Periparturient Period of the Mare Flashcards
What 3 vaccines are recommended for pregnant mares? What 5 are used to boost colostrum? What is risk-based?
- rabies - prior to breeding
- EVA - prior to breeding
- EHV - 5, 7, 9 months of gestation
tetanus, EEE, WEE, WNV, influenza - 4-6 weeks before predicted foaling
leptospirosis
What is the leading cause of infectious abortion in horses worldwide? How is it transmitted?
equine herpesvirus (EHV)
inhalation or ingestion of aborted tissues - infection persists in a latent state
What clinical sign is indicative of EHV in periparturient mares? What is the pathogenesis?
abortion between 5 months to term without any clinical signs of infection
- replicates in respiratory epithelial cells
- spreads to regional LNs and vascular endothelium of many organs
- placental invasion causes autolysis
What 3 gross lesions are seen in cases of EHV abortion?
- fresh aborted fetus
- hepatic necrotic foci
- fibrotic plug in trachea
What vaccines are recommended for mares against EHV? What schedule is typically done? What efficacy do they have?
EHV-1 and EHV-4 (killed)
5th, 7th, 9th months –> immunity to vaccination is short-lived
does NOT offer 100% protection, but does reduce incidence of abortion
What are the 4 morphological types of equine placentitis?
- ascending - most common, infection from cervix
- nocardioform - focal, mucoid, uterine body and base of uterine horns
- diffuse - hematogenous
- multifocal - rare, fungal plaques
What pathogens cause each form of equine placentitis?
- ascending - Streptococcus equi subsp zooepidemicus, Klebsiella pneumonia, E. coli, Pseudomonas aeruginosa
- nocardioform - Crossiella equi, Amycolatopsis spp
- diffuse - Leptospira spp
- multifocal - Candida albicans, Aspergillus spp
How does ascending placentitis develop? What are the 2 most common etiologies?
- pathogens migrate proximally through the cervix, starting at the cervical star region
- when organisms enter the chorioallantois, they release pro-inflammatory cytokines and prostaglandins
- this results in premature delivery –> red bag!
- failure of mucus plug
- weight of fetus and uterus - lack of cartilage allows cervix to stretch and open with increased weight
What are 4 signs of ascending placentitis?
- premature udder development*
- premature lactation*
- vulvar discarge
- abortion
What are the 2 most common causes of nocardioform placentitis? In what region is this most commonly seen?
Gram positive branching actinomycetes - Crossiella equi, Amycolatopsis spp
central KY - sporadic, hot and dry summer/fall
What is the most common result of nocardioform placentitis? What is the characteristic placental lesion?
late gestational abortion or delivery of premature stillborn or weak foals
copious mucoid exudate adherent to the surface of the chorion at the junction of the uterine body and base of gravid horn
What diagnostics are recommended for nocardioform placentitis? What is treatment like?
transabdominal U/S, culture following abortion
not very effective - difficult for antibiotics to reach this location and get past mucus
What are 3 parts of the routine examination in cases of suspected placentitis?
- transabdominal ultrasound - fetal viability
- vaginal exam - inspect cervix and look for discharge
- transrectal ultrasound - measure the combined thickness of uterus and placenta, assess placental separation
How is combined thickness of uterus and placenta calculated? What are the expected values at various points of gestation?
transrectal U/S - identify the middle uterine artery that runs parallel to the uterus and measure thickness of the uterus and chorioallantois just cranial to the cervix and calculate the average
- 151-270d = <7 mm
- 271-300d = <8 mm
- 301-330d = <10 mm
- 331d-term = <12 mm
What are 3 strategies of treating placentitis in mares?
- control infection - antimicrobials must be able to penetrate and accumulate in allantoic fluid (PPG + Gentamycin, TMS)
- reduce associated inflammation - Flunixin meglumine, Phenylbutazone, Firocoxib, Pentoxifylline (free-radical scavenger, promotes blood flow)
- promote uterine quiescence - Altrenogest
What predisposes to umbilical torsion? What typically results?
longer umbilicus - more room to twist (4-7 twists are normal)
vascular occlusion = fetal death and autolysis, typically at 6-8 months, when the fetus tends to have high mobility
What are 3 signs of prepubic tendon rupture? When in gestation does this typically occur?
- ventral edema
- dropped abdomen
- bloody mammary secretions
late-term gestation - increased fetal weight, weakened muscles cannot support
Where does uterine torsion in horses occur? What is the most common sign? When does this typically happen?
cranial to the cervix
colic
mid to late gestation
What toxicity can affect fetal development in horses? How?
ergot alkaloids produced by endophyte-producing fescue have dopaminergic-like activity, which decreases prolactin and inhibits ACTH secretion –> no fetal stress to induce parturition
What are 5 signs of fescue toxicosis in a pregnant mare? When is this most commonly seen?
- increased gestation length
- agalactia
- increased placental thickness
- oversized, dysmature foals
- abortion due to placental separation (red bag!)
last month of gestation
What are 2 parts to treating fescue toxicosis?
- remove from fescue 30-45 days from foaling
- supplement with domperidone (DOPA antagonist) - increases prolactin from mammary glands
What are 6 signs of impending parturition in mares? When are each seen? What is recommended before the due date?
- mammary gland development - 2-6 weeks
- perineal relaxation - 1-3 weeks
- teat engorgement - 7-10 days
- waxing of teats - colostrum leaks and dries, 48-72 hours
- elongation and swelling of vulva - 0-24 hours
- dripping milk from udder - 12-24 hours
remove vulvoplasty (Caslick) 1-2 weeks prior
What are 3 ways of predicting time of parturition?
- calcium level - calcium carbonate > 250 ppm
- pH < 6.4
- Na+/K+ inversion - decreased Na, increased K
all measured in mammary secretions
What are 2 options for monitoring timing of parturition?
- video camera
- vulvar device - Foalert senses water breaking
What happens in the 3 stages of mare parturition?
- preparatory cervical softening, fetus rotates dorsopubic to dorsosacral, myometrial contractions, chorioallantois ruptures
- expulsion of foal
- expulsion of fetal membranes within 3 hours post foaling
What is red bag?
emergency - premature placental separation results in no involution of placenta
- fetus unable to break through, must be cut open
What are 3 sequela of retained placenta?
- metritis
- laminitis
- endotoxemia
What is the 1-2-3 rule of foaling?
HOUR 1 - foal stands
HOUR 2 - foal nurses
HOUR 3 - foal passes meconium and pare passes placenta
How should the equine placenta be examined? What are the 2 surfaces?
laid out in an F or Y shape to identify all areas
- RED = chorionic surface (uterus side)
- BLUE = allantoic surface (fetal side)
What is the cervical star? What if one of the two horns of the placenta are missing upon examination?
pale area of the placenta which apposes the cervix - site of ascending infection into the placenta
retained placenta
What are some abnormalities that are looked for on examination of the placenta?
- avillous areas
- exudate - Nocardioform = purulent
- abnormal placental weight - should be ~10-11% of foal weight, heavier = placentitis
When does the first postpartum estrus occur in mares? Why is this possible? What is fertility like in this time?
7-9 days postpartum
less invasive placentation
controversial - ranges from normal fertility to 10-20% lower, may be better if delayed after histological involution (30 day heat after foal heat)
