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.

Okay, so we discussed phenols... now what about abietic acid?

Abietic acid is found in certain species of coniferous tree – including fir, pine, and spruce. It a component of resin (also known as 'rosin' when solid), and is both a known skin & respiratory irritant and is a commonly used argument to deem softwood unsafe. But, what this argument fails to consider is that it is only really been considered a danger in occupational workers (who are exposed to & inhaling large quantities of abietic acid dust and/or its fumes), and that skin irritation caused by resins in the average population is considered “possible but infrequent” & is estimated to affect between 1-3% of people in regular exposure, with many having a reaction to rosin dust/fine sawdust (not to be confused with wood shavings!). Just because it can elect an allergic response in the form of contact dermatitis in some, does not make it the devil - abietic acid has also shown healing properties in mice & humans, and is used as a form of treatment for both wound healing and skin inflammation.

What is also important to consider is that natural resin (which is where abietic acid is found) naturally occurs as a sticky liquid, and is said to be "extracted from various wood species in very small percentage, i.e. only about 2-5%", and is typically extracted from wood via tapping. Commonly used bedding brands in Europe like Chipsi and Allspan also both explicitly state that resins are reduced during manufacturing. While yes, traces of resin may remain on the wood even after extraction, it is possible that the remaining traces occur as <1% , and that it is simply too little to cause harm to us, or our pets.

In terms of respiratory risk: respiratory distress has been most prevalent amongst workers where abietic acid is heated & inhaled as vapour (i.e. soldering fumes), where it is inhaled as an aerosol, and in those in the wood working industry who are exposed to large quantities of wood dust (and thus inhaling large quantities of abietic acid). Cases of respiratory distress outside of the wood working & electronic industry (soldering) caused by abietic acid are few and far between and I have thus far only found evidence of occurrence in those where respiratory distress was caused by inhaling particles of abietic acid in its solid form. From my research, it would appear that abietic acid is considered a risk as a respiratory irritant when it is a) inhaled as fumes produced in soldering, b) inhaled in large quantities of wood dust or c) inhaled as solid particles. Indeed, even asthma caused by unheated abietic acid – while possible – is considered to be rare.

Above snippet taken from 4 month long study on mice, who arguably have a much more sensitive respiratory system than hamsters.

There is zero evidence to date to suggest that abietic acid present in quality pet bedding like Chipsi & Allspan, which are not only de-dusted and dried but also have resins further reduced during the manufacturing of the product, being a skin or respiratory irritant to your pet. On the contrary, there is only evidence to suggest that it is of no concern. It is not present as an aerosol, it is not capable of being inhaled as solid particles or in toxic fumes, and high quality wood shavings should have very low dust contents. I do not believe it to be accurate to state that abietic acid is of high concern when it comes to quality, de-dusted softwood shavings that undergo further resin removal: rather, I believe it to be more accurate to state that it would be a rare case for a hamster (or their human) to develop a respiratory or skin issue directly caused by abietic acid in their bedding. Given the sheer number of hamsters housed on these softwood brands, a problem like skin irritation in particular should be incredibly obvious - but we don't see these problems reported. Like we mentioned, there are no shavings or even paper based substrate that is 100% risk free. It would be a rare case for a hamster to be allergic to any and all levels of dust for example, but this doesn’t mean we use these rare instances to label any & all substrates dangerous on the basis that there is no substrate that is 100% dust free.

So how have Germany not experienced the issues English forums insist softwood shavings will cause?

While some claim that it is due to a difference of kiln drying process, I personally do not believe this to be the case based upon the barbiturate sleep time study which observed no significant difference in autoclaved (which is a heat treating process) vs non-autoclaved substrates in terms of phenol reduction. While this could be a matter of temperature, I am still not of the belief that the European brands are safe based upon their heat treating process alone as from my research it would appear that many softwood brands in Europe (like allspan) are also treated at lower temperatures (100-200C) compared to some American brands of kiln-dried pine shavings, which claim to be treated at temperatures of over 400C. If safety truly relied upon phenols being removed during heat treatment, American shavings should therefore be safer than European… but this is not what we see.

