I remember my first days of ‘seeing practice’ just under 20 years ago when everyone including the vet, herd manager, and even farm dog were huddled around a cumbersome ultrasound monitor. All eagerly awaiting a glimpse of something resembling a pregnancy…
Time has passed and the developments in technology have been marked, we are now fortunate to sport small, light portable units with binocular vision. Whilst appearing like a bit of a ‘space cadet’ this progression has significantly advanced the speed and accuracy of fertility management in both beef and dairy enterprises, but has one significant disadvantage…all but the operator fail to achieve a great viewing.
Ultrasonography has been a popular medical imaging technique adapted since 1939 with the scientific theory mostly unchanged for evaluation of the bovine reproductive tract. The transducer probe of the ultrasound ‘scanner’ generates and receives sound waves using a principle called the piezoelectric (pressure electricity) effect created by crystals vibrating rapidly within the hand held probe.
These high frequency pulses travel across the cow’s rectum and hit boundaries between uterine tissues, fluid and even bone as the waves reach these boundaries some will get reflected back to the probe and relayed to the machine. The machine then calculates the distances from the probe to the tissue/fluid/bone boundaries and display these with the intensity of the ‘echoed’ waves within the head set forming a two dimensional image. Essentially, fluid appears as ‘black’ regions on the screen, with highly dense tissues such as bone being white and everything in between appearing as variations of ‘mottled grey’.
(Images, courtesy of BCF Technology 2014)
Measuring and sizing can play a key role in both accurately ageing pregnancies and assessing uterine/ovarian architecture or pathology, to assist a superimposed grid overlays the image with each individual box 10x10mm.
In the pregnant animal, as the foetus grows in size the accuracy of ageing decreases significantly and in late gestation estimations of placentome size (Cotyledon-Caruncle units) are often required or even manual palpation of the calf. Therefore, if you would like to know which ‘day’ the animal conceived on you need to diagnose pregnancy fairly promptly i.e. 30 to 40 days post service. Pregnancy can be diagnosed earlier than this by skilled operators even at 17 days post service however the extra manipulation and additional time required to differentiate from a non-pregnant uterus can be associated with increased levels of embryonic losses. This reinforces a standard recommendation of scanning at least 30 days after service. Ultrasound has also facilitated the ability to assess foetal viability in addition to accurately diagnosing Twins at 40-70 days and sexing foetuses at days 55-60.
Hopefully that helps to prove that we are not just watching day time television through the goggles, as it could be inferred, although only time can tell what the next 20 years of technological advancements have in store for us and the cows!
Alex Walters BVSc MBIAC Cert AVP (CHP) MRCVS
Regional Director & Senior Veterinary Surgeon, Heathfield Practice