Gestation period | pregnancy length in different animals

Estimation of gestation length on the basis of fetus

Gestation period in animals can be assessed on basis of different parameters of fetus.
  • Pregnancy: Pregnancy period is the period from fertilization to parturition or birth of young and in this time the development of fetus in the uterus in female during this period simple cells derived and develop into highly organized individuals.

Beautiful cow


ANIMALSGestation length(Days)
  • Fetal Development:
    • The table below show the general finding of early development stage in the bovine embryo as well as comparing to other domestic species.
  • A historic general descriptive overview of fetal development :
1) First Month (20 Days):
  • The embryonic period, embryo is 9-10 mm long and sign of extremities appears.
2) Second month (30-60 days):
  • The extremities develop, the pregnancy cleft has in beginning of this month, the sternum still has a longitudinal tissue in middle closing toward the end of eight week at the ends of second months at the end of each extremity a letter terminal elevation which is colourless & transport, this first is indication of hoof, the length of fetus is 8 cm.
3) Third month (60-90 days):
  • Toward the end of this month, the fore stomach may recognize, the fetus measure 14 cm in length, the scrotum is present.
4) Fourth month (90-120):
  • In the beginning of the further hoof become quite distinct , they are firm non transport and have a yellow colour fetus is about 24cm long & weight up to 2 kg.
5) Fifth month (120-150)
  • In the beginning of month, appearance of lips, chin, upper eye lid & teat are planty invisible testicular into scrotum, fetus is about 35 cm long & weight 2-3 kg.
6) Sixth month (150-180 day):
  • The eyelid are more development of fetus, about 46 cm.
7) Seventh month (180-210 days):
  • At end this month fetal long hair appear at end of tail have about comet & sport where the horn appear fetus is about 60 cm long.
8) Eight month (210-240 days):
  • The back begin to be covered with hair about edges of ears length of fetus toward the 32nd wks 65 cm & toward end of this month.
9) Ninth month (240-270):
  • In beginning about body covered with hair and in cross greatly in size fetus is measure from 80-100 cm.
10) Tenth month (270-300 days)
  • Beginning this month fetus become mature.
  • Assesment of fetal age by Richerson method :
  • Richerson at (1970) has shown that long bone length convinently radius & fibula is reliable indicator of fetal age from 50 days gestation.
  • Richerson formulate for calculation the age has foetus from its crown anus length.
  • Pig x = 3(y+21)
  • Calf x=2.5(y+21)
  • Lamb x =2.1(y+17)
  • Where , x= development age in days
y= crown anus length in cm.
Measurement of fetus age:
  • There are certain measurement that can be made on fetus to determine age or growth rate of fetus.
Crown rump length (CRL)
  • It is measurement of length of embryos & foetus from top of head (crown) to bottom of buffalo’s rump.
  • It is typically determined from ultrasound imaging & can be used to estimate gestation age.
  • CR length provide a more reliable measure to estimate age of foetus.
Age of different animal at different CR length in BOVINE
Age  (days)CR Length (cm)Fetal weight 
3010.5 gm
6055.9 gm
901372.6 gm
1203083.1 gm
150383.81 kg
180569.51 kg
2107117.71 kg
2458128.6 kg
2808639.9 kg
Age of different animal at different CR length in OVINE & CAPRINE
Gestation  ageCR length
3 to 4 wks0.3 to 2 cm
5 to 6 wks2 to 9 cm
7 to 9 wks9 to 15.5 cm
10 to 13 wks15 to 35 cm
14 to 18 wks35 to 40 cm
19 to 21 wks40 to 48 cm
Age of different animal at different CR length in PORCINE
Fetal  Age (days)Length (mm)
 Age of different animal at different CR length in EQUINE
Age in daysFetus length (CR)
160.32 cm
250.6 to 0.85 cm
351.5 cm
503 to 3.5 cm
9010 to 14 cm
12015 to 20 cm
15025 to 37 cm
18037 to 60 cm
21055 to 70 cm
27080 to 90 cm
30070 to 130 cm
330100 to 150 cm
Gestational age :
  • It is week’s gestational age is not same as fertilization age.
  • It is takes about 14 days from the first day of last menstrual period for conception to take place and thus for the conceptus to form.
  • The age from this points in time (conception) is called the fertilization age is thus 2 week shorter than gestational age of pregnancy.
  • Gestational age = CRL(cm)+6.5
  • CVR Length: curved crown to rump length
  • VR Length : length of vertebrae column
  • VRT Length : vertebrae column to tail
  • BCVRT Length : total bent length of fetus.
i.e. from mouth to point of tail fetus length can also be measured by radiography or ultrasound technique.

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