Abstract

Cats may develop strong preferences for specific types of litter, which can impact their litter box usage and overall well-being. Understanding these preferences can help us to improve feline welfare, particularly in multi-cat households or in cats experiencing litter box aversion issues. While previous studies have explored some aspects of feline litter preference, limited research has examined a diverse range of alternative litters in direct comparison.

A case study on litter box preferences was performed to assess how cats respond to different litter substrates. Nine cats of varying ages and abilities were given access to seven different types of litter (clay, cereal, pea husk, grass seed, tofu, coffee ground, and olive pit). Data was collected separately for urine and defecation deposits to determine potential differences in substrate preference for each type of elimination. The findings indicate that cats vastly preferred clay litter for both urination and defecation. Otherwise, there was no strong overall preference among the alternative litters. However, cats showed a slight preference for urinating in grass seed litter over other non-clay options and a tendency to defecate in coffee ground litter over other non-clay litters. These results contribute to a broader understanding of feline litter preferences, which could be examined within a wider scale study. The subject warrants further investigation to help inform pet guardians and manufacturers in optimizing litter box setups.

Introduction

One of the most common behavioral issues cat guardians are faced with is unwanted elimination outside of the litter box (Salman et al., 2000). Although there are many reasons a cat may stop using the litter box, general dislike of what is being offered is perhaps considered to be the most prevalent (Carney et al., 2014). With many types of litter boxes and even more substrates on the market, most of which are designed for the convenience of the humans, not necessarily the cats, it can be difficult for cat guardians to know what to choose.

In cat behavior consulting, the “litter box buffet” is a common method used in order to confirm a cat’s preferred substrate and rule out litter type as a potential cause for undesirable elimination. Multiple litter options are offered to the cat at the same time, in the same location, in the same type of box, so that all factors are the same except for the substrate. This is a much more effective method than trying one litter at a time, as it allows the consultant and the cat guardian to definitively see what the cat prefers when given a choice. Research conducted by Grigg et al. (2012) supported the popular treatment recommendation of offering cats with house soiling concerns a litter box “cafeteria” (or buffet) in order to establish whether a substrate, location, or type of box preference exists. Similar to the cats in the Grigg et al. study, our population of cats were not currently suffering from an elimination disorder. However, Grigg et al. concluded that it is possible that cats with house soiling concerns may exhibit stronger or different preferences than those without.

In addition, Villeneuve-Beugnet and Beugnet (2018) published a study on substrate preferences using a similar method, testing wood pellets, silica microgranules, and clay granule litter. They ultimately concluded that clay was the preferred substrate for the majority of cats, testing 18 different cats across different homes. We decided to replicate our own version of this litter box substrate preference experiment, using methods similar to that of Vielleneuve-Beugnet and Beugnet, in our own home. With the rise of so many “boutique” substrates (cat litters that go beyond the traditional clay or silica options) on the market we wanted to find out whether any of them were truly designed with the typical cat’s preferences in mind. These newer litters are often marketed as more eco-friendly, visually appealing, or convenient for humans, using materials like walnut shells, tofu, paper, or grass. While they aim to meet cats’ needs, their features often cater more to human concerns, such as low tracking or compostability. To explore this further, we tested several newer litter types not yet represented in the scientific literature, including tofu and coffee grounds. We also included a few scented options: the tofu litter was “oasis cactus” scented, and the pea husk litter had a strong blueberry fragrance.

Methods

Our participants consisted of six adult cats, owned by the present researchers, and between three and five foster kittens (two kittens were adopted over the course of the study). The adult cats ranged in age from 4 to 20 ( M = 7, SD = 6.055) and many had other health, conformational, or cognitive considerations. None of the cats in the study were declawed.

Table 1. Participants

Name, Neuter Status, Age, and Other Considerations for Feline Study Participants

Before conducting this experiment, we offered the cats only unscented clumping clay litter, with eight litter boxes in total spread out over three different locations. We kept four of these boxes available to the cats throughout the study, two per floor of our two-story home. This decision was made to ensure that an environment containing multiple and separated key resources was maintained, in order to prevent inter-cat tension or conflict from being forced to eliminate in a single location only. In a separate room on the ground floor, we removed the litter boxes and replaced them with a “litter box buffet” consisting of the six unique types of litter, and three additional boxes with the same unscented clumping clay litter they were accustomed to. We elected to keep this clay litter in our lineup even though clay litter was given as an option in other locations, so that location would not be a factor in the recorded data. In all, there were nine boxes side by side. We used disposable cardboard litter boxes, and rotated the order several times throughout the two-week process in order to ensure that the cats didn’t simply have a location preference (closest to or farthest from the door, etc.). The cardboard boxes were chosen due to cost and space concerns. Other than rotating the boxes’ order, we did not change out the boxes over the testing period. Data was collected twice a day, once in the morning (“AM”) and once in the late evening (“PM”) for 12 days, with an extra data point in the AM of the 13th day. The adult cats always had access to the data collection site. The kittens were housed elsewhere at night, so only had access to the data collection site during the daytime. Hence, each AM data point is collected only from the adult cats, whereas data points collected in the PM consist of data from all participants. Data points consisted of cleaning each of the nine boxes one by one, marking how many and which type of deposits were found in each box. After the 25th instance of data collection, we had arrived at a sample size of 201 data points. This was initially deemed to be acceptable to determine the hypotheses.

