• Graph illustrating hormone levels, including oestrus, ovulation, progesterone, and oestrogen over a 21-day cycle.

    Why Progesterone (P4)



    A healthy cow has a 21-day cycle involving six different hormones. One of these hormones is progesterone. Your cow’s progesterone levels show in its milk. So testing the milk will tell you if your cow is cycling and when she’s ready for AI.

    The main external sign that a cow is cycling is standing heat. However, it’s only visible for short periods throughout the day, making it easy to miss. And some cows stand to be mounted when they’re not in heat, so it’s not always reliable.

    Another sign of oestrus is bulling. But false bulling is common, so again, this is not reliable. And some cows go through their entire cycle and display no outward signs of oestrus, even though they are perfectly healthy and fertile.

    This is why tracking progesterone is the most reliable way to confirm heat. And so improve the fertility and productivity of your herd.

    References: Friggens & Chagunda 2005, Wathes & Diskin 2015, Muasa et al. 2017 (review), Back et al. 2012.

  • A group of cows grazing on a grassy field under a clear blue sky.

    Detecting fertility status

    In commercial herds, milk progesterone has been shown to confirm true heat, identify cows in silent heat, and flag non-pregnancy within days of insemination.

    A field study of over 500 Kenyan dairy cows found a cow-side milk progesterone test accurate to roughly 87–97% as an aid to oestrus detection and non-pregnancy (Peters, 2022).

    In a separate study of more than 700 Jersey cows on a timed-AI programme, an on-farm milk progesterone test reliably identified cows that were not pregnant — so they could return to service sooner (Omontese, 2020).

    References: Peters 2022, Omontese 2020, Omontese 2017, Järvinen 2014, Ball et al. 2014, Ingenhoff et al. 2016, Mehmedi et al. 2021, Jahedi et al. 2019, Muasa et al. 2025, Bonev 2021, Turner 2014.

  • Fertility testing kit with bottles, test strips, instruction sheet, and packaging.

    Why lateral flow

    P4HeatRead brings that science out of the lab and into the parlour. It uses lateral-flow immunoassay to read progesterone from five drops of milk in 20 minutes, with nothing to send away.

    Lateral-flow milk progesterone tests have been validated directly against laboratory enzyme-immunoassay.

    References: Waldmann & Raud 2016, Ridgeway/P4Gold 2021

References

    • Wathes DC, Diskin MG. Reproduction, events and management: reference overview of bovine reproductive management including progesterone monitoring. 2015.

    • Friggens NC, Chagunda MGG. Prediction of the reproductive status of cattle on the basis of milk progesterone measures: model description. 2005.

    • Peters A, Wong, Williams, Muasa B, Makoni, Ngige, et al. Cow-side P4 Rapid lateral flow test as an aid for oestrus detection and non-pregnancy in Kenyan dairy cows. 2022.

    • Jahedi, Mostafalou, Moslemipour, Firouzeh. Accuracy of Rapid P4 milk kit for oestrus detection and early pregnancy in Holstein cows (Iran). 2019.

    • Järvinen M, Kajava S, Ruuska S, Mononen J, Lindeberg H. Reliability of P4 Rapid milk progesterone test for dairy cows — assessment of cyclic activity detection post-calving. 2014.

    • Back PJ, Martin NP, Purchas G, Susnjar M, Yapura J. Validation of a visual estrus scoring system for use in grazing dairy herds. 2012.

    • Mehmedi, Gecaj, Kastrati, Heltai, Turmalaj. Practical application of P4 Rapid in milk for early pregnancy detection at day 21 post-AI. 2021.

    • Omontese BO, Gomes, Santos, et al. Qualitative on-farm milk P4 lateral flow test to predict non-pregnancy in Jersey cows under timed AI. 2020.

    • Omontese BO, Santos AR, Silva LG, Merenda VR, Bisinotto RS. Use of milk progesterone data to predict non-pregnancy in dairy cows subjected to timed AI — preliminary findings. 2017.

    • Turner A. Literature review: can milk progesterone assay predict embryo survival post-AI? Review of P4 concentration thresholds on days 4–7. 2014.

    • Ridgeway Science / P4Gold Team. Progesterone profiling of three dairy cows using P4Gold and ELISA post-AI. 2021.

    • Ingenhoff, Hall, House. Diagnostic sensitivity and specificity of P4 Rapid milk assay for corpus luteum detection in NSW farms. 2016.

    • Waldmann, Raud. Comparison of lateral flow milk P4 test with enzyme immunoassay for reproductive status in dairy cows. 2016.

    • Muasa B, Chagunda MG, Onyango, Peters A. P4 Rapid test with activity monitors (CowAlert) in tropical and temperate dairy systems. 2025.

    • Bonev G. Application of P4 Rapid test and exogenous progesterone in prevention of early embryonic death in repeat-breeder Holstein dairy cows. 2021.

    • Muasa B, Chagunda MG, Ashworth C, Peters A. Cow-side reproductive performance monitoring technologies in dairy cows — a review. 2017.

    • Ball P, Rogerson R, Maconochie G, Peters A, Hollingshead M, Fisher M. The use of a cow-side lateral flow milk progesterone test (P4Rapid) to aid reproductive management in a dairy herd: a case study. 2014.