TYPE Original Research PUBLISHED 30 August 2023 DOI 10.3389/fvets.2023.1218198 Effects of flavour variety on the OPEN ACCESS intake and palatability of commercial feed in nursery pigs EDITED BY Isa Fusaro, University of Teramo, Italy REVIEWED BY Paolo Cornale, Elizabeth Huenul 1, Laura Salazar 2, Daniela Frias 3, Milivoy Videka 4, University of Turin, Italy Daniela Luna 4, Dominic M. Dwyer 5 and Jaime Figueroa 6* Ester Arévalo Sureda, KU Leuven, Belgium 1 Department of Animal and Food Science, Faculty of Veterinary Medicine, Autonomous University of *CORRESPONDENCE Barcelona, Cerdanyola del Vallès, Spain, 2Animal Behaviour and Welfare, Animal and Veterinary Sciences Jaime Figueroa Research Group, Scotland’s Rural College, Edinburgh, United Kingdom, 3Escuela de Ingeniería y recursos Jaime.figueroa@uoh.cl Naturales, Instituto Profesional DuocUC, Santiago, Chile, 4Departamento de Fomento de la Producción Animal, Facultad de Ciencias Veterinarias y Pecuarias, Universidad de Chile, Santiago, Chile, 5School of RECEIVED 06 May 2023 Psychology, College of Biomedical and Life Sciences, Cardiff University, Cardiff, United Kingdom, 6Instituto ACCEPTED 18 August 2023 de Ciencias Agroalimentarias, Animales y Ambientales, Universidad de O’Higgins, San Fernando, Chile PUBLISHED 30 August 2023 CITATION Huenul E, Salazar L, Frias D, Videka M, Luna D, Sensory-specific satiety (SSS) could negatively affect pigs’ feed intake, even when Dwyer DM and Figueroa J (2023) Effects of diets satisfy their nutritional requirements. We evaluated the short-term effects flavour variety on the intake and palatability of of SSS on feed intake and palatability. Thirty-two nursery pigs (tested in pairs) commercial feed in nursery pigs. Front. Vet. Sci. 10:1218198. were exposed to short-term feeding trials for 6 days. In Trial 1, animals received doi: 10.3389/fvets.2023.1218198 for 90 min over three consecutive days three feeders: with different flavours COPYRIGHT (VAR); the same flavour (MON); or a mixture of the three flavours (MIX) in a 3 × 3 © 2023 Huenul, Salazar, Frias, Videka, Luna, Latin square design. In Trial 2, with the same animals and different flavours, the Dwyer and Figueroa. This is an open-access article distributed under the terms of the three feeders were delivered successively (1 feeder every 30 min). In Trial 1, there Creative Commons Attribution License (CC BY). was a day-by-diet interaction (F 4,36 = 2.98; p = 0.032), where the VAR diet was The use, distribution or reproduction in other least consumed on the first day but most consumed subsequently. In Trial 2 a forums is permitted, provided the original author(s) and the copyright owner(s) are triple interaction between diet, day and delivery order modified pig’s intake (F credited and that the original publication in this 12,15 = 3.33; p = 0.015), and consumption patterns (F 12,15 = 3.52; p = 0.012); journal is cited, in accordance with accepted where VAR diet presented the highest values in the last delivery order on the third academic practice. No use, distribution or reproduction is permitted which does not experimental day. Flavour variety may decrease the effect of SSS, increasing feed comply with these terms. intake and hedonic value in nursery pigs when there was a previous experience with those flavours. KEYWORDS consumption pattern, feed intake, flavour variety, nursery pigs, sensory specific satiety 1. Introduction Pigs in a natural environment are opportunistic and omnivorous feeders that during most of their active time search and consume an extensive variety of foods (1). Their specialized oro-nasal system allows them to search above and below the ground for a wide range of foods including plants, seeds, tubers, insects, fruits, small mammals, and even reptiles in order to satisfy their nutritional needs (2, 3). In contrast, pigs raised in conventional farming do not have the opportunity to search for different food resources, although the pig industry offers a complete diet according to their specific nutritional requirements at their different productive stages (4). Depending on their local availability and price these diets include several ingredients and additives. Nevertheless, even though feeds may contain additives that contribute to increasing palatability, a mixed diet has the potential to create a unified flavour experience (5). Moreover, the organoleptic properties of feed differ little between and within production periods, which can generate problems of sensory-specific satiety (6). Frontiers in Veterinary Science 01 frontiersin.org Huenul et al. 10.3389/fvets.2023.1218198 Sensory-specific satiety (SSS) is a physiological phenomenon, served as subjects. After weaning at 28 days-old, animals were associated with the decrease in the specific hedonic value of the sensory individually identified by using numbered plastic ear tags, weighed properties of food after being continuously exposed during a feeding and randomly allocated in pairs to 16 nursery pens episode, and which recovers after time (6, 7). As an example, if someone (1.80 m × 1.28 m × 0.7 m, fully slatted floor), maintaining similar allowed us to consume