Due to the nature of the litter box set-up, it was not possible to collect data cat by cat, and as such the findings only reflect preferences across participant cats, as seen in Table 1. Of note, then, is that the study participants initially consisted of 11 cats, then briefly 10 cats, before landing on a participant count of nine cats. No data was excluded due to the population shift, and the data analysis method chosen did not rely on a static population size.

To analyze the data, a X² goodness-of-fit test was run at α=0.05 to see if cats statistically significantly showed a preference to a litter type regardless of deposit type. As can be seen in Table 2, since there were at least five deposits in each type of litter, the basic assumptions of the goodness-of-fit test can be run. Throughout this study, we have operationalized litter substrate preference to mean the proportion of deposits in one litter type is statistically significantly larger than the proportion of deposits in some other litter type. To that end, 126 two-sample proportion tests were run at α=0.05. For each test, the alternative hypothesis was that the proportion of deposits in LT₀ was greater than the proportion of deports in LT₁, where LT₀ could be any of the seven litter types, LT₁ could be any of the six remaining litter types, and the deposits could be either urine (n = 162), defecation (n = 39), or in total (without discrimination of deposit type, n = 201). For any results found to be statistically significant, the effect size was computed using Cohen’s h. To interpret Cohen’s h, a value between 0.00 and 0.19 will be considered as a “negligible effect,” a value between 0.20 and 0.49 will be considered as a “small effect,” a value between 0.50 and 0.79 will be considered as a “medium effect,” and a value above 0.80 will be considered as a “large effect” (Cohen, 1988). All statistics were computed using a combination of Microsoft Excel, Pearon’s StatCrunch, and a Casio fx-991EX Classwiz calculator.

Ethical Considerations

This study did not receive formal ethical approval from an institutional review board or ethics committee, as it involved the use of the author’s companion animals in a private household setting. All procedures were carried out in accordance with ethical guidelines for the care and treatment of nonhuman animals, with full consent from the animal caregivers. The well-being of the cats was prioritized throughout the study.

Results

The summary data can be found in Table 2, and the full results of the 126 two-sample proportion sample tests can be found in Tables A-1, A-2, and A-3 in Appendix A. The significant findings are articulated below.

Table 2.

Total Number of Deposits per Litter Type

In general, we found that cats showed no statistically significant preference amongst non-clay litter (p = 0.0521). However, in head-to-head tests using two-sample proportion testing, we found that cats prefer grass seed to cereal (h = 0.27), pea husk (h=0.19), and olive pit (h = 0.27). No other test yielded statistical significance.

With respect to urine, we found that cats showed a statistically significant preference amongst non-clay litters. In head-to-head tests, we found that cats prefer grass seed to pea husk (h=0.22), grass seed to cereal (h=0.29), grass seed to olive pit (h=0.29), and grass seed to coffee grounds (h=0.37). Cats additionally prefer tofu to coffee ground (h=0.20). No other test yielded statistical significance.

With respect to defecation, we found that cats again showed a statistically significant preference amongst non-clay litters. From Table 2, one can see that only three types of non-clay litter were defecated in. The proportion of defecations in the coffee ground litter was statistically significantly greater than the proportion of defecations in either pea husk or grass seed litter (h = 0.48). Hence, the cats in the research study statistically only defecated in clay and coffee ground litter. No other test yielded statistical significance.

Isolating the AM data from the rest of the data set, thus isolating the data to only the population of adult cats, yields nothing different than what has already been articulated above. Additionally, two of the litter types (pea husk and tofu) were scented. As was verified in the above results, scent is not a factor for litter preference. Three litter types (cereal, tofu, and pea husk) were “textured,” in that the litter was in the form of pellets instead of fine grounds. Statistically, this again does not factor into litter preference.

In statistics, the power of a study is the probability of making the correct determination in accepting the alternative hypothesis (Dorey, 2011). The full information about the power of the significant results can be found in Table A-4 in Appendix A. In brief, the power of the significant results spans from a low of 0.59 to a high of 0.93.The average power was 0.723 (SD = 0.125543), which is less powerful than desirable but not so underpowered as to dismiss the above results.

