Use of double-choice feeding to quantify feed ingredient preferences in pigs

Prenatal Exposure to Innately Preferred D-Limonene and Trans-Anethole Does Not Overcome Innate Aversion to Eucalyptol, Affecting Growth Performance of Weanling Piglets

Simple Summary

Weanling piglets appear to be poorly adapted and motivated to ingest solid feed due to the innate reluctance of young animals to ingest an unfamiliar feed or flavor, i.e., feed neophobia, which commonly results in a period of underfeeding. This, and other common wean stress factors, lead to gastrointestinal disorders and impaired growth performance. Increasing the preference or familiarity for a certain type of food or for specific flavors may improve voluntary feed intake in weanling piglets. Botanical compounds (BCs) are described as functional feed additives and include sensorial properties that are able to influence feed intake and growth in pigs by dietary supplementation or sensory maternal learning. In this study, the effects of BCs such as D-limonene, trans-anethole, and eucalyptol on innate feed preference and growth performance of weanling piglets were evaluated by means of a double-choice feeding test and pre- and postnatal exposure to these compounds.

Abstract

In the present research, two studies were performed to determine the effects of specific botanical compounds (BCs) on the innate feed preference and feed intake of piglets, as follows: Exp. 1 studied the innate feed preferences of post-weaning piglets using a double-choice feeding test. A total of 828 weaned piglets were distributed into 36 pens (23 pigs/pen) and assigned to three dietary pair choice feeding options (n = 12): unsupplemented prestarter diets (reference) versus reference plus D-limonene, trans-anethole, or eucalyptol. Piglets showed a preference for diets with D-limonene (53.8%) and trans-anethole (54.5%), and an aversion to eucalyptol (41.6%) (p < 0.05). Exp. 2 studied whether the prenatal and perinatal exposure to D-limonene, trans-anethole, and eucalyptol influences the feed intake and growth of newly-weaned piglets. Twenty-eight gestating and lactating sows were distributed into two dietary treatments (n = 14): unsupplemented Control diets or Control plus a blend of BCs (BBC; containing D-limonene, trans-anethole, and eucalyptol). D-limonene, trans-anethole, and eucalyptol were transferred into the placental fluid, and D-limonene and trans-anethole into the milk (p < 0.05). Furthermore, weanling piglets (n = 200; Control) and (n = 203; BBC) received the same treatment as their mothers in prestarter diets. The early response after weaning showed that piglets’ post-weaning BW gain was higher in the Control (p < 0.05) group than in those exposed to BBC. In conclusion, prenatal exposure to preferred D-limonene and trans-anethole, or familiarity to eucalyptol did not help to overcome the innate aversion to eucalyptol and its negative effect on weanling piglets’ BW.

Degree of Saturation and Free Fatty Acid Content of Fats Determine Dietary Preferences in Laying Hens

Simple Summary

Understanding fat sensing in chickens has the potential to improve least cost feed formulation relevant to poultry feeds. Acid oils (soybean acid oil and palm fatty acid distillate) are economical and sustainable feedstuffs with similar fatty acid composition to crude oils (soybean oil and palm oil) but richer in free fatty acids. However, potential issues relevant to the palatability of these oils have been raised. Four experimental diets were offered in a series of double-choice tests to study the effect of free fatty acid content and the unsaturated:saturated ratio on dietary preferences in hens. Hens showed a feed preference for palm oil added diets over soybean oil diets, with palm oil and palm fatty acid distillate being equally preferred. However, the hens demonstrated a preference for soybean oil when offered in choice with soybean acid oil. In conclusion, free fatty acid content and saturation degree affected feed preferences in hens. The use of oils with greater preference values may give rise to greater feed palatability, enhancing feed intake at critical stages.

