RELATIONSHIPS BETWEEN GENETIC MERIT OF SIRES FOR AD LIBITUM RESIDUAL FEED INTAKE AND TRAITS OF HEAVY PIGS RAISED UNDER RESTRICTED FEEDING CONDITIONS

Residual feed intake (RFI) is the most accurate measure of feed efficiency and to properly assess it, pigs must be under ad libitum feeding. Low-RFI pigs are more efficient, consuming less feed while maintaining similar performance levels compared to high-RFI pigs, but exhibited reduced backfat and leaner carcasses, with altered meat quality. The Italian Protected Designation of Origin (PDO) dry-cured ham production faces challenges due to restricted feeding conditions for heavy pigs, necessitating an assessment of the impact of low RFI leanness on pigs. Therefore, this thesis aimed to: i) evaluate how sires classified for their additive genetic effects on RFI of ad libitum-fed progeny influence growth performance, gain composition, carcass traits and dry-cured ham quality, including weight loss (WL) in restricted-fed progeny; ii) assess the effects of individual classification for RFI on the same traits in ad libitum-fed pigs; iii) estimate the effect of sire and individual classification for feed conversion ratio (FCR), on WL and dry-cured ham quality traits of both ad libitum and restricted-fed pigs. The study involved 23 C21 Goland sires and 420 offspring, each assigned to ad libitum or restricted feeding strategies. Pigs' weight, backfat, and feed intake were measured to estimate empty body weight, lipid and protein gains, and average daily feed intake. After slaughter, carcass traits, green ham quality, subcutaneous fat quality, WL, and quality attributes in dry-cured hams were assessed. Individual RFI was calculated for ad libitum-fed pigs as the residual of a linear regression of average daily feed intake on average empty body weight, body lipid, and protein daily gains. The additive genetic effects of sires on RFI of ad libitum-fed pigs were estimated using a linear animal model and sires were classified as low- (LRFI), medium- (MRFI), or high-RFI (HRFI) based on these estimates. This classification was used to assess how the genetic effects of sires on RFI influenced growth performance, tissue composition, carcass traits, dry-cured ham quality, and WL in restricted-fed progeny. Restricted-fed progeny of LRFI sires exhibited higher feed efficiency, with the lower daily feed intake and FCR, and a slight growth rate increase. They also showed the higher carcass weight gain, carcass yield, fat cuts and ham weight, but lower lean meat. LRFI progeny showed superior subcutaneous fat quality, with higher saturated fatty acid content and lower levels of unsaturated fatty acids. RFI classification did not adversely affect ham WL, and low-RFI progeny were more likely to receive favorable quality scores, including firmer subcutaneous fat, reduced oxidation, and greater consistency. The phenotypic relationship between RFI and carcass and carcass and ham quality traits were also assessed in ad libitum-fed pigs. Low-RFI pigs showed a higher proportion of lean cuts and thinner subcutaneous fat resulting in higher WL during curing. Finally, FCR's effect on WL and dry-cured ham quality traits in restricted-fed progeny was evaluated. FCR was calculated for ad libitum-fed pigs and sires were classified based on their additive genetic effects on FCR. Low-FCR progeny showed the lower WL, with thicker subcutaneous fat, less tissue separation, and increased marbling, suggesting improved fiber cohesion and sensory qualities. At the phenotypic level in ad libitum-fed pigs, low FCR was associated with higher WL without compromising ham quality. This study demonstrates that improving feed efficiency through the selection of low-RFI sires can maintain both carcass value and dry-cured ham quality in restricted-fed pigs. The findings suggest that RFI could be an effective selection criterion in breeding programs for sire lines of heavy pigs, with the potential to enhance both efficiency and PDO dry-cured ham quality.