Heat detection always requires some degree of human intervention. This is because our only indication of estrus is the cow’s abnormal behavior.

Consider these facts:

1. The average cow is in heat 10 of 504 hours of her estrus cycle (10 hours out of every 21 days).

2. Abnormal activity occurs in spurts (riding, being mounted) that last approximately eight seconds each.

3. Cows demonstrate significant variation in strength and length of this abnormal estrus activity due to footing, environment and number of herdmates in estrus at the same time.


Owners and managers of large dairies need to consider the optimum heat detection method to incorporate on their dairy. Options include observation, a crayon tail stripe, technologic aids such as pedometers or heat-mount pad systems or ovsynch. The method of heat detection you select is not as important as your ability to manage your workers who implement the system. Let’s examine your options and discuss how to maximize results through your workers.

Observation for estrus activity is no longer used on most dairies as a primary method to detect heat; it requires intense human interaction. Acceptable heat detection rates are attainable only when persons are available both day and night to observe cows continuously. Observation as the main type of detecting heats is generally thought to be not cost-effective for the man-hour investment required.

If you select this method as your main heat detection effort, be prepared to develop schedules for cow pushers, maternity personnel or outside workers to walk pens on a predetermined schedule to provide ample time for them to find cows in heat. Provide preprinted forms for workers to use so that heats reported throughout the day and night can be evaluated by the breeder the following day. Feedback for workers with this type of heat detection is crucial so they know their efforts are producing results. A casual approach to observing heats rarely works; you may hope your workers are always on the lookout for cows standing or riding, but this effort usually isn’t consistent enough to affect results.

A crayon tail stripe is a widely used technique that depends heavily on the ability of the breeder. The principle is to inspect every cow every day for evidence of crayon rub-off suggesting mounting activity since the last crayon application. Examining animals for secondary heat signs (e.g., swollen vulva, mucus, ruffled hair on the back or palpating for uterine tone) and mucus are additional steps a herdsman can use to determine estrus with this method. I find there is great variation in heat detection success with crayon tail striping due to “people error.”

Cows exhibit large variation in demonstrating signs of estrus. (See graphic on page 29.) Herdsmen or breeders may not be able to evaluate every cow daily, making reading the “partial rub-off” (the cow in heat but with weak signs of standing) extremely difficult. Many breeders do not understand that their routine requires two steps: Read the crayon tail stripe, then to reapply the crayon stripe once again.

When expected to evaluate several hundred cows every morning, herdsmen and breeders may hurry, cut corners and fail to take sufficient time to thoroughly evaluate the “questionable” cow. Breeders and herdsmen easily lose focus when unsupervised while doing tail striping. You can teach your breeder to follow a program to evaluate every cow daily and develop a “thought process” to make insemination decisions such as I’ve shown using the tail striping decision-making flow chart. (See Graphic 3 on page 29.) But monitor results and provide feedback daily so that breeders realize that they are being evaluated on their results.

Technology, such as pedometers and heat-mount patch systems, seemingly takes human error out of the heat detection program. But these systems have not gained widespread acceptance, possibly due to cost. Worker intervention is still essential; someone still needs to attach the pad or strap, account for those rubbed off or lost, read and analyze daily activity reports and make the ultimate cowside decision “to breed or not to breed.” If you use this technology, make sure reports are available to your workers on a timely basis and your workers have the information to make correct decisions.

To circumvent all human intervention and error, hormone injection programs to control ovarian activity are popular. While these seemingly eliminate “the human element,” this is simply not the case. Most ovsynch-type programs require a minimum of four critically timed hormone injections in sequence over 10 to 14 days on all cows enrolled in these programs. Several field studies have identified that, due to human error, compliance rates to inject all cows occurs only 85 percent of the time. So 15 percent of all cows inseminated will not become pregnant because injections are missed, poorly administered or not given at the correct hour.

Here is another consideration: even if all hormone injections and breeding are done correctly, only four out of every 10 cows will become pregnant (assumes a 40 percent conception rate). That means six of every 10 cows will come back in heat in 21 days ... who is going to find them?

Recognize that ovsynch does not replace heat detection on the repeat breeder cow unless you implement a resynch program with your veterinarian. There are many variations to implementing ovsynch programs in your herd; work with your veterinarian to determine the best system for you. Be sure your facilities are adequate to allow workers to inject every cow on a timely basis. And explain to workers how timing of injections is critical to success of the ovsynch program.

As I work on dairies across the U.S. and Mexico, I see the best heat detectors have these things in common:

1. They are organized ... cows are locked or available; their heat detection work system is planned, and these workers proceed through corrals or pens according to a consistent plan.

2. They are focused ... all attention is on cows and cow activity; no distractions allowed.

3. They like cows, their jobs and the challenge ... they are “the right person for the job.”

4. They know their results and try always to improve ... they are professionals at what they do and take pride in their accomplishments.

As an owner or manager, it is your greatest challenge to hire and focus your breeder or herdsman to demonstrate these characteristics. Even when you employ genetics companies who supply their personnel to breed your cows, you need to evaluate whether or not their representative is organized, focused, likes his/her job and produces results.

Let me describe one of the best heat detectors I’ve ever seen. He works in a 1,500-cow freestall herd that utilizes both ovsynch and crayon tail striping. Records identified his heat detection results to be above industry standards.

He wears a miner’s light headband (daytime and in the dark), which he focuses on the crayon-marked back of every single cow. He reads then reapplies crayon to every cow. He concentrates on both the crayon stripe on the cow’s back as well as the vulva for all signs of heat. He identifies the special marks used in this herd to identify cows in various stages of the ovsynch program. He carries a herd report of all previous heats for each cow in the herd. He strides through the pen at a rapid pace, restriping every cow. This technician is so focused on tailheads, cows’ backs and vulvas and making decisions, that he is seemingly unaware of anything or anyone else around him. He is a successful breeding specialist.

Heat detection is both an art and a science. You need to be certain your workers know the facts, and you must monitor their performance by both watching them and providing feedback on results. Your breeding program will be successful, if your breeders and herdsmen are successful professionals. PD