Heat detection analysis using an activity meter in grassland systems

The objective of this study was to evaluate how the increase of detection of heats, through an activity meter system, can contribute to the reproductive performance on a dairy in grassland conditions.


Heat detection has become a concern during the last years with in the dairy industry. The main reason for this is that the reproductive indexes have been negatively impacted by the high yield performance of the common cow breed. Many studies clearly shows that the heat signs are weakened and that the duration of the standing heat has shorten and that clear heats sign are more common during night hours. Figure 1 show the percentage of total mounting activity during 24 hours. It is notable that efficient heat detecting should be done during late evening or night.

After calving, the cows milk production increases and peaks after approximate 100 days. It is known that the energy balance is negative during this period of time and this affects the reproductive performance. The South American region has been growing significantly in milk production during the last years and has become a profitable business compared to other activities in the agricultural area. This is due to an increase in milk price in the world and that the cost of production in the region has been significantly lowered. The graph below shows the price paid to the producer in the different countries.

Country Milk Prices 12 Month Rolling Average

Materials and Methods

General reproductive management is a wide area and demands many activities from the dairy farmer, heat detection is being one of them. The DeLaval activity meter system is a tool designed to aid the farmer in heat detection. The DeLaval activity meter system registers the animal’s movement pattern via its neck mounted tag. A neck mounted tag gives best cow comfort compared to a leg mounted tag.

The activity tags sends its data via RF link on a 24 hour schedule, via an antenna,to the main processor, the data is continually updated. The processor does the analysis per individual cow and takes into account the specifics of the animal; a calm animal will be treated differently from a lively animal. The activity meter system delivers accurate heat alarms and start time for the heat. Start time for the heat will allow for optimum insemination time, imperative for the conception rates.

General studies world wide shows an increase of heat detection in the farms where this equipment is installed. As many of the studies were done on confined or semi confined systems, grassland countries have, until now, been limited due to the antenna reach. Research in Oceania combined with product development has resulted in a new directional antenna that has a reach up to 800 m distance. The farm selection for the study was done in the region of South America and a commercial dairy farm in Argentina, the Campazú located in Vicente Casares in Buenos Aires province, was selected. The duration of the research was established to be 6 months.

The Campazú farm has 260 Holstein cows with an annual average production of 28 liters per cow and day and was equipped with 100 activity meters. The nutritional aspects include pastures base with different species of grass and complement of corn silage and a mixed ration.





The cows are held in different day and night areas,all secluded by electric fencing, as seen in the scheme below.

The 260 cows are managed by three persons plus a fourth that operates the feed mixer. The first three are milking the cows in a double 8 milking parlour, they milk in 3 hours session twice a day; and they are also in charge of heat detection and breeding. Heat detection is done by visually inspection which includes inspections from 10 am to 12 pm in the field, during milking and in the evening from 6 pm to 8 pm in the field.

The reproductive performance registered in the farm until October 2005 was as follows:

Days to first service 101 days
Calving interval 15,5 months
Service per conception 3,7
Days open 198 days

The average Calving interval (CI) was 15,5 months and it was distributed as:
CI 12 to 13 months: 38%
CI 14 to 15 months: 19%
CI 16 or more months: 42%

As the study was focused on evaluation on how activity metering can contribute to the reproduction in the farm, only heat detection was assessed and modified according to the results of the activity meter equipment. Considering and discussing the condition of the reproduction with the owners of the farm, it was reached a common agreement not to do changes in the reproduction routines. The activity meter was installed in the herd and half a day of training was conducted with the three persons that interact with the cows.

The materials installed for the test were:

– 1 Processor: the main component that receives the information from the antennas and communicates with the local computer.

– 100 activity meters with neckband: Individual device installed in each open cow.

– 2 antennas: Two long distance antennas.

The installation was done in one day, installing the antennas, the laptop computer and a laser printer. The tags where mounted on the selected cows during a milking session (the selection criteria was that the animals where open). The data recording started 5 days after the installation was completed. The staff was instructed to use the high activity alarm report that was printed automatically before each milking session. The information that appears in the report is as seen below:

This report was added to the list of visual detections generated by the staff, containing cows that needed to be checked and evaluated for insemination. The only added work for the person that inseminates the cows was to get the report from the printer.
The coverage of the antennas was done on the area where the cows are in the night period as show the graph below:

The system is continually measuring the cows movement pattern no matter if it is in the reach of an antenna. Latest 24 hours of data is delivered every time the antenna receives data from the activity tag.

