Friday, August 28, 2015

How do animals sleep?

An aerial view of a hairless cat sleeping.

How did you sleep last night? Sleep is a funny thing. Get less of it than you need to and your function becomes impaired – driving, operating heavy machinery and performing complex tasks are risky when little sleep has been had. People talk about their sleepless nights, interrupted sleep, insomnia and sleep apnoea, but it’s rare for clients to discuss their pet’s lack of sleep with me. And when they go home on heavy pain meds or after a general anaesthetic, we don’t have to warn animals not to drive or operate heavy machinery. Point being that we don’t often notice when animals are drowsy, because it doesn't alter our interactions with them and so it doesn't matter to us.

But as I learned when reading The Science of Animal Welfare, sleep (or lack thereof) can significantly impact an animal’s welfare. The authors compiled an impressive review on the scientific literature around sleep in animals. It is a daily activity in all vertebrate species (with the exception of vet students the night before exams), and invertebrates exhibit “sleep like behaviour.”

A ferret sleeps.
Most animals don’t clean their teeth, throw on PJs and tuck themselves up in bed with a good book. But we know they’re sleeping because they generally exhibit behaviours characteristic of sleep, like specific postures. They’re also behaviourally quiet during this phase and they have an increased stimulus threshold (but they’re still easier to rouse than vet students at 3am on a dairy prac).

Scientists talk about monophasic sleepers (most humans and some animals) who sleep in one big chunk, and polyphasic sleepers who sleep in small bouts or as I like to call them chunkettes. Interestingly, carnivores sleep longest, herbivores shortest, and omnivores are in the middle. That makes sense: when you are at the top of the food chain and don't really need to worry about predators, you can rest easy. If you're a prey species you can't afford to bliss out in deep, long sleep lest a predator take advantage.

You know you need to jazz up your bedside manner with the patient sleeps through a weigh in and vaccination. 
Brain patterns are altered when we sleep. Interestingly, we engage in bihemispheric sleep, where both hemispheres of our brains show the same electrical activity (REM or non-REM), but aquatic mammals and loads of birds sleep unihemispherically – i.e. only half their brain shows the sleepy electrical patterns. The other half of the brain shows wakeful patterns on EEG. That is handy if you need to continue to swim or fly while you sleep. It’s a kind of autopilot. I am sure some students try to attend lectures unihemispherically, not sure it works though.

Newborn animals don’t really “wake up” until they are a few days old. This has complex implications around pain perception. The point I really want to discuss though is sleep in older animals.

Sleep, the authors conclude, has restorative function. We know this ourselves because without it most of us are unbearable, irritable, less than happy creatures. But we need to think about the conditions in which we keep animals that may impact on their ability to sleep. When it comes to farmed animals, for example, inappropriate lighting or light cycles, crowding or confinement in an area that precludes them adopting their preferred sleep posture can impact on their sleep.

Some animals can't let it all go. Koalas need to cling to branches when they sleep. 
Sleep deprivation is a form of torture, and ongoing sleep deprivation leads to immunosuppression. Sleep also enables animals that are sick a break from their discomfort. While they are sleeping they are generally insensible to any pain and discomfort (it’s one reason that we talk about euthanasia as “putting them to sleep” – the emphasis is on minimising suffering). Sleep enables sick animals to recover quicker.

The upshot is that sleep is an animal welfare indicator. Animals that have disrupted sleep patterns may be suffering or in pain, and lack of sleep can worsen that suffering. The authors conclude that we need to pay more attention to monitoring sleep in animals, and investigate the ways in which sleep can be used to improve the welfare of animals.

Hero has perfected the fine art of sleeping on anything I am trying to read at that very moment, even if it looks really uncomfortable.
In terms of my patients, the use of sedatives to facilitate sleep can be helpful (for example, senior patients with cognitive dysfunction syndrome). 

Understanding the implications of disrupted sleep gives us additional impetus to treat conditions that affect sleep, such as scratching all night (With flea season about to explode down under, I can guarantee there will be more sleepless animals). I wonder to what extent behavioural problems such as anxiety are exacerbated by lack of sleep?

Is there scope for using sleep and its associated properties therapeutically (e.g. pain control) and to improve animal welfare? Could we breed some animals to sleep more, or better? Are there non-pharmaceutical ways to induce sleep in animals? Maybe we need to look a bit harder at this.

If you want to find out a bit more about sleep check out The Sciences of Animal Welfare by DJ Mellor, E Patterson-Kane and KJ Stafford, published by UFAW.