only our favourite food for several days, the weights between pens (p > 0.05). The nursery room temperature (29°C sensation of pleasure when eating that food would diminish with the lowering 1°C per week) was controlled with a heater and automatically increased exposure. Thereby, sensory-specific satiety would be expressed forced ventilation. Each pen had one feeder with three feeding spaces as a decrease in the pleasantness of taste and a reduction in consumption and an individual water supply. Pigs were ad-libitum fed with an relative to other foods that differ in one or more sensory properties, unflavoured standard commercial diet according to their nutritional even if they have the same nutritional composition (8, 9). requirements (4) and they had constant access to fresh water Animals typically need to eat a varied diet to obtain all their throughout the experimental procedure (except for the removal of required nutrients (10) and food macronutrients are associated with unflavoured food during the period 1 h before and after each different sensorial qualities (11). Therefore, the SSS is considered an experimental session). The commercial formulation of feed was adaptive mechanism, one that ensures animals search the environment confidential but based mainly on Maize (611 g/kg), soy bean products to obtain different nutrients through a varied diet to fit their (168 g/kg), fish meal (80 g/kg), sweet milk whey (89 g/kg) and a physiological needs (12). The role of SSS and the adverse effects of complete premix with vitamins-aminoacids-minerals and other feed’s sensory monotony has been studied mainly in humans (7) and additives to enhance feed digestibility. Environmental enrichment was rats (13, 14), but also in other domestic animals like sheep (15), where not added to the pens. Animals were tested in two trials of three the absence of sensory variety over days can lead animals to reduce consecutive days each between 10 AM–12 PM, and the two trials were their intake, thus affecting their performance and welfare (16). separated by a rest week. During the second trial, the feeding However, when the humans or animals have the opportunity to eat behaviour of animals was recorded with 8 video cameras (IR exterior diets whose sensory properties have been varied, they start increasing ® 1/3 Sony 700tvl cmos; SENKO S.A, Santiago, Chile) distributed every their intake again, even during the same consumption episode (17– two pens in the ceiling of the nursery room. The videos were 19). In addition, a feed environment with a wide sensory variety downloaded at the end of the experimental period and were analyzed allows the animal to express their feed preferences and natural feeding by a trained observer. Behavioural observations were analyzed using behaviour, potentially having an important effect on animal welfare the Behavioural Observation Research Interactive Software [BORIS, (20). Such improvements in the performance and welfare of animals http://www.boris.unito.it/ (23)]. are the desired outcomes in animal production, such as pig farming. The positive effect of the dietary sensory variety has been little addressed in pigs. Recent experiments suggest that during the suckling 2.2. Experimental procedure period, creep feed with sensory variety or dietary variety increases feed intake and exploratory behaviour in piglets compared to a Before the beginning of trials pigs were acclimated to housing and sensory monotonous diet. However, no effect of diet variety was found experimental conditions (28–41 days-old). Experimental schematic in the performance parameters of piglets where similar weights and representation and procedures are summarized in Figures 1, 2, weight gain were observed at weaning (21, 22). Nevertheless, the respectively. Two feeding trials were performed with the same animals. maternal presence, with the constant availability of milk and the Each trial had a duration of 3 days, during which animals were marginal consumption of solid feed could mask positive results of exposed in the morning for 90 min to three pan-feeders with sensory variety in animals at this production stage. Therefore, it is commercial feed that contained either: (1) different flavours (VAR); necessary to understand the effect of sensory variety on pig feeding (2) the same flavour (MON); or (3) a mixture of the three flavours in behaviour in other production stages. The objective of the present each feeder (MIX). All animals experienced each of the three study was to evaluate the short-term effect of specific-sensory satiety experimental conditions with the order counterbalanced in a 3 × 3 on the consumption and palatability of flavoured feed in nursery pigs. Latin square design. In Trial 1, the feeders were given simultaneously during the 90 min of the trial. Flavours added to the feed were lemon, ® coffee and cherry at 0.075% [(24); Floramatic , Santiago, Chile], 2. Materials and methods where lemon was used in the MON diet. A similar procedure was conducted in the second trial, but feeders were rotated every 30 min Experiments were conducted at the swine experimental facility of until