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This study investigated the impact of calcium (Ca) and vitamin D supplements on bone metabolism, bone measurement, lameness, and selection rate in gilts fed five dietary treatments. Two Ca levels (6.85/6.42 [adequate; ACa] or 8.99/8.56 [high; HCa] g/kg) were combined with either 856 IU/kg vitamin D3 (Danish feeding standards; adequate; AD3) or 50 μg/kg 25-hydroxyvitamin D3 (high; HHyD) to create ACaAD3, HCaAD3, ACaHHyD, and HCaHHyD diets. The values 6.85/6.42 and 8.99/8.56 g/kg correspond to adequate and high Ca supply for gilts weighing 32 to 100 and 100 to 180 kg body weight (BW), respectively. The fifth diet was a combination of HCa and 2,000 IU/kg vitamin D3 (high; HD3) to create HCaHD3. Two hundred gilts were phase fed the dietary treatments from 32 to 100 and 100 to 180 kg BW until they were slaughtered, either at 100 or 180 kg BW. The gilts were weighed fortnightly, and plasma and urine samples were collected at 100 and 180 kg BW. At slaughter, the 2nd and 3rd metacarpal bones were collected for bone parameters measurements. Lameness and selection rate were assessed within the last 7 d at 100 and 180 kg BW. Dietary treatments did not affect gilts' growth performance and plasma concentration of Ca, but urinary concentration of Ca was greater in HCa-supplemented gilts at both 100 (P = 0.003) and 180 (P = 0.05) kg BW. Plasma concentration of vitamin D3 (P < 0.001) and 25-hydroxyvitamin D3 (P < 0.001) showed dose-dependent responses at both 100 and 180 kg BW. Bone-specific alkaline phosphatase was greater (P = 0.02) in the plasma sample collected at 180 kg BW in gilts fed the HCaHD3 diet and tended to be greater in gilts fed the ACaAD3 diet (P = 0.06). The bone ash content (P = 0.02) was greater in gilts fed the HCaAD3 diet and slaughtered at 100 kg BW compared with gilts fed the ACaAD3 and ACaHHyD diets. However, bone weight, length, thickness, dry matter, and mineral content did not differ among the dietary treatments at both 100 and 180 kg BW (P > 0.05). Neither lameness nor selection rate was affected by the dietary treatments. The average daily gain of gilts weighing 32 to 100 and 100 to 180 kg BW showed a positive correlation with bone strength (r = 0.37; P < 0.001) and bone ash content (r = 0.24; P = 0.02), respectively. In conclusion, higher Ca and vitamin D3 supplementation slightly increased bone ash content but had no effect on lameness or selection rate of the gilts compared to those fed according to the Danish nutrient standards., (© The Author(s) 2024. Published by Oxford University Press on behalf of the American Society of Animal Science.)

A study evaluated the effects of adding multi-enzyme mixture to diets deficient in net energy (NE), standardized ileal digestible (SID) amino acids (AA), standardized total tract digestible (STTD) P, and Ca on growth performance, bone mineralization, nutrient digestibility, and fecal microbial composition of grow-finish pigs. A total of 300 pigs (initial body weight [BW] = 29.2 kg) were housed by sex and BW in 45 pens of 7 or 6 pigs and fed 5 diets in a randomized complete block design. Diets were positive control (PC), and negative control 1 (NC1) or negative control 2 (NC2) without or with multi-enzyme mixture. The multi-enzyme mixture supplied at least 1,800, 1,244, 6,600, and 1,000 units of xylanase, β -glucanase, arabinofuranosidase, and phytase per kilogram of diet, respectively. The PC was adequate in all nutrients. The NC1 diet had lower content NE, SID AA, STTD P, and Ca than PC diet by about 7%, 7%, 32%, and 13%, respectively. The NC2 diet had lower NE, SID AA, STTD P, and Ca than PC diet by 7%, 7%, 50%, and 22%, respectively. The diets were fed in four phases based on BW: Phase 1: 29–45 kg, Phase 2: 45–70 kg, Phase 3: 70–90 kg, and Phase 4: 90–120 kg. Nutrient digestibility, bone mineralization, and fecal microbial composition were determined at the end of Phase 1. Pigs fed PC diet had greater (P < 0.05) overall G:F than those fed NC1 diet or NC2 diet. Multi-enzyme mixture increased (P < 0.05) overall G:F, but the G:F of the multi-enzyme mixture-supplemented diets did not reach (P < 0.05) that of PC diet. Multi-enzyme mixture tended to increase (P = 0.08) femur breaking strength. Multi-enzyme mixture increased (P < 0.05) the ATTD of GE for the NC2 