For me, the answer as to why Germans have not experienced the issues that English forums are insistent that softwood will cause is relatively simple: as we discussed, abietic acid really isn’t a concern with softwood shavings like spruce, pine & fir, & the brands used undergo resin removal - it’s phenol levels. On perhaps the largest English speaking forum, the majority of the user database are from north America where the softwood shavings available for animal use are either 100% pine or 100% cedar – on the contrary, 100% pine shavings aren’t very common in Europe and the majority use either 100% spruce or spruce/fir mix. Like we discussed earlier, spruce has very low phenol levels that are comparable with that of aspen therefore, 100% spruce savings are already 100% safe and a mix of both fir and spruce shavings should theoretically lower concentration levels of phenols from fir. Additionally, lower product standards in North America may mean these shavings are dustier, and more likely to cause problems. I don’t think is too far of a reach, either. If we look at the amount of Upper Respiratory Infections reported by European owners (where the majority use the aforementioned brands/types of softwood) vs the amount reported by North American owners (where the majority use hardwood or paper based substrates), North American owners seem to consistently be reporting issues – even when using well regarded safe substrates. There seems to be a quality issue with dust, whereas the European products are of a higher quality and standards. As we have already mentioned, dust can wreck just as much havoc on a hamsters respiratory system as high phenol levels. But overall, I believe the safety of European brands is due to them being fir/spruce shaving mixes with the high likelihood of these mixes being at least 70% (if not greater) spruce, thus phenol levels are not as concentrated as they would be in 100% pine (or fir) shavings, thus rendering these products safe for the usage of small animals which is evidenced by the overwhelming lack of reports of respiratory distress in animals housed on spruce/fir mixes.

This isn't to say that kiln-drying at temperatures of 400C doesn't reduce phenol levels - as the honest answer to this is that we don't know, even if companies claim they reduce phenol levels, just how much are they reduced? - but it is to show that the argument used to suggest that European shavings are safer based on their heat treatment process alone likely is not accurate, and that their safety is much more likely to be the result of the bulk of the shavings (70-100%) being spruce which have very low phenol levels to begin with.

To conclude:

Spruce softwood shavings can be used & recommended with confidence. It is of my opinion based on my personal research & observation that brands like Chipsi classic and Tierwohl classic (and others) where the shavings are a spruce/fir mix with the bulk of the shavings being spruce, can be considered very likely safe. I do not believe that it is accurate to label these products dangerous, and I believe owners in Europe should be encouraged to use Spruce shavings. They are the superior bedding choice in Europe where not only are aspen shavings not common, but the aspen shavings that are available are either very finely shredded and have very high dust contents. Furthermore, other bedding materials like CareFresh & Hemp often offer poor burrow stability, even when mixed with hay compared to bedding like Allspan which is arguably the best substrate available for burrow stability. Beddings like chipsi classic & tierwohl classic are also great at burrow stability and if owners feel comfortable using them, I do not see a reason for why they should be discouraged. Particularly in countries where these are the only bedding types available, as all current available evidence points to these substrate mixes being safe for our pets. Owners should not be made fear spruce shavings on the basis of it being a softwood when there is only evidence to support it being a safe substrate, and no evidence to support it being a risk to your pets health. Spruce has very low phenol levels, and is practically the aspen equivalent for European pet owners.

I do not recommend the usage of 100% pine (or 100% fir) bedding on the basis that long term studies are lacking, and available anecdotal evidence is both lacking & conflicting as of the time I am writing this post. However, my opinion on this may possibly change as more research & supporting evidence is released. As of now, however, I will advise to err on the side of caution. I also discourage the usage of cedar shavings on the basis that not only are they are a highly aromatic substrate, but have also shown to increase liver weights in rodents, and have shown a possible connection to increased risk of hepatoma (liver cancer).

Cat litter should also not be used: even if non-clumping, it can be dusty (even pellets further turn to dust when wet), it is uncomfortable for your pet to walk on, and it does not allow your hamster to exhibit natural behaviour. Especially for owners who only have the options of wood based cat litter (which is nearly always made of pine) or spruce/fir shavings, they should be encouraged to choose the shavings & not be made fearful of choosing them. With regard to pine cat litter pellets or pine shavings: there appears to be a belief amongst some in the hamster community that pine pellets are safer than pine shavings. This is simply someone's opinion, and there is no available evidence to suggest that solid cat litter made of pine wood is better or safer than pine shavings. Both can be considered equals, if not the shavings better than pellets on the basis that they allow your hamster to exhibit natural behaviour & burrow. The usage of cat litter pellets is perhaps albeit an unintentional "by-product" of labelling all softwood dangerous - it has pushed many European owners (& others) who often have the option of either 100% spruce shavings or spruce/fir shavings (i.e. chipsi) & nothing else (paper based substrates are uncommon outside of the UK) to using non-burrowable substrate like cat litter pellets (or shredded tissues: which is neither practically sustainable or good at providing appropriate absorbency/odour control) for their pets, thinking that they were doing the right thing by their hamster. I believe this to be incredibly unfair - to both owners & their pets - when claims against all softwood being dangerous are severely lacking in evidence. It is not doing hamsters or their owners any favours by making them fear all softwood shavings: rather, I believe it to be having the complete opposite effect. Not only has it pushed owners to using inappropriate substrate choices, but it has caused bullying amongst the community with owners who use softwood shavings being accused as being 'reckless' and installing fear into many younger owners in particular who often feel like they have to lie about what substrate they use in fear of the retaliation. It is simply inaccurate to state that all softwood shavings are dangerous to our pets, when spruce in particular has been scientifically demonstrated to be the opposite. Once again, I stress that spruce shavings can be used with confidence, and that spruce/fir shavings mix - where the bulk of the shavings are spruce (i.e. 70% spruce, as is the case for chipsi), and therefore overall phenol levels are less concentrated - have a very high likelihood of being safe for your pet.