the 90 min were completed and the flavours used were orange, the Centro de Investigación, Innovación Tecnológica y Capacitación ® chocolate and grape (Floramatic Santiago, Chile, 0.075%), where para la Industria Porcina Nacional (CICAP), belonging to the chocolate was used in the MON diet. Flavours used in both trials were Pontificia Universidad Católica de Chile (PUC) in Santiago, Chile. All selected based in previous unpublished trials and in the company experimental procedures were approved by the Ethical Committee on recommendations, considering similar preferences and intake Animal Experimentation of PUC (No. 190531007). between them. Flavours used in Trial 1 and 2 were different to ensure that test flavours were novel at the start of each of Trial 1 and Trial 2. Their commercial unflavoured feed was removed 1 h before the start 2.1. Animals and housing of each test and was returned to each pen 1 h after the end of the tests. Feed intake was measured by weighing the pan-feeders at the A total of 32 castrated male and female nursery pigs (PIC beginning and end of each test (spillage was not measured). During Genetics), 42 days-old (13.2 ± 1.2 kg) at the start of experiments, Trial 2 consumption time (time eating at the pan-feeder; CT) and Frontiers in Veterinary Science 02 frontiersin.org Huenul et al. 10.3389/fvets.2023.1218198 FIGURE 1 Schematic representation of the pen (front view) during Trial 1 and Trial 2 sessions. FIGURE 2 Schematic representation of monotonous (MON), varied (VAR), and mixed (MIX) diets delivered in both trials. In Trial 1, three pan-feeders were offered at the same time for 90 min. Lemon, coffee, and cherry flavours were used as added artificial flavours on feed. In Trial 2, one pan-feeder was offered every 30 min until completing 90 min. Orange, chocolate, and grape flavours were used. approaches (number of times the pan-feeder was approached with a analysis, the normality and homoscedasticity of the dataset were consumption result; A) were assessed from the video recordings by analyzed by using the UNIVARIATE procedure with the Shapiro– focal continuous sampling over the 90 min tests. Palatability was Wilk and O’Brien’s tests, respectively. The mean values are presented estimated through consumption patterns (CT/A) (25, 26), analogous as least square means adjusted by Tukey. The experimental unit was to the licks/bout measure used in rats in lick cluster size analysis the pen with results expressed as the average of both pigs’ data. (27, 28). Differences at p < 0.05 were considered statistically significant and differences at 0.05 ≤ p < 0.10 were considered a trend. 2.3. Statistical analysis 3. Results Feed intake and consumption patterns were analyzed with ANOVA by using mixed linear models with the MIXED procedure of 3.1. Trial 1: simultaneous exposure to ® statistical package SAS (SAS Inst. Inc., Cary, NC, United States), flavoured feed considering the effect of the diet (MON, VAR or MIX), experimental day (1, 2 or 3), delivery order of the given diet during Trial 2 (first, No intake differences were observed in nursery pigs during Trial second or third) and the interaction between variables. The pen was 1 according to the experimental day (F 2,36 = 0.90; p = 0.416) or diet considered as a repeated measure in the mixed model. Before ANOVA (F 2,36 = 1.34; p = 0.276). However, a significant interaction between Frontiers in Veterinary Science 03 frontiersin.org Huenul et al. 10.3389/fvets.2023.1218198 the experimental day and diet was found (F 4,36 = 2.98; p = 0.032), during the last delivery on the last experimental day (Figure 6): that where the VAR diet showed the lowest intake on day one and the is, the decrease in intake across the session was lowest in the VAR highest intake on days 2 and 3 compared to the other diets (Figure 3). condition once all flavours were familiar at the end of testing. By analysing separately, the effect of the day in each diet consumed, The experimental day influenced the pig’s consumption patterns the intake of VAR diet varied between days (F 2,13 = 6.27; p = 0.012), (F 2,15 = 16.29; p < 0.001), observing a lower consumption pattern on presenting a significant increase in its intake between day 1 and 2 the second day. No differences between diets were observed in the (p = 0.022) and from day 1 to 3 (p = 0.021) with no significant pig’s consumption patterns (F 2,15 = 0.26; p = 0.778). The delivery differences between day 2 and 3 (p = 0.990). Pigs equally consumed order of feed tended to affect consumption patterns (F 2,15 = 2.69; MIX diet (F 2,13 = 0.98; p = 0.403) or MON diets (F 2,10 = 0.36; p = 0.1), where feed presented the highest hedonic value during its first p = 0.709) across days. exposure. The interaction between the treatment and day is presented in Figure 7. Although it is observed that the variety group showed the least consumption pattern on day one and the highest on day 3, the 3.2. Trial 2: consecutive exposure to interaction was not significant (F 4,15 = 1.27; p = 0.324). The flavoured feed interaction between the diet and delivery order is presented in Figure 8. Although this interaction was