Applied reproductive endocrinology in LA

Question 1

How can you intervene to affect frequency of LH? 2

Answer 1

Environment/external signals: visual/olfactory

Internal signals

Question 2

Why might you get anoestrous? 4

Answer 2

season
lactation
postpartum
pre-pubertal

Question 3

What effect does E2 have?

Answer 3

negative feedback on pulsatile LH

Question 4

How do you treat anovulatory anoestrous/acyclicity in cows?

Answer 4

Make sure it is ‘true’ anoestrous
Correct underlying factors first (NEB, maternal bond, disease)
PRID/CIDR for 12 days OR PRID/CIDR for 12 days + 500iu eCG on day of removal

Question 5

How do you treat anovulatory anoestrous/acyclicity in cows?

Answer 5

P4 sponge + PMSG/eCG (500 iu) on day of P4 sponge removal

Question 6

How can photoperiod be manipulated (ewes)?

Answer 6

Melatonin implants: Regulin or Melovine. Placed under skin of ear. Breed 30-60 days later.

16 hours darkness and 8 hours light (less practical)

Question 7

What are the pre-conditions to the ram effect? 2

Effect?

Answer 7

• Isolation (sound, sight, smell, 4 weeks)
• Preception of male by females (visual, physical, pheromones)

RESULT: increased LH pulse frequency

Question 8

What is the luteal function in GnRH-treated seasonally anoestrous ewe with or without P4 priming?

Answer 8

2/3 animals have a defective CL if not primed.

Question 9

How can you induce puberty in gilts?

Answer 9

PG600 (PMSG + hCG) IM

No increase in FSH or LH by PMSG/eCG or hCG.

Question 10

What can be controlled to synchronise oestrous? 2

Answer 10

control of luteal phase and/or follicular growth

Question 11

Outline process of luteolysis in the cow.

Answer 11

P4 (CL) stimulates production of uterine PGF2a after d15 in cow –> PGF2a synthesis by uterine endometrium is released into uterine vein –> delivered back t ovary where it causes lysis of the CL

Question 12

How many follicles are there on a cow’s ovary at any one time?

Answer 12

usually 1 dominant, most follicles are atretic though

Question 13

How can you synchronise oestrous/ovulation?

Answer 13

PGF2a - control/shorten luteal phase

OVSYNCH: follicle wave synchrony + PGF2a, follicle wave synchrony with GnRH + control (shortening of luteal phase)

EXOGENOUS PROGESTERONE (PRID/CIDR) and PGF2a: follucle wave synchrony with P4 and control (extend) luteal phase

Question 14

When does P4 decline after giving PGF2a?

Answer 14

Rapid decline of P4 and oestrous 3-5 (range 2-7) days later.

Synchrony not sufficient to avoid heat detection following single injection.

Pregnancy rates acceptable

Question 15

What might be reasons for poor synchrony with PGF2a?

Answer 15

LUTEOLYSIS FAILURE:
non-responsive CL - luteolytic from day 6 of oestrous cycle (i.e. treatment too early in luteal phase)
incorrect injection technique

TIMING DEPENDENT ON FOLLICULAR WAVE STAGE

Question 16

How can PGF2a problems be overcome?

Answer 16

Diagnose CL, inject, observe
OR
2 doses PGF2a, 11 days apart to ensure responsive CL is present + fixed time AI [either 2 doses + FTAI at 72 and 96 hours (2+2 method) OR 2 doses + FTAI at 85 hours (2+1 method)

Question 17

Outline the ovsynch programme

Answer 17

GnRH - day 0 - synchronise new wave emergence
day 7 - PGF - cause luteolysis
day 9 - GnRH - control time of ovulation (by controlling LH surge in all animals)
day 10 - AI

Question 18

What signal from the foetus maintains pregnancy in a.) ruminants b.) pigs?

Answer 18

Ruminants = IFNt
Pigs = oestrogens

Question 19

For how long after insemmination is it hard to differentiate between pregnant and cycling by P4 levels?

Answer 19

Days 0-6 after insemmination, after that it is easier to tell if pregnant or cyclic

Question 20

When should P4 be supplemented during pregnancy?

Answer 20

Within first 6 days (i.e. first 6 days after insemmination)

Question 21

How do you treat luteal deficiency/ poor maternal recognition of pregnancy?

Answer 21

P4 supplementation
OR
GnRH day 11 (cows) or 9 (ewes)

Question 22

Why does COD occur?

Contributing factors?

Answer 22

defect in the ovulatory mechanism due to failure of the pre-ovulatory LH surge.

Contributing factors:
stress
lower oestradiol concentrations
lower hypothalamic sensitivity to oestradiol
uterine infection 
NEB

Question 23

How to treat cysts:
LUTEAL
FOLLICULAR
OTHER

Answer 23

LUTEAL - PGF2a - in heat after 3-4 days?

FOLLICULAR - not manual rupture, GnRH or hCG - luteinises cyst or other follicles?

OTHERS: pyometra (persistent CL), pseudopregnancy in goats (persistent CL)> Treatment of both is with PGF2a

Question 24

What initiates parturition in cows, sheep, goats and sows?

Answer 24

Foetus (all 4 species)

Question 25

What does increased PGF2a at parturition cause?

Answer 25

CL regression cervical softening increased myometrial contraction

Question 26

Which 3 enzymes does foetal cortisol raise in the mother?

Answer 26

17a hydroxylase (P4 --> 17a- hydroxyprogesterone) C17-20 lyase (17a- hydroxyprogesterone --> androstenodione) aromatase (androstenedione --> oestrogens)

Question 27

How can you increase ovulation rate? 2

Answer 27

Increase in follicular recruitment OR decrease in atresia

Question 28

What can you use to superovulate the donor?

Answer 28

``` recombinant FSH pFSH oFSH eCG (PMSG) Porcine pituitary extract (purified) ``` BUT there is variability in the superovulatory response (variation in ovulatory rate and recovery of viable embryos)

Question 29

What does flushing do?

Answer 29

Increases follicular recruitment since high energy intake lowers oestradiol concentrations and promotes FSH release

Question 30

How can you immunologically control reproduction? 2

Answer 30

immunisation against androstenedione | immunisation against GnRG

Question 31

Why immunise against androstenedione? | Examples? 3

Answer 31

removes negative feedback on hypothalamus and pituitary EXAMPLES: A commercial product (Fecundin, Glaxo) uses a dextran adjuvant. Single injection. Increases ovulation rate in ewe. Androvax Plus (Intervet) Ovastim (Virbac)

Question 32

What does immunising against GnRH do?

Answer 32

inhibits production of gonadotrophins and gonadal steroids reduces testicular size and function practised to control aggression and to reduce male-associated odours

Question 33

What are examples of vaccines against GnRH? 3

Answer 33

Vaxstrate - cattle Equity - horses (Pfizer) IMPROVAC - controls Boar Taint SpayVac - different species including wild animals