Avian Egg Medicine/Hatching Protocols

Question 1

All avian embryos assume the same hatching position. Describe the normal posture.

Answer 1

• Spine along the long axis of the egg
• Embryo head between legs
• Embryo head will gradually move along right side of body until head is tucked under right wing
• Egg tooth should be positioned to pierce the air cell

Question 2

What “state” leads the the cascade of events of hatching? What induces this “state”?

Answer 2

(1) Hypoxia and hypercapnia

(2) The chorioallantoic membrane will no longer meet the respiratory needs of the embryo

Question 3

Discuss the stages of hatching .

Answer 3

(1) State of hypoxia/hypercapnia
(2) Hatching muscle (musculus complexes) contract to move egg tooth
(3) Internal pip occurs (egg tooth breaks inner shell membrane)
(4) Pulmonary respiration starts with air within air cell
(5) Limited oxygen supply in air cell and inability to fully expand lungs b/c of shell triggers external pip and movement of embryo
(6) Embryo moves in counterclockwise rotation (breaks portions of shell and friction eliminates shell membranes)
(7) movement continues until chick is free

Question 4

Which avian groups lack an egg tooth?

Answer 4

Ratites
Megapodes (Brush turkey, they bury their eggs in dirt)

Question 5

Which group of birds air cell are offset from midline (most birds its on midline)?

Answer 5

Columbiformes (doves and pigeons)

Question 6

List 4 methods of external egg health evaluation

Answer 6

(1) Candling
(2) Digital monitoring (“Buddy”, similar mechanics to a pulse ox)
(3) serial weights
(4) floating

Question 7

What sign observed on candling indicated early embryonic death?

Answer 7

blood ring

Question 8

Define fertility and hatchability (ie. point out the difference).

Answer 8

Fertility = ratio of fertile eggs to total eggs laid

Hatchability = ratio of eggs that hatch to the total number of fertile eggs

Question 9

Which part of the egg/embryo is responsible for respiration and mineral transport?

Answer 9

chorioallantoic membrane

Question 10

Which late stage embryo malpositions are fatal?

Answer 10

(1) head between leg with failure to turn or lift head

(2) head under legt wing

(3) feet over head

(4) embryo crossways in egg, usually associated with other defects

Question 11

Discuss steps to assist hatch an embryo with a successful internal pip with no additional progress

Answer 11

(1) create hole at top of air cell

these will usually continue to hatch without further assistance

Question 12

Discuss steps to assist hatch an embryo with successful internal pip, external pip, but obviously dry shell membranes.

Answer 12

Moisten membranes with artifical tears or light mineral oil (can use sterile water or isotonic fluids but usually they are not long lasting)

Question 13

Discuss steps to assist hatch an embryo with no progress observed after “draw down”

Answer 13

(draw down = change in shape and increased volume of the air cell seen; right before internal pip)

Radiographs are indicated to determine embryo position. 4 views recommended (VD, then rotation of 45 degrees counterclockwise to create 360 degree view). If dark void observed in lungs and trachea, this implies respirations have been taken which is less urgent

Question 14

Discuss steps to assist hatch an embryo with malposition and no external pipping.

Answer 14

• Requires intervention beginning with creating an opening in the shell over the beak (locate on radiographs)
• Once the embryo has adequate access to air and sufficient space to move, monitor egg q1h to monitor for retraction of the yolk sac into the body, closure of umbilical seal, and complete shutdown of chorioallantoic membrane vasculature
• Embryos that have prolonged hatching periods and require invasive procedures should be treated with prophylactic antibiotics
• Umbilical vessels may be ligated to cauterize if needed 1 cm from the seal, treat with antiseptics

Question 15

What group of birds commonly have a thick chalky layer covering their eggs that prevent candling?

Answer 15

Cranes (Gruiformes)

Question 16

What pigment creates the appearance of Cassowary (Casuarius) and emu (Dromaius novaehollandiae) eggs?

Answer 16

biliverdin

Question 17

Venipuncture can be performed in ovo using what vessel (eg. for DNA sexing)?

Answer 17

vitelline vessel

Question 18

What are the 4 layers of egg shells?

Answer 18

Mammillary layer (innermost)
Palisade layer
Vertical crystal layer
Cuticle (outermost)

Question 19

What mineral is commonly found in egg shells?

Answer 19

calcium carbonate

Question 20

In a paper by Hall et al. in Zoo Bio published in 2023, a novel method of external egg health monitoring was described in emus (Dromaius novaehollandiae) and southern cassowaries (Casuarius casuarius johnsoni). Briefly, what was the technique utilized?

Answer 20

Partial fenestration in 2 areas of the egg was successful to aid in performing traditional candling techniques to determine the location of vascular development and embryo viability

Question 21

In a paper by Bryne, published in Zoo Bio in 2023 titled “Effect of four eggshell repair materials on weight loss during incubation of white leghorn chicken eggs”, how did the 4 methods compare?

Answer 21

(1) All treatment types showed egg weight loss equally
(2) Increasing egg coverage with all treatment types were negatively correlated to weight loss

Question 22

What necropsy finding on an unhatched egg would lead you to believe an infection as the cause of mortality? What bacterial infections are most commonly associated with death? What 2 viruses?

Answer 22

(1) discoloration and/or gas bubbles

(2) Salmonella, Mycoplasma, Staphylococcus, Chlamydophila, E coli

(3) Herpesvirus, Paramyxovirus

Question 23

Once a chick assumes the proper position to perform an internal pip, in what time frame should you expect hatching to occur?

Answer 23

2-3 days