The oestrus cycle and seasonality

Question 1

Describe what is meant by seasonality

Answer 1

The pattern of oestrus cycles throughout the year

Question 2

Give examples of seasonal polyoestrus animals

Answer 2

Long day (spring)= mare
Short day( ewe)= autumn

Question 3

How is seasonality controlled?

Answer 3

By light- this is detected by the pineal gland which activates the brain centre leading to release of FSH/ LH which activated development of follicles and secretion of oestrogen/ progesterone which in turn influences behaviour (receptivity)

Question 4

Describe the oestrus cycle

Answer 4

Waves of follicles develop until usually one becomes dominate and then ovulates. The corpus luteum is formed.

• When the corpus luteum regresses another dominant luteum
• Follicles can form/ regress under presence of high progesterone but they don’t mature/ ovulate successfully.

Question 5

Describe the behaviour of a female during oestrus and dioestrus

Answer 5

Oestrus: lordosis- receptive to male and has high oestrogen
Dioestrus: rejects male and has high levels of progesterone

Question 6

How does progesterone effect the female?

Answer 6

• High during the luteal phase
• Increases secretions by glands of uterine endometrium
• Gland secretions contain nutrients for fertilised oocyte
• Closes the cervix
• Prepares uterus for zygote
• Behavioural changes: reject males

Question 7

What does FSH do?

Answer 7

Stimulate maturation or germ cells (causes follicles to form)

Question 8

What does LH do?

Answer 8

Stimulates production/ secretion of steroid (testosterone, oestrogen, progesterone)

Question 9

What stimulates ovulation?

Answer 9

Surge of LH

Question 10

Briefly summarise the oestrus cycle

Answer 10

Elevated oestradiol and FSH leads to follicular development and exhibition of oestrus behaviour. A surge of LH stimulates ovulation. CL secretes progesterone and cycle enters luteal phase, female behaviour changes to reject males.
At the end of diestrus, if female is not pregnant the CL is lysed by PGF2a causing progesterone levels to decrease. If the female is pregnant the cenceptus releases a factor which prevents lysis from occurring hence high concentration of progesterone is maintained in order to keep the cervix closed and pregnancy to develop.

Question 11

What are the ovarian phases of the oestrus cycle?

Answer 11

Luteal and follicular

Question 12

Describe the oestrus cycle of the mare

Answer 12

-Seasonally polyoestrus
-Long day breeder
Oestrus: 6 days
Dioestrus: 15 days
Cycle length= 21-23 days

Question 13

Describe the oestrus cycle of the cow

Answer 13

• Polyoestrus
• Oestrus: 8 hours
• Dioestrus: 19-20 days
• Cycle length: 18-24 days
• Ovulation: 12 hours after the end of oestrus

Question 14

Describe the oestrus cycle of the ewe

Answer 14

• Seasonal polyoestrus
• Short day breeder
• Oestrus: 15-16 days
• Diestrus: 15-16 days
• Cycle length: 17 days
• Ovlation: towards the end of oestrus

Question 15

Describe the oestrus cycle of the pig

Answer 15

• Polyoestrus
• Oestrus: 53 hours (2 days)
• Dioestrus: 19 days
• Total cycle length: 21 days
• Ovulation: 35-45 hours after the start of oestrus

Question 16

Describe the oestrus cycle of the nanny goat

Answer 16

• Seasonal polyoestrus
• Short day breeder
• Oestrus: 30-40 hours
• Dioestrus: 20-21 days
• Cycle length: 21-22 days
• Ovulation: 12-36 hours after onset of oestrus

Question 17

Describe the oestrus cycle of the bitch

Answer 17

• Monoestrus
• Pro oestrus: 9 days
• Oestrus: 9 days
• Ovulation: 1-2 days after onset of oestrus
• Anoestrus= 3 months
• Interoestrus: 7 months

Question 18

Describe the oestrus cycle of the queen

Answer 18

• Seasonal polyoestrus
• Oestrus: 7-10 days
• Dioestrus: 10-14 days
• Cycle length: 21 days
• Ovulation: induced ovulator