diet, but unaffected the ATTD of GE for the NC1 diet. Multi-enzyme mixture decreased (P < 0.05) the relative abundance of the Cyanobacteria and increased (P < 0.05) relative abundance of Butyricicoccus in feces. Thus, the NE, SID AA, STTD P, and Ca could be lowered by about 7%, 7%, 49%, and 22%, respectively, in multi-enzyme mixture-supplemented diets without negative effects on bone mineralization of grow-finish pigs. However, multi-enzyme mixture supplementation may not fully restore G:F of the grow-finish pigs fed diets that have lower NE and SID AA contents than recommended by 7%. Since an increase in content of Butyricicoccus in intestine is associated with improved gut health, addition of the multi-enzyme mixture in diets for pigs can additionally improve their gut health. [ABSTRACT FROM AUTHOR]

Pigs (n = 192) from 64 commercial sites across 14 production facilities in the Midwest USA were used to evaluate baseline biological measurements used to determine bone mineralization in pigs. There were 3 pigs selected from each site representing: 1) a clinically normal pig, 2) a pig with evidence of clinical lameness, and 3) a pig with a history of recent low feed intake within a hospital pen (sick pig). Pigs ranged in age from nursery to market weight, with the three pigs sampled from each site representing the same phase of production. For each pig, blood, urine, and the right and left metacarpal, fibula, 2nd rib, and 10th rib were collected and analyzed. Serum was analyzed for Ca, P, and 25(OH)D3 as part of the serum chemistry profile. and. Each bone was measured for bone density and ash (non-defatted and defatted methods). Bone density was measured on each bone based on Archimedes principle. For defatted bone ash, all bones were cleaned of tissue and then placed in Soxhlet extractors containing petroleum ether for 7 days as a means of removing water and fat. Bones were then dried at 105°C for 7 days and then ashed in a muffle furnace at 600°C for 24 h. Healthy pigs had increased (P < 0.05) serum calcium and 25OHD3 compared with sick pigs, with lame pigs intermediate (Table). Healthy pigs also had increased (P < 0.05) serum phosphorus compared with sick and lame pigs, with no differences between the sick and lame pigs. For defatted bone ash and bone density, there was a pig type × bone interaction (P < 0.001). There were no differences between pig types for the fibulas, 2nd rib, and 10th rib, but metacarpals from healthy pigs had greater bone ash compared with sick pigs, with lame pigs intermediate. For bone density, healthy and lame pigs had greater (P < 0.05) bone density than sick pigs for the metacarpals and fibulas, with no difference observed for the ribs. In summary, there appear to be differences in serum analysis between a healthy, lame, and sick pig. Differences in bone mineralization between pig types were observed in the metacarpal and fibula, but not ribs. The metacarpal appears to be the most sensitive bone to detect differences in bone mineralization between pig types. There was also considerable range in values within pig type across production sites. [ABSTRACT FROM AUTHOR]

Pigs (n = 350; initial body weight = 11.9 ± 0.56 kg) were used to evaluate the effects of different bones and analytical methods on the assessment of rib bone mineralization response to dietary P and vitamin D in nursery pigs. Currently, there is little information available describing the effect of rib location (2nd through 10th) on measures of bone mineralization including density and ash. Pens of pigs (5 pigs/pen) were randomized to 6 dietary treatments in a randomized complete block design with 10 pens/treatment. Pens of pigs were assigned dietary treatments consisting of: 1) P at 0.19% STTD P (deficient); 2) P at 0.33% STTD P (NRC requirement) using monocalcium phosphate; 3) P at 0.33% STTD P using monocalcium phosphate and phytase; 4) P at 0.44% STTD P (industry level) using monocalcium phosphate, phytase, no vitamin D; 5) diet 4 with vitamin D (1,653 IU/kg), and 6) diet 5 with additional 2,000 IU/kg 25(OH)D3 (HyD). After feeding diets for 28-days, eight pigs/treatment were harvested for bone analysis. The 2nd, 3rd, 5th, 7th, and 10th ribs were collected from each pig and analyzed for bone density and non-defatted bone ash. All bones were cleaned of tissue and then dried at 