Oestradiol (E2)

Oestradiol can be used to detect the onset of oestrus in females or to detect ovarian tissue in spayed females. A single sample may be adequate if the animal is showing signs of oestrus. Detection of ovarian remnants may need a GnRH stimulation test to stimulate any remaining ovarian tissue to produce oestradiol. The protocol is identical for bitches at any stage and for queens when they are not showing oestrus behaviour. For queens showing oestrus behaviour, the hCG stimulation test and measurement of progesterone is reported to be preferable. A single sample is needed for the detection of Sertoli cell tumours in male dogs which typically produce significant levels of oestrogens.

GnRH Stimulation Test

This test is used to detect ovarian remnants in bitches at any stage and in queens when not showing oestrus behaviour.

  1. Take a basal blood sample (1.3 ml plain serum tube – NOT a gel tube).
  2. Inject I.V. 0.32ug Buserelin (Receptal, Hoechst or Intervet – NB not licenced for dogs or cats). A very small volume of Buserelin is required (83ul) and it is therefore most practical to dilute the drug 1:10 with sterile water for injection and then inject 0.83ml.
  3. Take a further blood sample 3 hours later.
  4. Label the pre- and post-stimulation tubes clearly and request Oestradiol (E2) assay.

Interpretation

Females in anoestrus should have undetectable levels of E2 (<10 pmol/l) which increase with GnRH stimulation. Females with no ovarian activity should have undetectable levels of E2 (<10 pmol/l) which do not increase with GnRH stimulation. Interpretation must be made in conjunction with the clinical history.

hCG Stimulation Test

This test induces ovulation to detect ovarian remnants in queens showing oestrus behaviour and should be performed between 1-3 days after the onset of these signs.

  1. Take a basal blood sample (1.3 ml plain serum tube – NOT a gel tube).
  2. Inject I.M 500 IU hCG (Chorulon, Intervet – NB not licenced for cats)
  3. Take a further blood sample 7 days later.
  4. Label the pre- and post-stimulation tubes clearly and request Progesterone assay.

Interpretation

Basal progesterone levels should be undetectable (<3.0 nmol/l) and increase (>15.0 nmol/l) in queens with ovarian remnants. Luteal tissue may be easier to visualise at exploratory surgery.