listing of developmental chronology

CHAPTER 18 Comparative listing of developmental chronology



Poul Hyttel



Table 18-1: Chronological listing of developmental events in cattle in relation to stage of gestation (Days post coitum). Information accumulated from various sources. Open boxes represent lack of data










































































































































































Day Event
 1 Fertilization and pronucleus development, minor activation of the embryonic genome
 2 2-cell embryo
 3 6–8-cell embryo
 4 Arrival in the uterus, 8-cell embryo, major activation of the embryonic genome
 5 16-cell embryo developing into morula
 6 Compact morula developing into blastocyst
 7 Blastocyst
 8 Expanded blastocyst around 220µm, hatching from the zona pellucida in some cases
 9 Hatching from the zona pellucida in all blastocysts
10 Blastocysts, 203–239 µm, hypoblast starts to form
11 Blastocysts, 145–818 µm
12 Blastocysts, 0.26–1.42 mm, hypoblast forms a complete lining
  Complete embryo (conceptus) Embryonic disc
13 Elongation initiated, 0.5–3.1 mm Circular about 140 µm
14 0.6–40 mm Circular (200–300 µm) to oval (210×400 µm), primitive streak starts to form
15 1.8–135 mm, maternal recognition of pregnancy by IFN-τ Amniotic folds start to form
16   Oval up to 450×600 µm, primitive streak with mesoderm and endoderm involution
17 12.5–24 cm Oval up to 400×750 µm, primitive streak
18 Conceptus elongated to fill pregnant uterus horn and to invade non-pregnant horn Allantois development initiated
19 Placentation initiated  
  Size of the embryo proper/fetus (length or CRL; weight) Developmental event
20 2 mm Neural groove, first somite pairs
21   Up to 6 somite pairs, neural tube, primitive gut formed by embryo foldings
22   16–20 somite pairs, heart development, first heart beat
23   18–19 somite pairs, first pharyngeal arch, optic and otic placodes, allantois anchor-shaped
24 3.1 mm Three brain vesicles, second pharyngeal arch, forelimb buds
25 3.5 mm Third pharyngeal arch, C-shaped embryo
26 5.6 mm Fourth pharyngeal arch, hind limb buds
30 10–12 mm, 69–280 mg Nasal placodes, paddle-shaped forelimb buds
34 13 mm Fusion of facial prominences, forelimb digits
38   Eyelids, genital tubercles, hind limb digits
50 3.9 cm, 5 g Eyelids partially cover eyes
56 4.8 cm Secondary palate fused
60 6.6–7.8 cm, 14–19 g Eyelids fused, differentiation of external genital organs, hoofs and horn primordia
75 10 cm Tactile hairs, hair follicles on body
83   Cornification of hoofs, development of scrotum
110 24 cm, 550 g Eruption of first teeth, hairs around mouth and eyes
142 38 cm, 2650 g Hairs on ears
150 37 cm, 2750 g Hairs on cheek, colour marks, hard hoofs, descent of testis completed
159 42 cm Hairs at umbilicus
182   Hairs at tail and horn primordium
187 56 cm, 9.2 kg Hairs at legs
230 73 cm, 18 kg Hairs on body
279–290 90 cm, 35 kg (dependent on breed) Birth


Table 18-2: Chronological listing of developmental events in sheep in relation to stage of gestation (Days post coitum). Information accumulated from various sources. Open boxes represent lack of data


















































































































































Day Event
 1 Fertilization and pronucleus development
 2 2-cell embryo
 3 Arrival in the uterus, 8–16-cell embryo, major activation of the embryonic genome
 4 16-cell embryo developing into morula
 5 Compact morula developing into blastocyst around 168 µm
 6 Blastocyst
 7 Expanded blastocyst around 184 µm in diameter
 8 Hatching from the zona pellucida, hypoblast starts to form
  Complete embryo (conceptus) Embryonic disc
 9 Ovoid 0.18 x 0.25 mm Circular about 45 µm
10 Ovoid 0.4 x 0.9 mm Complete hypoblast formed
11 Ovoid or elongated up to 6 mm Oval up to 33 x 260 µm
12 10–22 mm Primitive streak, mesoderm and endoderm involution
13 32–70 mm, maternal recognition of pregnancy by IFN-τ Oval up to 370 x 490 µm
14 Up to 35 cm Oval up to 612 x 1000 µm, development of amniotic folds, giant binucleate trophoblast cells
15 Placentation initiated Oval from 1.5 x 2 mm to 0.8 x 3.2 mm, neural groove, first somite pairs
  Size of the embryo proper/fetus (length or CRL; weight) Developmental event
16 2.5–4.2 mm, conceptus elongated to fill pregnant uterus horn and invade non-pregnant horn 8–15 somite pairs, neural tube, closure of amnion
17–18 4.0–5.5 mm 25 somite pairs, allantois anchor-shaped, three brain vesicles, first and second pharyngeal arch
19 5.0–7.0 mm Eye and ear placodes, third pharyngeal arch
20 7.0 mm Forelimb buds
21   C-shaped embryo, neural tube closed, fourth pharyngeal arch, hind limb buds
22 8.0–9.0 mm Paddle-shaped forelimb buds, nasal placode
23   Paddle-shaped hind limb buds
24–25 1.4 cm Lens formation, eye pigmentation
26 1.6 cm Formation of eye lids, forelimb digits
27 1.4–1.6 cm, 0.9 g External auditory meatus and auricles
30 1.6–2.2 cm Fusion of facial prominences, tongue
34 2.3–3.5 cm Tactile hairs at eyes
38 2.9–4.4 cm Tactile hairs at upper lip, secondary palate fused
43 3.3–5.5 cm Eyelids fused, differentiation of outer genital organs
57   Hairs on head
60–67 11.0–16.5 cm Hairs on body
70   External genital organs formed
80 19.8–23.7 cm, 340 g Descent of testis completed
104 27.5–34.3 cm Colour marks
144–152 47 cm (dependent on breed) Birth