Abstract

Behavioural and genetic evidence shows that the taste system is intimately related to the sensing of nutrients with consequences for poultry nutrition practices. A better understanding of how chickens may sense fat could provide the background for selecting feedstuffs used in poultry feeds. Acid oils have the potential to be economical and sustainable feedstuffs. These fat by-products from the edible oil refining industry possess a similar fatty acid composition to the crude oils but are richer in free fatty acids (FFA). An experiment was conducted to study the effect of FFA content and the unsaturated:saturated ratio (U:S) on dietary preferences in hens. Four fat sources were added to a basal diet at an inclusion rate of 6%, determining the experimental diets: soybean oil (SO; high U:S, 5% FFA); soybean acid oil (SA; high U:S, 50% FFA); palm oil (PO; low U:S, 5% FFA); and palm fatty acid distillate (PFAD; low U:S, 50% FFA). The experimental diets were offered in a series of double-choice tests to forty-eight Lohmann Brown laying hens housed individually in cages. Each hen was offered the ten potential binary combinations of the four diets including each diet compared to itself (referred to as four control double-choices). Feed intake was measured for two hours twice a day after one hour of fasting. Consumption was analysed as a standard preference index (% of test diet intake in comparison with the total intake). Preference values were compared to the random choice value of 50% using the Student’s t-test. None of the four control comparisons differ significantly from 50% (p > 0.05), indicating that the changes in preference values observed in the other binary comparisons were related to the dietary changes associated to fat ingredients. Hens showed a feed preference for palm oil added diets over soybean oil diets (p < 0.05), with PO and PFAD being equally preferred (p < 0.05). However, in this trial the hens demonstrated a preference for SO (low %FFA) when offered in choice with SA (high %FFA) (p < 0.05). These results suggest that the degree of saturation plays an important role in dietary fat preferences: hens prefer predominantly saturated oils even when these are rich in FFA. Furthermore, when presented with a choice between predominantly unsaturated oils, hens prefer feed with a low %FFA. In conclusion, %FFA and the U:S ratio affected feed preferences in hens. The use of oils with greater preference values may give rise to greater feed palatability, enhancing feed intake at critical stages.

Palatability in pigs, the pleasure of consumption1

Despite the importance of hedonic reactions in pig's intake, feed palatability has been typically inferred from preference or acceptance measures. However, these measures are influenced by factors beyond palatability, such as energy density and hunger. The aim of this study was to evaluate palatability responses in pigs to sweet and umami taste at different inclusions levels. Pigs (24 per experiment) were video recorded while exposed in pairs to different sucrose (Exp. 1) or monosodium glutamate (MSG, Exp. 2) solutions over seven consecutive 10 min tests (one concentration per day). In both experiments, palatability was estimated through consumption patterns (consumption time per approaches, CT/A), facial expressions (snout openings and tongue protrusions), and consumption during a brief 2 min period. Data were analyzed by sucrose or MSG concentration. Sucrose concentration affected total intake, producing an inverted-U function and a quadratic relationship with sucrose concentration (P = 0.012). In contrast, CT/A and snout openings showed a dose effect (P < 0.005) with a direct correlation between sucrose concentration and CT/A (R = 0.23, P = 0.033) but not for openings (R = 0.18, P = 0.105) where a quadratic relationship appears (P < 0.001). Tongue protrusions and brief consumption time were not affected by sucrose concentration (P = 0.144 and 0.205, respectively). MSG concentration affected consumption, CT/A, snout openings, and brief consumption time (P < 0.001), with significant (P < 0.001) positive correlations (R = 0.59, 0.56, 0.56, and 0.68), respectively. As with rats, CT/A appears to provide a novel and interesting measure reflecting the palatability of preferred ingredients in pigs. However, brief consumption time and orofacial reactions show less similarity between pigs and rodents. Thus further studies are necessary both to better understand the measurement methods themselves and relationship between hedonic reactions and simple consumption in pigs.

Effects of artificial sweeteners on feed palatability and performance in weaned pigs

In experiment 1, a total of 30 weaning pigs were allotted to three dietary treatments to check the palatability of the dietary feed. Diet treatments were as follows: reference diets = basal diets + 0.05% saccharin (50% Saccharin-natrium), TRT1 = 0.03% saccharin–neotame mix (50% Saccharine-natrium + 2% Neotame), TRT2 = 0.02% neotame (10% Neotame), and TRT3 = 0.02% saccharin–neotame mix (10% Saccharine-natrium + 10% Neotame). TRT2 group was significantly higher than other treatments in palatability (P < 0.05). In experiment 2, a total of 52 weaning pigs were allotted to four dietary treatments. In the average daily gain and average daily feed intake over 1 wk, the TRT2 group was significantly higher than the TRT1 and TRT3 groups (P < 0.05). The concentration of triglyceride in the blood was highest in the TRT1 treated group and the lowest in the TRT2 group (P < 0.05). The Lactobacillus was significantly higher in the TRT2 and TRT3 treatments compared with 0.05% saccharin (50% Saccharine-natrium) (P < 0.05). There was no significant difference in the number of Escherichia coli (P < 0.05). In conclusion, diets supplemented with neotame could improve palatability, and artificial sweeteners can affect nutrient digestibility, blood characteristic, and fecal microbiota.