105°C for 7 d and then ashed in a muffle furnace at 600°C for 24 h. Bone density was measured on each bone based on Archimedes principle. There was no interaction between bone and dietary treatment for bone density and non-defatted bone ash (P > 0.05; Table). Therefore, interpretation of results will focus on the effect of bone and treatment on measures of mineralization. Pigs fed deficient P (0.19%) had less bone density and ash percent compared with treatments fed NRC and industry levels of P. For bone density, there was a significant main effect of bone (P = 0.001), with the 10th rib having greater bone density than all other treatments and the 3rd rib having greater bone density than the 5th rib. Bone density of the 2nd and 7th ribs did not differ (P >0.05) from either the 3rd or 5th ribs. For non-defat bone ash, 10th rib had the greatest (P < 0.05) bone ash, followed by the 2nd rib which was greater (P < 0.05) than the 3rd rib, with the 5th and 7th ribs having the least non-defat bone ash percent. In summary, bone density and ash responses varied depending on the bone being measured. When measuring all of the bones, the 10th rib has the greatest value for bone density and bone ash percent, while the 5th rib has the least value for both bone density and bone ash percent compared with the rest of the bones analyzed. These results can help guide diagnostic investigations and aid in comparing results across different bones used to measure bone mineralization. [ABSTRACT FROM AUTHOR]

A total of 882 pigs (PIC TR4 × [Fast LW × PIC L02]; initially 33.2 ± 0.31 kg) were used in a 112-d study to evaluate the effects of different bones and analytical methods on the assessment of bone mineralization response to changes in dietary P, phytase, and vitamin D in growing pigs. Pens of pigs (20 pigs per pen) were randomized to one of five dietary treatments with nine pens per treatment. Dietary treatments were designed to create differences in bone mineralization and included: 1) P at 80% of NRC (2012) standardized total tract digestible (STTD) P requirement, 2) NRC STTD P with no phytase, 3) NRC STTD P with phytase providing an assumed release of 0.14% STTD P from 2,000 FYT/kg, 4) high STTD P (128% of the NRC P) using monocalcium phosphate and phytase, and 5) diet 4 with additional vitamin D3 from 25(OH)D3. On day 112, one pig per pen was euthanized for bone, blood, and urine analysis. Additionally, 11 pigs identified as having poor body condition which indicated a history of low feed intake (unhealthy) were sampled. There were no differences between treatments for final body weight, average daily gain, average daily feed intake, gain to feed, or bone ash measurements (treatment × bone interaction) regardless of bone ash method. The response to treatment for bone density and bone mineral content was dependent upon the bone sampled (density interaction, P = 0.053; mineral interaction, P = 0.078). For 10th rib bone density, pigs fed high levels of P had increased (P < 0.05) bone density compared with pigs fed NRC levels with phytase, with pigs fed deficient P, NRC levels of P with no phytase, and high STTD P with extra 25(OH)D3 intermediate, with no differences for metacarpals, fibulas, or 2nd ribs. Pigs fed extra vitamin D from 25(OH)D3 had increased (P < 0.05) 10th rib bone mineral content compared with pigs fed deficient P and NRC levels of P with phytase, with pigs fed industry P and vitamin D, and NRC P with monocalcium intermediate. Healthy pigs had greater (P < 0.05) serum Ca, P, vitamin D concentrations, and defatted bone ash than those unhealthy, with no difference between the two health statuses for non-defatted bone ash. In summary, differences between bone ash procedures were more apparent than differences between diets. Differences in bone density and mineral content in response to dietary P and vitamin D were most apparent with 10th ribs., (© The Author(s) 2024. Published by Oxford University Press on behalf of the American Society of Animal Science. All rights reserved. For commercial re-use, please contact reprints@oup.com for reprints and translation rights for reprints. All other permissions can be obtained through our RightsLink service via the Permissions link on the article page on our site—for further information please contact journals.permissions@oup.com.)

