Oestrous cycles

Question 1

Define Oestrus, Dioestrus, Anoestrus, Monoestrus, Polyoestrus and Induced Ovulatoes

Answer 1

Oestrus
• Regular periods of mating behaviour (Greek: erratic behaviour)

Dioestrus
• The period between oestrous cycles

Anoestrus
• Absence of oestrous cycles

Monoestrus
• a single oestrous period per season (bitch)

Polyoestrus
• several oestrous periods per season (lots of things)

Induced ovulators
• continuous oestrus until mating (rabbit, ferret)

Question 2

What causes Anoestrus?

Answer 2

Pre puberty - not yet cycling

Seasonal - out of breeding season

Pregnancy - high P4 levels ovveride cyclicity

Lactational - sensory input supress GnRH release

Stress - high cortisol levels suppress cyclicity

Pathology - anatomical or physiological abnormality

Question 3

What are the phases of the oestrus cycle?

Answer 3

Follicular phase - regression of CL to ovulation (20% of cycle)

Luteal phase - ovulation to regression of CL (80% of cycle)

Question 4

What is involved in the follicular phase?

Answer 4

• Follicles grow and mature
• incorporates proestrus and oestrus
• dominated by oestrogen which:
  - triggers LH surges
  - stimulates oestrus
  behaviour
  - prepares tract for
  sperm and ovum
  transport and fertilisation
• length of follicular phase variable within species
• longer the follicular phase, more variability between cycles and individuals

Hormones
- E2, LH & FSH

FSH acts on granulosa
LH acts on Theca

Question 5

How does follicular development occur?

Answer 5

random locations on the ovary (except in mare)

Corpora lutea may only be present at certain stages of the cycle

Genrally all types of follicles present at all times

Question 6

What is involved in follicular waves? (Follicles)

Answer 6

3 waves

1st wave - metestrus –> selected follicle becomes dominent but falls into atretic by start of diestrus

2nd wave - diestrus –> selected becomes dominant but turns atretic at time of proestrus

3rd wave - selected becomes dominant by time of estrus and leads to ovulation

Question 7

When is superovulation most effective?

Answer 7

female in luteal or early follicular phase

presence of dominant follicle can override FSH

Question 8

What are the characteristics of oestrus?

Answer 8

reddened vulva
open cervix
cornification of vaginal epithelium
cervical mucus thins and pH falls
vaginal lubrication
sperm transport
fertility
mating behaviour

Question 9

What is involved in the luteal phase?

Answer 9

CL is present
metoestrus and dioestrus
CL secretes P4 (essential for pregnancy maintenance)
at end of phase, CL regresses and P4 falls leading to new follicular phase

Question 10

how is the corpus luteum formed?

Answer 10

preovulatory follicle - grnulosa and theca cells merge as follicle starts to break down

corpus haemorrhagicun- small blood vessels rupture. follicle imploads and folds inward

functional CL - large luteal cells originally granulosa and small cells were theca

Question 11

WHat is luteolysis and what causes it?

Answer 11

Luteolysis = demise of CL

1. CL told to stay during pregnancy
2. CL infinite life and told to regress in absence of pregnancy

Question 12

How does the embryo signal its presence?

Answer 12

release of antiluteolysin

Question 13

How does embryo survive?

Answer 13

• occur in time to stop luteolysis
• must be in right place at right time
• reach uterus at right time for implantation to occur