Table 18-3: Chronological listing of developmental events in the pig in relation to stage of gestation (Days post coitum). Information accumulated from various sources. Open boxes represent lack of data







































































































Day Event
 1 Fertilization and pronucleus development
 2 Zygote to 2-cell embryo
 3 Arrival in the uterus, 2-, 4- or 8-cell embryo, major activation of the embryonic genome in 4-cell embryo
 4 8–16-cell embryo developing into morula
 5 Blastocyst
 6 Blastocyst
 7 Hatching from the zona pellucida
 8 Blastocyst around 1.2 mm
 9 Blastocyst 0.5–2.4 mm, embryonic disc forming
10 Blastocyst 2.3–10 mm, embryonic disc established
11 Elongation, 0.65–4.0 cm, embryonic disc with posterior crescent, maternal recognition of pregnancy by means of oestradiol
  Complete embryo (conceptus) Embryonic disc
12 Elongation, up to 6 cm Primitive streak, mesoderm and endoderm involution
13 Elongation Neural groove, first somite pairs
14–15 Elongation at a rate of 30–35 mm per hour 10–19 somite pairs, neural tube, first aortic arch
15–16 Elongation at a rate of 30–35 mm per hour 28–30 somite pairs, neural tube closed, second and third pharyngeal arch
17–18 Elongation, up to140–150 cm 36 somite pairs, closure of amnion, third, fourth, and sixth aortic arch, fore limb buds, C-shaped embryo, allantois anchor-shaped, otic placode, hind limb buds
  Size of the embryo proper/fetus (length or CRL; weight) Developmental event
20–21 14–19 mm, 0.5 g Eye pigmentation, nasal placode, physiological umbilical herniation, genital tubercles
22 11–13 mm, 0.5 g Completion of somite formation, mammary line, paddle-shaped fore and hind limb buds
28 21–25 mm Eylids, tactile hair follicles, differentiation of outer genital organs
34   Secondary palate fused
36 32.5–39 mm Eyelids cover eyes
44   Prepuce, scrotum, vulva, and clitoris formed
50 66–92 mm, 30.7 g Eyelids closed, gut returned to abdominal cavity
90 160–227 mm, 411 g Eyelids open
114–115 Size and weight dependent on breed Birth


Table 18-4: Chronological listing of developmental events in the horse in relation to stage of gestation (days after ovulation). Information accumulated from various sources. Open boxes represent lack of data



































































































































Day Event
 1 Fertilization and pronucleus development
 2 2–4-cell embryo
 3 8-cell embryo, major activation of the embryonic genome
 4 12–32-cell stage
 5 Morula
 6 Arrival to uterus, morula developing into blastocyst
 6–8 Blastocyst 250–780 µm, formation of capsule, hatching from zona pellucida
 9 Blastocyst 2.0–4.0 mm
10 Development of yolk sac
13 Blastocyst 6 mm
14 Blastocyst 16 mm
  Complete embryo (conceptus) Embryonic disc/embryo proper
16   Up to 4 somite pairs, neural groove
17–18   5–18 somite pairs, blastocyst ovoid, neural tube
18–19   13–22 somite pairs
20–21 Blastocyst 26–40 mm, loss of capsule 25 somite pairs, closure of amnion, first and second pharyngeal arch, optic vesicles, otic placodes, heart formation, yolk sac with sinus terminalis
  Size of the embryo proper/fetus (length or CRL) Developmental event
22 5.7–6.5 mm Second, third, fourth, and sixth aortic arches
23–24 5–6 mm C-shaped embryo, fore and hind limb buds, heart beat
25 7–8.5 mm Lens formation, otic vesicle
26   Eye pigmentation
28 9–9.5 mm Lens formation, cochlea and vestibulum, pulmonary arteries, complete enclosure of amnion by allantois
30 9–11.5 mm Genital tubercles
36 15 mm Complete conceptus about 75 mm ovoid structure, fusion of facial prominences
40 22–25 mm Placentation
45   Differentiation of outer genital organs
75   Prominent clitoris
80   Scrotum
112   Tactile hairs on lips
120   Fine hairs around mouth, eyes, and on cheek
150   Hairs on eyelids
180   Mane and tail hairs
270   Hairs on body
310–365   Birth