Figure 1 shows a cumulative time series graph for all urine deposits made in non-clay litter. While the preference to urinate in the grass seed litter is clear from the statistical analysis, Figure 1 is able to provide additional insight. In particular, approximately eight days (seen in Figure 1 at the 16th data point) into the 13-day experience, the cats began to urinate more frequently in the tofu litter. This had been previously noted anecdotally by both researchers. A less pronounced uptick in usage can be seen for pea husk litter a few days prior. Note that these represent two of the three pellet litter varieties. It may be the case that the cats needed time to adapt to pellet litter. The increased usage of tofu litter over time is not statistically significant at any point, but it would be interesting to see the results of a similar study conducted over a longer period of time, allowing the cats more time to adjust to the different textures of the litters.

Figure 1. Cumulative Time Series Graph for Urination in Non-Clay Litters

Discussion

In this study, we sought to explore preferences for various litter substrate types as a function of how frequently the cats made deposits in the various litter types (clay, cereal, pea husk, grass seed, tofu, coffee ground, and olive pit). The findings indicate that cats vastly preferred clay litter for both urination and defecation. Otherwise, there was no strong overall preference among the alternative litters. However, cats showed a slight preference for urinating in grass seed litter over other non-clay options and a tendency to defecate in coffee ground litter over other non-clay litters.

We used two scented litters in the experiment. The pea husk had a strong blueberry scent and the tofu had an “oasis cactus” scent. Although it is common knowledge that cats should be offered unscented litter — it is even part of the five pillars of a healthy feline environment to respect a cat’s sense of smell (Ellis et al., 2013) — we did not see any strong preference between scented or unscented litter. Similarly, three litter types (cereal, tofu, and pea husk) were “textured,” in that the litter was in the form of pellets instead of fine grounds. Again, the results indicated no strong preference with respect to litter texture.

Although our findings do seem to confirm that clay litter is the most highly preferred substrate within this sample of cats, there are multiple external factors at play that could have been influencing the cats’ decisions, including location, prior learning history, size of the box (the disposable boxes were significantly smaller than alternative boxes in other rooms), and more. Guy et al. (2014) found that cats show a definite preference for larger litter boxes and that other factors, such as box cleanliness and location, may also influence their toileting choices. Further research could be done amongst populations of kittens, offering multiple types of substrates from weaning in order to determine preferences in cats without any prior learning history in a more controlled environment. Kittens typically learn about using the litter box from their mother beginning around 3 to 5 weeks of age. By the time a kitten reaches 7 weeks of age, they may have already developed a preference for a certain type of litter and box (Grigg et al., 2013; Guy et al., 2014).

In addition to considering the preferences of adult cats versus kittens, we also had several other factors that could have influenced choices (see “Other Considerations” in Table 1). Our population included a blind cat, a geriatric cat, and two three-legged cats. Mobility issues and joint pain associated with old age or overcompensation from loss of limb can affect litter box usage. Cats with musculoskeletal issues might struggle to get to the litter box depending on location (Padalino et al., 2023).

In a multi-cat household, especially one as large as our sample population, some cats may form close social groups, while others prefer to be more independent. It was important to us to allow each social group to have access to their own set of resources without needing to share with others. We offered alternative locations around the home throughout the experiment, so these cats may have been more likely to choose more convenient options. We made the decision to keep these other locations in order to respect Pillar Two of the Five Pillars of a Healthy Feline Environment welfare assessment model: “Provide Multiple and Separated Key Resources.” Cats need to have easy access to important things like food, places to rest, and litter boxes without feeling threatened by other cats. Keeping these resources separate helps prevent competition, lowers stress and related health issues, and supports their natural desire to explore and stay active (Ellis et al., 2013).

Limitations

Options for litter boxes besides the data location site were made available due to the number of cats in the home and to avoid any clustering of resources that would force cats to be together who would otherwise typically choose to spend time apart. We recognize that this may have compromised the accuracy of our experiment, but it was best for the welfare of the population involved; the well-being of the cats was of the highest priority during this experiment.

Due to these alternative options, a few of the cats could choose to participate infrequently, if at all. The data site we chose to set the experiment in could have been a less preferred location, or they simply could have been choosing to stick to familiarity and avoid novelty. To help mitigate any response to novelty, we chose to line up all the boxes in a row and use the same cardboard disposable boxes for each substrate in order to make the options as uniform as possible with the only difference being the substrate, and we rearranged the order of the boxes several times to verify that location within the room played no part in litter substrate preference.

It is important to not generalize these findings to all populations of cats. It is worth noting that, of the cats who participated in the experiment, at least three were 5-month-old kittens who had been raised on clay litter for as long as they had lived indoors. It is hard to say if the data would have yielded different results if they had been started on, for example, tofu. It is possible they chose the option with which they were most familiar.

