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.