. provided by MPB Lamsor . However, since direct measurement of skin temperature
during the test would have interfered with the procedure, we report, following Fan et al. Ž
. 1995 , the actual energy supplied by the laser and the latency to respond rather than
skin temperature at the time of response. The laser was placed on a tripod approximately 2–3 m from the animal. Animals
were prepared by shaving the hair off the hind legs between the dew claws and the hock the day before the experiment. The laser was aimed at the shaved area and turned on
until the animal responded, immediately after which the laser was turned off. The response involved the animal moving the foot on which the laser was aimed, either by
kicking, lifting the leg or simply moving the foot. The laser was also turned automati- cally off within 20 s even if the animal did not respond. Tests were interrupted and
redone if the calf defecated, urinated, walked away or moved its body in response to disturbances. Testing was conducted by two persons, one acting as the laser operator, the
second as an observer. Examination of the animals’ legs throughout the experiment showed no signs of blistering or skin damage for any of the animals.
2.2. Animals and housing A total of 60 male Holstein calves were used. In experiments 1 and 4, we used
castrated calves, 6–8 months of age, which were held in individual crates, 2.5 m = 1.0 m, in a controlled environment facility. Water was available ad libitum to each animal,
Ž through an automatic water dispenser. Cubed alfalfa was presented twice daily 0800
. and 1500 h
according to NRC guidelines for the age and class of animal. In experiments 2 and 3, we used uncastrated calves between 3 and 5 months of age, which
were housed individually either in 1.8 m = 2.0 m pens, or 0.9 m = 2.0 m pens. The size of the pen was found to have no effect on the measures discussed here, and so this is not
discussed in this paper. In experiment 2b, the calves were bucket-fed a commercially available milk replacer following the recommended concentrations and volumes between
0700 and 0900 and between 1500 and 1700 h. Hay was available ad libitum. In experiments 2a and 3, the calves were fed grain ad libitum and were bucket-fed a
commercially available milk replacer following the recommended concentrations and volumes between 1500 and 1700 h. Hay was available ad libitum. In all experiments, the
calves were kept in the same room throughout testing.
3. Experiment 1
The aim of experiment 1 was to estimate the skin surface temperature at the area of laser contact and to establish the relationship between duration of exposure and skin
temperature. 3.1. Materials and methods
We used two calves. Due to the movement of the leg during the response, we could not measure the skin temperature directly on the leg itself. Approximately 24 h prior to
each test a 30 = 30 cm
2
area, located on the mid-thoracic region, was shaved. During testing the laser was aimed at this area. Testing was conducted between 1000 and
Fig. 1. Relation between skin temperature and duration of exposure to the laser. Each point is the result of one test. The best-fit regression line is shown.
1100 h. For each test the laser was set at 4.5 W and focussed on a single site and Ž
. allowed to run for a specified time ranging from 1.25 to 10.51 s Fig. 1 .
Temperature measurement of the skin at the focus site and the immediate surrounding Ž
tissue was done using an AGA Thermovision Model 782 thermography system AGEMA .
Infrared Systems, Burlington, ON . Analogue images were captured on video tape, converted to digital images, and the temperature was determined using DISCO Software,
Ž .
Version 3.0 GESOTEC, Danderyd, Sweden . The AGA Thermovision system is
Ž .
accurate to 0.18C plus or minus 2 . 3.2. Results
Final skin temperatures ranged from 37.98C to 77.98C with laser exposure ranging from 1.25 to 10.51 s, although there was considerable variation from animal to animal
Ž .
Fig. 1 . Despite this variation, there was a linear relationship between exposure time Ž
2
Ž .
. and skin temperature which was significant r s 0.703, F 1,11 s 26.089, p - 0.0001 .
4. Experiment 2
The aim of experiment 2 was to test the validity of the measures by examining the effect of various power settings of the laser on the animal’s responses.
4.1. Animals and procedure We used 30 calves at about 3 months of age. In experiment 2a, we used 14 calves on
each of which we conducted two sets of tests comparing their responses to two power
settings. A ‘‘high’’ power setting of 4.5 W was used while the ‘‘low’’ setting was 2.25 W. Each calf was tested at both settings during 1 day, following a balanced order, with
at least 30 min between the two sets of tests. At each power setting, we did six tests, alternating between the left and right legs, with a pause of 15 s between subsequent
Ž .