not significant (F 4,15 = 1.52; The experimental day and delivery order of the feed influenced p = 0.245), it is the case that the VAR diet showed the lowest pig’s intake, observing a lower consumption of the flavoured feed as the days go by (F 2,15 = 4.40; p = 0.031) and as the delivery order progresses (F 2,15 = 63.37; p < 0.001) respectively. No intake differences were observed in Trial 2 according to experimental diets (F 2,15 = 0.87; p = 0.441). The interaction between the diet and day is presented in Figure 4. Although it is observed that the VAR diet was the less consumed on day one but the highest on day 3, the interaction was not significant (F 4,15 = 1.91; p = 0.161). By analysing separately, the effect of the day in each diet consumed, pigs equally consumed the VAR diet (F 2,13 = 0.25; p = 0.779) across days. The intake of the MIX diet varied between days (F 2,12 = 6.23; p = 0.014), observing that animals decrease its consumption between days 1 and 2 (p = 0.041) and between days 1 and 3 (p = 0.021) with no differences between days 2 and 3 (p = 0.984). Finally, the intake of the MON diet did not significantly differ between days (p > 0.1). A significant interaction FIGURE 4 between diet and delivery order of feed was found (F 4,15 = 5.17; Total feed intake (mean ± SEM) of nursery pigs during a consecutive exposure of three feeders (for 30 min each) containing feed with p = 0.008), observing that the MON diet presented the highest intake different flavours (orange, chocolate, or grape; VAR), with the same on the first exposure compared with the other treatments but the flavour (chocolate; MON) and with a mixture of the three flavours lowest intake on the last exposure (Figure 5). Finally, a triple (orange + chocolate + grape; MIX). Results are expressed by pig and experimental day (1, 2, or 3). interaction between diet, day and delivery order was observed (F 12,15 = 3.33; p = 0.015), where the variety diet presented the lowest intake during the last delivery on the first day, but the highest intake FIGURE 3 FIGURE 5 Total feed intake (mean ± SEM) of nursery pigs during a simultaneous Feed intake (mean ± SEM) of nursery pigs during a consecutive exposure (90 min) of three feeders containing feed of different exposure of three feeders (for 30 min each) containing feed with flavours (lemon, coffee, or cherry; VAR), with the same flavour different flavours (orange, chocolate, or grape; VAR), with the same (lemon; MON) and with a MIX of the three flavours flavour (chocolate; MON) and with a mixture of the three flavours (lemon + coffee + cherry). Results are expressed by pig and (orange + chocolate + grape; MIX). Results are expressed by pig and experimental day (1, 2, or 3). diet delivery order (1st, 2nd, or 3rd). Frontiers in Veterinary Science 04 frontiersin.org Huenul et al. 10.3389/fvets.2023.1218198 FIGURE 6 Feed intake (mean ± SEM) of nursery pigs during a consecutive exposure of three feeders (for 30 min each) containing feed with different flavours (orange, chocolate, or grape; VAR), with the same flavour (chocolate; MON) and with a mixture of the three flavours (orange + chocolate + grape; MIX). Results are expressed by pig, diet delivery order (1st, 2nd, or 3rd) and day (1, 2, or 3). FIGURE 8 FIGURE 7 Means (±SEM) of consumption patterns [consumption time (CT)/ Means (±SEM) of consumption patterns [consumption time (CT)/ approaches (A)] (mean ± SEM) of nursery pigs during a consecutive approaches (A)] of nursery pigs during a consecutive exposure of exposure of three feeders (for 30 min each) containing feed with three feeders (for 30 min each) containing feed with different different flavours (orange, chocolate, or grape; VAR), with the same flavours (orange, chocolate, or grape; VAR), with the same flavour flavour (chocolate; MON) and with a mixture of the three flavours (chocolate; MON) and with a mixture of the three flavours (orange + chocolate + grape; MIX). Results are expressed by pig and (orange + chocolate + grape; MIX). Results are expressed by pig and diet delivery order (1st, 2nd, or 3rd). experimental day (1, 2, or 3). consumption pattern with the first feed delivery and the highest with 30). However, there is a paucity of information about the effect of the last one. Finally, a triple interaction between diet, day and delivery flavour variety on the feeding behaviour of nursery pigs. Previous order was observed (F 12,15 = 3.52; p = 0.012), where the VAR diet research demonstrated that suckling piglets increased feed exploration presented the lowest consumption pattern during the last delivery on and intake when sensory variety was implemented in their diets, by the first day but the highest consumption pattern during the last changing multiple sensory properties of the feed, however, no effects delivery on the second and the last experimental day (Figure 9): that on animals’ performance were observed and animals presented no is, the palatability responses were maintained across the session most differences in their body weight at weaning (22). Here, we investigated clearly in the VAR condition once the flavours were familiar. the short-term