Major aims in the study of animal welfare are to try and understand the
subjective mental experience of animals, to develop methods to assess their
responses to changes in mental state and to use this information to enhance animal
welfare. One of the most profound changes of mental state observable in all
mammals is the change between wakefulness and sleep. Electrophysiological
measurements, when combined with behavioural observations, provide a powerful
means of characterising the states of sleep and wakefulness of animals. The spectral
components of an electroencephalogram (EEG) reflect the differences in the
electrical activity of the brain between sleep and wakefulness.
When humans undergo an aversive, stressful, disturbing, or worrying
experience during wakefulness, their subsequent sleep can be affected. The present
series of investigations examined the hypothesis that sheep exposed to aversive
husbandry procedures would experience disturbances to their subsequent sleep. A
sleep disturbance might provide an indication of the effect of an aversive husbandry
procedure on the mental state of a sheep, that would not otherwise have been
detected using conventional methods such as behavioural observation, blood
biochemistry and heart rate.
Non-invasive electrophysiological hardware and software developed and
used for human sleep studies, was adapted and used to study sleep in sheep. To
assess the effectiveness of surface electrophysiological recordings to detect changes
in the electrical activity of the brain of a sheep, three validation studies were carried
out. They consisted of a) the post-mortem passage of electrical current through the
head of a sheep; b) changes in EEG in response to depth of general anaesthesia and
c) the EEG responses of a sheep in a sleep posture to an auditory stimulus.
The method was then applied to characterise the sleep of six, housed, adult
ewes. Three percent (± 0.2) of a 24-h period was spent in rapid-eye-movement
(REM) sleep and 15% (± 2.4) was spent in Non-REM sleep.
Three experiments were undertaken to assess the effects of potentially
aversive husbandry procedures on subsequent sleep. These consisted of a) movement
to a novel environment; b) an 8-h road transport journey and c) a 29-h space
restriction period (simulating times and space allowances used during road
transport). Changes were seen in the distribution, quality and quantity of sleep.
Although there were no significant effects on the duration of REM sleep or NonREM sleep, in two experiments, an increase in the number of REM sleep bouts was
seen post-treatment. In all experiments, a post-treatment increase in the percentage
of slow waves was seen in Non-REM sleep.
This work provided a greater understanding of the impact of potentially
aversive husbandry procedures on rest and sleep in sheep. All three of the potentially
aversive husbandry procedures used as experimental treatments were associated with
changes in subsequent sleep that may have been indicative of aversive experience
during wakefulness. Although the changes in sleep found post-treatment were not
large, they were consistent and reliable and therefore the methodology has potential
for use in other applied animal welfare studies.