By Nanna M. Andersen | Published: 2021 | Edited: 03.07.23 Pine, fir, spruce, aspen, and birch are a few of the available wood beddings. Pine, fir, and spruce are all softwoods, while aspen and birch are hardwoods. The composition of these two types of woods differs, and they lend themselves well to animal bedding. In the following section, I will discuss studies on heat-treating wood and the heat-treatment process, aiming to help people understand which types of beddings are safe for animals. Phenols are often mentioned as the main concern, but they are in fact merely a part of a group of compounds that exist all around us. These are called Volatile Organic Compounds (VOCs). It is important to consider all Volatile Organic Compounds present in these wood bedding types, such as phenols, p-cresol, indole, and skatole. VOCs are hydrocarbons that in high concentrations can be harmful when exposed to them for extended periods. Phenols can be found in various things in our surroundings, from food to flooring. VOCs are up to 10 times more concentrated indoors than outdoors, but maintaining a good indoor climate can help reduce these VOCs. The function of a substrate For a substrate to be marketed for animals, it needs to undergo a heating process to meet the pet industry standards, at least within the EU - I am told the same process is necessary in the US as well. In terms of qualities that a substrate needs to be useful for animals, it should be:
Sawdust typically contains a lot of dust and should be avoided. Wood chips and shavings marketed for animals, on the other hand, are usually dust-free or have reduced dust levels and should not cause any adverse reactions when using good quality chips/shavings. Wood chips and shavings have the ability to absorb up to 260% to 420% of their own weight, and sometimes even more. This high absorbency is likely why they are popular in the fancy and laboratory settings. Some companies incorporate enzymes and bacteria that feed off ammonia into their products, which helps lower ammonia levels and makes the bedding last longer. These specific products are typically used for horses or other livestock living in pens. The heating process Wood substrates are heated before being packed for shipment. Most wood substrates are processed in a rotary dryer designed to heat lighter materials like chips and shavings, see the picture below. The dryer is continuously fed substrate, which slowly moves down the horizontal dryer. The inside of the dryer is equipped with small shovels on the sides that prevent larger pieces from falling. The substrate remains in the dryer for approximately 30 minutes, sometimes longer. The drying temperature used in the process typically ranges between 100-200 degrees Celsius, which is considered "low-temperature drying" and is usually the standard treatment. However, there are machines available that use higher temperatures. One notable example is the Triple Pass dryer used by companies like Chipsi/TierWohl. This dryer passes the substrate through three chambers instead of one, making it the preferred and most effective machine, although the conventional rotary dryer is still commonly used. In an experiment conducted by Finn Englund and Ralph M. Nussbaum in 2000, the release of Volatile Organic Compounds (VOCs) was measured for three different types of wood. While these pieces of wood are not shavings, it still shows the effectiveness of heat-treatment on bigger pieces of wood. The study examined heartwood pine, sapwood pine, and sapwood spruce. Two main temperatures were used: normal temperature (NT, 60ºC), high temperature (HT, 110ºC). We also see 75ºC and 115ºC used one time respectively. The results show that the Norway Spruce in the study contain lower amounts of VOC to being with and the end result show VOC are within safe limits. The pine showed higher amounts of VOC, and the VOC had trouble escaping during heat-treatment. It showed that higher tempratures were more effective in eliminating VOCs. In another study by Marko Hyttinen, et al. in 2010, the release of Volatile Organic Compounds (VOCs) was measured after heat-treatment of three different wood species. The study focused on Norway Spruce, Scots Pine, and European Aspen. Unlike the previous test we discussed, this study utilized higher temperatures that better reflected the conditions of a rotary dryer as used by companies like Chipsi. It's important to note that the size of the wood samples used may vary across different studies, but in all cases, they will be larger than chips or shavings. The results speak for themself. The amount of VOC before and after heat-treatment shows that all the wood are within safe limits. Even before treatment the amount was not that high. In a study by Mindy J. Spiehs, et