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
The objective of experiment 3 was to assess the repeatability of the calves’ responses by examining differences between tests, between days and between legs.
5.1. Animals and procedure Twenty-four male Holstein calves at 5 months of age were used. On two separate
days, the calves were tested with the ‘‘high’’ laser setting used in experiment 2a. Three series of three tests were done. In the first series, the calves were tested on one leg, and
then 60 min later, in the second series, the calves were tested on the other leg. Half of the calves were tested first on their right leg and half first on the left leg. Finally, the
third series was done at the same time as the first series but on the next day. The calves were tested on the same leg that was used during the second series. In each series, the
calf was tested three times, with a pause of at least 30 s between tests.
5.2. Statistics Statistical analyses were similar to those used in experiment 2. The following GLM
model was used: Latency s b q b a
q b b q b c q b d q b e q b j q b k
1 i r n
2 j
3 k
4 l
5 m r j
6 n 7
n m r j
q b l q b i q ´
8 k l 9 jl
k l m n
Ž where a
, b , c , d , e , j represent differences due to the series of tests nested in
i r n j
k l
m n
. Ž
. Ž
day , the order of the legs right leg tested first vs. left leg tested first , the side right vs. .
Ž left leg , the number of the test, the calf identity nested in leg order and taken as a
. Ž
. random factor , and the day day 1 vs. day 2 , while k
and l represent the
n m r j k l
interactions between the day and the calf and between the side and the test number. To Ž
. examine the repeatability of the measure across the nine tests , we calculated the
coefficient of variance associated with the repetition of the test using the MIXED Ž
. procedure of SAS, taking all factors except the number of the test as random factors.
5.3. Results Significant variations in the latency to respond were observed between calves
Ž Ž .
. Ž
. F 22,16 s 2.26, P s 0.05 but not between the legs P 0.10 . Within each series of
Ž tests, calves reacted more quickly on the second than on the first and third test test 1, 2
Ž .
and 3: 7.0, 5.4 and 6.5 s, F 2,162 s 10.3, P - 0.001, Bonferonni post hoc compar- .
Ž isons . There was no significant difference between the 2 days day 1: 6.5 1.6 s and
. day 2: 5.9 1.6 s, P 0.10 and latencies on day 1 were positively correlated with
Ž .
those on day 2 r s 0.43, P s 0.04 . The coefficient of variation associated to the repetitions of the test was 36.
6. Experiment 4
