Characteristics of the acorns selected by free range Iberian pigs during the montanera season V. Rodríguez-Estévez ⁎, A. García, A.G. Gómez Departamento de Producción Animal, Campus Universitario de Rabanales, Córdoba 14071, Spain article info abstract Article history: Received 28 September 2007 Received in revised form 7 August 2008 Accepted 11 August 2008 Acorn weight, size, shape and composition vary a great deal among evergreen oaks (Quercus ilex rotundifolia); however these characteristics remain constant for a tree throughout the fruiting period. The number of consumed acorns under the canopy of a tree could be an indicator of preference for its acorn characteristics. This paper analyses the characteristics of the acorns selected by free-ranging Iberian pigs at the start (November) and end (February) of the montanera or acorn mast-feeding season, when these are sustained fattened. At these two stages, acorn samples were taken from 20 oak trees (Q. ilex rotundifolia) that had been rejected by the pigs (only eating between 2 and 9 acorns from the ground underneath the tree) and from 20 oak trees that were actively sought out by the pigs (eating at least 40 acorns). The differences observed between the sought out and rejected acorns at the start and end of the montanera season are too great to be only a matter of chance, suggesting that Iberian pigs must form associations between variables when choosing to eat or reject the acorns from a specific oak tree. The results show that pigs tend to select heavier acorns at the start of the montanera season, while at the end their selection is based more on the composition of the acorns. The greatest number of significant differences between the groups of acorns were found in the sought out acorns in November and February, owing to all the variables related with the composition of the acorns: crude fat (10.8 ± 0.3 vs. 7.4 ± 0.3), starch (58.3 ± 1.0 vs. 50.3 ± 0.4), sugars (6.8 ± 0.4 vs. 13.2±0.3); most of the fatty acids; dimensions: length (38.1±0.8 vs. 31.9±0.7) and diameter (16.6 ± 0.4 vs. 13.9 ± 0.1); acorn weights: fresh whole acorn (6.9 ± 0.3 vs. 3.4 ±0.1) and kernel DM (2.5 ± 0.2 vs. 1.7±0.1). Pigs prefer acorns with larger kernel. This selective consume goes along with the theory of Optimal Foraging and suggest that pigs learn to use visual stimuli when grazing. In conclusion, this study shows a constant selective acorn consumption and a variation in acorn preferences throughout the montanera period; consequently it is proven that acorn diet is not homogeneous and varies over the fattening period. © 2008 Elsevier B.V. All rights reserved. Keywords: Food discrimination Food preference Diet selection Agroforestry system Optimal Foraging 1. Introduction The traditional system of Iberian pig farming is linked to the sustained use of the dehesa pasturelands of Quercus ilex rotundifolia and Q. suber in the southwestern part of the Iberian Peninsula; acorns are used to fatten the pigs during the montanera or acorn mast-feeding season, which runs from early November to late February. During the montanera season, the pigs feed exclusively on fallen acorns and grass. Rodríguez-Estévez et al. (in press) suggest a daily DM intake of 3.1–3.6 kg of acorn kernel and 0.38–0.49 ± 0.04 kg of grass, which is achieved thanks to the functional characteristics of this breed as well as its ability to select and shell acorns (Aparicio Macarro, 1988; García et al., 2003). Studies that assess the quality of the products derived from Iberian pork using the fatty acid profile of subcutaneous and muscle fat (for example, Rey et al., 2006) assume that the pigs' diet is homogeneous throughout the montanera season, and that the acorns have similar characteristics, disregarding variations between trees and species of Quercus (Rodríguez- Livestock Science 122 (2009) 169–176 ⁎ Corresponding author. Tel.: +34 957212074. E-mail address: pa2roesv@uco.es (V. Rodríguez-Estévez). 1871-1413/$ – see front matter © 2008 Elsevier B.V. All rights reserved. doi:10.1016/j.livsci.2008.08.010 Contents lists available at ScienceDirect Livestock Science journal homepage: www.elsevier.com/locate/livsci