Heat Detection: Is Your Heat Detection Method Ineffective?

Why do we need heat detection?

Heat detection is an essential component of the dairy industry. Missed or mistimed heats lead to increased calving periods and a resulting financial burden. Similarly, wasted Artificial Insemination (AI) and loss of pregnancies caused by mistiming of AI adds to this financial burden. 

There is a plethora of heat detection aids on the market, ranging from simple mount detectors to fully automated robotic in-line systems. These heat detection aids all come with their pros and cons, and often the best strategy is a mix.

Traditional methods

Some cows vocalise more during heat.
Some cows vocalise more during heat.

The most traditional method of heat detection is observing for bulling behaviours. Farmers observe their herd and look out for the tell-tale behaviours of standing heat or bulling. This is when a cow will mount other cows, so allow other cows to mount her. Unfortunately, unless the herd is under observation 24/7, some heat behaviours will be missed. Some cows also experience ‘silent heat’ where they don’t show these behaviours.

Other visible signs of heat can be mucous discharge and swelling or reddening of the vagina, sniffing other cows’ genitalia, restlessness and many others. Standing to be mounted is the only true indicator of heat. However, even this behaviour sometimes occurs in cows which aren’t in heat. Other behavioural indicators can happen around oestrous but cannot be used as a clear indicator for timing of AI. Furthermore, other factors such as housing conditions, nutrition and weather can affect these behaviours. 

What heat detection aids are available?

Given the issues with missing signs, silent heat, and other factors, many producers now use alternative methods of heat detection. Sometimes these replace observation, or add to it. There is a wide range of aids available. Here are a few examples and a brief look at how they work.

Mount detectors

Pressure-sensitive mount detectors, tail paint, and electronic mount detectors all work using similar principles. The idea here is that the detector sits on the rump of the cow. The cow will stand to be mounted, and this mounting behaviour will be detected. It could be by rubbing off the tail paint, or by sending an electronic signal to the monitor. Issues will this type of aid can be misplacement of the detector, false bulling behaviour and silent heats. On the other hand, these can be valuable methods to detect mounting when farmers can’t observe their cows as frequently. Likewise, if farm workers are less experienced in recognising heat, a mount detector can be very helpful. 

Activity monitors

Pedometers measure the activity of cows. It is well known that cows in heat are generally more active. This can be great for use in busy farms without the resource to observe animals regularly, but it has its issues. It can also miss silent heats, like other behavioural measures, as these animals might not show increased activity. Agitated cattle or cattle being moved regularly may become more active than usual, causing inaccurate readings.

Vaginal electrical resistance

The resistance of vaginal fluid is measured using a probe. Electrical resistance changes throughout the cycle and this can be a great way of tracking a single cow’s heat. This technique is more hands-on and difficult to incorporate into a management system than others. For single cows or small herds, it could be a workable solution, but might be hard for large herds.

Heat expectancy charts

As cows generally have a regular 21-day cycle, careful tracking can help to predict when they will come into heat. Farmers can mark when cows were in heat or when they saw oestrous behaviours so they can time AI for the next heat. These charts are useful but not all cows follow a perfect 21-day cycle. It can be different for every cow and ranges from 19-24 days. Similarly, it requires close observation of individual cows, so can be extremely time consuming. This could be used alongside observation or other heat detection methods, but might be difficult to implement for a larger herd. 

Progesterone testing and monitoring

P4Gold is a farm-side progesterone test in milk for heat detection.
P4Gold is a farm-side progesterone test in milk for heat detection.

Progesterone testing is one of the most accurate and reliable heat detection methods. The hormonal cycle of cows is very predictable. Cows in true heat will have low progesterone levels, so this identifies false bulling. Progesterone is present in milk as well as blood, which provides a convenient and non-invasive method of testing.

This can be incorporated into the management of a herd using pen-side testing with products such as P4Gold, to help confirm heat in suspected cows, or by using in an in-line automated system. Similarly, milk samples can be tested in a laboratory to give more in-depth information regarding the cows’ oestrous cycle.

It can also be used on ‘problem’ cows who experience silent heats, or to assist in determining what is happening when cows are showing cycles of abnormal or varying lengths. Additionally, where sexed semen is a factor, timing is crucial to ensure expensive semen is not wasted. As a result, confirming heat prior to insemination is a must. For more information on how progesterone can be used in heat detection, read our article.

What is the solution?

Farmers may use heat detection methods for all of their herd, or use observation for the majority and only monitor or test animals that they are unsure of or have not observed any heat behaviours from. The issue with many heat detection aids is that they still rely on behaviour of the animal which can sometimes be unreliable and lead to missed heats or mistimed AI. These can also miss silent heats. The answer here would be to take a second test or use a progesterone test in conjunction with or instead of these, to obtain an accurate result based on the hormones being produced by the animal instead of behaviour that can be influenced by external circumstances.

In most instances, it is safer and more economically sound to test when unsure of heat, as the money wasted on an AI straw and an increased calving interval can turn into a large financial burden across a farm. Similarly, inseminating an already pregnant cow can lead to spontaneous abortion, again leading to a loss. In this instance, it pays to be sure.