sleep & biological rhythms

animals have a sense of time

-dogs wait for their owner to come home

-pigs know if they have been in crates for short/long periods of time

-chimps & ability to exhibit delayed gratification

-big cats & elephants in zoos pacing before meal time

biological rhythm

-”a cyclic change in behavior or internal physiological process that occurs at a regular rate in an organism”

-exogenous rhythms 

-endogenous rhythms 

exogenous rhythms

rhythms that depend on external stimuli in order to persist regularly

endogenous rhythms

rhythms that are independent of external stimuli & rely on internal clock mechanisms

internal clock mechanism

“self-regulating, self-sustaining neural signals that occur at regular intervals”

different rhythms frequencies

-high frequency 

-ultradian

-circadian

-diurnal

-infradian 

-annual

high frequency rhythm

occur in short periods → <30 mins

heart rate high frequency example

-conservative within species and age groups

-adult cows → 60-80 bpm

-calves → 80-100 bpm

-adult horses → 28-40 bpm

ultradian rhythm

period between 30 mins to 24 hrs

growth hormone ultradian example

-GH production from pituitary gland in cattle

-~every 3.5 hours

feeding behavior ultradian example

-if feed is ad lib

-every 2-3 hrs → dogs, cats, sheep, pigs, cattle

circadian rhythms

-repeat approx every 24 hrs

-common to see behaviors and hormones expressed

infradian rhythm 

longer than 24 hrs

cyclicity of polyestrous animals infradian example

-~21 days for cow & sow

-~17-24 days for mare

-~16-17 days for ewe

-repro hormone levels & behavior

-activity monitors on cows can detect when to breed

annual rhythm

-repeats annually

-seasonal breeders

seasonal breeders annual example

-horses = long day breeders

-sheep/goats = short day breeders

-goal → spring births for high prob of offspring survival

zugunruhe

-anxious behavior that migratory animals exhibit when unable to migrate

-in captivity

what do you see when zugunruhe is displayed?

increased activity around/after dusk → wing flapping, restlessness

circadian rhythm

-most well-studied

-period ~24 hrs

-influences by Zeitgeber → “time giver;” “entertainment”

circadian examples

-sleep/wake cycles

-hormone secretion in most mammals

-body temp

sleep/wake cycles

-depends on whether nocturnal or diurnal

-will have a reg period of wakefulness & sleepiness that repeats every ~24 hrs

hormone secretion in mammals

-peak cortisol early in the day

-various zeitgebers → depends on hormone → food, light, activity, other hormones

body temp

-peak in afternoon, lowest in early morning

-common across many species

circadian properties

1.must be ~24 hr period

2.must be endogenous rhythm

3.must persist (at least for a time) in constant conditions → “free running” rhythm

4.must be able to reset or “entrain” to an environmental factor

internal clock mechanism

-suprachiasmatic nucleus (SCN)

-paired nuclei that regulates circadian

-lives above optic chiasm

-each cell is its own clock, w own electrical signals

-cells in nuclei work together to create ~24 hr rhythm

diurnal rhythm

-~24 hr rhythms that rely on external cues in order to persist

-ex → foraging & hunting, stereotypies in many species, poultry perching behavior

foraging & hunting diurnal example

-foragers alter behavior depending on temp to conserve energy

-hunters alter behavior based on prey 

stereotypies in many species diurnal example

bar-biting in pigs → peak ~2 hr after feeding

poultry perching behavior diurnal example

depends on amount of light (photoperiod) & timing of darkness

sleep

-4 levels of alertness

1.alert wakefulness

2.drowsiness

3.quiet sleep

4.active sleep

-measured via EEG

alert wakefulness

-eyes fully open

-EEG → low voltage, fast activity output

drowsiness

-relaxed upper eyelids

-high arousal threshold/reduced alertness

-EEG → combo low voltage/high activity and high voltage/low activity

quiet sleep

-eyes closed or nearly closed, even more required to arouse

-EEG → all high voltage/slow activity

active sleep (REM sleep)

-eyes fully closed

-EEG → low voltage/fast activity (like wakefulness) → “paradoxical sleep”

-REM → rapid eye movement

dogs relative sleep behaviors and positions

-~50% of time spent sleeping → 20% of that in REM

-dependent on housing & schedule

cats relative sleep behaviors and positions

~45-65% of time sleeping → 20% in REM

cattle relative sleep behaviors and positions

-~25% of time sleeping

-sleep lying down, but rarely lateral

horses relative sleep behaviors and positions

-~20% of time sleeping

-sleep standing up majority of time

-must be in recumbency for REM → usually only ~5 mins at a time

pigs relative sleep behaviors and positions

-~30% of time sleeping

-many bouts of REM if in stress-free environment

poultry relative sleep behaviors and positions

-very dependent on light cycle

-definite difference in resting vs sleeping posture (head neutral vs head tucked)