The hidden impact of prenatal stress on dogs

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The hidden impact of prenatal stress on dogs

August 22, 2023 Uncategorised 0

Many dogs struggle to cope with all kinds of stressors in life. Often, I see strategies that focus on reducing stress in day-to-day living. Good quality sleep, exercise, mental stimulation and nourishment are a vital part of that.

However, sometimes we run the risk of thinking that we can turn a highly sensitive dog into a highly resilient dog. This can make us overly optimistic about the kind of lives our dogs are capable of living. It can also end really badly: we think we can fill in significant gaps in their development.

In the last post, I took you through genetic influences on emotional resilience in dogs. Traits like curiosity, emotional stability and optimism can have heritable elements. It stands to reason that trait anxiety, fearfulness and pessimism can also be influenced by the genetic contributions of a dog’s parents and grandparents too.

But genes are not the only way that our dogs may arrive into the world with the odds against them.

We also know that prenatal stress can influence how resilient mammals can be.

Research on gestational stress

Most research on gestational stress has been carried out on rodents, primates and humans. That’s not to say that it isn’t relevant for dogs. We can definitely generalise many of the common findings. We simply have no need to conduct stressful experiments on dogs in laboratory conditions in order to say, ‘Oh! Dogs too!’

That said, dogs are often used in experimental medical research. Since stress hormones affect how medicines are processed in the body, laboratories must take these into consideration when testing products. Therefore, considering research that wasn’t directly about stress in pregnant dogs can also be useful. It certainly avoids researchers having to conduct additional and unnecessary tests.

Across rodents, primates and humans, researchers agree that stress during pregancy certainly affects mammals. How it does so and what it does is complicated.

I often find myself answering questions with three answers. It depends. It’s complex and probably multifactorial. We don’t know enough yet. Those three answers are especially relevant when we’re thinking about how gestational stress affects our dogs.

Since the 1960s, researchers have been trying to explain how stress during pregnancy affects the foetus. That such stress has an impact is generally agreed. What that impact is – well, that is much less clear. In fact, it’s sometimes very contradictory.

What we know about stress during pregnancy

Stress during pregnancy mostly affects the parent, of course. We can certainly think of many dogs who are most likely exposed to high levels of gestational stress: dogs living in threatening environments in free-roaming situations; dogs who are in stressful kennels, puppy farms or other commercial breeding establishments; dogs who face enormous stress in the home.

Stress can also be good or bad. We tend to think badly of any kind of physiological arousal these days, but it’s also important to realise that the ‘stress axis’, the hypothalamic-pituitary-adrenal axis that activates our ‘fight-or-flight’ mode isn’t something that’s either ‘on’ or ‘off’. Chronic stress works differently than acute stress, for instance, and there can be many other dogs who experience peaks and troughs of adrenaline and cortisol.

It’s not just about how it affects the parent physiologically before the birth of her offspring. It’s also about changes to her behaviour after their birth. For instance, in rodents, gestational stress affects how much time females spend caring for their offspring after birth. In other words, it’s probably not just a biological impact, but a behavioural one too. In laboratories, ‘forced swim tests’ are often the method used to expose pregnant rats and mice to stress, and this has a depressive effect on their behaviour after their babies are born (e.g. Smith, Seckl, Evans et al. 2004; Champagne & Meaney, 2006).

Prenatal stress might not simply be about how it sensitises the growing foetus to stress hormones, but also how it affects offspring after birth. Maternal care also plays a crucial role in how resilient we are as adults, as we’ll explore in next week’s post.

Prenatal stress and the placental barrier

The placenta is an amazing organ. It acts as a gatekeeper for the foetus, providing them with exactly what they need during development. Certain molecules and hormones can pass the placenta, where others are kept waiting at the door. The placenta itself produces some hormones like oestrogen and progesterone, so it’s not just a filter. It also metabolises and processes other hormones like catecholamines and steroid hormones. And it releases several protein hormones itself. Modulator, producer, filter, metaboliser – the placenta is definitely a thing of evolutionary wonder.

Even so, we still have a lot to learn about it and how it works.

Prenatal stress doesn’t simply affect the physiology and psychology of the parent: because of the placenta, it also affects their offspring. That said, the way in which it does so and to what extent is still something researchers are at the beginning of understanding. For that reason, we should be very careful of blanket statements like ‘prenatal stress causes anxiety’ or that there is a direct, clear and dramatic correlation between what happens to the parent before birth and what happens to the offspring’s emotional health afterwards. This is clearly not the case and an over-simplistic approach can cause more harm than good.

