Metabolic Profile of Growing Immune- and Surgically Castrated Iberian Pigs Fed Diets of Different Amino Acid Concentration

SIMPLE SUMMARY: Pig immunocastration—vaccination against the gonadotropin-releasing hormone—prevents sexual development and boar taint, an unpleasant odor perceived in pork products. It is a feasible alternative to surgical castration that considerably increases pig well-being. Apart from this benefit, immunocastrated pigs perform better than surgically castrated pigs, which is of interest for pig production in general, and for native pig breeds in particular, as they show slow growth and lean tissue deposition compared to cosmopolitan pig breeds. These performance benefits were demonstrated in immunocastrated Iberian male pigs, a local pig breed from the Iberian Peninsula. The purpose of the study was to investigate the metabolic profile of immunocastrated male and female Iberian pigs compared to surgically castrated male pigs, which is the standard pig type for Iberian pig production. The surgically castrated males showed metabolic features of pigs prone to deposit more lipids, with less lean tissue and they were less sensitive to circulating insulin, whereas immunocastrated males presented increased plasmatic concentrations of some key amino acids and hormones (IGF-1) related to enhanced protein deposition. The immunocastrated female group showed intermediate traits. The results support the higher performance previously observed in immunocastrated male Iberian pigs compared to surgically castrated males and immunocastrated females. ABSTRACT: The purpose of the current study was to further characterize the performance and nitrogen retention differences previously observed between immunocastrated (IC) and surgically castrated (SC) pure Iberian pigs. Fifty-four pigs were used (three sexes: IC males, IC females and SC males), fed three isoenergetic diets (160, 140 and 120 g CP/kg DM; six pigs/treatment combination) from 40 kg BW until slaughter (105 kg BW). Plasmatic post-absorptive metabolites and hormones, and backfat tissue composition were determined. The IC males showed a trend towards higher plasmatic creatinine (p = 0.06) and IGF-1 concentrations than SC males and IC females (p < 0.001). SC males showed a higher predisposition to carcass fatness and insulin resistance compared to IC males. Plasmatic isoleucine concentration was higher in IC and SC males compared to IC females (p < 0.01), and valine was greater in IC males compared to the rest of the pigs (p < 0.001). Total branched-chain amino acids (AA) were greater in IC males than in IC females (p < 0.01). Total plasmatic essential AA concentrations tended to be greater in IC males (p = 0.09). The present results support the increased performance and nitrogen retention capacity previously observed in IC male Iberian pigs compared to SC males and IC females, which can be attributed to increased anabolic capacity related with lean growth in Iberian IC males.