Ultrasound Basics and Pregnancy Detection (ANSC 134 - Lecture 4)
Ultrasonography in Veterinary Pregnancy Detection – Study Notes
These notes summarize ultrasonography concepts and practical pregnancy-detection protocols from the provided transcript (ANSC 134, Lecture 4).
Focus areas: how ultrasound works, equipment, tissue appearance, benefits, species-specific detection timings, technique details, anatomical findings, and both ultrasound and palpation-based methods.
How an ultrasound machine works
A transducer/probe emits and receives high-frequency sound waves.
Sound waves travel through tissue and bounce back as echoes.
The machine’s computer converts echoes into real-time images of internal structures.
Key terms:
Echoes are reflections of sound at tissue interfaces.
The reality of imaging depends on tissue density and acoustic impedance.
Ultrasound equipment and costs
Ultrasound machines come in various sizes; handheld to large units.
Price ranges commonly cited: 600 ext{ to } 33{,}000 dollars.
Probes/transducers can be expensive: 300 ext{ to } 10{,}000 dollars.
How different tissues appear on ultrasound
Density and echo return determine appearance:
Bones: white (hyperechoic) due to many strong echoes.
Muscle: gray (hypoechoic) due to moderate echoes.
Fluid (e.g., amniotic fluid): black (anechoic) due to absence of echoes.
Example reference: fetal brain image showing white bone, gray tissue, and black fluid.
Benefits of ultrasound for pregnancy detection
Early pregnancy detection is possible across species:
Sheep and goats: as early as 40 days post-mating via transabdominal ultrasound.
Pigs: as early as 24 days post-mating via transabdominal ultrasound.
Cattle: as early as 30 days post-mating via rectal ultrasound.
Ultrasound can determine multiple fetuses in ewes/does.
It is non-invasive (especially transabdominal) in sheep, goats, and pigs.
High accuracy enables informed management decisions:
Nutrition planning
Culling decisions
Breeding strategies
Pregnancy detection in sheep/goats using ultrasonography
Method: transabdominal ultrasound.
Animal positioning: sheep/goats standing, held by a person, haltered and tied, or in a chute.
Gel application: apply ultrasound gel to the probe and to the inner flank to eliminate air and improve contact; if the image is dark, add more gel.
Probe placement: on a non-wooly/non-hairy area.
Contact quality: apply sufficient pressure to ensure good skin contact.
Probe orientation: aim toward the midline of the animal.
Practical considerations: think about the location of the reproductive tract; gel works best, but lube can be used as an alternative.
What to look for after ~40 days of pregnancy in sheep/goats
Key sign: placentome detected on ultrasound, indicating pregnancy.
Placentome: a structure where the placenta attaches the mother’s side to the fetal side; essential for nutrient and gas exchange between mother and fetus.
Components of placentome:
Caruncle: mother’s side.
Cotyledon: fetal side.
Significance: placentomes are characteristic in sheep, goats, and cattle; a donut-shaped tissue indicates pregnancy when observed.
Source notation in literature: Igwebuike and Ezeasor, 2013.
Identifying a fetus on ultrasound
Early gestation can be challenging; the placentome may be the first clear indicator.
Visual clues for a fetus:
Spine (visible as a linear structure).
Breast bone (sternum), ribs, and other skeletal elements become identifiable with experience.
With increasing experience, fetal sex determination may be possible.
Visualization examples (illustrative):
A: placentomes present, early signs.
B: identifiable spine, ribs, breast bone; more developed features.
Note: experience level impacts the ability to identify sex and finer anatomy.
Ultrasonography in cattle
Transducer/probe use: typically transrectal for early gestation.
Timing and accuracy: ultrasound around 30 days after the end of the breeding season can determine pregnancy status with accuracy between 95 ext{-}100 ext{ ext%}.
Visual indicators:
A fluid sac containing a tiny fetus.
Placentomes may be visible depending on how early gestation is.
Cattle ultrasound images (typical examples)
Common early pregnancy imaging examples include:
Bovine ultrasound around day 32 of pregnancy.
Later imagery around day 39 and day 40 of pregnancy.
Note: these image references demonstrate progressive fetal development detectable by ultrasound.
Determining pregnancy in mid-to-late gestation in cattle
When gestation is mid to late, rectal palpation becomes a practical alternative:
Procedure: insert the arm into the rectum to feel the reproductive tract.
Look for a “balloon” in the tract that can move or bounce; its presence indicates pregnancy (roughly after 90 days).
Later gestation (around 5 months and beyond):
The fetus may be palpated hanging over the pelvis.
Definition: Palpation is the process of feeling an object in or on the body to assess size, shape, firmness, or location.
Pregnancy detection in swine using ultrasound
Procedure: place the ultrasound probe under the rear flank area.
Early gestation: look for irregular black shapes representing fluid-filled embryonic vesicles; detection around 24 days after breeding.
Mid-to-late gestation: locate fetuses; skeletons are the easiest to identify (ribs, spine, head/skull).
Gestation length in pigs: G_{ ext{swine}} = 115 ext{ days} = 3 ext{ months } 3 ext{ weeks } 3 ext{ days}.
Practical note: ultrasound can monitor pregnancy progression in swine and aid in management decisions.
Practical tips and technique notes
Gel is essential to prevent air gaps and to facilitate sound transmission.
If an image is dark, reapply more gel.
Favor non-wooly or non-hairy areas for probe contact.
Apply adequate pressure to improve skin contact without causing harm or discomfort.
When assessing across species, remember the differences in gestation timelines and anatomical landmarks.
Ethical, philosophical, and practical implications
Non-invasiveness: ultrasound offers a non-invasive method to confirm pregnancy, reducing stress and risk to the dam and fetus compared with some invasive methods.
Early detection enables proactive management: nutrition adjustments, mating and culling decisions, and targeted breeding strategies.
Accuracy considerations: high reported accuracy in cattle (up to 100% at appropriate times) supports reliability but requires proper technique and operator expertise.
Knowledge application: early and accurate pregnancy status informs herd health management, resource allocation, and welfare considerations.
Quick reference: key figures and concepts (LaTeX-formatted)
Fishbone-style summary of detection timing by species:
t_{ ext{detection, sheep/does}} = 40 ext{ days post-mating} via transabdominal ultrasound.
t_{ ext{detection, pigs}} = 24 ext{ days post-mating} via transabdominal ultrasound.
t_{ ext{detection, cattle}} = 30 ext{ days post-mating} via rectal ultrasound.
Gestation lengths (example species):
G_{ ext{swine}} = 115 ext{ days} = 3 ext{ months } 3 ext{ weeks } 3 ext{ days}.
Rectal palpation timing for mid-to-late gestation in cattle:
Palpation effectiveness starts around 90 ext{ days} of gestation.
Ultrasound tissue appearances (concepts):
Bones: ext{hyperechoic}
ightarrow ext{white}Muscle: ext{hypoechoic}
ightarrow ext{gray}Fluid: ext{anechoic}
ightarrow ext{black}$$
Placental anatomy (placentome) definitions:
Placenta attaches mom’s side (caruncle) to fetal side (cotyledon).
Donut-shaped placentome indicates pregnancy.
If you want, I can tailor these notes further for a particular animal species (sheep, goats, cattle, or pigs) or prepare a one-page quick-reference sheet with the most exam-focused bullets.