The Oestrous Cycle

The cows reproductive cycle is termed the oestrous cycle and consists of several phases including a luteal phase (after ovulation the corpus luteum is formed) and a follicular phase (luteolysis and ovulation)1. A healthy cow typically has a cycle between 18-25 days long, during which the progesterone levels increase and decrease systematically.

What Is Progesterone?

Progesterone is a steroid hormone and is produced by the corpus luteum in the ovary after ovulation. If a cow falls pregnant, the corpus luteum will be maintained and continue to produce progesterone, which helps to maintain the pregnancy. Eventually the corpus luteum will disappear and the placenta will take over production until birth. If a cow remains unfertilised, the corpus luteum will reduce in size (lutolysis) and the levels of progesterone production will decrease. The production of progesterone is correlated with the oestrous cycle, and is inversely proportional to the production of Oestradiol, which stimulates oestrous behaviour2. Due to this correlation, progesterone can be measured in the blood (as plasma or serum) and the milk at any time during a cows oestrous cycle.

How Can Oestrous Be Detected?

Oestrous takes place in the follicular phase of the cycle and is what is known as standing heat in cows, where they display mating behaviours such as bulling signifying sexual receptivity and fertility. Typically, farmers and Artificial Insemination (AI) technicians will identify heat using behavioural observations such as increased activity, bulling, excess cervical mucous2 and many others. Additionally they will also use other measures such as mount detectors, pedometers, collars, milk yield to name a few. Though these measures have been popular for years, they are not necessarily sensitive or specific enough. In addition, these signs may only be visible for short periods of time or not exhibited at all if a cow is experiencing a silent heat. Cows may also stand to be mounted to exhibit bulling behaviour when they are not actually in heat at all. The environment the cow is kept in can also suppress heat behaviours. Due to these errors, it is typical that silent heats are missed, AI is mis-timed and even insemination of a cow already pregnant.

Progesterone measuring is an extremely accurate alternative to traditional methods of heat detection. By testing a milk sample, it can accurately be defined whereabouts a cow is in her cycle and thus lead to whether or not/when she should be inseminated. This is also a great tool to use for aiding diagnoses of ovarian cysts.

Tracking progesterone is the most reliable way to confirm heat, allowing assessment when cows are falsely displaying signs of heat and detecting heat in those cows which fail to show signs. By tracking progesterone, both fertility and productivity of the herd can be improved.

For an in depth explanation about reproduction in cattle that is easy to understand, visit NADIS.

RRL Progesterone Testing

In House Testing Service

RRL provide quality quick turnaround in house testing services of cattle milk and blood. All we require is your samples sent as fresh as possible. We also provide progesterone testing for many other species including sheep and goat. If you would like to enquire about in-house testing, how to send in your samples and for prices click here or contact Jeremy at

On Farm Tests

RRL manufacture a number of on farm tests available for use by veterinarians and farmers alike. For more info on this check out our products Heataid and P4Rapid.

Laboratory Immunoassays

RRL produce a range of quality immunoassay kits for laboratory use only. Please see Progesterone ELISA kits for more information.


1. N. Forde, M.E. Beltman, P.Lonergan, M. Diskin, J.F. Roche, M.A. Crowe. 2010. Oestrous cycles in Bos Taurus cattle. An. Repro. Sci. 124;163-169.

2. A.R. Peters, P.J.H. Ball. 1995. Reproduction in Cattle. Second Edition; pp. 23-62.