effect of flavour variety on feed intake and feed palatability in nursery pigs. It was observed that pigs presented an improve in feed intake and perceived palatability when different 4. Discussion flavoured feeds were delivered simultaneously or at the end of a consecutive delivery compared with monotonous flavoured diets. A Sensory variety could reduce the effect of sensory-specific satiety significant interaction between day and diet was found, observing the by increasing the hedonic value of food during animal’s intake (29, importance of familiarity of flavours cues to reduce neophobia when Frontiers in Veterinary Science 05 frontiersin.org Huenul et al. 10.3389/fvets.2023.1218198 FIGURE 9 Means (±SEM) of consumption patterns [consumption time (CT)/approaches (A)] (mean ± SEM) of nursery pigs during a consecutive exposure of three feeders (for 30 min each) containing feed with different flavours (orange, chocolate, or grape; VAR), with the same flavour (chocolate; MON) and with a mixture of the three flavours (orange + chocolate + grape; MIX). Results are expressed by pig and diet delivery order (1st, 2nd, or 3rd) and day (1, 2, or 3). sensory variety is implemented to increase voluntary feed intake in higher latency time to approach novel feeds and a decrease in their nursery pigs. These results could encourage the swine industry to intake (34). The negative effects of neophobia are greater at weaning change the way animals are feed, and could improve animal welfare or when new ingredients or additives are added to commercial diets by allowing pigs to express their natural feeding behaviour (20) and (35). In the present experiment, the animals were not previously increase their perceived palatability (26) by consuming sensory variety exposed to the flavours. Therefore, the effect of neophobia could diets. Thus, presenting both a challenge and opportunity for the pig explain the non-significant difference observed in animals´ industry in terms of animal welfare and sustainability. consumption between treatments at the start of testing. Similar results were reported by Middelkoop et al. (22), where pigs exposed to novel flavours decrease their feed intake during the first exposures. Although 4.1. Trial 1: simultaneous exposure to feed neophobia causes pigs to eat small amounts of feed, this behaviour flavoured feed can dissipate with repeated exposure to that feed and its related sensory cues. Thus, animals can verify that the consumption of that In a natural environment, there are a variety of foods with feed does not cause negative post-ingestive effects (36). Strategies to different nutritional, chemical and physical characteristics available increase the familiarity of flavours cues has been reported in suckling for pigs. These animals are able to select between different and nursery pigs. Probably the most practical strategy is to include consumption options to meet their nutritional requirements even in those flavours into the gestational diets of sows and prenatally expose commercial facilities (20). In Trial 1, no overall differences were pigs to them, generating benefits because of familiarity and associative observed in pigs’ feed intake when they were offered three pan feeders learning between flavours and the positive effects of aminiotic fluid with different flavoured feeds (VAR) vs. three pan feeders containing (35, 37). Another option is to include those flavours in high digestive the same flavoured feed (MON) or three mixed flavours (MIX) during and palatable diets at the beginning of solid feed consumption. the test (276 g vs. 234 g vs. 258 g, p = 0.276) respectively. However, a clear interaction between the experimental day and treatment was found, whereby the consumption of the variety diet (VAR) increased 4.2. Trial 2: consecutive exposure to as the days went on compared to the other diets. It was observed an flavoured feed increase of 64% of feed intake between experimental day 1 and 2 for diet VAR in contrast with only a 7% of increase and a 17% of decrease In addition to the effects of neophobia, a different intake of the in feed intake for MON and MIX diets. In agreement with Miller and flavoured feed was observed related to delivering order (i.e., 1st, 2nd Holzman (31), it is possible that the animals have experienced fear of or 3rd delivered pan feeder). In this experiment, pigs’ feed intake consuming different flavours when they were exposed to the sensory decreased considerably in the second pan feeder delivered, and a little cues for the first time. Animals may develop behavioural more in the third pan feeder delivered (thus, intake was reduced predispositions oriented to rejecting the consumption of food, whose across the session overall). These intake differences were more post-ingestive consequences are unknown, thus avoiding possible pronounced in MON treatments, observing an interaction between toxic effects (32, 33). Pigs without previous experience with particular delivery order and treatment. This lower feed intake as feed exposure feeds and its related flavours may display neophobia resulting in a increases could be considered a direct