4.4 Food-Animal & Equine Reproduction and Theriogenology

4.4 Food-Animal & Equine Reproduction and Theriogenology

Reproductive management is central to food-animal and equine practice, and the NAVLE expects entry-level competence in normal parturition, dystocia decision-making, and neonatal care. These questions reward knowing normal reference values (gestation lengths, stage durations) so that abnormal findings trigger the correct intervention.

Normal Gestation Lengths

Memorize the species baselines; questions often hinge on whether a pregnancy is premature, term, or prolonged.

A foal born before 320 days is premature and at high risk of dysmaturity and failure of passive transfer. Cattle bred to certain sires or carrying twins may deviate, but marked prolongation warrants investigation (e.g., fetal anomalies, adenohypophyseal aplasia in prolonged bovine gestation).

The Three Stages of Parturition

Parturition proceeds through three stages in all species:

1. Stage 1 — Cervical dilation. Uterine contractions begin, the cervix softens and dilates, and the dam becomes restless and off feed. In the cow this may last hours and often goes unnoticed. The chorioallantois ("water bag") may appear at the end.
2. Stage 2 — Fetal expulsion. Marked by abdominal press and rupture of membranes. This stage is fast in the mare (usually 12-30 minutes) and any delay is an emergency; it is more prolonged in the cow (up to a few hours in heifers). Normal anterior presentation is head and both forelimbs first.
3. Stage 3 — Placental passage. Expulsion of the fetal membranes. In the cow the placenta should pass within 8-12 hours.

Dystocia: Recognition and Decision-Making

Dystocia (difficult birth) is a leading cause of neonatal and dam loss. The exam tests when to intervene and how to correct malpositions.

• When to intervene: In the mare, any stage 2 exceeding ~30 minutes without progress is an emergency because the equine placenta separates quickly and the foal becomes hypoxic. In the cow, intervene after ~30-60 minutes of unproductive straining or if only the tail/one limb presents.
• Vaginal examination determines presentation (anterior/posterior), position (dorsosacral is normal), and posture (extended head and limbs). Common corrections include extending a retained head or flexed carpus.
• Mutation, forced extraction, fetotomy, or cesarean section are the escalating options. Excessive traction risks fetal injury and maternal trauma; a fetus that cannot be delivered per vagina requires a C-section.
• Fetal oversize, twins (equine), and uterine torsion (common in cattle) are frequent causes. Uterine torsion is corrected by rolling the cow or manual detorsion.

Retained Fetal Membranes

A bovine placenta not passed within 12 hours is retained (RFM). Do not forcibly remove it — traction damages caruncles and causes hemorrhage and metritis. Management is observation, systemic antibiotics only if the cow is febrile/septic, and supportive care; the membranes usually slough in 4-7 days. Risk factors include hypocalcemia, dystocia, twinning, abortion, and selenium deficiency.

Equine 'Red Bag' — Premature Placental Separation

Normally the amnion (translucent white/blue) presents at the vulva. If a velvety red membrane bulges instead, the chorioallantois has separated prematurely ("red bag"), meaning the foal is no longer receiving maternal oxygen. This is a true emergency: immediately rupture the red membrane and deliver the foal rapidly to prevent hypoxic-ischemic injury. It is associated with placentitis and fescue toxicosis.

Failure of Passive Transfer (FPT)

Ruminant and equine neonates are born agammaglobulinemic because the epitheliochorial (equine) and syndesmochorial (bovine) placentas do not transfer immunoglobulins in utero. The neonate must absorb colostral IgG through the gut, and that absorptive window closes rapidly.

• Maximal absorption occurs in the first 6-12 hours and effectively ends by 24 hours as specialized enterocytes are replaced.
• Definition (foals): serum IgG measured at ~18-24 hours; >800 mg/dL adequate, 400-800 mg/dL partial FPT, <400 mg/dL complete FPT. The same thresholds are applied to calves and crias.
• Diagnosis: stall-side tests include glutaraldehyde coagulation, zinc sulfate turbidity, and ELISA (SNAP/CITE); colostrum quality is estimated with a colostrometer/refractometer (specific gravity >1.060 or Brix ≥22% indicates good IgG).
• Correction: if the gut is still open (foal <18-24 hours), give good-quality colostrum orally (1-2 L for a foal, divided). If the window has closed or the neonate is compromised, give intravenous plasma with an IgG concentration >1,200 mg/dL, then recheck IgG. FPT strongly predisposes to neonatal septicemia.

Exam Traps

• Confusing peace/calla lily (oral irritant) versus true lily is a small-animal trap; the reproductive analog is confusing normal amnion (white) with red bag (emergency).
• Remember that oxytocin aids milk letdown and uterine involution but should not be used to force a fetus through an undilated cervix.
• Do not pull a retained bovine placenta; the correct answer is almost always conservative management.