D. Solà-Oriol

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 preference in pigs: Effect of cereal sources at different inclusion rates

The palatability of different cereals was studied in 2 two-way choice (preference) experiments using pigs of 56 d of age and 17 kg of BW. In Exp. 1, the effect of 24 cereals vs. a common reference diet containing white rice on feed preference in pigs was studied. Pigs were offered free choice between the reference diet and a diet with the cereal under study for 4 d. Barley, corn (2 sources), wheat, cassava meal, biscuit meal, rye, sorghum, and 1 source of oats were tested at inclusion rates of 300 and 600 g x kg(-1). Short-grain rice (whole, brown, or extruded white), long-grain white rice (raw and cooked), extruded barley, extruded corn, extruded wheat, oats (2 sources), thick rolled oats, cooked oats, and naked oats (raw, extruded, or micronized) were tested at inclusion rates of 150, 300, and 600 g x kg(-1). Relative preference of cereals (% of total feed intake) was affected by type of cereal and by rate of inclusion. The diets containing extruded rice (150 g x kg(-1)), extruded naked oats (150, 300, and 600 g x kg(-1)), or naked oats (150 and 300 g x kg(-1)) were preferred (P < 0.05) by pigs to the reference diet. However, the reference diet was preferred (P < 0.05) to the diets containing 150, 300, and 600 g x kg(-1) of cooked long-grain rice, oats, or cooked oats, 300 and 600 g x kg(-1) of extruded wheat, wheat, corn, sorghum, or unhulled short-grain rice, and 600 g x kg(-1) of thick rolled oats, extruded corn, rye, extruded barley, micronized naked oats, barley, cassava, or biscuit meal. Extrusion improved (P < 0.05) preference values for corn and naked oats by pigs, but had no effect on barley, rice, or wheat. In Exp. 2, the preferences of pigs for oats and barley were studied using mash and pelleted diets. Diet form did not affect preference in oats diets. However, for barley, greater preference values were obtained when measured in pelleted form compared with mash form. Additionally, direct 2-way choices were also performed between oats and barley diets and between diets presented in mash and pelleted forms. Pigs preferred barley to oats, and preferred diets presented in pelleted form to those presented in mash form. In conclusion, cereal type, inclusion rate, and diet form affected feed preference in pigs. Using cereals with greater preference values may contribute to the formulation of more palatable feeds, which enhance feed intake of piglets at critical stages such as weaning time.

Feed preference in pigs: relationship with feed particle size and texture.

In previous studies, we observed important differences in the feed preferences of pigs resulting from changes in only 1 dietary ingredient. The present experiment was conducted to study the relationship between the feed preference values of feeds reported previously and their particle size and texture characteristics. The effect of individual feed ingredients was studied when added to a common basal diet. In addition to the basal diet, which included rice, a soybean meal product containing 56% CP, sunflower oil, and wheat bran, a total of 126 diets were studied. Of these, 63 were prepared by replacing the rice in the basal diet with another cereal, 29 by replacing the soybean product with different protein sources, 19 by replacing the sunflower oil with different lipid sources, and 6 by replacing the wheat bran with different fiber sources. Cereals were studied at inclusion rates of 150, 300, and 600 g x kg(-1); protein sources were studied at 50, 100, and 200 g x kg(-1); lipids were studied at 15, 30, and 100 g x kg(-1); and fiber sources were studied at 65 and 130 g x kg(-1). The particle size profile of all the diets was determined by using a 9-screen sieve shaker. The geometric mean particle size, particle size uniformity, number of particles per gram, surface area (cm(2) x g(-1)), and percentage of fine (passing through a 250-microm sieve) and coarse particles (remaining in a 2,000-microm sieve) were calculated. The texture properties (hardness, fragility, chewing work, and adhesiveness) of the feeds were also determined by using a texture analyzer. The Pearson correlation coefficients of these variables with feed preference were as follows: geometric mean particle size (r = 0.07; P = 0.45), particle size uniformity (r = 0.16; P = 0.07), number of particles per gram (r = -0.05; P = 0.61), surface area (r = -0.07; P = 0.46), percentage of coarse particles (r = 0.04; P = 0.65), percentage of fine particles (r = -0.12; P = 0.19), hardness (r = -0.21; P = 0.02), fragility (r = -0.20; P = 0.03), chewing work (r = -0.33; P < 0.001), and adhesiveness (r = 0.02; P = 0.78). It was concluded that the texture properties of the feed could explain in part the feed preferences observed in pigs, whereas particle size characteristics had less impact.

