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 = 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 = 0.62, 0.66, and 0.63, respectively; P < 0.01), AID DM (digestible and nondigestible: R = 0.41 and 0.44, respectively; P < 0.05), ATTD DM (digestible and nondigestible: R = 0.67 and 0.70, respectively; P < 0.01), AID OM (digestible and nondigestible: R = 0.45 and 0.43, respectively; P < 0.05), and ATTD OM (digestible and nondigestible: R = 0.64 and 0.66, respectively;

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 , dried porcine hydrolyzed protein at 50 g·kg , and lupine, soybean meal with 44% CP, and dried skim milk at 100 g·kg 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 , and dried porcine hydrolyzed protein, soybean protein concentrate, wheat gluten, and sunflower meal at 200 g·kg . 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 ) was preferred (P < 0.05), whereas feeds with linseed oil (at 30 and 100 g·kg ) and soybean oil (at 100 g·kg ) 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 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 palat ability 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-kg-1. Shortgrain 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-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·kg-1), extruded naked oats (150, 300, and 600 g·kg-1), or naked oats (150 and 300 g·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·kg-1 of cooked long-grain rice, oats, or cooked oats, 300 and 600 g·kg-1 of extruded wheat, wheat, corn, sorghum, or unhulled short-grain rice, and 600 g·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·kg -1; protein sources were studied at 50, 100, and 200 g·kg -1; lipids were studied at 15, 30, and 100 g·kg-1; and fiber sources were studied at 65 and 130 g·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 (cm2·g-1), and percentage of fine (passing through a 250-μm sieve) and coarse particles (remaining in a 2,000-|μm 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