The same could be said of the remaining six adult cats in the study. Out of six, four had been with us since kittenhood and always used clay litter. The two remaining had been using clay litter exclusively for at least five years in our home, although since they were adopted as adults, we can’t know their history prior. Although not recorded, the researchers did informally observe that these two cats adopted as adults, Juniper and Sunny, appeared to try new choices perhaps more often than the other adult cats.

Additionally, the use of a convenience sample and smaller sample size introduces some limitations. In particular, the sample size contributed to results that carried less than the desired statistical power. In fact, the lowest statistical power provided in the results would quantify some of our findings as “questionable.” However, we personally found the results to be powerful enough to change our practices, offering grass seed litter full time to the cats in one litter box indefinitely. Further research should consider collecting more data points, limit the scope of the study to only test preferences for grass seed litter (the most popular in the present study), or otherwise design a more specific and pointed study in order to increase the power or effect size of any findings presented here.

Conclusion

The findings of this study demonstrate that cats, at least this specific population, have a strong preference for unscented, clumping clay litter for both urination and defecation. Among non-clay options, cats demonstrated a slight preference for grass seed litter for urination and coffee ground litter for defecation, though these preferences were not as pronounced. Scent and texture did not appear to influence litter selection, suggesting that factors such as substrate composition and familiarity may play a more significant role in cat litter preferences.

While the study design allowed for meaningful insights, the results may have been influenced by the availability of familiar clay litter in other parts of the home, potentially limiting full exploration of non-clay options. The findings highlight the importance of considering individual preferences and introducing new substrates gradually when addressing litter box concerns. Future research could explore longer study durations and the potential impact of scent, texture, and substrate novelty over time to provide further clarity on cat litter preferences.

References

Carney, H. C., Sadek, T. P., Curtis, T. M., Halls, V., Heath, S., Hutchison, P., Mundschenk, K., & Westropp, J. L. (2014). AAFP and ISFM guidelines for diagnosing and solving house-soiling behavior in cats. Journal of feline medicine and surgery, 16(7), 579-598.

Cohen, J. (1988). Statistical power analysis for the behavioral sciences (2nd ed). L. Erlbaum Associates. Dorey, F. J. (2011) In Brief: statistical power: what is it and when should it be used? Clin Orthop Relat Res, 469, 619-620.

Ellis, S. L., Rodan, I., Carney, H. C., Heath, S., Rochlitz, I., Shearburn, L. D., Sundahl, E., & Westropp, J. L. (2013). AAFP and ISFM feline environmental needs guidelines. Journal of feline medicine and surgery, 15(3), 219-230.

Grigg E.K., Pick L, Nibblett B. Litter box preference in domestic cats: covered versus uncovered. Journal of Feline Medicine and Surgery. 2012, 15(4), 280-284.

Guy, N. C., Hopson, M., & Vanderstichel, R. (2014). Litterbox size preference in domestic cats (Felis catus). Journal of Veterinary Behavior, 9(2), 78-82.

Padalino, B., Zappaterra, M., Felici, M., Ricci-Bonot, C., Nanni Costa, L., Houpt, K., & Tateo, A. (2023). Factors associated with house-soiling in Italian cats. Journal of Feline Medicine and Surgery, 25(11)

Salman, M. D., Hutchison, J., Ruch-Gallie, R., Kogan, L., New Jr, J. C., Kass, P. H., & Scarlett, J. M. (2000). Behavioral reasons for relinquishment of dogs and cats to 12 shelters. Journal of applied animal welfare science, 3(2), 93-106.

Villeneuve-Beugnet, V., & Beugnet, F. (2018). Field assessment of cats’ litter box substrate preferences. Journal of Veterinary Behavior, 25, 65-70.

Appendix A

Full results for the two-sample proportion tests are presented in the next three tables below, using the alternative hypothesis that the proportion of deposits LT₀ is greater than the proportion of deposits in LT₁.

Table A-1.
p-values for Two-Sample Proportion Tests, All Deposits, n=201

*: significant at α=0.05

Table A-2.
p-values for Two-Sample Proportion Tests, Urine, n=162

*: significant at α=0.05

Table A-3.
p-values for Two-Sample Proportion Tests, Defecation, n=39

*: significant at α=0.05

Note: Entries with N/A are because there must be at least one deposit to run a
two-sample test of proportions.

The results of the ex post facto power analysis for the statistically
significant two-sample proportion tests is presented below.

Table A-4.
Result of the Power Analysis for Statistically Significant Results

Laura and Cody Cassiday reside in Baltimore, Maryland, sharing their home with a large and variable population of special needs cats. Laura is the certified cat behavior consultant and full-time cat behavior specialist behind Pawsitive Vibes Cat Behavior and Training, while Cody is a math professor at the Community College of Baltimore County.