Oestrus cycles: species differences

Question 1

Describe the oestrus cycle of the rat

Answer 1

• 4 day cycle
• pro-oestrus - 1 day - increase in oestradiol induces GnRH and LH surge, increase in prolactin
• oestrus - 1 day - mated, ovulation occurs before end
• met-oestrus - 1 day - CL forms and progesterone increases
• di-oestrus - 1 day - progesterone peaks and declines, CL regresses

Question 2

Describe the oestrus cycle of the bitch

Answer 2

1. Pro-oestrus:

• 7-9 days
• rise in oestradiol from cohort follicles
• causes behaviour and signs of oestrus

1. Oestrus:

• 9 days
• follicles mature and luteinise, progesterone production, no oestradiol production
• behavioural oestrus
• end of oestrus immune cells invade endometrium

1. Metoestrus:

• 70 days
• slow decline in progesterone, rise in prolactin
• prolactin supports progesterone and CL function

1. Anoestrus:

• 2-4 months
• low level of hormones
• at end rise in LH & FSH readies for next follicular phase/cycle

Question 3

Describe the repro. cycle in the queen

Answer 3

• induced ovulator
• no luteal phase during normal cycle - ovulation only occurs when mated
• recurrent oestradiol rises associated with heat periods
• pseudopregnancy occurs if oocyte ovulated but not fertilised (CL maintained for 35 days)

Question 4

Describe the repro. cycle in the ewe

Answer 4

• seasonal short day breeders
• increasing day length in Spring gives timing for onset of next breeding season
• change in day length percieved by pineal gland - melatonin secreted in circadian rhythm during dark
• melatonin communicates with repro. axis via G-protein linked receptors

1. onset of breeding season:

• decrease in oestradiol - lifts -ve feedback on GnRH
• GnRH surge and LH secretion
• follicle growth but no oestrus, ovulation diretly followed by short luteal phase before next cycle

1. onset of non-breeding season:

• oestradiol has strong -ve feedback on hypo
• infrequent LH pulse, abscence of oestrus