Oestrous (also oestrus/estrous) detectors are a revolutionary and relatively new technology designed for optimum productivity in breeding. Not only are these devices easy to use, they’re inexpensive, and able to reliably detect the best time for conception. They can also be used to make an early detection of gestation, or of the next oestrous cycle in the absence of gestation.

The pioneering and most successful of these instruments is the Draminski Oestrous Detector, which comes in a variety of types designed for cows, pigs, sheep, goats, or dogs.

Oestrous detectors are the product of numerous studies on the relationships between the oestrous cycle and its effects on vaginal mucous. Researchers have discovered that hormonal changes during oestrous (or “heat”) affect the chemical composition of the vaginal mucous, resulting in differences in its electrical composition.

At different points of the oestrous cycle, the mucous has different electrical charges. A higher electrical charge results in a higher detector reading value, and a lower charge will have a lower value.

In cows, sows, mares and ewes, oestrous follows a pattern of a gradual decline in vaginal electrical resistance (VER) preceding the cycle, meaning gradually lower readings on the detector. During oestrous itself, the VER reaches its lowest levels. Following oestrous, the VER levels begin increasing (higher detector readings) until ovulation. After ovulation, the resistance levels stabilise. Therefore, the timing of oestrous can be indicated by its signature low readings on a detector.

Click here to see the detector readings for sheep

Click here to see the resistance level readings for cows

Click here to view the resistance graph for horses

Click here to view the graph for pigs

The only exception to this VER pattern (for animals that the Draminski Oestrous Detector is designed for) would be the dog. The dog has a pattern which is characterised by a high peak, which actually proceeds oestrous. This may be because the canine, while in heat, exhibits small amounts of vaginal bleeding, which would affect the electrical resistance reading.

Studies have linked resistance values to changes in plasma progesterone concentrations [1, 2, 3, 6, 7], urinary oestrogens [2], luteinizing hormone levels [2, 3, 4], as well as follicle-stimulating hormone levels [2], all of which change reliably during oestrous.

For example, on the 21st and 24th day following insemination, plasma and milk progesterone levels in cattle can be used to diagnose possible pregnancy (or failure of it) in cows. A cow’s oestrous cycle operates on an approximately 21 day cycle; if she becomes pregnant, she will no longer be in oestrous, and her progesterone levels will rise instead of dropping [8]. Because progesterone levels are significantly correlated to VER, the two increase and decrease in value together. And so on the 21st following insemination, a high detector reading indicates a likely successful pregnancy.

This shows that not only is the Draminski Oestrous Detector responsive to the hormonal changes that coincide with oestrous, but it can also replace the more costly procedure of progesterone-based pregnancy detection, and is a much simpler and more efficient process [1]. According to researchers Million Tadesse et al., who measured electrical resistance values during the oestrous cycle and induced-oestrous cycle in cattle, “it can be concluded that VER of vaginal mucus can be satisfactorily used to predict the ovarian status and stage of the estrus cycle” [5].

As mentioned before, changes in VER reflect circulating levels of hormones, which in turn signify where the animal is along the oestrous cycle.

Why are there changes in electrical resistance? While there is no doubt that hormones are responsible, scientists are not entirely sure what the exact mechanisms are. The onset of oestrous is characterized in part by increasing levels of oestrogen. It is theorised that as the levels of oestrogen rise, they increase the activity of a metabolic pathway which produces two other hormones, adrenocorticotropic hormone, and aldosterone. One effect of these hormones is that they increase the levels of NaCl (sodium chloride) in the vaginal mucous. NaCl itself decreases electrical resistance. Summarily, it is postulated that during oestrous, oestrogen levels are at their highest; this causes NaCl levels to be high, resulting in a significantly lower level of electrical resistance than usual [4]. But regardless of the uncertainty of exactly how differences in VER readings result from the oestrous cycle, they accurately correspond to its phases, providing vital information for efficient and effective breeding.

References

1. — I. TASAL, M.B. ATAMAN, M. AKSOY, A. KAYA, F. KARACA and T. TEKELI : Estimation of early pregnancy by electrical resistance values of vaginal mucosa in cows and heifers.

2. — D. SCHAMS, E. SCHALLENBERGER, B. HOFFMANN and H. KARG : The oestrous cycle of the cow: hormonal parameters and time relationship concerning oestrus, ovulation, and electrical resistance of the vaginal mucus.

3. — M.B. ABOUL-ELA, J.H. TOPPS and D.C. MACDONALD : Relationships between intravaginal electrical resistance, cervicovaginal mucus characteristics and blood progesterone and LH.

4. — R.J. FEHRING : A Comparison of the Ovulation Method With the CUE Ovulation Predictor in Determining the Fertile Period.

5. — M. TADESSE, J. THIENGTHAM, A. PINYOPUMM, S. PRASANPANICH, and A. TEGEGNE : The Use of Vaginal Electrical Resistance to Diagnose Estrus and Early Pregnancy and Its Relation with Size of the Dominant Follicle in Dairy Cattle.  

6. — P.M. BARTLEWSKI, A.P. BEARD, and N.C. RAWLINGS : The relationship between vaginal mucous impedance and serum concentrations of estradiol and progesterone throughout the sheep estrous cycle.

7. — A.-R. GÜNZEL, P. KOIVISTO and J.A. FOUGNER : Electrical resistance of vaginal secretion in the bitch.  

8. — F. MOREIRA and P.J. HANSEN : Pregnancy Diagnosis in the Cow.