The effects of stress in pregnancy are nuanced

You would expect stress to have a clear negative effect on the offspring if stress hormones can pass the placental barrier, yet the correlation isn’t always as clear as all that and it may also be affected by other factors such as when it occurs during the pregnancy, how much stress was involved, and the sex of the foetus.

Some of the effects have included increased emotional reactivity across a number of mammalian species. That doesn’t just affect the offspring in all probability. It also affects the mother (Darnaudéry et al. 2004). Compared to rats who’d never given birth, post-natal mums who were exposed to stress pre-natally were much more hesitant in novel environments and they were also more responsive to environmental triggers of fear.

In some cases, the offspring are more emotionally responsive. That means when novelty or threat is introduced into the environment, they had a stronger response to it. What we’re beginning to see is how highly nuanced this is, depending on the sex of the offspring and when the mother experienced stress during pregnancy, as well as the type and duration of stress experienced. Prenatally stressed mammals also have stronger fear responses in some cases as well more variable arousal levels. In cognitive bias tests, many mammalian species show pessimistic cognitive biases which clearly affect them. For instance, when faced with challenge, they may be more likely to give up.

Of course, it also affects physiological health and the immune system, leaving the offspring more vulnerable to infection too.

Prenatal stress affects emotions, cognition and behaviour

Gestational stress affects more than emotional reactivity. It also affects the way we view the world as an inherently safe place or a place of threat. Pigs, sheep and goats are among the species studied for the effect of stress during pregnancy in terms of how it affects cognition. It’s very likely that dogs are little different.

What that means is that prenatal stress can affect how our dogs approach the world. Are they going to notice every unfamiliar detail and tend towards considering it as a likely threat, or are they going to view the world as a relatively benign place, where the unfamiliar doesn’t come with a *potential threat* tag attached to it.

Prenatal stress can also affect how we interact with others of our own species. For dogs, that may affect how they interact with us too. It may alter things like how we interact with those familar to us, but also how we approach those who are unfamiliar too. Social mammals like rats who were exposed to prenatal stress cried less and interacted less. This probably doesn’t sound like a bad thing at first glance, but the behaviour of infants affects the behaviour of the mother. If we vocalise less, our parents may pay less attention to our needs. It sets the situation for mild neglect.

Stress during pregnancy is not just a risk factor for anxiety and fear. Gestational stress has been shown to affect frustration levels and impulse control too. That can have transgenerational effects. It’s sometimes said that ‘mothering begets mothering’ – and how that works is complex. But undoubtedly one part of it is that if we experience lower-quality maternal care ourselves, we never learn through social mechanisms how to replicate that with our own children. It pays forward to future generations.

The nuances of gestational stress

Knowing all of this, it can be very tempting to think it would be best to completely protect the growing foetus from stress. Doing so, we could reduce the impact of gestational stress as a potential risk factor. But is that really the case?

As it turns out, no.

A small number of studies show that mild to moderate levels of stress at certain points in foetal development might be beneficial. It’s perhaps more useful to think of stress in pregnancy as having context-dependent factors that can contribute to potential vulnerability. Without any stress at all, we may be creating puppies who have low coping skills when the world throws them a curveball.

In reality, what’s perhaps most useful to conclude is that where gestational stress matches the potential stressors that the puppy will face in life, then that will in part prepare the foetus for life beyond the womb. Where there is a mismatch in those worlds – say for instance a puppy from a commercial breeding establishment who faced a lot of in utero stress then going to live in a home where they are expected to be confident, curious and social adults, this may cause problems. If you’re born expecting the world to be a threatening place and you’re expected to behave as if the world is your best friend, you can understand how some pups may struggle.

Implications for guardians and caregivers

Where we know puppies have been exposed to prenatal stress, we’ll need to do a bit of work to help support them (and mum) as they move to resilience. Early neurological stimulation and Puppy Culture programmes should be essential.

Knowing also that we can’t undo the effects of genes and prenatal stress also means we need to take post-natal experiences seriously.

Rescues need to make sure that puppy fosterers are informed rather than simply well-meaning. A dry room in a garage or a pretty, painted out-building or kennel isn’t enough.

We also need to put pressure on our governments to legislate against puppy farms and to ensure commercial breeding establishments aren’t putting financial concerns over ones of welfare and well-being. Sadly, far too many governments are protecting business interests and factory-style facilities at the expense of developmental concerns.

In fact, it’s ironic that most of the research into mammalian gestational stress, if not to inform us about our own species, is simply to see just how much pregnancy stress breeding females can tolerate before it adversely affects the offspring. This is not good enough.

In next week’s post, I’ll look at the effects of maternal care and other interventions on very young puppies. You’ll also find some ideas about how we can mitigate some of these risk factors with early interventions.

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