The use of the serum progesterone strip test as a clinical tool for assessing reproductive status in replacement gilts

Identifying the reproductive status of replacement gilts at the appropriate age can improve mating efficiency and reduce non-productive days. This study aimed to evaluate the reproductive status of gilts and assess the accuracy of a serum progesterone strip test. A total of 112 Landrace × Yorkshire gilts, aged 196–238 days, were enrolled. Estrus detection was performed daily from 189 days of age using the back-pressure test with fence-line boar exposure. Blood samples were collected from all gilts, and serum progesterone levels were determined using both ELISA and a progesterone lateral flow assays (LFAs) strip test. Puberty was defined by an ELISA-based serum progesterone concentration ≥5.0 ng/ml. The LFAs employed a competitive assay using a monoclonal antibody against progesterone. A single test line indicated a ‘positive’ result (pubertal), while two lines indicated ‘negative’ (prepubertal). To perform the test, 2–3 drops of serum were applied to the strip, with results read after 15 min. Based on ELISA, 51.8 % of gilts were pubertal and 48.2 % were prepubertal. Pubertal gilts had significantly higher serum progesterone levels than prepubertal gilts (30.8 ± 11.4 vs. 0.8 ± 0.8 ng/ml; P < 0.001). The LFAs correctly identified 98.2 % of pubertal gilts and 94.4 % of prepubertal gilts, yielding a sensitivity of 98.2 % and specificity of 94.4 %. In conclusion, the progesterone strip test demonstrated high accuracy and shows strong potential for on-farm use in identifying pubertal gilts based on serum progesterone concentration.