Innovative feeding strategies in heavy pigs and their impact on the quality of cured hams

The PDO dry-cured ham industry is a key sector of the Italian agri-food system. Until recently, production rules required pigs to reach 160 ± 16 kg at a minimum age of nine months, which led to restrictive feeding strategies. However, modern genetics has produced pigs that are excessively lean, with thighs lacking fat coverage, thus unsuitable for high-quality PDO hams. This has necessitated revising of production standards. This PhD thesis investigates three innovative feeding strategies compared with the traditional one: • a low-protein, lysine-reduced diet aimed at prolonging the rearing period and producing fatter carcasses with higher marbling and sensory quality, based on the idea that reduced protein intake shifts energy toward fat deposition; • two ad libitum diets, without amino acid restrictions, designed either to reach 170 kg at the minimum age or to achieve maximum weight at nine months. The first chapter assessed the effects of these strategies on technological traits and chemical composition of hams produced under Prosciutto Veneto PDO rules. A total of 336 pigs (90 kg start weight) were allocated to eight pens with automatic feeders. After 607 days of curing, 60 representative hams were analysed. The ad libitum strategy to target age gave the best results, yielding heavier deboned hams, thicker backfat, greater marbling, and lower PUFA levels in fat. The second chapter evaluated slaughter weight and backfat thickness in relation to processing losses and ham quality. Across four production cycles (423 pigs), animals were grouped by slaughter weight (light, medium, heavy). Higher slaughter weight reduced relative losses at almost all stages, while thicker backfat increased trimming but lowered curing losses. Overall, heavier pigs with thicker fat cover improved technological traits. The third chapter modelled chemical growth, metabolisable energy, and SID lysine requirements of pigs under non-limiting vs. restrictive feeding. Data from chapter one were used to fit Gompertz models for empty body weight, protein, and lipid mass. Results showed that ad libitum feeding with age-related reduction of SID lysine improved growth performance. Moreover, current commercial SID lysine levels were found to exceed actual requirements. The fourth chapter characterised the microbiota of 72 hams aged 12 months, obtained from pigs under different strategies. A 16S metabarcoding multi-amplicon approach identified 2,845 ASVs, with Staphylococcus, Tetragenococcus, and Brevibacterium as core genera. β-diversity analysis revealed a significant effect of feeding strategy. The ad libitum ad libitum diet applied until the target age was reached showed the highest number of unique microbial communities, including potentially beneficial taxa for maturation, poorly characterised ones, and some spoilage organisms. In conclusion, the regulatory move toward heavier carcasses for PDO ham production is consistent with the need for greater fat coverage, as confirmed by this work. Feeding strategies should favour ad libitum or minimally restricted intake to maximise growth through adequate protein and amino acid supply. From a microbiological perspective, however, further studies are required in the later curing stages due to the persistence of spoilage organisms after 12 months.