Effects of Different Maturation Systems on Bovine Oocyte Quality, Plasma Membrane Phospholipid Composition and Resistance to Vitrification and Warming

The objective of this study was to evaluate the effects of different maturation systems on oocyte resistance after vitrification and on the phospholipid profile of the oocyte plasma membrane (PM). Four different maturation systems were tested: 1) in vitro maturation using immature oocytes aspirated from slaughterhouse ovaries (CONT; n = 136); 2) in vitro maturation using immature oocytes obtained by ovum pick-up (OPU) from unstimulated heifers (IMA; n = 433); 3) in vitro maturation using immature oocytes obtained by OPU from stimulated heifers (FSH; n = 444); and 4) in vivo maturation using oocytes obtained from heifers stimulated 24 hours prior by an injection of GnRH (MII; n = 658). A sample of matured oocytes from each fresh group was analyzed by matrix associated laser desorption-ionization (MALDI-TOF) to determine their PM composition. Then, half of the matured oocytes from each group were vitrified/warmed (CONT VIT, IMA VIT, FSH VIT and MII VIT), while the other half were used as fresh controls. Afterwards, the eight groups underwent IVF and IVC, and blastocyst development was assessed at D2, D7 and D8. A chi-square test was used to compare embryo development between the groups. Corresponding phospholipid ion intensity was expressed in arbitrary units, and following principal components analyses (PCA) the data were distributed on a 3D graph. Oocytes obtained from superstimulated animals showed a greater rate of developmental (P<0.05) at D7 (MII = 62.4±17.5% and FSH = 58.8±16.1%) compared to those obtained from unstimulated animals (CONT = 37.9±8.5% and IMA = 50.6±14.4%). However, the maturation system did not affect the resistance of oocytes to vitrification because the blastocyst rate at D7 was similar (P>0.05) for all groups (CONT VIT = 2.8±3.5%, IMA VIT = 2.9±4.0%, FSH VIT = 4.3±7.2% and MII VIT = 3.6±7.2%). MALDI-TOF revealed that oocytes from all maturation groups had similar phospholipid contents, except for 760.6 ([PC (34:1) + H]+), which was more highly expressed in MII compared to FSH (P<0.05). The results suggest that although maturation systems improve embryonic development, they do not change the PM composition nor the resistance of bovine oocytes to vitrification.

Flavour preferences conditioned by protein solutions in post-weaning pigs

Prior studies report in various mammalian species that a neutral flavour can become strongly preferred after being associated with a positive consequence of its consumption. Two experiments were performed to study flavour preferences conditioned by a protein source in weaned pigs. In experiment 1, pigs were trained to drink (30 min/day) one flavour (CS+) mixed into a 2% protein solution (Soybean Protein Concentrate; SPC or Porcine Digestible Peptides; PDP) and another flavour (CS-) mixed into water during 6 alternate sessions. The pigs in the SPC and PDP groups consumed more CS+ than CS- in the two-choice tests with both flavours presented in water (552 vs. 409 mL, 571 vs. 414 mL, respectively). In the last choice SPC and PDP animals preferred the CS+ over the CS- when both flavours were present in feed rather than water (650 vs. 536 g and 678 vs. 513 g, respectively). No differences were observed between the conditioning effects of the two proteins. In experiment 2, pigs were trained (30 min/day) with a garlic flavour (CS) mixed with 4% PDP in sessions 1, 3, 5 and 7 unflavoured tap water in sessions 2, 4, 6 and 8 (Conditioned group) or with garlic flavour in water in sessions 1, 3, 5 and 7 and 4% PDP without added flavour in sessions 2, 4, 6 and 8 (control group). In subsequent choice tests conditioned pigs consumed more PDP+Garlic than PDP in Tests 1 (550 mL vs. 372 ml, P<0.05) and 3 (763 mL vs. 503 mL, P<0.05). In addition, pigs in the Conditioned group made significantly more first contacts (FC, number of piglets at a pan during the first 15s) with the PDP+Garlic solution than PDP solution in Tests 1 and 2 but not in Test 3. In contrast, the control group did not differ in their intakes of or first contacts to the two PDP solutions. The present results indicate that piglets can acquire preferences for a cue flavour added to protein products (PDP and SCP). The conditioned flavour preference also enhanced the attraction to the palatable protein (PDP) when the flavour and protein were combined.