al. in 2012, the focus was on the VOC (Volatile Organic Compounds) profiles of various substrates. The study examined eight different substrates: soy stover, corn cob, corn stover, paper, wheat straw, switchgrass, pine chips, and pine shavings. The goal was to evaluate the concentration of odorous compounds and Escherichia coli (E. coli) in each substrate, we will solely focus on the VOC results. The researchers sought substrates with low VOC concentration profiles and a low total concentration overall. The results shows that pine shavings had the lowest VOC profile overall, with paper and corncob having the highest concentrations. In a study by Ellen Smith, et al. in 2004, the focus was on controlling ammonia levels in rodent cages. The study examined the effects of different substrates on ammonia concentration in closed, aquarium-like cages, with a ventilation attached. It is important to note that rodents should always be housed in well-ventilated cages in a pet setting to ensure their health and safety. The maximum allowable ammonia concentration in a rodent cage is 25 parts per million (ppm). Concentrations above 50 ppm can cause respiratory issues and potentially irreversible harm to the animals. A concentration of 100 ppm or higher is likely to result in permanent damage or even death. Humans can detect ammonia concentrations around 5 ppm, with concentrations of 30 ppm causing irritation to the airways, eyes, and lungs. A concentration of 50 ppm will cause a strong and immediate reaction. Therefore, if you can smell ammonia in the cage, the concentration is above 5 ppm, and if you experience irritation in your nose, eyes, or lungs, it is crucial to change the substrate immediately. The study tested seven different substrates: Alpha-dri (cellulose), corn cob, hardwood shavings, recycled newspaper, CareFresh Ultra, and pine shavings. They used 3 control cages with no mice, only bedding, as well as the ammonia concentration of the room. After observing the considerably higher concentration of ammonia in CareFRESH Ultra compared to pine shavings, an additional test was conducted focusing solely on CareFRESH and pine shavings. The results of this new test (see next page) revealed a lower concentration of ammonia in CareFRESH compared to the previous test. However, even in this new test, the concentration of ammonia in CareFRESH was still three times higher than that in pine shavings. This finding serves as definitive evidence that CareFRESH Ultra is not effective in controlling ammonia levels. If an individual chooses to use CareFRESH despite this evidence, it is crucial to remain vigilant about odor detection and regularly change the substrate. Neglecting to do so can pose a potential health risk to the animals if the substrate is left unchanged for too long. My conclusion
There is sufficient evidence to safely and ethically recommend spruce and pine as suitable bedding options, alongside aspen or even hemp. In the study by Finn Englund, et al. it was demonstrated that untreated spruce had a VOC percentage ranging from 0.018% to 0.096%, significantly lower than the spruce in the study by Marko Hyttinen, et al., which had a VOC percentage of 0.54%. The discrepancy in VOC percentage could be attributed to the origins of the trees or the heat treatment applied to the spruce used in Finn Englund's study, which was purchased from a hardwood store. In the study by Marko Hyttinen, et al., it was observed that spruce had lower VOC percentages compared to aspen, and after heat treatment, the VOC percentages were reduced to 0.09% for spruce, 0.22% for pine, and 0.15% for aspen. Once again, spruce exhibited lower VOC percentages compared to aspen. This indicates that spruce has a VOC profile similar to that of aspen. In the study by Mindy J. Spiehs, et al. it was revealed that pine had lower VOC percentages than newspaper and corn cob. The VOC percentages observed in spruce were significantly lower than other softwoods and closer in profile to hardwood. This further supports the safety of spruce. Fir, another softwood, shares a similar profile and is a component of Chipsi wood substrate, which consists of 70-75% spruce and 25-30% fir. Spruce and pine belong to the same subfamily, Piceoideae, while fir belongs to the subfamily Abietoideae. Moving on to the study by Ellen Smith, et al., issues with ammonia control were observed with CareFRESH. It is important to remember that cages and ventilation system used in this study does not correlate with pet husbandry. Additionally, regular cage cleaning is key to ensure sanitary conditions. The use of CareFRESH, and possibly other paper beddings, can be problematic, particularly if regular cleaning is neglected. References
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