Drivers of Palatability for Cats and Dogs—What It Means for Pet Food Development

Round 1

Reviewer 1 Report

This review describes current knowledge regarding the drivers for petfood palatability for cats and dogs, with some comments regarding implications for the manufacture of nutritious pet food. Citations appropriately range from older classical works by Boudreau and others to more recent studies and cover both peer-reviewed and industry-derived publications. The manuscript is generally well-written and well-organized. 

I do have some major and minor comments.

(1) The manuscript would be strengthened by more insight and a clear set of conclusions or recommendations identifying the gaps and knowledge and how companies might best apply what is known.

(2) While I was expecting some more specific recommendations regarding improvements in behavioral testing methods, this was missing. The single point that the one and two-bowl methods don't shed insight into why a particular choice is made is not accurate. This has more to do with experimental design than testing format. Two bowl tests could certainly be the basis for studies to determine, for instance, whether differences in fat or protein source or type can be discriminated and elicit a preference. Repeated, Single-bowl tests using diets of different composition could be used to gain insight into drivers of eating rate and volume.  Either do not set it up in the abstract as a goal or include more content.

(3) It would also be nice to have some consideration of the industry trend for 'humanization' of pet foods, which seems to be counter to the goal of sustainability.  No mention of the work on bitter receptor genetics was made, which has implications for the use of more sustainable ingredients such as plant proteins. 

(4) The last sentence of the paragraph from lines 264 - 268 is not comprehensible - I can't even tell what you are trying to say to suggest an alternative, so perhaps something was cut by mistake?

 

Author Response

Thank you for your comments on the document. Please find attached our response.

1. The manuscript would be strengthened by more insight and a clear set of conclusions or recommendations identifying the gaps and knowledge and how companies might best apply what is known.

Response: We have re-written the conclusion section of the manuscript to more clearly spell out the gaps in current knowledge and where more modern techniques can play a role alongside the more “traditional” pet food testing methods.

 

2. While I was expecting some more specific recommendations regarding improvements in behavioral testing methods, this was missing. The single point that the one and two-bowl methods don't shed insight into why a particular choice is made is not accurate. This has more to do with experimental design than testing format. Two bowl tests could certainly be the basis for studies to determine, for instance, whether differences in fat or protein source or type can be discriminated and elicit a preference. Repeated, Single-bowl tests using diets of different composition could be used to gain insight into drivers of eating rate and volume. Either do not set it up in the abstract as a goal or include more content.

Response: We understand that use of repeated two-bowl test can determine differences between foods tested. However, the likelihood of manufacturers repeating and retesting diets using traditional one- and two-bowl testing to assess singular changes can be time-consuming depending on the number of iterations required – addressed in lines 536-542. Additionally, many pet food manufacturing companies do not have in-house companion animal nutrition testing facilities to undergo unlimited palatability testing. Therefore, the cost of outsourcing palatability testing for multiple iterations may not be justifiable.

 

3. It would also be nice to have some consideration of the industry trend for 'humanization' of pet foods, which seems to be counter to the goal of sustainability. No mention of the work on bitter receptor genetics was made, which has implications for the use of more sustainable ingredients such as plant proteins.

Response: Trends in the Pet food Industry which talks of humanization and emerging trends for 2023 has been added as Section 8 into the revised manuscript.

 

4. The last sentence of the paragraph from lines 264 - 268 is not comprehensible - I can't even tell what you are trying to say to suggest an alternative, so perhaps something was cut by mistake?

Response: These lines have been removed as they did not relate to the discussion point above – likely copying error when transferring content into the document

 

Reviewer 2 Report

The work is very clear and comprehensive.

I would ask the authors to better specify what they mean by "trained panel of cats" line 536.

It would be appropriate to elaborate on the method used to define trained.

Also interesting is if this method is also applied to dogs.

Author Response

 

Response to Reviewer 2

1. I would ask the authors to better specify what they mean by "trained panel of cats" line 536.

Response: “Trained panel of cats” are cats that are able discriminate foods with different sensory properties (added to line 567-568).

 

2. It would be appropriate to elaborate on the method used to define trained.

Response: In terms of other training, cats used in palatability studies are likely to have been exposed to periods of isolation in individual testing booths to be used as suitable subjects for feeding trials. Not all cats can go for periods in time in cages alone so would not be suitable as palatability cats. Also, cats that show “side bias” as described in lines 580-581 may not be suitable subjects. These are key factors researchers consider when evaluating their suitability in feeding trials..

