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

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Abstract 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.