PHYSIOLOGY - Resumption of Ovulation after Parturition

Question 1

In the cattle industry, how often should calving occur for maximum production efficiency?

Answer 1

The aim is to calve down every twelve months for maximum production efficiency

Question 2

In a healthy cow, what is the normal length of postpartum anoestrus?

Answer 2

Six weeks

Question 3

What occurs during postpartum anoestrus?

Answer 3

Postpartum anoestrus allows the uterus to involute and the endometrium to regenerate to ovulation and oestrus can be resumed

Question 4

When do cattle resume ovulation?

Answer 4

Cattle resumed ovulation during lactation

Question 5

When do mares resume ovulation?

Answer 5

Mares resume ovulation during lactation

Question 6

When do ewes resume ovulation?

Answer 6

Ewes resume ovulation after weaning

Question 7

When do sows resume ovulation?

Answer 7

Sows resume ovulation after weaning

Question 8

When do bitches resume ovulation?

Answer 8

Bitches resume ovulation after weaning

Question 9

What hormonal influences are required for the resumption of ovulation after parturition?

Answer 9

FSH needs to rise to stimulate cohort emergence, following by GnRH pulsatility to replenish LH stores and LH pulse frequency to allow for follicular oestrodiol production and the GnRH surge leading to ovulation

Question 10

Why do animals generally express signs of oestrus during the second ovulation after parturition?

Answer 10

Because before signs of oestrus can be expressed, behavioural centres must first be primed with progesterone which is produced during the short luteal phase after the first postpartum ovulation, and thus, signs of oestrus are not able to be expressed until the second postpartum ovulation

Question 11

What are the two main infleunces on LH pulsatility and thus the resumption of ovulation?

Answer 11

Metabolic status
Disease status

Question 12

What is the main influence on the postpartum metabolic status of dairy cattle and thus the resumption of ovulation?

Answer 12

Dairy cows are influenced by the postpartum negative energy balance induced by the onset of lactation and their slow appetite recovery and dry matter intake, ultimately leading to an energy deficit

Question 13

What is the term used for the lowest point in a postpartum energy deficit induced by the negative energy balance in dairy cattle?

Answer 13

Nadir

Question 14

How is the resumption of ovulation in dairy cattle influenced by a long period of nadir?

Answer 14

The longer the period of nadir, the more resumption of ovulation will be delayed due to the decreased LH pulsatility

Question 15

What are the main two influences on LH pulsatility and thus the postpartum resumption of ovulation in beef suckler cattle?

Answer 15

Body condition score at calving
Maternal bond

Question 16

At what body condition during calving will postpartum resumption of ovulation be delayed in beef sucker cattle?

Answer 16

Body condition less than 2.5 at calving will delay resumption of ovulation in beef sucker cattle

Question 17

How does the maternal bond in beef cattle influence the resumption of ovulation?

Answer 17

Maternal bonding leads to the inhibition of LH pulses, delaying the resumption of ovulation

Question 18

What are the main two influences on LH pulsatility and thus the postpartum resumption of ovulation in the sow?

Answer 18

Body condition score during lactation
Maternal bond

Question 19

Why are conception rates so low when horses are bred during ‘foal heat’

Answer 19

Conception rates are so low when horses are bred during ‘foal heat’ because the uterus hasn’t had a chance to fully involute and the endometrium hasn’t had time to fully regenerate

Question 20

What treatment can be used to delay ‘foal heat’ in the mare and thus increase conception rates?

Answer 20

Progestagen treatment for 14 days will reduce LH pulsatility, delaying foal heat for 14 days to allow the endometrium to regenerate and the uterus to involute

Question 21

What are the three methods that be used to advance postpartum ovulation and oestrus in cattle?

Answer 21

Breaking the maternal bond
Restricting suckling
Hormone treatments

Question 22

What are the two methods of hormone treatments used to advance postpartum ovulation and oestrus in cattle?

Answer 22

• GnRH injection at the start of progesterone treatment
• Equine chorionic gonadotropin (eCG) at the end of progesterone treatment

Question 23

Why are progesterone treatments (progesterone devices) often used in combination with GnRH and eCG hormone treatments?

Answer 23

Progesterone devices synchronise oestrus within the herd and prime the behavioural centres to the cattle will express heat allowing for more efficient breeding and artificial insemination