| Summary: | 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 (<i>p</i> = 0.06) and IGF-1 concentrations than SC males and IC females (<i>p</i> < 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 (<i>p</i> < 0.01), and valine was greater in IC males compared to the rest of the pigs (<i>p</i> < 0.001). Total branched-chain amino acids (AA) were greater in IC males than in IC females (<i>p</i> < 0.01). Total plasmatic essential AA concentrations tended to be greater in IC males (<i>p</i> = 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.
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