440 The effects of reducing dietary nutrient density after the second dose of GnRF immunization (Improvest) on growth performance and carcass characteristics of gilts and intact males

Objectives were to determine the effects of reducing dietary nutrient density after the second dose of GnRF immunization (Improvest; Zoetis Inc.) on growth performance and carcass characteristics. Pigs (n = 1,008) were fed in five diet phases during the 102-d grow-finish period. Diets were formulated to meet 100% of recommended SID Lys to net energy established by PIC (2021) for physically castrated (PC) barrows/non-immunized gilts (regular diet), while diets for GnRF-immunized pigs were formulated with 120% SID lysine than PC barrows/ non-immunized gilts (nutrient-dense diet). During diet phase-4 (2 d after the second GnRF analogue dose), SID lysine and vitamins/trace minerals for the nutrient-dense diet were either maintained at 100% or reduced to 95% or 90%. During diet phase-5 (18 d after second GnRF analogue dose), SID lysine and vitamins/trace minerals nutrient-dense diet were either maintained at 100% or reduced to 90% or 80%. The study consisted of six pen replications (21 pigs/pen) of the following eight treatments: CON-NEG: traditional mixed-sex pigs (PC barrows and non-immunized gilts) that received the regular diet; CON-POS: traditional mixed-sex pigs that received the nutrient-dense diet; I-MALE-100: immunized males (I-MALES) that received the nutrient-dense diet with 100% density; I-MALE-95/90: I-MALES that received the nutrient-dense diet with 95% density during diet phase-4 and 90% density during diet phase-5; I-MALE-90/80 I-MALES that received the nutrient-dense diet with 90% density during diet phase-4 and 80% density during diet phase-5; I-FEM-100: immunized females (I-FEM) that received the nutrient-dense diet with 100% density; I-FEM-95/90: I-FEM that received the nutrient-dense diet with 95% density during diet phase-4 and 90% density during diet phase-5; I-FEM-90/80: I-FEM that received the nutrient-dense diet with 90% density during diet phase-4 and 80% density during diet phase-5. Data were analyzed with PROC MIXED of SAS, with pen serving as the experimental unit. In addition, linear effects of diet dilution for I-MALE and I-FEM pigs were tested using contrast statements. There were not significant linear effects of diet dilution for gain:feed or hot carcass weight in either the I-MALE (P > 0.28) or I-FEM (P > 0.78) pigs. For the overall period, gain:feed was improved by 7.4% for I-MALE pigs compared with the CON-NEG pigs and was improved by 1.6% for the I-FEM pigs compared with the CON-NEG pigs. Hot carcass weight was 3.6 kg greater for the I-MALE pigs compared with the CON-NEG pigs and 1.6 kg greater for the I-FEM pigs compared with the CON-NEG pigs. The results would suggest that removing nutrients during the post-second dose period of GnRF immunization does not negatively affect growth performance or carcass characteristics, while both I-MALE and I-FEM pigs are more efficient and heavier when compared with traditional mixed sex pigs.