Effect of reductions in feed allowance and dietary amino acids content on feeding behaviour, growth performance, nutrient excretion and meat quality of growing pigs belonging to different genetic types

Pig industry is required to reduce its environmental footprint, in order to satisfy the increasing demand of eco-friendly products. Moreover, the producers need to cut down with the feeding costs, by improving the pigs’ feed efficiency. Despite the rich literature, knowledge about the effect of some feeding strategies on feeding behaviour, performance, and quality of meat and meat products seems still controversial or scarce. With this background, the aims of this Ph.D. project were: i) to assess the influence of a reduction in dietary indispensable amino acids (AA) on feed intake, growth performance, N excretion and carcass and meat quality traits of fast growing pigs fed according to an ad libitum or a restricted feeding regime; ii) to study the feeding behaviour of group-housed pigs fed individually from single-space feeders and subjected to feed restriction and a reduction in the dietary indispensable AA content; iii) to explore the influence of feeding behaviour on growth performance, carcass and meat characteristics of pigs; iv) to investigate the influence of low-protein and AA diets on the characteristics of San Daniele like dry-cured hams obtained from two genetic groups of pigs with different lean growth potential. In the 1st Chapter, 96 barrows were individually fed through automatic feeding stations, according to an ad libitum or restricted feeding regime and to a conventional or low-AA diet. Feed restriction decreased feed intake, average daily gain, carcass weight, backfat depth, but increased gain:feed ratio. The low-AA diets increased feed intake, carcass weight and the intramuscular fat content, with no effects on the feed efficiency and the estimated Pr. Nitrogen excretion was reduced by feed restriction and by the reduction of the dietary AA content. In the 2nd Chapter, the data recorded by the automatic feeding stations were used to study the effects of the feeding regime and the dietary AA restriction on the feeding patterns of the pigs of the previous contribution. Feed restriction decreased daily feed intake, the number of visits and the time spent feeding, but increased feed consumption per visit and feeding rate. The low-AA diets increased daily feed intake, tended to increase feeding rate and interacted with feeding regime for the number and duration of feeding visits. The pigs were able to adapt their feeding patterns to compensate for a reduction in feed allowance or nutrient restriction. In the 3rd Chapter the phenotypic correlations among feeding patterns, growth performances and carcass traits were studied. The records of each pig were classified into feeding rate tertiles. Pigs eating faster showed greater final body weights, average daily gains, estimated protein gains, estimated lipid retention, carcass weights, weights of lean cuts, weights of fat cuts, proportions of fat in the carcass, and lower proportions of carcass lean cuts than pigs eating slowly. Manipulating the eating rate, through management or genetic strategies, could affect growth performances and carcass quality, with little influence on feed efficiency. The 4th Chapter investigated the influence of diets lowered in protein and AA contents on the quality of 40 San Daniele like dry-cured hams produced by pigs of two genetic groups (Danbred and Anas) characterized by different potential for lean growth, eating conventional or low-protein diets. The Danbred fresh hams were heavier, but showed greater seasoning losses and thinner fat cover than Anas hams. Dry-cured hams from Danbred had higher protein content than the Anas ones. Dietary protein restriction had small influence on dry-cured ham quality. Due to its positive effects on sustainability of dry-cured ham chain by decreasing pig farm nitrogen excretion and feeding costs, the use of low-protein diets seems an advisable strategy for the feeding of traditional PDO heavy pigs