Dietary energy density affects the preference for protein or carbohydrate solutions and piglet performance after weaning

Physiological state or dietary nutrient content can be determinants of the sensory perception with consequences for feed preferences. The aim of the present study was to assess whether the preference for protein or carbohydrate of piglets is affected by dietary energy density. In total, 240 weanling piglets (28 d old; initial BW 7.2 ± 1.1 kg) were allocated to 24 pens (10 pigs/pen) according to BW. Piglets were split up into 2 groups and had ad libitum access to a high energy (HE; 3.90 Mcal DE/kg; crude fat 129 g/kg) or a low energy (LE; 3.35 Mcal DE/kg; crude fat 60 g/kg) diet with similar CP content (190 g/kg). Piglet performance and preference for protein [porcine digestible peptides (PDP; Palbio 62SP, Bioibérica, Palafolls, Spain) 20 g/L] or carbohydrate (sucrose 20 g/L) solutions were measured on days 14 and 21 after weaning using a double-choice test (DCHT). The LE diet promoted a higher (P < 0.05) ADFI and ADG than the HE diet. Final BW on day 21 was higher (P < 0.001) for piglets fed the LE diet than piglets fed the HE diet (12.8 vs. 11.5 kg). Preference (P > 0.05) was not observed for protein or carbohydrate solutions on day 14 or 21 in piglets fed the LE diet. On the other hand, piglets fed the HE diet had higher (75% on day 14 and 65% on day 21; P < 0.01) preference for the sucrose solution. Dietary energy level and consequent nutrient imbalances, such as dietary protein-to-energy ratio, may affect feed preference for protein or carbohydrate solutions in piglets.

Influence of the protein status of piglets on their ability to select and prefer protein sources

Pigs may have retained the capacity to choose feeds based on their nutritional requirements, even after decades in which they are not allowed to select their diet composition due to the common feeding systems of the intensive pig industry. We used 480 early-weaned piglets in two experiments to assess their ability to select and prefer protein-related sources, depending on their protein status. Piglets were fed after weaning with two isoenergetic diets formulated to contain an optimal or sub-optimal crude-protein (CP) content, a high-protein (HP, 204g CP/kg as-fed) or a low-protein diet (LP, 142g CP/kg), respectively. In Experiment 1, the preference of piglets was assessed by using a choice test between protein (porcine digestible peptides [PDP] 40g/L) and carbohydrate (sucrose 40g/L) water-based solutions for a period of 3min. Piglets showed higher intake and preference for the sucrose 40g/L than for the PDP 40g/L solution, independently of the dietary CP content (9.8mL/kg body weight [BW] vs. 3.7mL/kg BW and 10.4mL/kg BW vs. 4.3mL/kg BW in HP and LP pigs, respectively). In Experiment 2, piglets were given eight training sessions in which two equally preferred flavors were mixed with protein (porcine animal plasma 60g/L, CSp) or carbohydrate (maltodextrin 60g/L, CSc) solutions. In the subsequent choice test, piglets fed the HP diet showed a tendency to a higher intake of CSc than of CSp (6.5mL/kg BW vs. 5.4mL/kg BW). On the other hand, piglets fed the LP diet showed a higher intake and preference for CSp than for CSc (15.5mL/kg BW vs. 10.2mL/kg BW), differences being higher for medium and low BW piglets than for heavy ones. The results show that piglets are unable to express a specific appetite for protein to correct previous underfeeding with it; however, they may show an appropriate dietary selection pattern in order to overcome protein deficiency through associative learning.

Anhedonia in pigs? Effects of social stress and restraint stress on sucrose preference

The fact that consumption of normally palatable foods is affected by stress in both humans and rats suggests a means to assess hedonic reaction in non-verbal animals. However, little is known about anhedonia and stress in productive animals such as pigs. Thus we examined the separate effects of social stress and restraint stress in 42-day old pigs on the preference for dilute sucrose solutions over water. Pigs in the social stress group (SS) were mixed with unfamiliar animals from separate pens for two 20 minute periods (Experiment 1). Pigs in the restraint stress group (RS) were immobilized three times a day, for 3-min periods, on 3 consecutive days (Experiment 2). Consumption of dilute sucrose solutions and water was examined after these stress manipulations and in the unstressed control groups (CG). Pigs were tested in pairs (12 control and 12 experimental) with a choice between water and sucrose solutions (at either 0.5% or 1%) during 30 min sessions. In both experiments CG pigs showed higher intakes of 0.5% and 1% sucrose solutions over water. Neither SS nor RS pigs consumed more 0.5% sucrose than water, but both groups did consume more 1% sucrose than water. Both social stress and restraint stress reduced sucrose preference at low concentrations but not at higher concentrations suggesting that stress may limit food consumption in pigs unless a palatable feed is present. In addition, the results suggest that stress reduces the hedonic impact of dilute sucrose. Therefore, sucrose preference may be a useful test for the presence of stress and anhedonia in pigs.

