Placenta Types, Teratoogy and Twins | Animal Husbandry & Veterinary Science Optional for UPSC PDF Download

Types of Placenta in Domestic Mammals

1. Deciduate Placenta:

   • Found in humans and primates.
   • The entire placenta, both fetal and maternal parts, is shed off after birth.

2. Indeciduate Placenta:

   • Seen in domestic animals.
   • The association between fetal and maternal parts is not as close, and the maternal endometrium is not shed.

Types of Indeciduate Placenta:

1. Cotyledonary:

   • Chorionic villi form projections called cotyledons.
   • Maternal and fetal cotyledons connect like a button, seen in ruminants.

2. Diffuse:

   • Chorionic villi are scattered all over the chorion.
   • Found in animals like the mare and sow.

3. Zonary:

   • Chorionic villi form a band above the middle of the chorionic sac.
   • Connected to the endometrium in a circular zone that is shed during birth, seen in carnivores.

Structural Differentiation of Placenta:

• Epitheliochorial:
  • Chorion rests on intact uterine epithelium (e.g., pigs).
• Syndesmochorial:
  • Varying amounts of uterine epithelium may be absent, bringing chorion into contact with uterine connective tissue (e.g., deer, cattle).
• Endotheliochorial:
  • No maternal connective tissue intervenes between maternal vessels and chorionic epithelium (e.g., dogs).
• Haemochorial:
  • Chorion is bathed in maternal blood (e.g., humans).
• Haemoendothelial:
  • Endothelium of fetal vessels is in direct contact with maternal blood (e.g., rabbits).

Stages in Prenatal Development:

1. Period of the Ovum (15 days):

   • Initial stage after fertilization.

2. Period of Embryo (Second to Eighth Week):

   • Critical developmental phase.

3. Period of Fetus (Eighth Week to End of Gestation):

   • Continued growth and maturation until birth.

Teratology

Teratology - Study of Abnormalities:

• Teratology is the science that studies abnormalities during development.

Causes of Faulty Development:

1. Intrinsic Factors (Hereditary):

   • Abnormalities passed down from parents through their germ cells (sperm and egg).
   • Hereditary transfer of genetic information can lead to developmental issues.

2. Extrinsic Factors (External Influences):

   • Abnormalities caused by external factors during pregnancy.
   • These can include physical trauma, violence, exposure to X-rays, and changes in environmental conditions like a decrease in oxygen.

Twins and Twinning

Types of Twins:

1. Identical Twins (True or Duplicate):

   • Result from a single fertilized egg.
   • Both individuals share the same chromosomal heritage.
   • Always of the same sex.
   • Strikingly similar in physical, mental, and other characteristics.

2. Fraternal Twins:

   • Result from independent ripening of multiple eggs after fertilization.
   • Have the same degree of family resemblance, like siblings of different ages.
   • Can be of the same or opposite sexes.

Examples in Animals:

• In animals like cows, identical twinning occurs.
• A condition called freemartin is observed in bovines, where a female fraternal twin of a male is sterile.
• Freemartinism is caused by shared blood circulation between the twins and the influence of male hormones.