Table 18-5: Chronological listing of developmental events in the dog in relation to stage of gestation (Days post coitum). Information accumulated from various sources. Open boxes represent lack of data







































































































Day Event
 1–3 Completion of meiotic maturation, fertilization, pronucleus development
 4 2–8-cell embryo,
 5 16–32-cell embryo forming the morula, major activation of the embryonic genome in 8-cell embryo
 8 Arrival in the uterus, blastocyst 275–544 µm
11 Blastocyst 500–715 µm
13 Blastocyst up 0.22–1.14 mm
15 Blastocyst up to 0.53–2.0 mm, initial formation of swellings in uterus
  Size of the embryo proper/fetus (length or CRL) Developmental event
16 1.2–1.5 mm Neural groove, first somite pairs
17 1.3–2.0 mm, 8 somite pairs, placentation, neural tube, three brain vesicles, optic vesicle
18 2.3–5.0 mm 10 somite pairs, allantois starts to form
20   30 somite pairs, first and second pharyngeal arch
21   Amnion closed
22   C-shaped embryo, third pharyngeal arch, fore and hind limb buds
24 7.5 mm Genital tubercles
25 9–15 mm 49 somite pairs, fourth pharyngeal arch, external acoustic meatus
25–28   Paddle-shaped forelimb buds, eye pigmentation
29 19–21 mm Differentiation of male gonad
30–33 13–25 mm Eyelids, tactile hairs on lips, primordia of external genital organs, physiological umbilical herniation, secondary palate fused
35 21–24 mm Eyelids partially covering eyes, external male genital organs
36–38 29–38 mm Tactile hairs, regression of mesonephros
40 38–42 mm Eyelids closed, gut returned to abdominal cavity
43 53–57 mm Hair follicles on head, fore limb digits well separated
44–46 96–121 mm Hair on body, colour marking
52–54 124–158 mm Hair formation completed
62–63 (58–68) >160 mm Birth


Table 18-6: Chronological listing of developmental events in the cat in relation to stage of gestation (Days post coitum). Information accumulated from various sources. Open boxes represent lack of data











































































































Day Event
 2 Ovulation (induced by coitus)
 3 2–8-cell embryo,
 4 16-cell embryo
 5 24–40-cell embryo forming morula
 6 Arrival in the uterus, early blastocyst
10 Expanded blastocyst
12 Blastocyst up to 2 mm, hatching from the zona pellucida
  Size of the embryo proper/fetus (length or CRL) Developmental event
13 2 x 4 mm 5 somite pairs, initiation of placentation, neural plate
14 5.5 x 6 mm Up to 8 somite pairs, invasion into endometrium, optic vesicles, otic placodes, neural tube
15   20 somite pairs, first, second, and third pharyngeal arch
17 5–6.3 mm Fourth pharyngeal arch, otic vesicles, optic placodes
18 5–8 mm Forelimb buds, nasal placodes, lens formation
19 7–11 mm Hind limb buds
20 8–9 mm Paddle-shaped forelimb buds
21 10 mm Eye pigmentation, external auditory meatus, physiological umbilical herniation
22 10 mm Mammary lines, auricles
24 14–17 mm Eyelids, forelimb digits, tactile hair follicles on lips
26 20–22 mm Hind limb digits
27 20–22.5 mm All digits well separated, tongue, hair follicles on body
28–29 24–26 mm Eyelids closed
30 26–28 mm External auditory meatus covered by auricles
32 37–38 mm Secondary palate fused
37 55 mm Tactile hairs on head
46 Up to 100 mm Hair on body, pigmented nose
50 70–98 mm Colour marks
60–63 (58–65) >125 mm Birth


FURTHER READING



Rüsse I., Sinowatz F. Lehrbuch der Embryologie der Haustiere, 2nd edn. Berlin: Parey Buchverlag; 1998.

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Jul 18, 2016 | Posted by in PHARMACOLOGY, TOXICOLOGY & THERAPEUTICS | Comments Off on listing of developmental chronology

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