This semester, my upper-division Animal Behavior class (BIOL 330) conducted a study on the feeding behavior of house cats. We recruited our friends and families to volunteer their cats as research subjects. Students in the class came up with a research plan and carried out all aspects of the project. Pairs of students wrote short blog posts about the results. I’ve posted a great one below by seniors Shane McWirther and Nick Loken. There were several other great ones, and we had contributions from every class member (listed below). Thanks so much to all of the participants that took the time to complete the study. Check out the results – they’re great!
To Eat or Not To Eat Protein? That Is The Question
It’s that time again – Snickers is sitting at his empty bowl with a look of despair. You completely forgot to run to the store and get him his usual bag of Fancy Feast. Finals are coming up and you have a term paper due tomorrow. As much as you don’t want to waste time driving through traffic to get more food, nobody likes an agitated cat. You rev up your 96’ Honda and speed down to PetSmart. This trip has been made many times before; walk through the doors, take a right and awkwardly power walk down to aisle 8 where the Frisky Feast awaits you. You go to grab the bag but it’s nowhere to be found. What now? The term paper looms over you and you grab the first bag of cat food you see. He won’t even know the difference. It’s just cat food. But what if he could?
Researchers have discovered that food preferences for many animals are not simply determined by chance. Balancing macronutrients through selective foraging has been found throughout the animal kingdom. Primates (Felton et. al 2009) and mice (Sorensen et. al 2008) are known to maintain stable protein levels in their diet over time regardless of caloric intake. These observations are potentially explained by the Protein Leverage Hypothesis, which posits that animals adjust their level of food intake to reach a constant protein intake level.
The aim of the current study is to see whether cats adhere to the Protein Level Hypothesis and choose foods based on their macronutrient content. Specifically, we tested 3 predictions: (1) If cats selectively forage to maintain stable protein levels, those pre-treated with low protein foods will compensate by eating protein rich foods when given a choice between foods with varying protein content; (2) If cats do not selectively forage, they will prefer whatever food they are pretreated with regardless of its macronutrient composition; (3) If a cats current nutritional state does not affect its foraging habits, pre-treatment will have no effect on foraging habits of cats when given access to foods with varying macronutrient content. The results of the study could provide support for the Protein Leverage Hypothesis and in turn inform pet owners on eating habits of their beloved felines and help them make better choices when scouring the grocery aisles for the perfect cat food.
Table 1. Major components of Purina One Urinary Tract (UT) and Healthy Metabolism (HM) dry foods
Thirty-eight cats (from 25 cat owners) were recruited to participate in the study. Cat owners received a package containing one bag of low carbohydrate + fat, high-protein cat food (Purina Healthy Metabolism (HM)), one bag of high carbohydrate + fat, low-protein cat food (Purina Urinary Tract Health (UT)), one bag containing a mixture of both formulas, and one pre-treatment bag containing solely UT or HM formula (complete dietary information is listed in Table 1). All food bags were labeled and weighed prior to distribution. Cats were weaned onto bags containing a mixture of the two formulas for four days by serving it along with their customary food brand. On day five, cats were given access to only the pre-treatment bag containing solely HM or UT formula. On day six, cats were given equal access to both HM and UT formulas. Bags from days five and six were returned to the researchers and weighed upon arrival in the lab. Multiple cat homes were treated as one participant. Data was analyzed using JMP.
Results & Discussion:
Figure 1. Relationship between pre-feeding treatment and % protein eaten when cats free fed one day later
We found that cats consumed the same amount of pre-treatment food on day five of the experiment regardless of what formula the bag contained (Average intake of UT = 120.4g, HM = 126.4g, p>0.05). This result shows that cats ate whatever was given to them in the absence food choice. However, cats were observed to eat almost twice as much of the high protein HM formula compared to the low protein UT formula when given equal access to each on day six (Average intake of HM = 82.0g, UT = 43.1g, p<0.05). This result indicates that cats were selectively foraging for protein. However, we also found that pre-feeding conditions significantly affected foraging behavior on a subsequent day. Specifically, we found that cats pre-treated with the low-protein UT formula ate a significantly higher proportion of protein (higher HM:UT consumption) on day six compared to cats pre-treated with HM formula (Figure 1, p<0.05).
Our study is the first to test for nutrient balancing in domestic cats using a citizen-science study design. The protein compensation that we found on day six observed in UT pre-treated cats provides strong support for our main prediction – that cats selectively forage to maintain nutrient balance. Prediction two was supported by the fact that UT pre-treated cats did not consume a larger ratio of UT:HM formula which would be indicated by consumption of a lower proportion of protein on day six (Figure 1). These results are consistent with a recent study using lab cats (Hewson-Hughes et al. 2011). Although the exact feeding methods of the cat owners were not directly observed, we do not believe that this impacted our results since owners were given detailed instructions on the protocol.
Many cat owners do not take into account the macronutrient composition of the cat food they are buying even though it may be in their cat’s best interests. Being force-fed low-protein foods may cause many cats to over-eat in order for them to stabilize protein intake in their diet. Over-eating can lead to several different health disorders, possibly shortening the lifespan of cats. So next time you’re rushing through the store looking to buy a new bag of cat food, take the time to stop and look at its nutritional composition. This simple choice could be the difference between a fat cat and a happy cat.
Felton AM, Felton A, Raubenheimer D, Simpson SJ, Foley WJ, Wood JT, Lindenmayer DB (2009) Protein content of diets dictates the daily energy intake of a free-ranging primate. Behavioral Ecology 20: 685-690.
Hewson-Hughes AK, Hewson-Hughes VL, Miller AT, Hall SR, Simpson SJ, Raubenheimer D (2011). Geometric analysis of macronutrient selection in the adult domestic cat, Felis catus. Journal of Experimental Biology 214: 1039-1051.
Sørensen A Mayntz D, Raubenheimer D, Simpson SJ (2008) Protein-leverage in mice: The geometry of macronutrient balancing and consequences for fat deposition. Obesity 16: 566-571.
About the authors: Shane McWhirter & Nick Loken our senior Neuroscience majors at the University of St. Thomas. Other class contributors were Sam Bach, Maureen Carberry, James Giorgi, Justin Hummelgard, Cory Jensen, Angela Kramlinger, Lauren Kvam, Abby Lown, Mike McGoldrick, Lauren Mumm, Losha Ndemeno-Tegomoh, Jillian Nielsen, Zac Novaczyk, Meghan O’Reilly, Luis Ortega, Danny Oseid, Marchellie Sheldon, Tori Shepard, Kale Siebert, Ariel Steele, Lexi Tartar, Asha Urban, and Carissa Van Slooten.