation of embryos has been reviewed by Romanoff . The normal position changes that occur throughout development have been described by Kuo  and Freeman and Vince . There are variations of the normal position that are considered to not be detrimental to successful hatching. However, there are many positions that are associated with difficulty in hatching or are found in increased incidence in cases of poor hatchability. These are termed malpositions.
Six embryonic malpositions were described in early studies [e.g., 6, 7, 8, 91. The following classifications of malpositions have been generally accepted [ 1 ]:
I Head between thighs.
II Head in small end of the egg (opposite air cell).
III Head to left instead of right.
IV Head in normal position but rotated with beak pointed away from air cell.
V Feet over head.
VI Beak (or head) over right wing.
Many variations and combinations of these malpositions have been described [9, 10]. Malpositions V and VI were considered too minor by Byerly and Olsen  to be classed as abnormal. Waters  and Robertson  described the head between the legs, or thighs (I), as a transition position, normal at earlier stages and probably due in part to retarded development.
It has been estimated that in commercial stocks 1 to 4% of all 18-d embryos will be malpositioned . Examination of hatch residue in a commercial hatchery in Panama revealed that 49.9% of the unhatched embryos that were more than 18 d in incubation were malpositioned, which was 1.54% of all eggs set (81,025) . The observed incidence for malpositions I through VI, respectively, were 9.5, 17.8, 6.6, 6.8, 17.5, and 41.8%. Tona et al.  observed an incidence of 83.5% embryonic malpositions in broiler embryos that had died at 18 d of incubation or later. They also reported that the incidence of malpositions decreased as breeder age increased to 42 wk and then increased thereafter.
A major cause of malposition III, especially in broiler eggs, is setting eggs small end up (air cell down). In commercial hatcheries the incidence of misoriented eggs varies from 0.3 to 3.4% [171, and in addition, there is an increased incidence of cull chicks among those that do hatch [17, 18].
Apparent strain differences have been observed in the incidence of malpositions when assessing hatchability problems in commercial broiler stocks . Genetic effects have been reported in some studies [10, 20] but not in others . The objective of the present studies was to establish a baseline incidence of embryonic malpositions in broiler chickens and bobwhite quail prior to hatch and to determine if differences in incidence of malpositions exist among strains examined.
MATERIALS AND METHODS
Eggs of two broiler strain crosses, Ross x Ross  and Ross x Arbor Acres , were obtained from a commercial hatchery that had a history of reduced hatchability. After eggs were received, they were held overnight at 70 deg F and then set in Jamesway 252  incubators at 99.5 deg F and 61% relative humidity. Eggs from each strain were placed in alternating cradles on each incubator tray. The eggs were candied prior to setting to locate the air cell and assure placement of the eggs with air cell end up. Eggs were turned each hour around the small axis to about 450 until pipping. Beginning at 19 d of incubation (DOI), eggs that were pipped were removed from the incubator; embryos were euthanized via carbon dioxide asphyxiation and examined for embryonic position in the egg. Only eggs that pipped from 19 to 21 DOI were examined; those that survived to 19 DOI or later but did not pip were inadvertently lost. We examined 456 embryos for Ross x Ross and 451 embryos for Ross x Arbor Acres.
A second study was conducted to further establish a baseline of position incidence for all embryos prior to hatching. Eggs from Cobb x Cobb  broiler breeders were collected when the breeders were 45 and 50 wk of age. Eggs were stored large end up (LEU) at 55 deg F for up to 6 d after lay and then incubated as in experiment 1. The eggs were candled at 7 DOI, and infertile, dead, and air cell down eggs were removed. Beginning at 19 DOI, pipped eggs were examined for embryonic position. At 21 DOI, all remaining eggs were examined. The gonads of all embryos were exposed to determine gender. The number of embryos examined was 888 and 709 in the first and second setting of eggs, respectively.
Embryonated eggs of six strains or crosses of broiler breeders were examined to determine the effect of strain on incidence of embryonic malpositions. The eggs were obtained from a primary breeder when the breeder flocks were approximately 49 and 62 wk of age. The breeders were maintained under the same conditions of age, farm, management, and diet. The six strains were Arbor Acres Regular x Arbor Acres Classic, Arbor Acres Yieldmaster x Arbor Acres FSY (feather sex), Cobb x Cobb, Hubbard x Hubbard , Ross x Ross, and Avian Main x Avian 24 K . The Hubbard x Hubbard strain was not included in the second setting. Three hundred sixty eggs of each strain were shipped by air resulting in about 300 intact eggs each for incubation. Eggs from each strain were placed on each incubator tray and incubated as in experiment 1.
Eggs were candled at 10 DOI, and infertile, dead, broken, and air cell down eggs were removed. All remaining eggs were placed in carbon dioxide at 20 DOI to euthanize the embryos; eggs were then examined to determine embryonic position. Only embryos older than 18 DOI were included in the data set.
CONCLUSIONS AND APPLICATIONS
1. A background level of embryonic malpositions was observed in broiler and bobwhite quail eggs.
2. The incidence of embryonic malpositions was not significantly different due to gender of the embryo or to broiler strains (lines); thus, these factors are not major causes of malpositions.
3. Strain and breeder age did not significantly affect the incidence of embryonic malpositions in quail.
4. Long-term pre-incubation storage of quail eggs increased the incidence of embryos with head between the thighs (I), possibly associated with delayed embryonic development.
5. Setting quail eggs with small end up resulted in 75% of the embryos with head in the small end.
6. Not turning quail eggs set with air cell up resulted in increases in head in small end (II), beak away from air cell (IV), and head over right wing (VI) malpositions.
7. The most commonly observed malposition in both broiler and quail embryos was head over right wing (VI).
8. Although higher incidence of malpositions is often associated with low hatchability, while malposition may be a contributing factor, it is not usually definitive of the cause.
1 Florida Agricultural Experiment Station Journal Series Number R-08921.
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H. R. Wilson,2 S. L. Neuman,3 A. R. Eldred, and F. B. Mather
Department of Animal Sciences, University of Florida, P.O. Box 110910, Gainesville, Florida 32611-0910
2 To whom correspondence should be addressed: firstname.lastname@example.org.
3 Present address: Embrex, Inc., Research Triangle Park, NC 27709.
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