Resumption of ovarian activity Flashcards
Describe the strategies used to advance/ delay puberty in domestic animals
- Nutrition: used in lambs/ heifers, high plane of nutrition causes early puberty and vice versa
- Hybrid vigour: in heifers cross breeding decreases age of puberty
- Photoperiod: ewes
What are the controlling factors of seasonality?
- Photoperiod
- Melatonin: direct influence on HPO axis
Give examples of how seasonality can be manipulated both physically and artificially
- Physical: shuttle stallion from northern to southern hemisphere
- Artificial: put mares under lights at Christmas
What can be used in sheep to help bring about oestrus more quickly?
-Melatonin: if given for a sustained length of time it makes oestrus occur faster.
What are the different periods for ovarian rebound to occur in different species?
Dog= 135 days
Horse=5-12 days
Cow= beef=50-60, dairy= 18-25
Sheep= 180 days
Describe anoestrus during gestation
- Presence of prolonged, high progesterone levels causes HPO axis to be suppressed. Resulting in decreased GnRH, low FSH and LH, fewer follicular waves and no ovulation.
- Parturition causes a decline in progesterone and transient increase in oestrogens.
Describe anoestrus Post partum
- Uterine involution occurs
- Lactation and suckling
- Ovarian inactivity: period of low P4 and low E2
Describe the mechanism of ovarian rebound
- HPO axis has to reinitiate: Pituitary gland has period of unsensitivity to GnRH, low E2 and P4 means FSH isn’t inhibited so is high. Follicle wave stimulated by FSH.
- Full ovarian activity increases by increased sensitivity to GnRH. Larger follicles means E2 increases. Increased pulses of LH activity, often have a silent oestrus. Shorter oestrus cycle
Which factors can cause an extended anoestrus?
- Lactation/ suckling: prolactin (prevents pregnancy before weaning), mammary stimulation / suckling suppresses GnRH. Presence of offspring
- Seasons e.g. melatonin in the ewe
Describe ovarian rebound in the mare
- Rapid onset- 5 to 6 days PP
- “foal heat”
- Pregnancy can be established but fertility is decreased
- Can be delayed due to season/ ‘foal shy’
In which species does weaning have a big impact on ovarian rebound?
- Pigs
- Prolactin suppresses LH, and weaning initiates LH surge within 7 days
What are the influences of ovarian rebound?
- Suckling: prolactin/ presence of offspring and ACTH/ corticosteroids
- Peri-parturient abnormalities: retained fetal membranes and endometritis
- Milk yield/ nutrition: BCS, neg energy balance
Describe the impact of a negative energy balance on a dairy cow
-Results in decreased GnRH secretion–> decreased LH secretion –> poor follicle growth/ oestradiol production –> poor oestrus and inadequate LH surge
What are the impacts of abnormal ovarian rebound?
- Delayed onset of cylclicity
- Cessation of ovarian activity
- Ovarian pathologies (follicular/ luteal cysts and persistent CL)
