Choosing The Right Substrate + A Discussion on Softwood - Is It Really The Devil?

Choosing The Right Main Substrate:

Often being presented with so many substrate options along with many often conflicting opinions as to what substrate is best can be pretty daunting, especially to new keepers. Today we’ll go over the basics of what you want in a substrate, which will hopefully make that choice an easier one to make.

First, we’ll discuss substrates that you don’t want to use for your main substrate:

Substrates like corncob, sand, coconut fibre (or similarly, peat moss and similar soil substrates), kaytee soft granules, etc are all safe substrates to offer to your hamster. However, should not be used as the main substrate for a variety of reasons, most notably being that these types of substrates offer very poor burrow stability which, given the burrowing nature of hamsters, do not make them optimum main substrate choices. Some of these substrates are hard & can mould easily (i.e. corncob) and so are best being kept offered in a smaller section where they are easier to monitor & change as required. Soil substrates are generally not recommended to be the main substrate as they dry out very quickly, and can be difficult to maintain in larger areas. Again, all these substrates are fine to offer in smaller, contained areas where they can be easily monitored – just not as the main substrate of the enclosure.

A quality main substrate should be:

Low dust.
No added scents, these are highly concentrated than say, sprinkling flowers & herbs throughout the enclosure, and can be very overpowering to your hamsters respiratory system.
Offer good burrow stability (mixing hay in-between layers is also advisable, as this offers even more stability acting similarly how roots would in the wild). If using wood based substrate, it should ideally be small flakes, and not very large ones. Larger flaked shavings are often very poor at offering burrow stability.
Offer appropriate absorption + odour control. (simply using shredded tissues or newspapers will not offer appropriate absorption).

Examples of safe substrate types:

Aspen wood shavings, smaller flakes if possible. Note: Finely shredded aspen (i.e. reptile aspen, and Harlan teklad) has a reputation for being very dusty!)
Birch wood shavings.
Non-scented Paper based substrates (i.e. uber, boxo, kaytee. Use CareFresh with caution as there appears to be poor quality control, with many batches being too dusty for safe use).
Hemp (this can be not so great at holding burrows).
Spruce wood shavings such as Allspan for reasons we will discuss why on the following slides. Out of all brands mentioned, Allspan is arguably the best substrate for burrow stability.

Wait, spruce? That’s a softwood. Isn't all softwood terrible for hamsters?!

I’m sure even if you’ve been in the hamster community for even just a week, you’ve been told all softwood is the devil and will 100%, without any inkling of a doubt, kill your hamster. This is because of phenols that are present in softwood shavings being a known respiratory irritant. But despite these claims being widespread within the English hamster community, do they even have a basis of fact?

To put it simply, yeah – there is actually evidence against phenols that have shown it to be a respiratory irritant but before you take that statement and run with it, different species of softwood will have varying levels of phenols and this is a fact that is far too often ignored (if even thought about at all!).

Softwood shavings have perhaps most noticeably been used by owners in Germany for years, who have arguably some of the highest standards of pet care and perhaps easily thee highest when it comes to hamsters. While it seemed the English community was hellbent on ridding them from the shelves, the Germans reported practically no issues - but how, if they're seemingly so dangerous? We’ll discuss.

Not All Softwoods Are Equal:

In Germany, and much of Europe at that, the most popular bedding brands commonly available include Chipsi Classic, Tierwohl (which is also produced by Chipsi), and Allspan Classic. What do all of these brands have in common? While they are 100% softwood shavings, they are not pine shavings nor are they even 100% fir shavings. They are either spruce shavings, or spruce/fir mix. Chipsi Classic/Tierwohl are partial fir and spruce. Allspan Classic? That’s 100% spruce. So great, they’re two species of softwood – why does that even matter?

Well, it’s actually of a huge importance to this discussion because it has scientifically shown that spruce has exceptionally low phenol levels that are so low that they are comparable to that of hardwoods (i.e. aspen). A study published demonstrated that the barbiturate pattern of sleep times for mice kept on four different substrates: hardwood, pine, spruce & cedar . ‘Barbiturate sleep time’ refers to the length of time the animals remained ‘asleep’ (or ‘knocked out’) when administered the exact same dose of anaesthetic. I’m referencing this study not to demonstrate the impact phenols can have on liver enzymes, but because it demonstrates the concentrations of phenols of these various substrate choices. As we discussed earlier, softwood contains phenols. Phenols are basically a toxin so in simple terms, will elevate the animals liver enzymes as their liver processes the toxin from their body, which will in turn makes the liver process medication at an increased rate thus if the medication administered is anaesthetic (as is the case for this study), the animal will process the anaesthetic more quickly and therefore wake up sooner as a result. The sleep times observed in the mice housed on hardwood shavings were not statistically different to those observed in the mice kept on spruce, indicating that while yes, phenols are present, the levels are so low that they should be of no concern/be the reason for ill health of your pet.