Work routine:

Daily: consists in using the two reports per day, each one before the milking session. The cows that appeared in the report where inseminated or checked. The heats were registered only if the cow did not achieve the Voluntary Waiting Period (VWP) of 60 days. The insemination was done twice or three times a day and the start time of the high activity was considered.

A registration form was established in order to evaluate the performance of the equipment. The cow number, if the cow was detected by the Activity meter system, if the cow was detected by visual observation, the heat starting time of both and the insemination time and the name of the bull was registered.

Every pregnancy check: Cows were checked 60 days after service and that were not found in heat. If the cows did not reach a pregnant diagnosis, the tag was removed and stored to be mounted on another open cow.


Different aspects were evaluated in order to asses the benefits and drawbacks of the reproductive performance in the dairy.

  • a) Calving Interval: When the study was started 38% of the cows were in the range of 12 to 13 months of calving interval with an average of 15.5 months. After the study finished the calving interval was estimated to 13.4 months with 57% of the cows estimated to calve every 12 to 13 months.


The economic impact on milk production is clear. If we do an estimate on only increase in milk production for the coming 4 years, the results are as below:


Without the system
1st Year 2nd Year 3rd year 4th Year
 1.612.202  1.635.410  1.709.958 2.127.689
With the system
1.602.251 1.736.000 1.861.441 2.322.060

Taking only into account the increase in milk production in the coming 4 years ,it represents a gain of 226,000 pesos (75,000) USD.

  • b) Service per conception: The heat start time provided by the activity meter system helps significantly the breeder at the moment to decide to breed the cow or not and at what time inseminate. This generated a reduction on the Service per conception from 3,7 in October 2005 to 1,9 in April 2006. As the farm have 200 pregnancies per year and considering a semen cost of 40 USD per dose, the cost of semen for pregnating a cow was reduced from 148 to 76 USD per cow and year (14,400 USD per yea)r. The study also shows a great increase in the conception at first service, here the time of the insemination played an important role.
  • c) Heat Detection: The evaluation took in consideration the total numbers of heats found in 22 days before and after the start of the study and considering the heats detected by the system that where added to the ones detected by visual observation.

The increase of heat detection from visual observation only and from using the visual observation combined with the activity system is shown in the two graphs.

If we compare the number of cows that where to be inseminated before and after the system was installed we can see the following results:

  cows to inseminate   cows inseminated   % inseminated of 60 days 
Without activity system    81  37    45
With activity system  59  49  83

There is a clear increase of the number of cows inseminated during a 60 days period after the installation of the system. This clearly reflects the fact that more cycles where detected and obviously more cows where inseminated.

Heat registered was as the graph shows below. We can see that 53% of the heats were registered between 7 pm to 6 am. This clearly establishes the importance using a system that can detect heats during the night.

Considering the collected data and the recommended time to inseminate the cows (10-16 hours from the registered time from the herd management system) the results were as show below.

As the best conception rates were registered when cows were inseminated between 6 to 8 hrs, a decision to inseminate cows earlier was taken and the results from November 05 to April 06 was the one presented below:

This measure increased the conception rate in the entire herd and concluded that the best insemination is 7-8 hours from the activity meter systems high activity start time.

The final analysis that was done was to evaluate the different conception rates that both system had (visual detection and the activity meter). A clear advantage of the activity meter system was shown from the fact that 42% of conception rate on the cows that were detected only by the meter versus 33% of conception rate of the cows detected by visual observation. The graph below shows the results.


The conclusion of this study is that heat detection increases through the activity meter system, this can contribute in the different parameters of the reproductive performance in grassland conditions.

Night heat observation is the key of the success of the system. Through the activity meter the cows are measured 24 hrs a day and during night hours visual heat detection is difficult to do specially in grassland systems were the cows are in the field during the night.

A clear advantage is that the system provides a tool that delivers a starting time of the heat. This allows the breeder to inseminate the cow in the optimum time, achieving increased conception rates.


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Patrick D. Burns, PhD Reproductive Physiology, CSU

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