Intro to Equine Pregnancy & Parturition Flashcards
how long is the mare estrous cycle
21-22d cycle
how many follicular waves are in the mare estrous cycle
1-4 waves per cycle
how long is the luteal phase in the mare
14d
how long is estrus
5-6d
when does ovulation occur
24-48hrs before the end of estrus
when does LH production peak and why
LH during estrus phase which is what supports the dominant follicle
LH peaks after ovulation –> different to the cow
Causes extremely rapid luteinization of the follicle wall (much quicker than cow)
what are the external characteristics of estrus
Favourable response to stallion
Clitoral ‘winking’ and frequent urination
what is seen on US during estrus
Large follicle(s) +/- soft
Follicle may be pointing near ovulation
No corpus luteum
what is the appearance of the cervix during estrus
Short, wide and relaxed
Pink and drooping
Lumen open
what are the external characteristics in diestrus
Switch tail, kick, squeal
Attempt to bite/avoid stallion
what are the ovarian characteristics during diestrus
Corpus lute
Follicles variable in size
what is the appearance of the cervix during diestrus
Long, narrow and firm
Pale and dry
Closed lumen
what is readiness for serving based on
External signs of estrus
Ultrasound and palpation
- Uterus and cervix:
- Closed and relaxed
- Edematous —> cartwheel appearance
- Follicle size and softness
- Most 40-45mm in diameter before ovulation w
when is the timing of breeding
Max pregnancy rates when breed from 48hrs before to 6 hours after ovulation
how can ovulation be induced hormonally
Human chorionic gonadotrophin (hCG)
- Hastens ovulation in cycling mares
- Has luteinizing hormone (LH) activity
- Follicle > 35mm ovulation within 48hrs of injection
Gonadotrophin releasing hormone (GnRH; deslorelin)
- When follicles > 30mm induces ovulation within 48hrs of introduction of a subcutaneous implant
- Stimulates release of FSH and LH from anterior pituitary gland
how is estrus synchronized in the mare
Progestogens/progesterone (regumate):
- Administered for 14d
- Estrus 4-7d after treatment
- Ovulation occurs 7-12d after treatment
Prostaglandin F2a:
- Mares with a mature CL — shortens luteal phase
- Estrus 2-4d after injection
- Ovulation occurs 7-12d after injection
what day does the embryo implant
day 16
what is the gestation length
330-345 days
Average 335 days
what day is fetal loss considered abortion
Abortion = before 300d
what day is the foal considered premature
300-320d
what type of placenta does the mare have
Diffuse, epitheliochorial
The entire surface of the chorioallantois is in contact with the endometrium, apart from a small area over the cervix (cervical star) where it will rupture at parturition
what is the appearance of the placenta that is in contact with the endometrium
Velvety, ‘villi’ surface of the chorioallantois that is in contact with the endometrium
how is the pregnancy maintained in the first 5 months
Maintained for the first 5 months of gestation via progesterone produced by the primary corpus luteum and supplementary corpora lutea
- Initially pregnancy is maintained solely via progesterone released by primary CL associated with the original ovulation
From around day 40 equine chorionic gonadotrophin (eCG) released by the endometrial cups assist (along with pituitary gland hormones) in the formation of supplementary of corpora lutea
eCG may also help maintain the primary corpus luteum
what takes over maintenance of pregnancy after the first 5 months
There is then a transition period during which pregnancy maintenance by ovarian progesterone transfers to placental progestogens:
- From around 1-2 months of pregnancy the fetoplacental unit produces progestogens (pregnanes) in increasing concentrations, peaking at 10 months of gestation
- These concentrations are sufficient to maintain pregnancy from mid to late gestation
what are the nutritional requirements of the pregnant mare
Similar to maintenance for the first 8 months but there will be a need to gradual increase in nutrition in the last 3 months as 65% of fetal growth occurs in this period
Avoid overfeeding
what vaccines should the pregnant mare recieve
Tetanus vaccination (also influenza) 4-6 weeks before parturition
Boost immunity that will be transferred to the foal
If EHV-1 risk abortion, vaccination protocol for this disease
Given during the 5th, 7th and 9th month of pregnancy
what anthelmnitic control should the mare recieve
Normal parasite monitoring/control should continue, such as FWEC and anthelmintics used if required (generally not in last month of gestation)
which parasite can transfer to the foal via the milk
strongyloides westeri
why is deworming the mare not 100% protection to the foal
Deworming mares in late stages of pregnancy will not prevent infection, as foals are just as likely to acquire from the environment
Foals are asymptomatic and develop immunity by 5 months, patent infections are only seen in foals less than this age
Symptomatic foals display ill thrift and diarrhea — a differential within the incorrectly named ‘foal heat diarrhea’ syndrome
what are non infectious causes of aboriton
Twins
Premature placental separation
what are infectious causes of abortion
Viral:
- Hematogenous spread ex. EHV-1
Bacterial:
- Principally ascending infection ex. Streptococcus spp
Fungal:
- Aspergillus
how can parturition be predicted using the serving date
Important to know the date to be able to estimate the possible window for parturition but it will be no guide as to when it will actually happen
Based on time from serving, often 7d before due date, and on some of the below signs it is usual to move the mare to a foaling box
when does the udder begin to enlarge prior to parturition
~4-6 weeks
Especially last 2 weeks
when does ‘waxing’ up occur
24-48hrs before parturition
Milk will leak in the final few hours