A total of 120 Iberian pigs of the Lampiña line that grew under outdoor conditions were used to study the effect of the age at the beginning of Montanera period (AM) on meat characteristics and fatty acid (FA) profile of subcutaneous fat. AM period is a free-range fattening phase from November to February in which pigs ate mainly acorns and grass. There were two treatments with two AM (20 pigs per treatment); 18 (P18) and 12 months (P12). Barrows and gilts were in the same proportion within each treatment. All the animals were slaughtered at the same time (at the end of Montanera period) reaching an average 160 kg of body weight. Meat from P18 had less protein and was more red (a*) (P < 0.05), but tended to show higher intramuscular fat content (P < 0.10) than meat from P12. Loin from P18 had lower thawing (P < 0.001) and cooking losses (P < 0.10) than loin from P12. The fat from P18 had higher monounsaturated FA content than fat from P12 pigs (P < 0.01) due to the higher level of C18:1 (P < 0.01) and C20:1 (P < 0.001). However, fat from P12 had higher polyunsaturated FA content than fat from P18 pigs (P < 0.01) because of the higher level of C18:2 (P < 0.001). It is concluded that both 12 and 18 months are adequate AM for purebred Iberian pigs from the commercial point of view. However, if the aim is to produce high-quality dry-cured Iberian products, the P18 pigs would be more advisable because had better meat and fat characteristics than the P12 pigs.

This investigation was designed to evaluate the effects of feeding either free range or in confinement using concentrated diets with the same ingredients and oil source (5.5% of olive oleins) but with different antioxidant supplementation [control diet with a basal level of α-tocopheryl acetate (control); 200 mg/kg synthetic all-rac-α-tocopheryl acetate (Eall-rac); 200 mg/kg natural RRR-α-tocopheryl-acetate (ERRR-); flavonoid extract-enriched diet (AFlav); and phenolic compound-enriched extract (APhen)] on the fatty acid composition and lipid oxidation of Iberian pig muscle longissimus dorsi. The α-tocopherol concentration was significantly higher in muscles from free-range and ERRR- pigs than in muscles from Eall-rac pigs, and γ-tocopherol was only detected in muscles from free-range pigs. Longissimus dorsi muscles from free-range pigs had a significantly lower content of saturated fatty acids and higher content of polyunsaturated fatty acids than muscles from the other five groups of pigs fed in confinement; however, no significant effect on monounsaturated fatty acids was observed. No effect of dietary antioxidant supplementation (synthetic or natural α-tocopherol, flavonoid extract, or phenol extract) on the fatty acid composition of muscles was observed. A significant influence of dietary treatment on lipid oxidation was observed after 3 (P < 0.01), and 7 and 10 (P < 0.001) days of refrigerated storage, respectively. The lowest thiobarbituric acid-reactive substances (TBARS) values were found in pork chops from the free-range and ERRR- groups, intermediate values from the Eall-rac group, followed by AFlav and APhen, while the highest TBARS values corresponded to muscles from pigs fed the control concentrate. The source of α-tocopherol had a significant effect on lipid oxidation (P < 0.05), whereas the AFlav and APhen groups had similar TBARS values.

Twenty-four finishing pigs (twelve Iberian and twelve Landrace) were used in a growing and slaughtering experiment. Animals were fed two diets differing in their ingredients, maize (diet C) or sorghum–acorn (diet A). At an average weight of 107·0 kg pigs were slaughtered and hindgut digesta sampled to study the effect of breed and diet on large bowel fermentation. Flows of digesta to the hindgut compartment were estimated based on an indigestible flow marker (Cr2O3) and were higher in Iberian than in Landrace pigs (P<0·001), and higher in animals fed diet A than diet C (P=0·07). The higher flows in Iberian pigs were mainly associated with a higher voluntary feed intake (3·50 v. 2·70 kg/d, P<0·01) and lower ileal digestibility of NSP (−12·8 v. 47·8, P<0·01). Differences between diets were mainly associated with a lower ileal digestibility of starch from diet A (89·2 v. 96·9%, P=0·06), although no differences in the resistant starch content were observed in vitro. Fermentation of different carbohydrates through the large bowel showed that NSP-glucose had lower digestibility in Iberian than in Landrace pigs (62·5 v. 94·2%, P<0·001), but no differences were observed in starch, or other NSP-fibre fractions (arabinose, xylose and galactose). The type and amount of carbohydrates reaching the large bowel were related to the diet but also to breed, and promoted differences in the fermentative activity associated with different volatile fatty acid patterns and changes in microbial enzymic activity.

The effects of dietary protein content and feeding level on the utilization of metabolizable energy (ME) and on the rates of gain, protein and fat deposition have been studied in seventy-two Iberian pigs growing from 15 to 50 kg body weight (BW) by means of comparative slaughter experiments. The animals were fed on six diets providing 223, 192, 175, 156, 129 and 101 g crude ideal protein (N×6·25; CP)/kg DM and 14·64, 14·14, 14·37, 14·80, 15·36 and 15·53 MJ ME/kg DM respectively. Each diet was offered at three levels of feeding: 0·60, 0·80 and 0·95×ad libitum intake. Protein deposition (PD) increased significantly (P<0·01) with each decrease in dietary CP content and reached a maximum value (74·0 g) when the diet providing 129 g CP/kg DM (6·86 g digestible ideal protein/MJ ME) was offered at the highest feeding level. This feeding regimen resulted in average values for live-weight gain and retained energy (RE) of 559 g/d and 10·9 MJ/d respectively. RE increased significantly (P<0·001) from 480 to 626 kJ/kg BW0·75 with each decrease in dietary CP content from 192 to 129 g/kg DM. Raising the level of feed intake led to significant linear increases in PD and RE irrespective of the diet fed (P<0·001). When diets approaching an adequate supply of CP were given, the net efficiency of use of ME for growth (kw) and the maintenance energy requirements were 58·2 % and 422 kJ/kg BW0·75 per d respectively.