Bovine oesturs cycle

What hormones are involves in the control of reproduction in cows?

At what stage is this ovary?

Coming towards oestrus

What does the ovary look like after ovulation?

• Active ovary lost its structures & smaller

• Both ovaries small

• Follicle becomes corpus haemorrhagicum (bottom image)

Several days after oestrus what does the ovary look like?

Protruding head of CL

Explain follicular development in cows

• When follicles becomes responsive to LH & FSH they grow

• When they become dependent one becomes dominant

How long is follicle growth? How is this relevant to fertility?

3 months —> pre antral

• If there is poor fertility in post calving period look over last 3 months because of pre antral follicle growth & also take it to a herd level

In terms of the follicle what can directly influence oestradiol?

• Size of dominant follicle

• yellow = follicles undergoing atresia

• follicular wave q. 7d depending on LH —> affected by stress etc.

• dom follicle undergoes atresia if progesterone remains high

When will prostaglandin work on the CL?

• Prostaglandin only works on CL if >2cm, usually 6 days after ovulation

What are the features of each stage of the oestrus cycle?

• Oestrus —> dominant follicle presence varied

  • Very toned uterus, bulling slime, behavioural signs

• Metoestrus —> follicle gone, ovary small, CH grows becomes CL and then begins to produce progesterone

  • Blood on vaginal exam, metoestral bleed, uterus toned

• Dioestrus —> CL continues to produce progesterone

  • Waves of follicles and they become atresic bc of progesterone

• Proestrus —> CL stops producing progesterone, LH and FSH cause follicle dominance

  • May still be palpable follicle but CL will be big as well

How do FSH, LH, & progesterone vary in the cycle?

• FSH —> Peaks to help form dominant follicle

progesterone falls, LH surge (& vice versa)

How many follicular waves are there usually?

2 for high yielding cows (3 for heifers)

When would you see an anovulatory period?

• Suckling beef

• Cows in negative energy balance/ dx

How does a dairy cow start cycling post partum?

• Usually have first ovulation within a few days but follicle not exposed to progesterone so not a 'good ovulation' then start to ovulate

Compare reproductive parameters in the early postpartum period of dairy, and beef cows (suckling calves)

What is the success of AI dependent on?

• Use of proven / fertile sires

  • higher genetic merit when AI used

• Reliable oestrus detection

What are the optimum timing of AI in relation to oestrus events?

AM:PM rule (serve 11-12hrs after onset of oestrus)

• See oestrus in AM -> serve in PM

• See oestrus in PM -> serve in AM

worse to be late serving animal vs early —> can serve a second time if early

How long is the average oestrus in a cow?

18 hours but actually best time to inseminate probably shorter

What are the behavioural signs of oestrus

• Sniffing of vulva (to get pheromones from other cow & to see if other cow in oestrus)

  • 100% of cows do this when in oestrus

• Chin resting on another cow in oestrus (both cows in oestrus)

  • 100% of cows do this when in oestrus

• Licking

• Head butting

• Mounting head to head (the one mounting is in oestrus)

• Standing to be mounted

• Wrinkling of upper lip (flehman response —> sucking air into vomeronasal organ)

  

How does the number of cows in a group affect oestrus duration?

The more animals in a group in oestrus at one time, the longer the oestrus period.

What can you use as aids to detect oestrus?

• Paint / chalk or Kamar/Ambic as mount detectors

  • kamar —> blister pack containing capsule of red dye → burst when brisket of cow mounting → colour change from white to red

  • ambic —> scratchcard —> silver rubbed off by cow mounting to reveal bright colour

• Cow detected only when stand to be mounted —> at least 2 cows in/near oestrus (not all animals show standing heat)

• Record keeping —> any cows 18-24d after last oestrus = watch them (start looking 18d after last oestrus)

• Teaser animals

• Chinballs

• Milk progesterone (low level = not in oestrus)

• Activity meters (a lot better when combined with other methods) —> leg, neck, ear

  • can measure mobility, lying, rumination etc. depending on location of tag

  • higher activity ass. with higher conception rate

How does rumination change during oestrus?

Rumination tends to go down @ oestrus

green line = oestrus

brown line = rumination

How long is the sperm production cycle?

2 months —> ask hx

Describe these sperm

Stained to show live or dead, acrosomes & tail abnormalities present

Where do you aim for with the AI straw?

Into body of uterus or up one horn if you know which one follicle is on

What should you consider if pregnancy rates reduced with AI?

• Has flask become empty and sperm thawed then refrozen?

• Have they used fingers rather than tweezers

• Thaw @ 37 deg. for 40 seconds

• Dry thoroughly

• Load gun, snip off end of straw

• Disposable sheath

• Keep warm

• Chilling once thawed bad!

• Thaw one at a time!

Where does fertilisation occur?

In oviduct

How can progesterone from CL affect the embryos if not enough / not good enough quality ?

• Small embryos (because stimulates embryo growth)

embryo must grow enough to make body aware it is there —> stop oxytocin receptors to stimulate release of prostaglandin → stop luteolysis otherwise cow starts cycling again

Describe luteolysis vs maternal recognition of pregnancy

• Either pregnancy —> maternal recognition of pregnancy

• OR Prostaglandin released which is stimulated by progesterone & oxytocin → luteolysis

Describe placentomes in a cow

Fixed location (same as in sheep)

(fetal cotyledons, maternal caruncle)

(cf diffuse in horse)

What maintains pregnancy in cattle?

CL dependent

What initiates calving physiologically?

Control is by calf