Pigs from 64 commercial sites across 14 production systems in the Midwest United States were evaluated for baseline biological measurements used to determine bone mineralization. There were three pigs selected from each commercial site representing: 1) a clinically normal pig (healthy), 2) a pig with evidence of clinical lameness (lame), and 3) a pig from a hospital pen that was assumed to have recent low feed intake (unhealthy). Pigs ranged in age from nursery to market weight, with the three pigs sampled from each site representing the same age or phase of production. Blood, urine, metacarpal, fibula, 2nd rib, and 10th rib were collected and analyzed. Each bone was measured for density and ash (defatted and non-defatted technique). A bone × pig type interaction (P < 0.001) was observed for defatted and non-defatted bone ash and density. For defatted bone ash, there were no differences among pig types for the fibulas, 2nd rib, and 10th rib (P > 0.10), but metacarpals from healthy pigs had greater (P < 0.05) percentage bone ash compared to unhealthy pigs, with the lame pigs intermediate. For non-defatted bone ash, there were no differences among pig types for metacarpals and fibulas (P > 0.10), but unhealthy pigs had greater (P < 0.05) non-defatted percentage bone ash for 2nd and 10th ribs compared to healthy pigs, with lame pigs intermediate. Healthy and lame pigs had greater (P < 0.05) bone density than unhealthy pigs for metacarpals and fibulas, with no difference observed for ribs (P > 0.10). Healthy pigs had greater (P < 0.05) serum Ca and 25(OH)D3 compared to unhealthy pigs, with lame pigs intermediate. Healthy pigs had greater (P < 0.05) serum P compared to unhealthy and lame pigs, with no differences between the unhealthy and lame pigs. Unhealthy pigs excreted significantly more (P < 0.05) P and creatinine in the urine compared to healthy pigs with lame pigs intermediate. In summary, there are differences in serum Ca, P, and vitamin D among healthy, lame, and unhealthy pigs. Differences in bone mineralization among pig types varied depending on the analytical procedure and bone, with a considerable range in values within pig type across the 14 production systems sampled., (© The Author(s) 2024. Published by Oxford University Press on behalf of the American Society of Animal Science. All rights reserved. For commercial re-use, please contact reprints@oup.com for reprints and translation rights for reprints. All other permissions can be obtained through our RightsLink service via the Permissions link on the article page on our site—for further information please contact journals.permissions@oup.com.)

This study evaluated the effect of dietary calcium (Ca) levels and deoxynivalenol (DON) contamination on Ca and phosphorus (P) utilization and bone mineralization in piglets. During an initial 13-d depletion phase, 64 piglets (15.7 ± 0.7 kg) received a control (DON-) or DON-contaminated treatment (DON+, 2.7 mg DON/kg) with either a low Ca (Ca-, 0.39%) or normal Ca level (Ca+, 0.65%) with a constant digestible P level (0.40%). A second group of 16 piglets received DON- or DON+ treatments for 9 d for gene expression analysis. During the subsequent 14-d repletion phase, all piglets were fed a Ca+ DON- diet containing 0.65% Ca and 0.35% digestible P without DON. After 5 d of the depletion phase, the absorption of P (DON × Ca; P < 0.05) and Ca was increased by the Ca- (P < 0.01) and DON+ (P < 0.01) diet. After 13 d, feed conversion ratio (P < 0.01) and average daily feed intake (P = 0.06) tended to decrease with the Ca- diet. The bone mineral content (BMC) gain was decreased by Ca, especially with Ca- DON + (DON × Ca, P < 0.05). The P absorption was increased by Ca- DON + (DON × Ca, P < 0.01), although the P retention efficiency was only increased by Ca+ DON + (DON × Ca, P < 0.001). The absorption