You can use electronic vaginal probes which can be used to monitor the vaginal resistance pattern. You can look it up in detail in Theriogenology literatures.

Thank you so very much Sir for this info.

of course, i can use vaginal probes to detect at least the "estrus" phase/stage. but what of pro estrus, metestrus and diestrus? thats my dilema. am running away from buying kits. 

Many thanks to David and Mehdi.

The usual, and simplest method is rectal palpation. Needs some training to be accurate.

I use rectal palpation of ovaries, uterus and cervix to determine cyclus stage in cattle, but it might not be accurate enough for Your purpose? Ultrasound is another useful methode.

Thanks Adrian and Berit. 

Ultrasound  for detecting different stages. thanks for the reminder. 

The old and good rectal palpation would be simpler way top assess estral phase. But it requires practice!

Thanks Paulo. What of Metoesrus, dioestrus. With physical signs and behaviours, it is easier for detection of estrus and may be proestrus. but the other two???

Besides the uterine tone, the texture of the CL and follicles gives some indications about the phase of the cycle,

Vaginoscopy often gives supplemental informations. If you are lucky, you will see some bleeding in the metoestrus, particularly after having handled the uterus rectally.

The ultrasound may give you data confirming your findings and giving a more accurate and complete diagnosis, but is not essential.

Dear Innocent,

Regarding your question, the simplest and accurate and also practical method for diagnosing estrous cycle in cattle  is using ultrasonography. 

Estrus: you should see a large folicle (diameter: 15-19 mm) in the absence or lysing  of  a CL.

Metestrus: a CH that is hyperechogene than a CL. keep in mind that its diagnosis is difficult than a CL, without any folicle.

Diestrus: an active CL throughout the cycle. additionally, you will see folicles with various diameters (smaller than 10 mm).

Proestrous: a CL that is lysing and one or two large folicles.

If you want more details, see Bovine Reproduction (2015).

Best regards,

Rectal palpation and ultrasound methode.

Best regards,

Vaginal smear methods is a simple way to indentify every stage of cycle. I have some publication about it. the methods as follow:

Sampling of vaginal smear were done by scraping the inside of the epithelial cells of the vaginal wall using a cotton. The smear were stainined using Giemsa.. Determination of the estrous phase is was carried out by observing the morphological changes of vaginal epithelial cells. Epithelial cell shape of each estrous cycle have different characteristics. Criteria phase of the estrous cycle was determined by a percentage based on the description of the morphology of epithelial cells was observed

The biggest and easiest is mapping out her/their cycle.  I would start with initial heat and go from there. semen companies world-wide hand out charts for estrus cycles and breeding records. Rectal palpation of the ovaries are a very useful tool but requires proper training. Both of these allow for easy diagnostic trends. They also have P4 "snap tests" for milk samples that can be run within 5-10 minutes and can be done on farm if you would like a diagnostic tool to help also. Its not a hard thing. Don't over complicate it! Good luck to you!!

Thanks so much Jacob