Electronic Detection of Estrus in Dairy Cattle
by Eeman E. At-Taras and Sidney L. Spahr
TAKE HOME MESSAGES
- Estrous detection was improved by both electronic activity tags (Heat SeekerTM)
and heatmount sensors (HeatWatchTM).
- A new algorithm based on mean activity plus two standard deviations of the
cow's two hour activity counts resulted in earlier detection of estrus than
did the activity ratio algorithm.
- Hot weather decreased the total duration of standing mount activity significantly.
Sound reproductive management is the foundation of a successful
dairy operation, and detection of estrus is essential in an effective dairy
reproductive management program using artificial insemination. It is estimated
that the dairy industry loses $300 million as a result of erroneous diagnosis
of and failure to detect estrus. Significant decreases in milk production, delays
in days to first service, prolonged days open, and extended calving intervals
are all contributing factors to this loss. Traditionally, estrus detection was
accomplished through visual observation of estrous-related signs. This method
is both tedious and time-consuming. Hence, alternate and more efficient methods
of estrous detection are needed.
Recently several sensors have become available as aids for detection
of estrus. We compared the operational characteristics of two of the systems,
HeatWatchTM and Heat SeekerTM, and tested a potential
new algorithm for the Heat SeekerTM system. We also used the sensors
to determine the range and variation for length of estrus under specific conditions.
Description of the sensor systems:
The HeatWatchTM system consists of a pressure sensitive
transmitter (contained in a pouch and attached to the rump of the cow), a receiver
(which receives the signal from the transmitter), a buffer (stores mounting
data until retrieved), and HeatWatchTM software on a personal computer.
Mounts are recorded as they occur and are stored in the buffer until the HeatWatchTM
program is accessed on the computer. The Boumatic Heat SeekerTM
system consists of a battery powered activity tag, a reader, and data acquisition
software. The tag is placed on the leg of a cow and a strap is fitted around
the leg to secure the tag. The tag contains a mercury switch and a memory file
that records leg movements by two-hour intervals. In addition, there is also
a built-in algorithm that determines an activity ratio for each two hour period
by comparing the activity during the last 12 hours with activity from the same
12 hour period in the previous two days. We postulated that this algorithm could
be improved by incorporating standard statistical approaches, comparing recent
activity with the mean plus two standard deviations of the cows 2 hour activity
during non-estrus. Using a retrospective analysis to test this hypothesis, we
compared activity around estrus with activity counts two days before and two
days after the day of estrus to test this hypothesis. Hence, both the increased
activity ratio (> 2.0) and increased activity count were used as indicators
of increased activity associated with estrus.
Sixty Holstein, Jersey, Brown Swiss, and Ayrshire cows housed
in free stalls and a concrete lot were fitted with a Boumatic electronic activity
tag (HeatSeekerTM) on the right foreleg and a HeatWatchTM heatmount
detector on the rump. Physical and mounting activity data were collected for
120 estrous cycles (82 single estrous cycles and 38 concurrent cycles). Twenty-three
of the cows were monitored during spontaneous estrus; these cows were kept on
the trial until diagnosed pregnant (at 35 to 45 days post-breeding) or until
150 days on the trial. The remaining 37 cows were given 5 ml of LutylaseTM
(Upjohn, Kalamazoo, MI) in groups of three or more upon confirmation of a corpora
lutea via rectal palpation; these cows were removed from the trial upon
breeding. All cows were observed daily for visual signs of estrous. Data were
analyzed using a statistical model that included parity (primiparous vs. multiparous),
group (single or multiple cows in estrous), and weather (hot or cool). Summer
was considered as hot while the other seasons were considered cool.
The efficiencies of estrous detection for the HeatWatchTM,
increased activity ratio, and increased activity threshold count were 80.2%,
82.3%, and 86.9% respectively; visual observation only detected 54.5% of all
predicted estrous periods. Parity and single or multiple cows in estrus had
no effect on mounting activity. However, weather had a substantial impact on
standing mount activity; average standing mount duration was decreased from
6.76 hours under cool conditions to 2.97 hours under hot conditions (P # 0.05).
Figure 1 shows a typical graph indicating start of increased activity
count and increased activity ratio. The activity count threshold algorithm detected
estrus earlier (2.61 hours) than did the activity ratio algorithm when considering
33 of the 35 estrous periods (P # 0.02). The remaining two estrous periods were
characterized by increased activity both before and after peak mounting, but
contained periods of low activity that coincided with recorded mounts; these
cows were omitted from the analysis. The duration of time above the increased
activity ratio threshold (2.0) exceeded the time above the increased activity
count threshold (24.0 hr vs. 9.7 hr) in the 33 estrous periods that were analyzed;
in spite of this, increased activity count above the threshold overlapped with
mounting activity for a significantly longer period of time than did increased
activity ratio (6.13 hr vs. 4.41 hr). This supports our hypothesis that the
activity count threshold algorithm may be a better indicator of estrus since
it corresponds more closely with standing mount behavior and detects estrus
earlier than does the activity ratio algorithm.
In summary, both sensor systems used in this study improved detection
of estrus relative to visual detection. The HeatWatchTM system was
particularly attractive because it recorded actual standing mounting behavior.
However, keeping the sensor transmitters attached to the cows required considerable
maintenance; a more secure method of attaching transmitters to the cows would
improve efficiency of the system immensely.
The Heat SeekerTM system required little maintenance.
However, its data acquisition system (collection of the summary of activity
ratios for the past 12 hours as the cow passes through an antenna at milking
time) may result in an undesirable time lag relative to the instantaneous transmission
of data in the HeatWatchTM system. Our results suggested that efficiency
of estrous detection by the Heat SeekerTM system could be improved
by collecting the activity counts at periodic intervals throughout the day,
and using an algorithm to detect the presence of estrus that was based on standard
statistical procedures. This procedure would require telemetric collection of
activity counts between milkings, and a personal computer to perform the test
to detect increased activity. Collection of activity data between milkings would
require changing the method for transmission of data from the current Heat SeekerTM
system that requires the cow to enter an electromagnetic field around an antenna
to one that could send its data upon command to a more distant antenna, similar
to the method used with the HeatWatchTM system.
The figure may be viewed in the PDF