 

3. Also interesting is if this method is also applied to dogs.

Response: Dogs are less selective of foods, but we have included additional measures that take place when dogs are used as test subjects as outlined in lines 505-507.

Reviewer 3 Report

Major Comments

 

372: Probably is necessary to discuss more about the problems of a vegetarian diets in dogs and cats and that affect not only the nutrition of animals but their welfare.

 

447-448: It is true that palatability is related with feed acceptance. However, because animals regulate its feed intake by the input of nutrients and the caloric density is directly related with palatability (because pleasure is related with the adaptive value of a behavior): Palatability is not directly related with food intake (acceptability)

 

457: this method (one bowl test) is contraindicating to address palatability. As I said more palatable foods (I.e with more energy/protein/fat content) will stop the consumption behavior before than other diets because animals regulate very fast by oral and post-oral receptors its food intake. Because of this, a more consumed food (From data of 1 bowl test) is not always the most palatable food (think about honey vs rice). One possible option is to reduce the testing time to decrease animals oral or post-oral satiety, to study consumption patterns (Lick cluster size in rats) that relate consumption time with the number of visits to the feeder or to study facial expressions (taste reactivity test). In this method also the latency time to the first approach could be measure

 

Dwyer, D. M. 2012. Licking and liking: The assessment of hedonic responses in rodents. Q. J. Exp. Psychol. 65:371–394. doi:10.1080/17470218.2011.652969

 

Figueroa, J.; Frias, D.; Sola-Oriol, D.; Tadich, T.; Franco-Rossello, R.; Nunez, V.; Dwyer, D.M. Palatability in

pigs, the pleasure of consumption. J. Anim. Sci. 2019, 97, 2165–2174.

490: preference test is not indicated neither to estimate palatability. Animals have two food options and they eat from both being not able the quantification of a palatability value rather than a relative intake or percent of consumption.

570: You need to include 3 closer approaches to palatability than acceptability or preference tests. Short term feed intake (1 min or less), Lick cluster size (consumption patterns) and taste reactivity test.

Because this is a review you need to include the effect of 1) obesity, stress and age on dogs and cats feeding behavior/flavor preferences

Luna, D., Carrasco, C., Álvarez, D., González, C., Egaña, J. I., & Figueroa, J. (2020). Exploring Anhedonia in Kennelled Dogs: Could Coping Styles Affect Hedonic Preferences for Sweet and Umami Flavours?. Animals, 10(11), 2087.

Minor Comments

 

113-114: Neophilia an neophobia depends on the age of animals. Puppies need to explore the environment to learn (by trial and error or social learning) to eat new foods, showing a higher neophilia than adults animals. However, neophobia is an adaptive behaviour to prevent possible intoxications and appears a little more in adults. In both (puppies and adults) when changing commercial food is necessary to do it gradually (90-10, 80-20 70-30% etc) to prevent digestive disorders but also neophobia.

 

114-118: Metaphilia in cats or in other animals is related to Sensory Specific Satiety where a sensory-monotonous diet will decrease animals feed intake and welfare. This could be an important issue when commercial diets are given to pets or livestock.

 

Manteca, X., Villalba, J.J., Atwood, S.B., Dziba, L., Provenza, F.D. (2008). Is dietary choice important to animal welfare?. Journal of Veterinary Behavior 3(5), 229-239.

 

Middelkoop, A., Choudhury, R., Gerrits, W.J., Kemp, B., Kleerebezem, M., Bolhuis, J.E. (2018). Dietary diversity affects feeding behaviour of suckling piglets. Applied Animal Behaviour Science 205, 151-158.

 

FIGUEROA, J.; SALAZAR, L.; VALENZUELA, C.; GUZMÁN-PINO, S. 2018. Flavour variety increases the acceptability of feed in nursery pigs. In: 14th International Symposium on Digestive Physiology of Pigs (DPP2018). Brisbane, Australia. 21-24 agosto 2018. Cambridge University Press – Adv. Anim. Vet. Sci. pp. 187-188.

 

264-268: It is necessary to revaluate commercial food delivered to cats?

337: Here and elsewhere you talk about palatability but there is no a clear definition of the concept (you mentioned a couple of pages after)

Dwyer, D. M. 2012. Licking and liking: The assessment of hedonic responses in rodents. Q. J. Exp. Psychol. 65:371–394. doi:10.1080/17470218.2011.652969

 

Forbes, J. M. 2010. Palatability: principles, methodology and practice for farm animals. J. Anim. Sci. 229–243. doi:10.1079/PAVSNNR20105052

 

Figueroa, J.; Frias, D.; Sola-Oriol, D.; Tadich, T.; Franco-Rossello, R.; Nunez, V.; Dwyer, D.M. Palatability in

pigs, the pleasure of consumption. J. Anim. Sci. 2019, 97, 2165–2174.

