Placentation in Small Ruminants

Question 1

describe key structures of the ruminant reproductive tract and placenta

Answer 1

1. cervix has 5-6 rings
2. broad ligament holds tract in place and provides blood supply
3. ovaries: in goats, the maintenance of pregnancy remains dependent on the CL throughout gestation!! lutectomy will result is loss of pregnancy!
4. uterus: holds baby

Question 2

describe key structures of the ruminant placenta (4)

Answer 2

1. chorioallantois:
   chorion touches maternal endometrium, allantois contacts fetus
2. amnion: fluid sac immediately surrounding fetus
3. umbilical cord: blood supply
4. placentomes: fetal portion are cotyledons, maternal portion are caruncles

Question 3

describe the main placental functions (3) and key hormones (4) produced during pregnancy

Answer 3

functions:
1. provides nutrients to developing fetus via diffusion of nutrients from maternal blood into fetal blood
2. eliminates waste from fetus via diffusion of waste products from fetus back to dam
3. produces hormones (a transient endocrine organ)

hormones:
1. chorionic gonadotropin (horses and primates only)
2. progesterone
3. estrogen
4. chorionic somatomammotropin

Question 4

describe how fetal health is determined (5)

Answer 4

1. fetal heart rate: stress decreases
2. fetal fluid echogenicity: the more echogenic, the more cause for concern
3. fetal movement
4. placental appearance
5. dam health

Question 5

describe methods to estimate month of gestation (7)

Answer 5

1. fetal heartbeat (visible by d25-35)
2. crown-rump length
3. fetal ossification
4. biparietal diameter, thoracic diameter, +/- aortic diameter
5. appearance of organs (motile intestines develop latest)
6. placentomes (visible by day38)
7. heart rate (declines later in gestation as stress increases)
8. mammary development and colostrum production (watch for false early in dairy breeds with giant knockers)

Question 6

describe BNCs

Answer 6

bi-nucleate trophoblastic cells form the foundation of placental cotyledons and express placenta-specific genes like pregnancy-associated glycoproteins and placental lactogens