of Ca was increased by DON+ (P < 0.001), and the Ca efficiency was increased by Ca- DON- (DON × Ca, P < 0.01). After 9 d, the gene expression of intestinal claudin 12 (P < 0.01) and CYP24A1 (P < 0.05), femur cortical RANKL (P < 0.05) and OPG (P = 0.06), and renal calbindin D9K (P < 0.05) and Klotho (P = 0.07) were decreased by DON+. The Ca (P = 0.06) and magnesium (P < 0.01) concentrations were decreased by DON+, and the Ca (P = 0.06) and P digestibility (P < 0.01) were increased. After the repletion phase, Ca- piglets recovered their BMC deficit, but not those receiving DON+ (DON × Ca; P = 0.06). The Ca (P < 0.05) and P (P = 0.06) retention efficiency tended to increase with Ca-. The absorption of Ca and P was increased by Ca- and DON+ (DON × Ca, P < 0.05). The results show that piglets increased their Ca and P utilization efficiency, allowing them to recover the BMC deficit caused by Ca-, but not when the piglets were exposed to DON. Pigs previously receiving Ca-deficient diet with DON still have lower body Ca and P, leading to elevated calcitriol concentrations and enhanced Ca and P intestinal absorption. The fact that DON decreased the expression of genes implicated in Ca intestinal and renal transport and P excretion after 9 d can potentially explain the reduced plasma Ca concentration., (© The Author(s) 2024. Published by Oxford University Press on behalf of the American Society of Animal Science.)

A study was conducted to determine the standardized total tract digestible phosphorus (STTD P) requirement for 24- to 130-kg finishing pigs housed under commercial conditions. A total of 1,130 barrows and gilts (PIC 359 × 1050, Hendersonville, TN; initially 24.2 kg) were used, with 26 to 27 pigs per pen with 7 replicates per treatment. Pens of pigs were allotted to treatments in a randomized complete block design with body weight (BW) as the blocking factor. The dietary treatments were fed in 4 phases and were formulated to contain 80%, 90%, 100%, 115%, 130%, and 150% of the National Research Council (NRC) requirement estimate for finishing pigs within each phase. Weight ranges for each phase were: 27 to 49, 49 to 76, 76 to 90, and 90 to 130 kg. Treatments were achieved by increasing the amount of monocalcium phosphate at the expense of corn in the diet with no added phytase. All diets were formulated to contain a similar 1.14:1 to 1.16:1 total Ca:P ratio across treatments in all phases. Increasing STTD P resulted in a quadratic response (P < 0.05) in average daily gain (ADG), gain-to-feed ratio (G:F), and final BW. The greatest improvement was observed with STTD P at 130% of NRC for ADG and final BW and at 115% STTD P for G:F. Average daily feed intake increased linearly (linear, P < 0.05) with the inclusion of STTD P. Increasing STTD P resulted in an increase (quadratic, P < 0.05) in hot carcass weight (HCW) and carcass ADG with the greatest response observed with STTD P at 130% of NRC. There was a marginally significant response (quadratic, P < 0.10) in carcass G:F, with the greatest improvement with STTD P at 115% of NRC. Carcass yield decreased (linear, P < 0.05) with increasing STTD P, while there was a marginally significant (linear, P < 0.10) decrease in backfat and increase in fat-free lean. At the end of the study, a metacarpal was collected and analyzed for bone ash. Increasing STTD P resulted in an increase (linear, P < 0.05) in bone ash weight and percentage ash. For ADG and G:F, the quadratic model demonstrated the best fit. The maximum response in ADG and G:F was estimated at 122% and 116% of NRC STTD P, respectively. The broken-line linear model best fit the data for percentage bone ash, with a plateau achieved at 131% of the NRC STTD P. In conclusion, the estimated STTD P requirement of 24 to 130 kg ranged from 116% to 131% of the NRC publication (2012) requirement estimate. [ABSTRACT FROM AUTHOR]