Physiological and metabolic control of diet selection

The fact that most farm animals have no dietary choice under commercial practices translates the dietary decisions to the carers. Thus, a lack of understanding of the principles of dietary choices is likely to result in a high toll for the feed industry. In healthy animals, diet selection and, ultimately, feed intake is the result of factoring together the preference for the feed available with the motivation to eat. Both are dynamic states and integrate transient stimulus derived from the nutritional status, environmental and social determinants of the animal with hard-wired genetic mechanisms. Peripheral senses are the primary inputs that determine feed preferences. Some of the sensory aspects of feed, such as taste, are innate and genetically driven, keeping the hedonic value of feed strictly associated with a nutritional frame. Sweet, umami and fat tastes are all highly appetitive. They stimulate reward responses from the brain and reinforce dietary choices related to essential nutrients. In contrast, aroma (smell) recognition is a plastic trait and preferences are driven mostly by learned experience. Maternal transfer through perinatal conditioning and the individual’s own innate behaviour to try or to avoid novel feed (often termed as neophobia) are known mechanisms where the learning process strongly affects preferences. In addtition, the motivation to eat responds to episodic events fluctuating in harmony with the eating patterns. These signals are driven mainly by gastrointestinal hormones (such as cholecystokinin [CCK] and glucagon-like peptide 1 [GLP-1]) and load. In addition, long-term events generate mechanisms for a sustainable nutritional homeostasis managed by tonic signals from tissue stores (i.e. leptin and insulin). Insulin and leptin are known to affect appetite by modulating peripheral sensory inputs. The study of chemosensory mechanisms related to the nutritional status of the animal offers novel tools to understand the dynamic states of feed choices so as to meet nutritional and hedonic needs. Finally, a significant body of literature exists regarding appetite driven by energy and amino acids in farm animals. However, it is surprising that there is scarcity of knowledge regarding what and how specific dietary nutrients may affect satiety. Thus, a better understanding on how bitter compounds and excess dietary nutrients (i.e. amino acids) play a role in no-choice animal feeding is an urgent topic to be addressed so that right choices can be made on the animal’s behalf.

Impact of sensory feed additives on feed intake, feed preferences, and growth of female piglets during the early postweaning period

Our study aimed at investigating the effect of feed supplementation, from weaning, with 3 sensory feed additives (FA1, FA2, and FA3) on feed preferences, feed intake, and growth of piglets. The FA1 contained extract of Stevia rebaudiana (10 to 20%), extract of high-saponin plants (5 to 10%), and excipients (70 to 85%), the FA2 was mainly composed of a natural extract of Citrus sinensis (60 to 80%), and the FA3 was made of a blend of extracts of hot-flavored spices (5 to 15%) and excipients (85 to 95%). At weaning (d 1), a total of 32 female piglets housed in individual pens were allocated to 4 treatments (FA1, FA2, FA3, and control [CON]) of equivalent mean weight. The pigs were fed a standard pelleted prestarter diet from weaning (d 1) to d 15 and a starter diet from d 16 to 28. The diets were supplemented with the feed additives (FA) corresponding to their treatment, while the CON treatment was the standard diets with no additive. Feed refusals were weighed daily and piglets were weighed weekly on d 1, 7, 14, 21, and 28. On the day of feed transition (d 16) as well as 7 (d 23) and 10 d (d 26) later, the animals were consecutively subjected to 1- and 22-h double-choice feeding tests to investigate their preferences during a short period and a longer period of time for the CON starter diet and the starter diet added with the FA corresponding to their treatment. No overall effect of the feed additives was observed on ADFI, ADG, G:F, and final BW. No overall preference was highlighted for the FA1 treatment, except for a preference for the FA1 starter diet during the 1-h test on d 23 (78% of total feed intake; P < 0.01). For the FA2 treatment, the pigs consumed the FA2 starter diet more than the CON starter diet during the 22-h tests on d 16 (67% of total feed intake; P < 0.05) and 26 (62% of total feed intake; P < 0.01). For the FA3 treatment, on d 26, the FA3 starter diet was and tended to be consumed more than the CON starter diet during 1- (69% of total intake; P < 0.05) and 22-h (60% of total intake; P < 0.10) tests, respectively. In conclusion, feed supplementation with the FA1, FA2, and FA3 from weaning did not induce beneficial effects on feed intake and growth performance during the early postweaning period. The FA2 increased palatability and acceptance of the unfamiliar starter diet the day of feed transition, while the FA1 and FA3 increased palatability of the starter diet only after a few days of exposure, most likely through long-term familiarization processes.

