sion, thus increasing health and longevity to increasing yield traits afforded by genetic selection. Oestrus detection is often cited as the most costly component of an AI
program. An estimated annual loss of US300 million to the USA dairy industry Ž
occurs because of the failure to detect oestrus or the misdiagnosis of oestrus Senger, .
1994 . The efficient and accurate detection of oestrus and the timing of resulting AI remain major challenges to improving reproductive and economic efficiencies of many
Ž dairy farms Foote, 1974; Gwazdauskas et al., 1986; Heersche and Nebel, 1994; Senger,
. 1994 .
Methods of oestrus detection used in investigating time of ovulation have varied. Ž
Some investigators have used frequent visual observation DeSilva et al., 1981; Larsson, .
Ž 1987 , frequent exposure to teaser animals or other cows Brewster and Cole, 1941;
. Nalbandov and Casida, 1942; Mattoni et al., 1988 , or a combination of frequent visual
Ž .
observation with oestrus detection aids Rajamahendran et al., 1989 . Physical verifica- tion of ovulation in most studies has been by palpation of the ovaries per rectum at
Ž frequent intervals Brewster and Cole, 1941; Nalbandov and Casida, 1942; Trimberger,
. Ž
1948; Mattoni et al., 1988 or by frequent ultrasonography Larsson, 1987; Rajamahen- .
Ž dran et al., 1989 . Ovulation has been timed from the cessation of oestrus Brewster and
. Cole, 1941; Nalbandov and Casida, 1942; Trimberger, 1948 and from onset of oestrus
Ž .
Larsson, 1987; Mattoni et al., 1988; Rajamahendran et al., 1989 . In general, these studies did not contain either an adequate number of observations or continuous
observation for behavioral oestrus to accurately determine the relationship of behavioral oestrus and occurrence of ovulation to determine the optimal time of AI.
Traditionally, AI has followed the a.m.–p.m. guideline established in 1948, which recommended that cows observed in oestrus in the a.m. should be submitted for AI in
the p.m., and cows observed in oestrus during the p.m. should be submitted for AI the Ž
. following a.m. Trimberger, 1948 . Although ovulation time was reported from the end
of oestrus, it was noted that initiation of oestrus was important for AI. Timing of AI from the onset of oestrus is important and quite evident when reviewing results of recent
Ž research using electronic methods that determine the onset of standing oestrus Maatje et
. al., 1997; Dransfield et al., 1998 .
There are many physiological, behavioral, and hormonal changes that take place Ž
. during the oestrous cycle of the heifer or cow Allrich, 1994 , but many of these changes
are highly variable among animals and are impractical to measure routinely. This manuscript will emphasize several manifestations of oestrus, which can be measured and
have been correlated with ovulation and succeeding conception.
2. Pedometry
Almost 70 years elapsed between the first published recognition that female mam- mals display a predictable increase in physical activity when in oestrus and the first
Ž .
potentially useful field application of pedometry Kiddy, 1977 . The first critical
description of the relationship between physical activity and stage of the oestrous cycle Ž
. utilized 13 Guernsey cows on pasture Farris, 1954 . Cows equipped with mechanically
activated pedometers were characterized as having a 218 higher physical activity
during oestrus than during late diestrus and proestrus or during metestrus. More than 20 years elapsed after this report before research at USDA in Beltsville, MD revived
Ž interest in pedometry as a practical tool for oestrus detection of dairy cows Kiddy,
. 1977 . The average increase in activity at the time of oestrus was 393, or approxi-
mately four times the activity of cows not in oestrus when housed in a free stall barn. When cows were housed in comfort stalls, cows in oestrus were about 2.76 times more
active during oestrus, indicating that the type of housing influences the magnitude of change in physical activity. It was noted that the daily activity for each cow must be
monitored and activity associated with oestrus compared to that obtained during the other stages of the oestrous cycle for pedometry to be most effective in identifying cows
in oestrus. Individual cows differed significantly in the amount of activity expressed
Ž .
