The main objective was to determine the nitrogen and P retention and energy digestibility of immunological castrates (IC), entire males (EM), physical castrates (PC), and gilts (G) during 3 growth phases. A second objective was to compare growth performance among the sexes. The final objective was to determine the carcass iodine value (IV) among the sexes. Twelve individually housed pigs (PIC 337 x C22/29) of each sex with an initial mean BW of 35.7 +/- 0.6 kg and a final BW of 145.0 +/- 1.3 kg were evaluated. Anti-gonadotropin-releasing factor injections were administered at d 23 and 15 for groups 1 and 2, respectively. The second injection was given on d 56 of the 98-d experiment. Nitrogen, P, and energy digestibility were measured the last 3 d of the 10-d metabolism period starting at mean BW of 39.5 +/- 0.6, 73.7 +/- 0.8, and 105.5 +/- 0.9 kg for periods 1, 2, and 3, respectively. The third collection started 14 d after the second injection. Entire males and IC had superior overall ADG compared to PC and G (P < 0.05). Entire males and G had the lowest overall ADFI, and PC had the greatest, with IC being intermediate (P < 0.05). Entire males were overall the most efficient, followed by IC, with PC and G being the least efficient (P < 0.05). Immunological castrates and EM had similar nitrogen retention (g/d) for the first 2 collection periods (P > 0.05). In the third collection period, nitrogen retention of IC was similar to that of both EM and PC (P < 0.05). Phosphorus retained (g/d) was not different among the sexes in the first collection; during the second collection, EM retained the greatest amount of P, G and PC retained the lowest, with IC being similar to all sexes. For the third collection, IC had P retention similar to that of EM, EM had retention similar to that of PC, and PC had retention similar to that of G (P > 0.05). However, G retained less P than EM or IC (P < 0.05). Apparent total tract digestibility of DM and GE and the DE of the diet did not differ among the sexes in any of the collection periods (P > 0.05). The jowl IV was the lowest in IC and PC and highest in EM, with G being similar to all sexes (P < 0.05). For the belly, EM had the highest IV, with the other 3 sexes being similar. In conclusion, 2 wk after the second injection, IC transition to become more similar to PC in terms of nitrogen utilization but are still similar to EM in P utilization. These data suggest a feeding program for IC that is intermediate between EM and PC is required to meet their nutritional requirements.