Ž .
tests. According to Svensson et al. 1991 , Zaric et al. 1996 , and Jacobson et al. Ž
. 1985 , this delay is sufficient to avoid habituation to the stimulus, at least when verbal
reports and behavioural observation are considered. All six tests were completed during a period of between 1.5 and 5 min. All tests were carried out between 1200 and 1430 h.
At each application of the laser, we noted the latency to move the leg and the latency to flick the tail, which usually preceded the movement of the leg. However, since the
laser was turned off as soon as the leg response occurred, we could not measure tail-flick latencies if this occurred after the movement of the leg. Thus, we also report
the latency of the first response to occur, regardless of whether this was the leg or the tail, as well as the latency of the leg response and the tail-flick response. We also
Ž recorded the type of leg movement, which was scored as kicking, lifting the leg a
. Ž
vertical movement judged to be of at least 5 cm , or other leg movement which usually .
involved the animal taking a single step . If the laser turned off automatically once the threshold of 20 s was reached, we continued to observe the calves’ behaviour for a
further 5 s. Thus, the maximum latency was 25 s. We also noted the occurrence of unsuccessful tests, that is, whenever the procedure had to be interrupted because the calf
walked away, urinated, defecated, or moved in response to disturbances. In addition, after the animal had responded on each test, and before the next test began, we recorded
whenever the animal licked its leg, licked another part of its body, jumped, kicked, or flicked its tail. We continued to observe the animal’s behaviour until the sixth successful
laser test had been finished.
In experiment 2b, the 16 remaining calves were submitted to a wider range of power settings: 2.0, 3.0, 4.0, 4.5, 5.0, and 5.5 W. At each setting, the calves were tested three
times on one leg, with a delay of about 30 s between each test. At least 1 min lapsed between each setting. Half of the calves were tested by increasing the power settings,
while the other half were tested with the power settings in decreasing order. On each test, we recorded only the latency of the leg response.
4.2. Statistics After having checked that the data corresponded to a Gaussian distribution and that
Ž variances were homogeneous, we used the GLM procedure of SAS SAS Institute,
. 1988 to analyse the latency to react to the laser. We used the following model:
Latency s b q b a q b b q b c q b d q b e
1 i
2 j
3 k
4 l
5 m r j
q b 6 f b g
b h b i
´
i jq 7
i mq 8
i lq 9 jlq
i jk l m
where a , b , c , d , e represent differences due to the power setting, to the order
i j
k l
m r j
Ž .
that the two power settings were applied low then high vs. high then low , to the leg on
Ž .
which the laser was applied right vs. left, experiment 2a only , to the number of the test Ž
. Ž
. repetition , and to the calf nested in power order and taken as a random factor , and
where f , g , h , i represent the interactions between the power setting and the order
i j i m
i l jl
of the power settings, between the power setting and the calf, between the power setting and the number of the test, and between the order of the power setting and the number
Ž .
of the test experiment 2b . We used the same GLM model to analyse the relative frequency of responses during
the test that consisted of kicks, leg lifts, or other movements, and the frequency of the Ž
. different behavioural patterns that occurred between the tests experiment 2a . However,
Ž .
the factors associated with the leg on which the laser was applied right vs. left and the test number were removed. The frequency of behaviours that occurred between the tests
were expressed as a frequency per minute, since the intervals between tests were not Ž
constant. Pearson correlations were calculated between the response to the tests based on the mean response latency and the proportion of responses that involved kicks during
. the six tests and the behaviour between tests.