Two experiments were conducted to determine the effects of calcium to phosphorus (Ca:P) ratio in diets adequate in standardized total tract digestible (STTD) P on performance of 26- to 127-kg pigs fed diets with or without phytase. Pens of pigs (n = 1,134 in Exp. 1 and n = 1,215 in Exp. 2, initially 26.3 and 25.3 kg) were blocked by body weight (BW) and allotted to treatments in a randomized complete block design. There were 27 pigs per pen with 7 and 9 replicates per treatment in Exp. 1 and Exp. 2, respectively. Treatments were formulated to contain 0.75:1, 1.00:1, 1.25:1, 1.50:1, 1.75:1, and 2.00:1 analyzed Ca:P ratios in Exp. 1, and 0.75:1, 1.00:1, 1.25:1, 1.50:1, and 2.00:1 analyzed Ca:P ratios in Exp. 2. These correspond to a range of 0.96:1 to 2.67:1 and 0.95:1 to 2.07:1 STTD Ca:STTD P ratios in Exp. 1 and Exp. 2, respectively. Experiment 2 diets contained 1,000 phytase units of Ronozyme HiPhos 2500 (DSM Nutritional Products, Inc. Parsippany, NJ) with release values of 0.132% STTD P, 0.144% total Ca, and 0.096% STTD Ca. Diets contained 122% of NRC (2012) STTD P estimates for the weight range across 4 phases. In Exp. 1, increasing Ca:P ratio increased (quadratic, P < 0.05) average daily gain (ADG) and average daily feed intake (ADFI). Feed efficiency (G:F) worsened (quadratic, P < 0.05) at the highest ratio. Hot carcass weight (HCW) and bone ash increased (quadratic, P < 0.05) while carcass yield decreased (linear, P < 0.10) with increasing Ca:P ratio. The maximum responses in ADG, HCW, and bone ash were estimated at 1.38:1, 1.25:1, and 1.93:1 analyzed Ca:P and at 1.82:1, 1.64:1, and 2.57:1 STTD Ca:STTD P, respectively. In Exp. 2, increasing Ca:P ratio increased (quadratic, P < 0.05) ADG and bone ash, and improved G:F (linear, P < 0.05). There was a quadratic increase (P < 0.05) in HCW and decrease in carcass yield (P < 0.10). The maximum responses in ADG, HCW, and bone ash were estimated at 1.63:1, 1.11:1 to 1.60:1, and 1.25:1 analyzed Ca:P and at 1.75:1, 1.28:1 to 1.71:1, and 1.40:1 STTD Ca:STTD P, respectively. Expressing ADG on a STTD Ca:STTD P basis provided a more consistent estimate of the ideal Ca:P ratio among the 2 studies than analyzed Ca to analyzed P ratio. A STTD Ca:STTD P ratio between 1.75:1 to 1.82:1 can be used for 26- to 127-kg pigs that are fed diets adequate in STTD P with or without added phytase to maximize growth rate without reducing bone ash. [ABSTRACT FROM AUTHOR]

A study was conducted to determine the standardized total tract digestible phosphorus (STTD P) requirement for 24- to 130-kg finishing pigs housed under commercial conditions. A total of 1,130 barrows and gilts (PIC 359 × 1050, Hendersonville, TN; initially 24.2 kg) were used, with 26 to 27 pigs per pen with 7 replicates per treatment. Pens of pigs were allotted to treatments in a randomized complete block design with body weight (BW) as the blocking factor. The dietary treatments were fed in 4 phases and were formulated to contain 80%, 90%, 100%, 115%, 130%, and 150% of the National Research Council (NRC) requirement estimate for finishing pigs within each phase. Weight ranges for each phase were: 27 to 49, 49 to 76, 76 to 90, and 90 to 130 kg. Treatments were achieved by increasing the amount of monocalcium phosphate at the expense of corn in the diet with no added phytase. All diets were formulated to contain a similar 1.14:1 to 1.16:1 total Ca:P ratio across treatments in all phases. Increasing STTD P resulted in a quadratic response (P < 0.05) in average daily gain (ADG), gain-to-feed ratio (G:F), and final BW. The greatest improvement was observed with STTD P at 130% of NRC for ADG and final BW and at 115% STTD P for G:F. Average daily feed intake increased linearly (linear, P < 0.05) with the inclusion of STTD P. Increasing STTD P resulted in an increase (quadratic, P < 0.05) in hot carcass weight (HCW) and carcass ADG with the greatest response observed with STTD P at 130% of NRC. There was a marginally significant response (quadratic, P < 0.10) in carcass G:F, with the greatest improvement with STTD P at 115% of NRC. Carcass yield decreased (linear, P < 0.05) with increasing STTD P, while there was a marginally significant (linear, P < 0.10) decrease in backfat and increase in fat-free lean. At the end of the study, a metacarpal was collected and analyzed for bone ash. Increasing STTD P resulted in an increase (linear, P < 0.05) in bone ash weight and percentage ash. For ADG and G:F, the quadratic model demonstrated the best fit. The maximum response in ADG and G:F was estimated at 122% and 116% of NRC STTD P, respectively. The broken-line linear model best fit the data for percentage bone ash, with a plateau achieved at 131% of the NRC STTD P. In conclusion, the estimated STTD P requirement of 24 to 130 kg ranged from 116% to 131% of the NRC publication (2012) requirement estimate. [ABSTRACT FROM AUTHOR]

Two experiments were conducted to determine the effects of calcium to phosphorus (Ca:P) ratio in diets adequate in standardized total tract digestible (STTD) P on performance of 26- to 127-kg pigs fed diets with or without phytase. Pens of pigs (n = 1,134 in Exp. 1 and n = 1,215 in Exp. 2, initially 26.3 and 25.3 kg) were blocked by body weight (BW) and allotted to treatments in a randomized complete block design. There were 27 pigs per pen with 7 and 9 replicates per treatment in Exp. 1 and Exp. 2, respectively. Treatments were formulated to contain 0.75:1, 1.00:1, 1.25:1, 1.50:1, 1.75:1, and 2.00:1 analyzed Ca:P ratios in Exp. 1, and 0.75:1, 1.00:1, 1.25:1, 1.50:1, and 2.00:1 analyzed Ca:P ratios in Exp. 2. These correspond to a range of 0.96:1 to 2.67:1 and 0.95:1 to 2.07:1 STTD Ca:STTD P ratios in Exp. 1 and Exp. 2, respectively. Experiment 2 diets contained 1,000 phytase units of Ronozyme HiPhos 2500 (DSM Nutritional Products, Inc. Parsippany, NJ) with release values of 0.132% STTD P, 0.144% total Ca, and 0.096% STTD Ca. Diets contained 122% of NRC (2012) STTD P estimates for the weight range across 4 phases. In Exp. 1, increasing Ca:P ratio increased (quadratic, P < 0.05) average daily gain (ADG) and average daily feed intake (ADFI). Feed efficiency (G:F) worsened (quadratic, P < 0.05) at the highest ratio. Hot carcass weight (HCW) and bone ash increased (quadratic, P < 0.05) while carcass yield decreased (linear, P < 0.10) with increasing Ca:P ratio. The maximum responses in ADG, HCW, and bone ash were estimated at 1.38:1, 1.25:1, and 1.93:1 analyzed Ca:P and at 1.82:1, 1.64:1, and 2.57:1 STTD Ca:STTD P, respectively. In Exp. 2, increasing Ca:P ratio increased (quadratic, P < 0.05) ADG and bone ash, and improved G:F (linear, P < 0.05). There was a quadratic increase (P < 0.05) in HCW and decrease in carcass yield (P < 0.10). The maximum responses in ADG, HCW, and bone ash were estimated at 1.63:1, 1.11:1 to 1.60:1, and 1.25:1 analyzed Ca:P and at 1.75:1, 1.28:1 to 1.71:1, and 1.40:1 STTD Ca:STTD P, respectively. Expressing ADG on a STTD Ca:STTD P basis provided a more consistent estimate of the ideal Ca:P ratio among the 2 studies than analyzed Ca to analyzed P ratio. A STTD Ca:STTD P ratio between 1.75:1 to 1.82:1 can be used for 26- to 127-kg pigs that are fed diets adequate in STTD P with or without added phytase to maximize growth rate without reducing bone ash. [ABSTRACT FROM AUTHOR]