Feed preference in pigs: effect of selected protein, fat, and fiber sources at different inclusion rates

Three double-choice feeding experiments were conducted to study the effect of different feedstuffs on feed preference in pigs. Fifteen protein sources, 6 fat sources, and 3 fiber sources were evaluated in Exp. 1, 2, and 3, respectively. Pigs were offered a series of double choices between a common reference diet and the diet with the ingredient under evaluation. The reference diet contained a soybean meal product with 56% CP (SBM-56), sunflower oil, and wheat bran, which were considered as the feedstuffs of reference for the protein, fat, and fiber sources, respectively. Preference, expressed as percentage of the tested diet to total feed intake, was affected by feedstuff nature and by its inclusion rate. In Exp. 1, feeds with fish meal at 50 and 100 g·kg⁻¹, dried porcine hydrolyzed protein at 50 g·kg⁻¹, and lupine, soybean meal with 44% CP, and dried skim milk at 100 g·kg⁻¹ were preferred (P < 0.05) to the reference feed with SBM-56. On the contrary, relative to SBM-56, an avoidance (preference less than 50%) was observed for potato protein at all inclusion rates tested, rapeseed meal and acid milk whey at 100 and 200 g·kg⁻¹, and dried porcine hydrolyzed protein, soybean protein concentrate, wheat gluten, and sunflower meal at 200 g·kg(-1). The storage of dried skim milk, soybean protein concentrate, and potato protein for 10 mo resulted in a reduction (P < 0.001) of their preference values. In Exp. 2, the feed with palm oil (at 30 g·kg⁻¹) was preferred (P < 0.05), whereas feeds with linseed oil (at 30 and 100 g·kg⁻¹) and soybean oil (at 100 g·kg⁻¹) were avoided (P < 0.05) when contrasted with the reference feed with sunflower oil. Finally, in Exp. 3 diets with dehydrated alfalfa and sugar beet pulp at 130 g·kg⁻¹ had a reduced (P < 0.05) preference compared with the reference diet with wheat bran. It is concluded that feedstuff nature, inclusion rate, and freshness affect feed preference in pigs. Feedstuff preferences should be taken into account during diet formulation, particularly at critical stages such as immediately after weaning.

Feed preferences and performance of nursery pigs fed diets containing various inclusion amounts and qualities of distillers coproducts and flavor

We evaluated the preferences of nursery pigs for diets containing increasing distillers dried grains with solubles (DDGS), varying in color, or high-protein distillers dried grains (HP-DDG) and the effects of flavor supplementation on pig preference and growth performance. In Exp. 1 through 5, diet preference was determined in weanling pigs adjusted to a commercial diet for at least 10 d, and then housed individually for a 2-d double-choice preference test. In Exp. 1, a total of 60 pigs (11.6 ± 0.3 kg of BW) were given a choice between a reference diet (0% DDGS) and test diets containing 0, 10, 20, or 30% DDGS. In Exp. 2, a total of 80 pigs (10.8 ± 0.1 kg of BW) were given a choice between a reference diet (0% HP-DDG) and diets containing 0, 10, 20, or 30% HP-DDG. In Exp. 3, a total of 80 pigs (10.3 ± 0.2 kg of BW) were given a choice between a reference diet (0% DDGS) and a diet containing 0%, 30% light, or 30% dark DDGS. In Exp. 4, a total of 80 pigs (11.2 ± 0.2 kg of BW) were given a choice between a reference diet without DDGS and a diet containing either 0% DDGS, 10 or 20% light DDGS, or 10 or 20% dark DDGS. In Exp. 5, a total of 108 pigs (9.0 ± 0.2 kg of BW) were given a choice between a reference diet (0% DDGS and no flavor) and a diet without or with flavor and containing 0, 10, or 20% DDGS. In Exp. 1 and 2, DDGS and HP-DDG, respectively, linearly decreased (P < 0.01) pig preference. In Exp. 3, dark DDGS were preferred (P < 0.05) compared with light DDGS. In Exp. 4, preferences were linearly reduced (P < 0.01) with DDGS inclusion, and dark DDGS tended (P = 0.06) to be preferred compared with light DDGS. In Exp. 5, DDGS reduced preference (P < 0.01) and flavor reduced preference (P < 0.01) regardless of DDGS level. In Exp. 6, a total of 192 pigs (6.7 ± 0.1 kg of BW) were fed starter 1 diets without or with flavor for 1 wk. Subsequently, pigs were fed starter 2 and 3 diets (2 wk each) containing 0, 10, or 20% DDGS while continuing to receive their respective flavor treatment. Flavor addition during the starter 1 phase increased ADFI (P = 0.02), and DDGS inclusion tended to decrease ADG (P = 0.06) and decreased ADFI (P = 0.03) during the starter 2 phase. Volatile components in DDGS and HP-DDG varied greatly depending on the source. Nursery pigs preferred a diet without DDGS or HP-DDG, and this appeared to be unrelated to color differences between sources. Knowledge of volatile compounds that enhance or suppress the palatability of feed may lead to further development of feed additives for masking relatively unpalatable, albeit cost-effective, ingredients.