bithc|in|heat|progesterone

Determination of heat and whelping dates in bitches using progesterone assessment

Identifying the optimal time for mating a bitch can be critically important, particularly if the mate lives some distance away, with lengthy ill-timed journeys something to be avoided at all times but particularly at present. At the other end of pregnancy, as whelping approaches, knowing when a bitch is going to whelp can be helpful in making the necessary arrangements for whelping. Progesterone measurement can assist in decision making in both of these circumstances as progesterone levels rise in the bitch from late pro-oestrus and remain high throughout pregnancy until about 48 hours before parturition when levels decline rapidly. Although requiring a blood sample, the information obtained is often well worth it.


Assessment of different methods of measuring progesterone

In 2010, Moxon et al conducted a comparative study of three different methods of measuring the level of progesterone in blood samples from bitches at the Guide Dogs Breeding Centre, sampled as part of their reproductive management. The study compared the comparability and cost of the three methods, using the radioimmunoassay (RIA) as the “gold standard”. The other two comparators were a quantitative ELISA (Ridgeway Science) and a semi-quantitive ELISA (Ovucheck Premate 10, Biovet). A total of 60 blood samples were analysed twice using the quantitative ELISA and the semi-quantitative ELISA and a further two aliquots were sent to two different laboratories offering RIA analysis.

Analytical results by all methods were categorised as low (<3ng/mL), intermediate (3 – 9.9ng/mL) and high (≥10 ng/mL). The two sets of RIA analyses were similar with 22 or 23 samples categorised as low progesterone, 21 as intermediate and 17 or 16 as high. There was 100% agreement of the quantitative ELISA at low progesterone samples with the RIA results, 57.1% (12/21) agreement of intermediate samples and 76% of high progesterone with the RIA results. For the semi-quantitative ELISA there was 95.5% agreement at low progesterone, 42.9% at intermediate and 100% at high progesterone compared with the RIA results.

Sensitivity, specificity, positive and negative predictive values and accuracy values were calculated for each ELISA and are summarised in the table below.

ParameterCalculationQuantitative ELISASemi-quantitative ELISA
SensitivitySE=TP/(TP+FN)70.6100
SpecificitySP=TN/(TN+FP)10095.5
Positive predictive valuePPV=TP/(TN+FN)10073.9
Negative predictive valueNPV=TN/(TN+FN)7177.8
AccuracyAccuracy = (TP+TN)/(TP+FP+TN+FN)9089.2

TP: true positive, TN: true negative, FP: false positive, FN: false negative

Overall there was 76.7% agreement of the quantitative ELISA with the RIA and 78.3% agreement between the semi-quantitative ELISA and RIA. The inter-assay coefficient of variation for the quantitative ELISA was 23.4% and 11.7% for the semi-quantitative ELISA.

The authors calculated the theoretical costs of running one, five and ten samples per week for a year. If one sample was run per week the cost was comparable for each of the methods (between £686 and £738), excluding the purchase of a reader that would be necessary for the quantitative ELISA. As the number of samples increased then the quantitative ELISA became the most cost-effective with an annual cost of £1132.71 for 10 samples per week, compared with £2640.00 for the semi-quantitative ELISA and £7280.00 for the RIA.

The RIA has the disadvantage of turnaround time being longer as the sample has to be despatched and the results awaited. The semiquantitiative ELISA will tend to be early in showing a high progesterone value and so several matings may be possible before the end of heat, whereas the quantitative will tend to show a high level later. To compensate for the latter the authors recommend that mating begins as soon as progesterone reaches 6ng/mL.

Conclusions

Progesterone measurement is a useful tool for bitch owners to time mating and as an indicator of whelping. Measurement requires a blood sample to measure the levels in plasma but the value is often worth the intervention. Veterinary surgeons offering progesterone measurement as a service have a choice of tests available, with the quantitative ELISA cost effective where large numbers of samples are processed each year and where the practice has a plate reader.

Reference

Moxon R et al, 2010. Technical and financial evaluation of assays for progesterone in canine practice in the UK. Veterinary Record 167 528 – 531