Why lighting regimes?
Horses are long day breeders - induces ovulation
How does the light regime work in regards to hormones
Longer day simulations decreases melatonin levels.
This induces higher GnRH secretion.
Stimulates FSH and LH secretion that induces oestrus cycle in horses earlier than normal time
How does the lighting regime work
Turn on lights 30 mins before sunset and increase light to 16 hours a day
Effect takes 60-90 days
What is included in the stud fee
Vet services
Pregnancy checks
Breeding
What is not included in the stud fee
Transport
Livery
What is a group 2 race
Second division of horse racing
Why would a mare not be served at first oestrus event
Risk of foal being born late December - want it to be born close to 1st January so can be as old as possible in racing group
Better chance of conception second time
Why use prostaglandin
Causes luteolysis to progress cycle by shortening lute all phase and prevent pregnancy until a more suitable time
Why use hCG
To mimic LH to induce ovulation when pregnancy wanted
Why would a mare be served twice
To ensure pregnancy
Ovulation occurs before end of oestrus and length of oestrus varies so serving twice allows a greater chance for viable sperm to fertilise.
How can you ensure that the mare is mated at the right time with regard to ovulation
Ultrasound follicular monitoring - transrectal
Hormone assays
Comparative species how to ensure correct time to mate
Cattle AM/PM rule
Bitch - vaginal cytology, progesterone levels rise towards oestrus
Camelids - induced ovulators, spitting off good indication one week later after ovulation (not receptive to male)
Why is ultrasound scanning for pregnancy carried out multiple times
Day 11 = earliest diagnosis
Day 14 - 16 = check for twin pregnancy
Day 24 = heartbeat check
What other methods of PD checks are there
Manual palpation from day 20
Blood endocrinology - eCG levels from day 40
Transrectal ultrasound
What happens if there is twin follicles found in the mare
- Two mature follicles means there is a chance of twins if 2 eggs are released. Horses with twins most likely to abort one or both foetuses – so important to monitor.
Issues of twin pregnancy in mare and how can you manage this
- Mares with unicornual twins typically abort one.
- Mares with bicornual twins typically abort both.
- Horses are physiologically incapable of having twins. In the case that twins are conceived, there would be too little space in the uterus to allow both to be stable and grow. If one of the twins is larger or is growing more than the other, since there is a diffuse placenta and it doesn’t get enough nutrients, it will die off. The death releases chemicals and toxins into the uterus which triggers abortion resulting in both foetuses dying.
When to confirm pregnancy in cow
Day 28-30
Why may a mare be thought to be in oestrus after pregnancy has been confirmed?
- Secondary follicular wave even when pregnant
- Hormonal abnormality
- Early embryonic death (lost pregnancy so back in oestrus)
- Behavioural oestrus
Are night time births common in mare
- Yes, often late at night or early in morning, due to being a prey animal, so feeling safest then. (around 80%)
Pros and cons of foaling at home v stud
- Stud:
- Pros: experts on scene to deal with complications, onsite vets.
- Cons: High costs, and stress of transport there, contact with other horses so risk of disease transmission?
- Home:
- Pros: reduced stress as mare in a more familiar place, usual familiar vet, cheaper.
- Cons: may not have a vet on hand when needed
What hormonal changes take place as parturition approaches
- Foetus initiates stage 1 of parturition as it gets too big for the uterus, so it becomes stressed – increases foetal ACTH hence foetal cortisol
- Causes progesterone to decrease and prostaglandin & oestrodial to increase
- Prostaglandin causes relaxin to be synthesised
- Oestradiol also produced
- This results in stronger myometrial contraction which initiates the start of parturition with a positive feedback mechanism until foetus is birthed (neuroendocrine Ferguson’s reflex and spinal reflex).
What is different in mares compared other species with regard to hormones towards end of pregnancy
Progesterone increases
Oestrogen decreases
Stages of parturition
Stage 1 = initiation of myometrial contractions and dilation of the cervix.
Stage 2 = expulsion of foetus, foal should be delivered after 30 minutes of the water breaking.
Stage 3 = expulsion of foetal membranes.
Zinc sulphate test
- Tests the quality of colostrum in the mare.
- Tests to see if the newborn foal has absorbed sufficient antibodies.
- Important to prevent infection in foal, tests if they have achieved successful passive transfer of antibodies.
