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Heifer estrus cycle
| Question | Answer |
|---|---|
| What is progesterone abbreviated as? | P4 |
| What is estradiol abbreviated as? | E2 |
| What does GnRH stand for? | Gonadotropin repleasing hormone |
| Where does GnRH come from? | GnRH neurons |
| Gonadotroph | A cell that makes LH and FSH and secretes them into the blood |
| Endocrinology | The concept that hormones must pass through the blood to stimulate reactions in target organs |
| Puberty in heifers | First ovulation |
| Ovulation | The rapture of an ovarian follicle and release of a female gamete |
| Gamete | An egg or oocyte |
| Follicular wave | How follicles develop |
| Steps of a follicular wave in heifers | Recruitment, selection, dominance, artersia (sometimes) |
| Recruitment | A group of follicles initiate development |
| Selection | Not all follicles are needed to breed and most will die |
| Dominance | The best follicle that ovulates |
| Artersia | A dominant follicle that does not ovulate and dies |
| How long does a follicular wave take? | 7-10 days |
| Super ovulation | Put a cow on a ton of FSH to get a lot of ovulation |
| Prepubertal heifers | Development of follicles without ovulation |
| How does puberty happen in heifers? | The follicles get large enough to create enough E2 to trigger and LH surge |
| LH surge | Causes follicles to ovulate |
| What happens to a follicle when it has ovulated? | It ruptures and creates the corpus luteum |
| What is the best way to tell if a heifer is in heat? | If it stands still after being mounted |
| What are other ways to tell if heifers are in heat? | Restlessness, mounting behavior, mucous secretion from the vagina |
| How is estrus detected in heifers? | Tail patches, chalk or spray paint, activity collars |
| Tail patch | A scratchable patch on the cow's tail that rubs away after the cow has been mounted |
| Activity collars | Provide robust method to detect estrus ion farms through movement |
| Why might a heifer not reach puberty? | Is already pregnant, too small, or is a freemartin |
| Freemartin | A female calf born with a male twin |
| Why do freemartins happen? | Because twins share the same placenta, cells from the male migrate to the female and damage her ovary |
| How long is the estrus cycle in heifers? | 21 days |
| How does the estrus cycle begin? | The CL regresses |
| DF1 | Dominant follicle 1, develops in the first follicular wave and becomes atresic |
| DF2 | Dominant follicle 2, develops in the second follicular wave and ovulates |
| What stops ovulation? | If there is a CL on the ovary |
| How do follicles help ovulation happen? | Use estradiol to make uterus release PGF2a and regress CL |
| DeLaval system | Tracks reproduction of heifers by measuring progesterone in milk |
| What do spikes mean in the DeLaval system? | The cow is cycling |
| What does a plateau mean in the DeLaval system? | The cow is pregnant |
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