consequence of the SSS (9). In Frontiers in Veterinary Science 06 frontiersin.org Huenul et al. 10.3389/fvets.2023.1218198 the VAR diet, the feed intake was the one that decreased the least, that offering a variety of foods to rats successively did not have the compared with MON and MIX diets. As with Trial 1, this effect was same significant positive effects as simultaneous exposure to a most apparent in the later testing days once the flavours were familiar variety of food. Nevertheless, this could be explained by the low which decreases neophobia. These results suggest that flavour diversity frequency of the food’s rotation (12 h intervals) on successive modifies feed intake in pigs and that they prefer varied diets instead exposition. Furthermore, a varied diet treatment has a better of consuming a diet with similar sensory cues to the one that they response in the SSS when animals are exposed to different food for experienced before (22). Our findings are in concordance with studies less than 2 h (39). carried out in humans, where the access to a varied diet increases food Flavours are usually used in the pig industry to enhance feed intake compared to a monotonous one (38–41). intake because of their palatability (22) and their sensory continuity In addition to changes observed in feed intake, the SSS also could effect when milky flavours are incorporated after weaning (25, 46). affect the pleasure perception, as was observed in the significant effect The present results demonstrated that the variety of flavours, between of delivery order, where the consumption pattern of flavoured feed or within consumption episodes, improved feed intake and palatability decreased as the delivery order progressed. This has been previously in nursery pigs. However, neophobia should be considered (35) when seen as an effect of repetitive exposure to food in humans (42). The flavours are included for the first time. By repeating the rotation of results are consistent with the investigation of the mechanism of SSS, flavours, we could take advantage of both variety and familiarity. In where pleasure perception decreases until consumption stops and, the present study, flavours were used to generate feed variety since thus, concludes an eating episode (43). Moreover, consumption they are easily detected by pigs due to their developed oro-nasal patterns in VAR treatment were highest in the last feed delivery than system and because the nutritional content of the diets does not in the first one, unlike MON and MIX treatments where the change. However, other sensory stimuli may be used to generate consumption pattern was lower in the last delivery than in the first sensory variety in the feed. In humans, it has been shown that one. However, only a tendency was observed in the interaction presenting the same food in a second dish with different condiments between treatment and delivery order. Results obtained in the VAR could restore the hedonic value of foods (38). Moreover, SSS can even treatment show that the effect of SSS was reduced due to sensory occur in a simulated feeding where participants chew food but do not changes that produced the delivery of different flavours (8). swallow it (47). Moreover, it has been shown in humans that the Considering the results in Trial 1, an interaction between colour and shape of food also have affect SSS (42). Therefore, the SSS treatment and day was expected because of neophobia and flavour is specific to the sensory modality (48). In pigs, studies have shown variety. However, no effects of this interaction were observed on feed that feeds that are more diverse in terms of sensory properties increase intake or consumption patterns. In line with previous studies, where feed intake (22). Considering this, it is possible that not only flavour consumption increases when several feed options have been offered could produce effects on the SSS of pigs, but also taste, texture, or throughout the days (44), and similar to the results in Trial 1 where colour. It would be important to identify which sensory modality is flavours were simultaneously exposed, VAR treatment presented the the most effective in avoiding the effects of SSS. highest feed intake and consumption pattern on the last experimental Dietary variety studies in pigs conducted by Middelkoop et al. day compared to MON and MIX treatments, but the lowest intake and (22) have focused on the suckling period, where an improvement in consumption patterns on the first experimental day. Moreover, it is animal welfare but not in the performance of suckling piglets has been observed that in the third pan feeder delivered, animals had a higher reported. Specifically, the animals had an increase in exploratory satiety due to continuous exposure to feed. However, VAR treatment behaviour, but not in growth performance (22). This last may be due in the last pan-feeder delivered presented a smaller decrease in to the number of non-controlled factors during this productive consumption and a higher consumption pattern than MON and MIX period, such as the presence of the mother and the choice of compared to the