Like I mentioned, we know phenols are a respiratory irritant – it’s not a secret, and it’s a well regarded fact. However, ill effects have only been observed in animals exposed to very high concentrations of phenols: while spruce is not 100% phenol free, the phenols that are present aren’t going to be the reason for why your pet is sick because they are simply too low to have any effects on your pets health.

So what about Fir/Spruce mixes then? Are they safe or not safe, because they still contain fir?

The answer isn’t really black and white like spruce. I can’t find any studies explicitly on fir shavings, but I do not believe that it is beyond a reasonable doubt that it is likely very similar to pine shavings, if not an average of pine and spruce due to the similarities between these three species of coniferous tree. If I refer back to this same study – that is, the one that observed low phenol levels of spruce shavings – this study also observed the effect of both autoclaved and non-autoclaved pine shavings on the sleep times of mice. The results shown (see Table 1) depict the average sleep times observed from a combined average from both autoclaved and non-autoclaved beddings, as there was no notable difference observed between autoclaved & non-autoclaved substrates. Assuming that fir is similar to pine and spruce, the barbiturate sleep times one would expect to observe would lie between 85-123 minutes. If we consider fir to have the same phenol levels as pine (thus a sleep time of 85 minutes) and as neither of these brands state what percentage spruce or fir make up of their shavings, assuming that at least 50% of the product is spruce, the expected sleep times observed of a spruce/fir bedding mix would be around 104 minutes . All this really tells us is that a substrate mix of fir/spruce is closer in comparison to the phenol levels of spruce than cedar, even more so if the bulk of the shavings are spruce.

This could perhaps suggest why fir/spruce bedding mixes, such as that of Tierwohl/Chipsi (along with other brands) are commonly used without issue as it has been scientifically demonstrated that spruce shavings have low phenol levels, thus arguably mixing fir shavings with spruce shavings further dilutes the phenol levels of fir and thus likely bringing them further within a safe range for our pets. While it is impossible to say what exactly those phenol levels are due to lack of clear labelling of these products with regards to exactly what percentage of them are spruce & fir, it is likely that they are mostly spruce and that a smaller percentage of fir is added to perhaps give the product more of a natural scent (or for whatever other reason it may be): this isn’t necessarily a bad thing as again, negative effects on the respiratory system of rodents have only been observed in high concentrations of phenol levels. Taking a closer look at the Chipsi classic shavings, I personally believe this to be the likely case: that is, that a smaller percentage of fir is added to give the shavings a more pleasant aroma as if we take a look at these shavings, you can see that the shavings appear to be at least 50% spruce (if not more). Fir shavings tend to be a more red in colouration, compared to spruce which is more yellow.

If the fir/spruce shaving are at least 50-80% spruce (as is the likely case based on my personal observation), this would imply that a mix of spruce & fir shavings would observe sleep times between 104-116 minutes. Barbiturate sleep times aside, in a spruce/fir mix of shavings with 50-80% of the shavings being spruce, phenol ranges would be closer to that of spruce and - most importantly - overall much less concentrated.

As mentioned, negative impacts on the respiratory system on rodents have only been observed when they are subjected to high concentrations of phenols. If at least 50% of the shavings are spruce (which, based on my observations, is the most likely case) the phenol levels of fir are therefore much less concentrated, likely rendering them within safe levels for small animals. Furthermore, anecdotal evidence must also not be ignored. These brands, along with other fir/spruce shavings, are largely popular amongst the German Hamster Community where many hamsters are kept in very large enclosures with very deep bedding (thus the hamster is burrowing deep down into the substrate) with little to no issue reported. While one persons experience does not necessarily prove anything, the experience of the majority does and it is simply poor science & illogical to ignore these experiences. I would consider fir/spruce mix shavings to be likely to be used with no issue.

While spruce/fir mixes like Tierwohl/Chipsi can be considered likely to be safe, Allspan on the other hand, being a 100% spruce bedding, should be considered absolutely safe for small animal usage and will not cause any *average hamster any problems. *There is always an exception to the rule, or an isolated case where an animal has issues with a bedding – some hamsters are allergic to wood shavings in general, some are sensitive to any amount of dust, it happens. This is why I am careful to use the word ‘average’ instead. This applies to literally any bedding type! Just because something is a known safe bedding, does not mean that we don’t occasionally have the odd isolated case – if we used these isolated cases to deem a product dangerous, we would be keeping our hamsters on bare bottom enclosures because there is not a single substrate that is 100% risk free.

With softwood shavings, phenols are always present. But we must not forget that the dose makes the poison. Phenols have only been demonstrated to be a health risk in high concentrations. Just like dust: there are no shavings or even paper based substrate that is 100% dust free. Dust is a known respiratory irritant, but this doesn't mean that any and all levels of dust cause respiratory distress. It is the same situation for phenols: phenols are only a cause for concern when they are highly concentrated.

*UPDATE: 30/5/20: Chipsi have since responded to my enquiry, and have confirmed that their products are between 70-75% spruce. Therefore, my theory that these products are predominantly spruce shavings (a safe softwood) thus diluting the overall concentration of phenols found in fir, rendering the products safe for small animals, stands.