Feed preference in pigs: Relationship between cereal preference and nutrient composition and digestibility

The present work aimed to identify the nutritional characteristics that best explain cereal feed preference in pigs. A total of 25 cereals of known preference (at 60% of inclusion in complete feed) from a previous study were evaluated. The cereals were analyzed for DM, OM, crude fiber, ether extract, CP, GE, digestible starch, and glycemic index. Additionally, for 12 of the cereals, complete feeds (the same composition as those previously used to measure preference) were prepared, analyzed for DM, OM, CP, and starch, and fed to pigs (33 ± 5.1 kg BW) fitted with ileal T-cannulae to assess the apparent ileal (AID) and total tract digestibility (ATTD) of these nutrients using titanium dioxide as an indigestible marker. The relationships among the different energy and nutrient contents were studied by principal component (PC) analysis, and the correlations between the generated PC scores and cereal preference were analyzed. A correlation between preference and the second PC obtained with data of the 25 cereals was observed (P < 0.01), which indicated that crude fiber (negatively) and digestible starch, OM, and glycemic index (positively) were correlated with feed preference. Statistically significant linear relationships with preference were confirmed for crude fiber, digestible starch, and glycemic index (R(2) = 0.38, 0.36, and 0.23, respectively; P < 0.02). Similarly, the first PC obtained with data of the 12 feeds also correlated with preference (P < 0.01), indicating that the digestible nutrients (positively) and the nondigestible nutrients (negatively) were correlated with preference. Statistically significant relationships with preference were observed for the contents of starch (total, digestible AID, and digestible ATTD: R(2) = 0.62, 0.66, and 0.63, respectively; P < 0.01), AID DM (digestible and nondigestible: R(2) = 0.41 and 0.44, respectively; P < 0.05), ATTD DM (digestible and nondigestible: R(2) = 0.67 and 0.70, respectively; P < 0.01), AID OM (digestible and nondigestible: R(2) = 0.45 and 0.43, respectively; P < 0.05), and ATTD OM (digestible and nondigestible: R(2) = 0.64 and 0.66, respectively; P < 0.01). It is concluded that cereal preference in pigs is positively related with their content in digestible nutrients, such as starch, and negatively related with their nondigestible nutrients, such as crude fiber.

Flavor preferences conditioned by postingestive effect of sucrose and porcine digestive peptides in postweaning pigs

Pigs can learn to prefer a flavor if it has been previously associated to positive consequences. The aim of this experiment was to study flavor preferences conditioned by the postingestive effect of nutrients in pigs. In total, 240 weanling piglets were allocated in 24 pens (10 piglets/pen) and distributed to 2 groups of animals (12 pens per group). Pigs in Group 1 (G1) were trained during 8 d with one flavor [positive conditioned stimulus (CS+)] into a protein solution [4% porcine digestible peptides (PDP)] on odd days and another flavor [negative conditioned stimulus (CS-)] into 100 mM of monosodium glutamate (MSG) solution on even days (5-L bottle for 24 h). In the second group of pigs [Group 2 (G2)], CS+ was mixed into a 4% sucrose solution in odd days and CS- into 1% sucrose + 0.08% saccharine on even days. Therefore, treatments were defined as CS+, the flavor associated with PDP or sucrose, on odd days, which were assumed to have a higher postingestive effect than MSG or saccharine + sucrose, the ingredients associated to CS-. Concentration of ingredients in the solutions were chosen to ensure that hedonic attraction for PDP and MSG solutions and for sucrose and saccharine + sucrose were similar (checked in previous double-choice studies). The amount of solution offered during training period was prepared to be totally consumed each day to equalize flavors intake. Flavors (0.0375% anise or garlic) were counterbalanced across replicates to act as CS+ or CS-. Double-choice test between flavors dissolved in water (CS+ and CS-) were performed by selecting 2 pigs/pen on days 1, 6, and 8 after the training period. Solution intake was measured after 30 min. Piglets showed higher intakes for CS+ than CS- in G2 [212 vs. 76 mL and 168 vs. 86 mL (P < 0.05) and 195 vs. 78 mL (P = 0.15)] on days 1, 6, and 8, respectively. Differences between CS+ and CS- consumption were observed in G1 on day 8 (231 vs. 130 mL; P < 0.05). In conclusion, weanling pigs can acquire flavor preferences through associative learning between a flavor and postingestive effects of some nutrients.