Ž .
under the same conditions. Hurnik et al. 1975 and Amyot and Hurnik 1987 studied the activity of cows continuously monitored with time-lapsed video recording. Their
investigations revealed that cows spend considerably more time walking when in oestrus and less time resting and eating than when they were not in oestrus.
Continuous visual observation combined with pedometer measurements confirmed that continuous observation is more reliable than pedometry and periodic observations
Ž .
Pennington et al., 1986 . A pedometer modification was made that internally compared the activity change during a specific time interval to the five previous a.m. or p.m.
activities recorded. This modification was implemented to account for individual activity variation reported in previous studies. Sexual activity during periods of moderate
weather was shifted markedly by management practices, but only slightly by diurnal tendencies. It was recommended that when establishing a schedule for periods of visual
observation more concern should be given to disruptions of activities caused by management practices such as feeding and milking than the possible increase of the
nocturnal occurrence of oestrus. Their recommendations for visual observations of oestrus focused on location with least crowding and best footing being primary to time
of occurrence.
Using a similar pedometry system simultaneously with time-lapsed video recording, Ž
. Varner et al. 1994 reported that walking activity increased in the 4 h prior to the onset
of oestrus. Peak mounting activity occurred during times of low walking activity for the entire herd. This may have been influenced by the social dynamics of mounting
behavior. Cows may be able to locate a sexually willing partner easier when there is less overall herd activity. Alternatively, the oestrual cow may be occupied with eating and
milking activities, similar to her herdmates, which prevents them from engaging in mounting activities. Behavior trends of high mounting activity during times of low
pedometer readings should be considered by system designers to increase the sensitivity of pedometry as a tool for the detection of oestrus.
A commercial pedometry system designed for dairy cows where activity is recorded Ž
. as steps per hour Afimilk Pedometer, Afikim, Israel was used to determine the effects
Ž of cow age, parity, milk yield, and days in milk on activity identified at oestrus Arney
. et al., 1994 . Mean dioestrous activity was not correlated with any other animal
characteristics. Activity measurements were significantly greater in the p.m., 160 steps
y1 y1
Ž .
y1
h , than the a.m., 145 steps h
. Arney et al. 1994 determined that steps h from 72
to 16 h before oestrus gradually increased linearly. From 16 h to oestrus, steps h
y1
increased more rapidly and linearly to peak oestrus, followed by an exponential decay with no refractory period post-oestrus.
The optimal time of AI based on pedometer readings was predicted using mathemati- Ž
. cal models and rectal palpation of 171 cows Maatje et al., 1997 . The pedometers
Ž
w
. Boumatic Heat-seeker-TX ; Dairy Equipment, Madison, WI were set to produce an
Ž .
alarm signal flashing light when the mean activity of the last six 2-h periods was more than double the mean activity of the last six corresponding 2-h periods for the previous 2
days. Retrospectively, the time of the onset of oestrus and the number of hours from the beginning of increased activity to the time of AI was determined. The onset of oestrus
was determined as the first 2-h period in which the mean pedometer reading for the current 12-h window was twice the running mean of a comparable period in the previous
2 days. Chance of pregnancy was highest between 6 and 17 h after increased pedometer activity, and the calculated optimum time of AI was 11.8 1.7 h. The aim of most
Ž .
published applications of pedometers until Maatje et al. 1997 has been to improve rates Ž
. of oestrus detection. A review by Lehrer et al. 1992 stated that 70 to 80 of cows in
oestrus are detected by pedometer measurements. Pedometry systems, which allow identification of the onset of oestrus in addition to efficient and accurate oestrus
identification, will increase the usefulness of such technology in animal breeding. However, all current pedometry systems do not use real-time data transfer, thus
requiring the activity information to be retrieved by an interrogation device. Therefore, system requirements dictate that retrieval of activity measurements can occur two or
three times daily, usually at milking, reducing the effectiveness of determining the timing of insemination.
3. Pressure sensing radiotelemetric system