4.3. Results 4.3.1. Experiment 2a
For the 14 calves submitted to the high vs. low power settings, both leg-response Ž Ž
. latency and tail-flick latency were significantly affected by the power setting F 1,12 s
. 116 and 64 respectively; P - 0.0001 in both cases ; latencies with the low power setting
Ž .
were about three times longer than with the high power setting Fig. 2 . On the low power setting, the calf did not respond within the 25 s allowed on 12 of the tests,
while on the high power setting this occurred only on 1.2 of the tests. The latency to Ž
move the leg or the tail was not significantly affected by the number of the test i.e., the . Ž
. Ž
. repetition
Fig. 2 , the side on which the laser was applied right vs. left leg , or with Ž
. Ž .
the order of the power settings high then low vs. low then high P 0.10 . The power
setting also had an effect on the nature of the leg response, with more kicks and fewer Ž
other leg movements occurring with the high power setting means SE, kicks:
. Ž
1.79 0.43; other movements: 2.14 0.52 than with the low power setting kicks: . Ž Ž
. .
0.21 0.16; other movements: 4.57 0.50 F 1,12 s 10 in both cases, P - 0.01 .
There was no significant difference in the frequency of leg lifts. Ž Ž
. The power setting had an effect on the frequency of kicking between tests F 1,2 s
. Ž
. 5.1, P s 0.05 , with more kicking occurring at the higher power setting Fig. 3 . Neither
frequency of licking, of tail flicking nor of jumping between tests were affected by the Ž
. Ž .
power setting P 0.10 Fig. 3 .
Large variation was observed between calves during the test; this was significant for Ž Ž
. .
Ž Ž .
the tail-flick response F 12,10 s 3.7, P - 0.05 but not the leg response F 12,12 s .
1.8, P 0.10 . However, the standard deviations within calves were always greater than Ž
. the standard deviations between calves Table 1 both for the latency of the leg response,
Ž and for the latency of the first response which could be either the leg response or the
. tail-flick response . The standard deviations between and within calves were lower at the
higher power setting.
Ž .
Fig. 2. Meanstandard error of latencies of the leg response and the tail flick at a high 4.5 W and a low Ž
. 2.25 W power setting of the laser, when calves were tested six times at each power setting.
Significant variation was observed between calves also in the frequency of licking the Ž Ž
. .
leg between tests F 12,10 s 4.6, P - 0.01 but not in the frequency of the other
behaviours that occurred between tests. The behaviour that occurred between tests was related to that during tests. There were positive correlations between the frequency of
Ž .
kicking during tests and the frequency of kicking r s 0.70, P - 0.01 and licking of the Ž
. body r s 0.57, P - 0.01 between the tests. Furthermore, there was a negative correla-
tion between the latency of the leg response during the tests and the amount of kicking Ž
. between tests r s y0.56, P - 0.01 . No other correlations were significant.
There was no significant effect of any factor on the frequency of interruptions of the Ž
procedure, although this tended to be higher at the low power setting 1.6 and 0.8 .
interruptions at the low and the high power setting respectively . 4.3.2. Experiment 2b
For the 16 calves submitted to a wide range of power settings, the latency to react Ž Ž
. .
varied with the power setting F 5,70 s 109, P - 0.001 . It decreased with increased
Fig. 3. Meanstandard error of frequency of each behaviour that occurred between the laser tests at a high Ž
. Ž
. 4.5 W and a low 2.25 W power setting.
Ž .
power setting up to a setting of 4.5 W, after which it did not decrease further Fig. 4 . The order of the power setting tended to have an effect, with calves tending to react
Ž more quickly when subjected to decreasing power settings decreasing vs. increasing
Ž .
. power settings: 8.6 0.6 s vs. 9.9 0.3 s, F 1,14 s 3.6, P s 0.08 . There was no
interaction between the power setting and the order with which the power settings were used and no difference between the three repetitions of the test at each power setting
Table 1 Variability within and between calves for response latency at two power settings
Mean Within calves
Between calves Ž .
Ž . SD
CV SD
CV Leg response latency power
2.25 W 15.1
11.9 75
3.6 24
4.5 W 5.3
2.7 51
1.5 28
First response latency power 2.25 W
10.9 6.8
64 3.4
31 4.5 W
4.4 2.7
61 1.5
33
Fig. 4. Meanstandard error of latency of the leg response at a range of power setting of the laser.
Ž .
Ž Ž .
P 0.10 . There were significant differences between calves F 14,70 s 3.4, P -
. 0.001 .
5. Experiment 3
