Learning Reproduction in Farm Animals

08-Early Embryonic Development and Placentation

Leaning Objectives:

Time comparisons from ovulation during cleavage for different farm species.
1 cell 8 Cell  Blastocyst  Enter Uterus  Length of
Species (hours) (Days) Gestation 
Cattle 24  3.5  281
Horse 24 3 6 5 337
Sheep 24 2.5 7 3 148
Swine 14-16 2 6 2 114
  Certain organs that have been identified as forming from specific germ layers.
Germ Layer Organs
Ectoderm 1. Central nervous system 
2. Sense organs 
3. Mammary glands 
4. Sweat glands 
5. Skin 
6. Hair 
7. Hooves
Mesoderm 1. Circulatory system 
2. Skeletal system 
3. Muscle
4. Reproductive systems 
(male and female) 
5. Kidney 
6. Urinary ducts 
Endoderm 1. Digestive system 
2. Liver 
3. Lungs 
4. Pancreas 
5. Thyroid gland 
6. Most other glands 
7. Primordial germ cells

Function of Fetal Membranes and Fluids
Yolk sac: Early nutrient supply for early embryo.
Amnion: Protects fetus from injury, provides lubrication for parturition, reservoir for urine and wastes. 
Allantois: Fuses with chorion (chorio-allantoic placenta), carries blood vessels of placenta, reservoir for nutrients and wastes. Umbilical cord attaches fetus to allantois.
Chorion: Attaches to uterus, absorbs nutrients from uterus, allows maternal/fetal gas exchange, Produces hormones. 

Attachment of the placenta to the uterus. (Implantation)
Cow  Sow Ewe Mare
Days 30-35  12-20  18-20 50-60 

Types of Implantation.

     B. Interstitial - Embryo invades endometrium and develops in endometrium.


Maternal Recognition of Pregnancy

Establishment of Pregnancy Sow Mare Cow Ewe
Days of Estrous Cycle        
Embryonic Signal        


 Placental lactogens (Protein Hormones)

Types of placental attachments



High surface area at placental-uterine attachment.

Fetal Nutrition (Farm Animals)

Hormonal Control of Gestation

Sources of Progesterone During Gestation

Sheep  CL to day 50 then placenta  148 days
Cow CL throughout gestation. However, after ~ day 215 placenta 
and adrenal are producing enough progesterone to maintain pregnancy. 
280 days
Sow All from CL  114 days
Mare 1st CL produces progesterone up to ~ 180 days, FSH stimulates follicle 
growth and eCG causes CL's to form from follicles. They secrete 
progesterone and are active from day 40-180. Progesterone is low until 270 days- rises in last 5 months due probably to placental progesterone production. 
337 days 

 Mare Hormone Levels During Pregnancy

Illustrated Notes

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