Veterinary Obstetrics 101

Pregnancy Diagnosis in Cattle

• Learning Objectives:
  • Describe the stages of fetal development during bovine pregnancy.
  • Discuss the physiological changes in the reproductive tract during gestation.
  • Compare pregnancy diagnosis methods (advantages/disadvantages).
  • Identify cardinal signs of pregnancy via transrectal palpation and ultrasound.
  • Explain chemical pregnancy diagnosis methods (pregnancy-associated glycoproteins).

Why Diagnose Pregnancy?

• Detect non-pregnant cows (for re-breeding, treatment, or culling).
• Measure reproductive management success.
• Early detection of reproductive problems.
• Resynchronize non-pregnant cows.

Impact of Erroneous Results

• False Positive: Animal remains unproductive.
• False Negative: Receipt of PGF2α, resulting in economic losses (e.g., $550-800). Culling of pregnant cows.

Observation Methods

• Non-return to Estrus (18-24 days): Presumptive, non-invasive, but lacks sensitivity & specificity; costlier/unreliable.
• Weight Gain: Presumptive, non-invasive, but lacks sensitivity & specificity; costlier/unreliable.
• Udder Development: Presumptive, non-invasive, but lacks sensitivity & specificity; costlier/unreliable.

Cessation of Estrus Cycle

• False Positive: Non-return to estrus (potential causes: cystic ovarian disease, hydrometra (in does), metritis, pyometra, mummies, nutritional anestrus, poor heat detection).
• False Negative: Some pregnant females show behavioral estrus. Can lead to PGF2α or AI use.

Direct Methods: Trans-rectal Palpation

• Most common/accurate for cows.
• Sensitive, specific, economic, immediate results, and aging.
• Useful as early as 32 days (depending on experience, age of dam, and size).
• Cardinal signs (4): membrane slip (MS), amniotic vesicle (AV), placentomes, fetus.
• Secondary signs: asymmetry of uterine horns, uterine wall fluctuation (fluids), cervix fixation, fremitus of middle uterine artery, presence of CL.

Cardinal Signs (Trans-rectal Palpation)

• 1. Membrane Slip (MS): Compressing the uterine horn, membranes slip from the wall (35-100 days). (35 days-gravid, 60 days-non-gravid).
• 2. Amniotic Vesicle (AV): Spherical, turgid, fluid filled structure; palpable at 28 days in heifers and 32 days in cows.
  • By 60-65 days: less turgid, difficult to recognize (starts to elongate). Fetus becomes palpable. Be careful before 40 days, as the heart is external and can be ruptured.
• 3. Placentomes: Endometrial caruncles + fetal cotyledons; 75-120 placentomes. Formed early in gestation, palpable by 75-80 days; size increases with gestation, larger in the middle of gravid horn, consistent size cranial to cervix
• 4. Fetus: Palpable at 60 days (AV loses turgidity). Grasp fetus in early stages; ballot (re-bounce) later.
  • Sizes
  • 70 days: 15 mm
  • 80 days: 35 mm
  • 90 days: 55 mm
  • 100 days: 90 mm
  • 120 days: 105 mm
  • During the 2nd-4th month: it's free-floating. 5th-6th months: it increases weight, fluids move the uterus ventrally and cranially; rests on the abdominal floor. 7th-9th months: continues growing, moving closer to the maternal pelvis.
  • False positives: rumen sac/kidney/tumors. False negative: at 5-7 months.
  • Fetal size is used to estimate gestation age.

Secondary Signs of Pregnancy

• Asymmetry of uterine horns
• Fluctuation of uterine wall (fluids)
• Fixation of cervix. (Uterus retracts until 70-75 days; difficult after 90).
  • Possible false positives (hydrometra, mucometra, pyometra, maceration, mummification, adhesion after C-section, large uterine or ovarian tumors).
• Fremitus of middle uterine artery. (Blood flow increases with gestation). Increased size detectable in heifers 75d and in cows at 90d.

Indirect Methods

• Progesterone Test: Blood/milk levels remain high in pregnancy (2 ng/mL @24 days post AI); RIA or ELISA. Reliable for non-pregnant cows but specificity is low, high cost, Not practical. 
• Pregnancy-Associated Glycoproteins (PAGs): Aspartic proteinases. Expressed by placental ruminants,
• Bovine Pregnancy Specific Protein B (bPSBP): ELISA using blood; useful for ≥28 days in cows and 25 days in heifers; low cost, high accuracy; false positives may occur (similar levels in pregnant vs. pregnancy-loss animals; persistent levels in pregnancy-loss animals; and higher loss rates). Half life of 7.2 days.

Trans-rectal Ultrasonography (TRUS)

• Minimally invasive, accurate, quick.
• Accurate @ 24-26 days post AI; detects heartbeat in viable embryos; heifers 3 days earlier than cows.
• Advantages: earlier, accurate, sensitive, specific, less pregnancy loss.
• Embryo viability (heart beat) and defects.
• Detection of Twin Pregnancies.
• Fetal Sexing
• Aging the pregnancy.
• Diagnosis of Ovarian/Uterine pathologies.
• Which TRUS Findings should be considered?
• Important points for identification.

Practical Protocol

• TRUS, Re-synch Open Cows and GnRH.
• Blood sample @28 days post AI.
• Ultrasound/Palpation.
• Faster resynchronization. Help reduce calving intervals (<110 days to conception).

Summary

• TRP, Ultrasound & bPSBP are accurate, but TRP is the practical way, not all one test can replace the other.
• Combine methods strategically within the repro program for monitoring herd fertility.

Test your knowledge on key concepts in veterinary obstetrics with this quiz. Questions cover topics such as fetal identification, uterine changes during gestation, and important palpation guidelines in pregnant cows. Each question will challenge your understanding of pregnancy signs and cow reproduction.