353: Same here. Please define acceptance. It is the amount consumed when only one food option is given?

 

432: It is necessary to talk about the ingredient order. In several pet foods (specially with low prices) the first ingredients are cereals and this may affect the nutrition of animals. High cereals foods also have sprayed fat film that increase palatability (because palatability is related with the nutritional value) and intake. So, part of the industry is selling a lot of “palatable cereals” that increase animal’s food intake, with a lower protein digestibility. Also obesity could be related with these foods.

 

443-448: Here you added the palatability definition. Probably this definition could be included before in the text. You said that palatability depends on the food characteristics to increase acceptance/intake. However, palatability also depends on the animal’s pleasure perception that is related with its internal status or homeostasis (temperature, illness, satiety etc.). Because of that, I prefer to described palatability as the “pleasure that an animal perceives during consumption”

 

447. “palatability relates to pleasure perception or liking during consumption”

 

490 How could be prevent that dogs eat all the food in a short time? If this happened dogs will redirect its consumption to the feeder that still have food inside, making consumption of both option more similar.

509 Preference tests need to compare the experimental diet (new flavor) vs a control diet (without flavor) and no only vs another flavoured diet. This is important because some flavours could generate neophobia reaction and decrease food intake

519-522: Taste reactivity test?

526: how diets differed in their palatability?

560: What kind of taste receptor? Umami T1R1 T1R3? Please explain more this sentence/paragraph

576: what kind of diets were offered?

581: Prenatal learning (of flavours cues) also occurred in Dogs, Sheep, Humans, rats, ets in most mammals. Please clarify.

605: Taste receptors only in oral tissue or also in post oral tissue like other animals?

616: Umami flavour also?

705-710: Maybe a critic to the industry?

Author Response

Response to Reviewer 3

Your in-depth assessment is greatly appreciated. Here are our additions and comments to you discussion points.

1. 372: Probably is necessary to discuss more about the problems of a vegetarian diets in dogs and cats and that affect not only the nutrition of animals but their welfare.

Response: The review is focused on palatability and known drivers. We felt it was not necessary to discuss vegetarian diets in detail – rather provide reference to work that has been done in this area. However, we have added a statement about the implications of vegetarian diets on only their health but also the welfare of cats (line 382-383).

 

2. 447-448: It is true that palatability is related with feed acceptance. However, because animals regulate its feed intake by the input of nutrients and the caloric density is directly related with palatability (because pleasure is related with the adaptive value of a behavior): Palatability is not directly related with food intake (acceptability)

Response: I think the confusion is that palatability testing consists of two main consumption tests:

• Acceptance (one-bowl) where one the intake of one food is examined without reference to another food.
• Preference (two-bowl) – comparing two different foods to determine which is more preferred over another.

In terms of acceptance, we can determine how much is eaten and define a threshold amount to deem a food as being acceptable to cats.

 

3. 457: this method (one bowl test) is contraindicating to address palatability. As I said more palatable foods (ie. with more energy/protein/fat content) will stop the consumption behavior before than other diets because animals regulate very fast by oral and post-oral receptors its food intake. Because of this, a more consumed food (From data of 1 bowl test) is not always the most palatable food (think about honey vs rice). One possible option is to reduce the testing time to decrease animals oral or post-oral satiety, to study consumption patterns (Lick cluster size in rats) that relate consumption time with the number of visits to the feeder or to study facial expressions (taste reactivity test). In this method also the latency time to the first approach could be measure

Response: As previously described, it is possible to define an intake amount relative to a threshold level of dry matter intake in one-bowl testing (amount of grams consumed) ie. less grams for a dry food and more for a wet food. However, one-bowl does not specifically compare intakes of different foods. That is where two-bowl testing is used for comparative purposes. Taste reactivity tests in cats have been examined, however, it has been hard to distinguish between patterns of liking and aversion as movements can appear similar. Cats will tend to keep eating a food that is more preferred when given a choice.

 

4. 490: preference test is not indicated neither to estimate palatability. Animals have two food options and they eat from both being not able the quantification of a palatability value rather than a relative intake or percent of consumption.

Response: Preference testing does reveal which food is preferred. If no difference is observed between the intake of the two foods and it meets a defined threshold, then they are both deemed palatability and as tasty as each other. This can be valuable for companies particularly when comparing their product to the top-of-the-line product within an existing category.

