Monday, 03 September 2018 13:36

Helping to detect cows on heat

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Tail-painted cows on heat. Tail-painted cows on heat.

Gain insight into which cows should be cycling once mating starts with pre-mating heat detection.

The time when a cow is on heat is defined as the period during which a cow will stand to be ridden by her herd mates or a bull. 

It occurs every 18-24 days, averaging 21 days in non-pregnant cows, and it lasts on average 14-15 hours. This time can vary from 2-30 hours.

Pre-mating heat detection is an opportunity to practise heat detection skills and gain insight into which cows should be cycling once mating starts.  

It is also the easiest way to identify non-cycling cows, and gain insight on whether intervention is required. It also gives the team an opportunity to practice their heat detection skills before AB starts.

Use tail paint to identify cycling cows. Use one colour tail paint to start, then a second colour to re-paint as cows cycle and need to be re-painted. Within two weeks about half the cycling cows should have been identified. At three weeks, cows with the original colour are the non-cyclers or cows that have had very weak cycles.

Calculate the herd’s pre-mating cycling rate, if cycling is less than 75% of the herd by 10 days before the planned start of mating, heat detection has not been fully effective and/or there are too many non-cyclers.

At that stage it is time to consider the options to improve heat detection during AB and whether to treat non-cycling cows.

Heat detection aids

The best heat detection starts with careful planning, good observation and the effective use of detection aids.

Being able to interpret cow behaviour and other signs is critical, as is good record keeping and training for the people doing heat detection.

Start by reviewing the farm’s heat detection skills: does everyone know what to look for when detecting cows on heat? Then decide which combination of aids the farm will use (tail paint, heat mount detectors, activity meters and heat synchronisation).


Tail paint is an inexpensive and effective way to detect cows on heat. Correct use of tail painting can identify almost 90% of cows on heat.

Tail painting helps pick up cows that are only on heat for a short time and would otherwise be missed without a heat detection aid.

How to tail paint

- Use commercially available specifically formulated products

- A strip about 60mm wide and 150mm long (2” x 6”), painted along the ridge of the backbone immediately above the tail will do the job.

- Remove loose hair and dirt before applying tail paint. Don’t apply paint too thickly.

- When applying tail paint for the first time apply the paint from the tail pushing towards the cow’s back; this will lift the hair and make it easier to detect heats when the cow is ridden. A cow that is ridden will either have the paint rubbed off or have the hair pushed down and dirtied by mounting.

- Check the paint strip each milking. In 90% of cases, most of the paint will be rubbed off when a cow is on heat. A further 5% of cows will lose some paint, and with the remaining 5% confusion can occur so experience in reading tail paint is needed for these cows. Paint is rarely removed by occasional mounting of cows not on heat in the yard or race.

- Cows detected on heat and then inseminated should not be repainted until the following milking. Use a different colour when re-painting inseminated cows. Unmated cows are then easier to identify.

- Touch paint up at least weekly.

Heat mount detectors

- There are two types of heat mount detectors: pressure-activated tubes or scratch-off patches. Applied to the cow’s backbone, the detectors will become brightly coloured and easily recognised.

- Heat mount detectors should be applied just before mating starts, then monitored for activation and removed at insemination. If they are damaged or coming loose they will need to be replaced.

- Heat mount detectors can be particularly effective on farms with staff who are less skilled at checking cows on heat since less ‘technique’ is required to apply or read them. 

They also reduce the time required to re-fresh tail paint. However, they are more expensive and can still provide false and missed heats.

Using heat mount detectors

Apply heat mount detectors according to manufacturers’ instructions.

Check for other signs of heat if the detector is lost as it may indicate the cow is on heat.

Consider combining heat mount detectors with tail paint. Combining two heat detection aids may reduce the risk of missed heats.

Electronic heat detection

There are a variety of electronic heat detectors in cameras and activity meters.

The heat detection cameras ‘read’ heat from heat mount detectors.  The camera systems work with drafting systems so both need to be installed to use the product.

Activity meters are electronic transponders that detect movement, either attached to the cow’s leg or hung around their neck.  They record cow movement as cows on heat typically walk more as they are restless, mounting and being mounted by other cows.  

The amount of activity is compared to previous days to identify spikes in activity and ‘identify’ heat.  Some brands compare cow activity to the rest of the mob on the same day.  

This can be adjusted for days when there might be a long walk to a back paddock.  

• Article sourced from DairyNZ

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