Ultimately I hope that this discussion has shed light on a topic that is far too often overlooked, if even thought about by many. For at least the past 10 years, the hamster community has shunned any and all softwood (including spruce) on the basis of assuming that they all have high phenol levels, and that abietic acid should be of high concern. Based on my research, the community has been wrong - and it is overdue for a revamp of acceptable standards.

ADDED NOTE:

There appears be reports of inconsistency with the quality of Chipsi Classic that appears to be most prevalent amongst 1-3kg packets. The issue reported is that very large shards of wood can be present in large quantities, and appears to be an issue reported largely amongst owners in Asia- however, this may also apply to 1-3kg products available in Europe. I have personally used 24kg bales of Chipsi Classic (who also produce the 24kg bales of Tierwohl - it is the same product, with different packaging) and have not noticed such a problem. Often you may find smaller pieces of wood (similar to hemp, or slightly larger - they are usually 2cm in length, and about 2-3mm in thickness: these are normal), but this is not a cause for concern and is completely normal for wood bedding. However, if you find your bag of wood shavings (this can also apply to aspen, or birch) has very large shards of wood throughout the entire substrate that cannot just be easily sorted through & removed, please do not use it: you have gotten a bad batch of bedding, and these large shards may cause injury to your pet.

Photo above shows what is NORMAL to find in wood based beddings. These are wood chippings, usually about 2cm in length & 2-3mm in thickness. They are often plentiful in any type of wood shavings, and are absolutely nothing to be concerned about.

Photo above shows what is ABNORMAL. These are large shards of wood, and can end up in wood beddings - however, you must remove them or they may cause injury to your pet. If they are so plentiful that they cannot be easily removed, DO NOT USE the bedding: this is simply inappropriate, and poses a risk for your pet.

Thank you to zoid_tho_ri for the photo example of larger shards of wood! You can also check out their blog here.

 

Sources:

  1. Barbiturate sleeptime in mice exposed to autoclaved or unautoclaved wood beddings

  2. Evaluation of Cage Micro-Environment of Mice Housed on Various Types of Bedding Materials

  3. The Effects of Chronic Exposure to Common Bedding Materials on the Metabolic Rate and Overall Health of Male CD-1 Mice

  4. The Truth About Pine Shavings

  5. Exposure To An Environment Containing The Aromatic Red Cedar, Juniper US Virginia: Procarcinogenic, Enzyme-Inducing and Insecticidal Effects

  6. Preference for bedding material in Syrian hamsters

  7. Abietic Acid

  8. Asmtha Caused by Unheated Colophony [Abietic Acid] is Rare

  9. Abietic acid isolated from pine resin (Resina Pini) enhances angiogenesis in HUVECs and accelerates cutaneous wound healing in mice

  10. Dehydroabietic acid as a biomarker for exposure to colophony

  11. Occupational asthma due to unheated colophony

  12. Music and matrimony – hazards for the colophonium allergic patient

  13. Immune responses to colophony, an agent causing occupational asthma

  14. Rosin Allergy [Abietic Acid Allergy Symptoms]

  15. Is abietic acid the allergenic component of colophony?

  16. Refined Spruce Resin to Treat Chronic Wounds: Rebirth of an Old Folkloristic Therapy

  17. Rosin: Chemistry, Derivatives, and Applications: a review

  18. What to do about softwood? A review of respiratory effects and recommendations regarding exposure limits

  19. Wood Dust

  20. Wood Shaving as Animal Bedding in Stables

 

"The illiterate of the 21st century will not be those who cannot read and write, but those who cannot learn, unlearn, and relearn”

 

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