first delivery order. consumption between milk and feed. Other studies carried out during A triple interaction was observed between treatment, day, and the rearing period with lambs (49), showed that animals exposed to a delivery order on feed intake and consumption patterns, where the multi-forage diet had higher performance (e.g., greater daily gain and VAR treatment showed the highest consumption patterns and feed dry matter intake) and better welfare parameters (e.g., fewer intake on the last day and last delivery order, differing from MON and stereotyped behaviours) compared to animals exposed to single MIX treatments, which presented lower feed intake and consumption forage. These simple and innovative feeding strategies could patterns. This could be explained by the neophobia effects on the first be replicated in weaning or fattening pigs. In both productive stages, day. As the days go by, there is greater exposure to the VAR treatment; the feed provided to pigs is often solid and invariant from a point of the feed became more familiar and consequently, the order effect is view of its sensorial properties, generating SSS with its potential higher on the last day. Therefore, the VAR treatment had a better negative consequences on performance and welfare. Therefore, a response when satiety occurs during continuous exposure to flavoured varied diet, that could be rotated weekly or when diet formulation feeds, but only when the pigs had a previous experience with those change according to productive stages, could have a positive impact, flavours, avoiding neophobia effects. considering that in the present study there were positive results in It appears that if Trial 1, where the feeding options were terms of palatability and feed intake. Moreover, having a variety of delivered at the same time, had lasted only 30 min, the interaction flavours pigs can express their exploratory behaviour at the time of between treatment and day would not have been observed. This feed consumption. However, it is necessary to complement with result contrast with previous research by Ackroff et al. (45) in rats, behavioural and/or physiological indicators, to determine whether where no differences were found in solution intake when bottles of effectively there is an increase in animal welfare, for instance, through sucrose solution with different flavours were offered simultaneously, the expression of positive affective states by varying the sensory compared to unflavoured sucrose solutions. Rolls et al. (6) observed properties of the feed. Frontiers in Veterinary Science 07 frontiersin.org Huenul et al. 10.3389/fvets.2023.1218198 5. Conclusion Author contributions The variety of flavours, between or within consumption episodes JF and DD: conceptualization. JF and LS: methodology, may improve feed intake and palatability in nursery pigs. However, investigation, and supervision. JF, LS, DF, and MV: data curation. JF, is important to consider the effect of neophobia when pigs are EH, and MV: formal analysis. JF: funding acquisition, methodology, exposed to a novel flavour to prevent a possible decrease in their feed project administration, resources, and visualization. EH and JF: intake. The results of this study suggest that sensory varied diets writing original draft. JF, DL, and DD: writing review and editing. All might be used as a strategy to reduce SSS in nursery pigs in authors contributed to the article and approved the submitted version. conventional industry. Future research must be done to investigate whether a periodic rotation (weekly or when formulation is changed) of feeds that differ in sensory proprieties could be a practical Funding management for pig’s industry to try to increase intake and performance during growing (nursery and/or fattening periods) as This research was funded by the National Research and has been found in other production systems. Moreover, the increase Development Agency (ANID) through the Programme FONDECYT in perceived feed palatability could improve animal welfare since pigs Regular grant number 1200643. would increase their pleasure perception for feed when have the opportunity to “choose” (simultaneous exposure) or to received (continuously exposure) different flavoured cues, expressing, Acknowledgments somehow, their natural feeding behaviours. Finally, that variety of other sensory properties like taste, texture or colour on sensory The authors want to thank CICAP animal caretakers for their specific satiety could be explored in growing animals in order to see excellent job regarding animal feeding, animal health management the most effective way to reduce the negative effects of sensory and collaboration during experimental procedures. monotony in pigs. Conflict of interest Data availability statement The authors declare that the research was conducted in the The raw data supporting the conclusions of this article will absence of any commercial or financial relationships that could be made available by the authors, without undue reser be construed as a potential conflict of interest. vation. 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