An experiment was conducted to determine the quantitative relationships between standardized total tract digestible P (STTD P) and total Ca intakes with their retention and excretion by growing pigs fed corn-soybean meal diets. Forty-eight crossbred barrows (BW = 22.7 ± 2.9 kg) were allotted to 1 of 8 diets, housed individually in pens for 3 wk, and then moved to metabolism crates and allowed 4 d for adaptation and 5 d for collection of urine and fecal samples. Eight corn-soybean meal diets were formulated for similar NE, fat, and AA concentrations but to increase the STTD P from 0.16 to 0.62% using monocalcium phosphate. Dietary treatments were formulated for a constant Ca:STTD P ratio (2.2:1). The STTD P intake increased (P < 0.001) from 64 to 242% of the daily requirement (4.59 g/d of STTD P). Fecal and total excretion of P and Ca were linearly associated with mineral intake (P < 0.001). Constant urinary P excretion of 0.03 g/d P was observed, but at 4.96 g/d of STTD P intake, the urinary P excretion increased (P < 0.001). In contrast, Ca excretion in urine decreased (P < 0.001) with Ca intake, but constant excretion of 0.40 g/d Ca was reached at 17.97 g/d of Ca intake. The daily intakes of STTD P and Ca moderately explained

A total of 2,156 weaned pigs (6.75 ± 0.11 kg BW) were used in a 42-d study to evaluate whether improvements in growth performance associated with super-dosing phytase can be explained by the complete dephosphorylation of phytate and liberation of inositol. Two phytase doses (0 and 2,500 FTU/kg) and 3 inositol concentrations (0%, 0.15%, and 0.30%) were combined to create 6 dietary treatments in a 2 × 3 factorial arrangement. Pigs were fed a 3-phase feeding program, with periods being 10, 10, and 22 d, respectively. Blood samples were collected on days 0, 21, and 42 from a subset of 48 pigs to analyze mineral and myo-inositol concentrations. During Phase 1, super-dosing phytase tended to improve ADG compared with pigs fed diets without phytase (P = 0.09). Increasing concentrations of inositol improved the efficiency of gain in pigs fed diets without phytase (1,022.1, 1,040.9, and 1,089.2 g/kg), but not diets with phytase (1,102.2, 1,087.2, and 1,076.2 g/kg), and this improvement was equivalent to that observed with super-dosing phytase in the absence of inositol (interaction, P = 0.015). During Phase 2, super-dosing phytase improved ADG (P = 0.001), resulting in heavier BW (P = 0.007). During Phase 3 and overall, inositol supplementation increased ADG and ADFI in a quadratic manner (P < 0.10), with the highest ADG and ADFI observed for pigs fed 0.15% of inositol. Super-dosing phytase increased serum Zn on day 21, but not on day 42 (interaction, P = 0.008), increased serum Cu (P = 0.01), but decreased serum Fe (P = 0.02). Plasma myo-inositol increased linearly from 66.9 to 97.1 and 113.2 nmol/mL with increasing inositol (P < 0.001). When plasma myo-inositol was analyzed within the subgroup of pigs fed diets without added inositol, super-dosing phytase increased plasma myo-inositol from 57.81 to 76.05 nmol/mL (0 and 2,500 FTU/kg, respectively; P = 0.05). Results demonstrate that exogenous inositol improved efficiency of gain in weaned pigs to the same level as that observed with super-dosing phytase, but this occurred only during the first 10 d of the nursery period. This suggests that the improvement in efficiency of growth when applying super-dosing phytase could be linked, in part, to complete dephosphorylation of phytate and liberation of myo-inositol, and that myo-inositol had a greater metabolic impact in piglets immediately after weaning. Consequently, myo-inositol may be a conditionally essential nutrient for young pigs during weaning stress, but further research is needed to prove this hypothesis.

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 × 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 ( < 0.05). Entire males and G had the lowest overall ADFI, and PC had the greatest, with IC being intermediate ( < 0.05). Entire males were overall the most efficient, followed by IC, with PC and G being the least efficient ( < 0.05). Immunological castrates and EM had similar nitrogen retention (g/d) for the first 2 collection periods ( > 0.05). In the third collection period, nitrogen retention of IC was similar to that of both EM and PC ( < 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 ( > 0.05). However, G retained less P than EM or IC ( < 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 ( > 0.05). The jowl IV was the lowest in IC and PC and highest in EM, with G being similar to all sexes ( < 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.

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The main objective of this experiment was to determine the standardized ileal digestible (SID) Lys requirement of immunologically castrated (IC) and physically castrated (PC) male pigs during 3 growth phases. An additional objective was to compare the ADFI of PC and IC after the second anti-gonadotropin releasing factor (GnRF) injection. Three hundred male pigs (PIC 359 × C29), 150 each of IC and PC, were allotted to 1 of 5 treatments: 80, 90, 100, 110, or 120% of the estimated Lys requirement using the modeling program. Pigs remained on the same treatment throughout each of the 3 phases. Lysine requirements were determined at 3 stages of growth starting at a BW of 30.0 ± 0.8, 64.7 ± 1.4, and 111.9 ± 1.9 kg for IC and 32.4 ± 0.6, 69.8 ± 1.0, and 114.5 ± 1.3 kg for PC. Anti-GnRF injections were administered to IC at 11.5 and 19 wk (average BW = 96.3 ± 1.8 kg) of age. The one-slope broken line regression and quadratic plateau models were used, and the best model was selected based on the Akaike information criterion. The IC SID Lys requirements based on ADG were 1.03, 0.97, and 0.55% and for G:F, the requirements were 0.99, 0.72, and 0.55% for phases 1, 2, and 3, respectively. For PC, the SID Lys requirements based on ADG were 0.86, 0.62, and 0.47% and for G:F were 0.86, 0.58, and 0.47% for phases 1, 2, and 3, respectively. Immunologically castrated pigs had greater SID Lys requirements for phases 1 and 2 compared to PC (0.17 and 0.35% points greater for ADG and 0.13 and 0.14% points greater for G:F for phases 1 and 2, respectively). After the second injection, when IC pigs are believed to become physiologically more similar to PC pigs, the SID Lys requirements continue to be greater for IC (0.55 vs. 0.47% for both ADG and G:F). The ADFI of IC increased 4 d after the second injection relative to PC. By 2 wk post second injection, the ADFI of IC exceeded that of PC ( < 0.05). Adopting immunological castration as a management tool requires an understanding that IC need to be fed differently compared to PC, to maximize growth performance. Immunologically castrated pigs have a greater SID Lys requirement throughout the grower and finishing periods compared to the PC.