 

5. 570: You need to include 3 closer approaches to palatability than acceptability or preference tests. Short term feed intake (1 min or less), Lick cluster size (consumption patterns) and taste reactivity test.

Response: There is discussion of consumption patterns and taste reactivity tests in Section 6.4.

 

6. Because this is a review you need to include the effect of 1) obesity, stress and age on dogs and cats feeding behavior/flavor preferences

Response: We have not examined the effect of obesity or stress on feeding behavior in this review, as in pet food development, palatability testing is carried out using animals with optimal body condition scores that are healthy.

7. 113-114: Neophilia an neophobia depends on the age of animals. Puppies need to explore the environment to learn (by trial and error or social learning) to eat new foods, showing a higher neophilia than adult animals. However, neophobia is an adaptive behaviour to prevent possible intoxications and appears a little more in adults. In both (puppies and adults) when changing commercial food is necessary to do it gradually (90-10, 80-20 70-30% etc) to prevent digestive disorders but also neophobia.

Response: Have added this to lines 121-124.

 

8. 114-118: Metaphilia in cats or in other animals is related to Sensory Specific Satiety where a sensory-monotonous diet will decrease animals feed intake and welfare. This could be an important issue when commercial diets are given to pets or livestock.

Response: have not added this into the discussion.

 

9. 264-268: It is necessary to revaluate commercial food delivered to cats?

Response: Have removed this paragraph as it was a copy error when transferring content into the manuscript format.

 

10. 337: Here and elsewhere you talk about palatability but there is no a clear definition of the concept (you mentioned a couple of pages after)

Response: Have added a brief description of acceptance and palatability in lines 455-456.

 

11. 353: Same here. Please define acceptance. It is the amount consumed when only one food option is given?

Response: Addressed above.

 

12. 432: It is necessary to talk about the ingredient order. In several pet foods (specially with low prices) the first ingredients are cereals and this may affect the nutrition of animals. High cereals foods also have sprayed fat film that increase palatability (because palatability is related with the nutritional value) and intake. So, part of the industry is selling a lot of “palatable cereals” that increase animal’s food intake, with a lower protein digestibility. Also obesity could be related with these foods.

Response: Have added a statement about economy pet food brands having cereals and grains as first ingredient (lines 440-441).

 

13. 443-448: Here you added the palatability definition. Probably this definition could be included before in the text. You said that palatability depends on the food characteristics to increase acceptance/intake. However, palatability also depends on the animal’s pleasure perception that is related with its internal status or homeostasis (temperature, illness, satiety etc.). Because of that, I prefer to described palatability as the “pleasure that an animal perceives during consumption”

Response: Have briefly provided a definition as discussed in points 10 and 11 above.

 

14. “palatability relates to pleasure perception or liking during consumption”

Response: We have included this as the definition in lines 454-455.

 

15. 490 How could be prevent that dogs eat all the food in a short time? If this happened dogs will redirect its consumption to the feeder that still have food inside, making consumption of both option more similar.

Response: Have added further discussion on dogs in lines 498 to 500.

 

16. 509 Preference tests need to compare the experimental diet (new flavor) vs a control diet (without flavor) and no only vs another flavoured diet. This is important because some flavours could generate neophobia reaction and decrease food intake

Response: redefined and included in lines 528-530.

 

17. 519-522: Taste reactivity test?

Response: These are discussed in lines 536-539.

 

18. 526: how diets differed in their palatability?

Response: Added description of diets to lines 544-550.

 

19. 560: What kind of taste receptor? Umami T1R1 T1R3? Please explain more this sentence/paragraph

Response: Additional discussion included in line 579-585.

 

20. 576: what kind of diets were offered?

Response: one of four poultry-flavoured dog diets is what was all that has been provided in the article and included in line 599

 

21. 581: Prenatal learning (of flavours cues) also occurred in Dogs, Sheep, Humans, rats, ets in most mammals. Please clarify.

Response: Additional information added in line 605-606

22. 605: Taste receptors only in oral tissue or also in post oral tissue like other animals?

Response: Oral tissue in this sense is what has been researched in cats.

23. 616: Umami flavour also?

Response: Yes, but through presence of amino acids and elaborated further along in section 7.2

 

24. 705-710: Maybe a critic to the industry?

Response: No, these are results obtained from more classical scientific studies obtained in cat and dog research.

Round 2

Reviewer 1 Report

The authors have incorporated or addressed all prior comments noted. No further suggestions.