A pig trial was performed to analyze the effect of different dietary phytase levels on bone mineralization and ileal phytate degradation in 2 different growing stages. Fifty-six postweaned piglets were fed 4 diets differing in P, Ca, Na, and phytase contents. Diets contained either recommended (positive control [PC]) or reduced (negative control [NC]) mineral levels and phytase was added to NC diets at 500 or 2,000 phytase units/kg feed (NC500 and NC2000, respectively). At d 42 and 98, samples (n = 7) were taken for analyses in rib bones (Ca, P, Fe, Mg, Mn, Se, and Zn) and in ileal digesta (myo-inositol phosphates [myo-inositol hexakisphosphate {InsP6}, myo-inositol pentakisphosphate {InsP5}, myo-inositol tetrakisphosphate, and myo-inositol trisphosphate] were analyzed by high-pressure ion chromatography and inositol was analyzed by HPLC). Data were analyzed by ANOVA and means were separated by the Tukey's test with significance set at P < 0.05. Dietary mineral reduction reduced bone mineral content, except in ribs collected at d 42 (P < 0.05). The NC500 diet compared with the NC improved all minerals except Se in ribs (d 98; P < 0.05). The higher phytase dose (NC2000) restored nearly all bone minerals to the level of PC pigs (P > 0.05). Phytate degradation up to the proximal ileum was not influenced by dietary mineral level (PC compared with NC, P > 0.05) whereas phytase reduced InsP6 and InsP5 levels in ileal digesta (P < 0.05 for NC and PC at both phytase application rates) with the lowest levels seen in NC2000 (d 98; P < 0.05). The efficient phytate degradation could explain the improvements in bone mineralization, especially at high phytase application level, probably due to improved mineral availability. [ABSTRACT FROM AUTHOR]

A trial was conducted with 144 weaned pigs (26 d of age) to evaluate a newly developed bacterial 6-phytase (Enzyme Commission number [EC] 3.1.3.26) at different dose levels. Pigs were kept in 48 pens and fed 6 diets consisting of a positive control (PC; adequate in Ca and P), a negative control (NC; limiting in Ca and P), and the same NC supplemented with 125, 250, 500, or 1,000 phytase units (FTU)/kg of the phytase under test. Piglets' performance (for 42 d) and Ca and P apparent total tract digestibilities (ATTD) were investigated using TiO2 as an indigestible marker. Mineralization of the left os metacarpale III from 8 piglets per treatment was also determined at d 48. Piglets on the PC and the phytase-supplemented diets had higher ADG and ADFI than those on the NC diet (P < 0.05). Phytase improved ATTD for P at all levels and for ash and Ca at levels above 250 FTU/kg compared with the NC (P < 0.05). The os metacarpale III of pigs fed the phytase diets had higher weight and ash content than those of pigs fed the NC (P < 0.05). Linear responses (P < 0.05) to phytase addition were observed for ADG, ADFI, and G:F; P, Ca and ash ATTD; and os metacarpale III weight and ash content. It is concluded that the novel 6-phytase strongly improves performance, Ca and P digestibility, and bone mineralization in piglets fed Ca- and P-limiting diets. [ABSTRACT FROM AUTHOR]

Pigs [n = 882; initial body weight (BW) of 33.2±0.31 kg] were used to evaluate the effects of different bones and analytical methods on assessment of bone mineralization response to dietary P, phytase, and vitamin D in growing-finishing pigs. Pens of pigs (20 pigs/pen) were completely randomized to 5 dietary treatments with 9 pens/treatment. After feeding diets for 112-d, nine pigs/treatment were harvested for bone analysis. Treatments were: 1) P at 80% of the NRC STTD P (deficient), 2) NRC STTD P using monocalcium phosphate, 3) NRC STTD P including phytase, 4) Industry P using monocalcium phosphate and phytase, 5) diet 4 with additional 2,000 IU/kg 25(OH)D3 (HyD). All diets contained vitamin D at 1,653 IU/kg. There were no significant differences for final BW, ADG, ADFI, G:F (P>0.10) or non-de-fat bone ash (bone ash×bone interaction, P>0.10). The response to treatment for bone density (Archimedes principle) and bone mineral content (DEXA) tended to depend on the bone (density×bone interaction, P=0.053; mineral density×bone interaction, P=0.157). There were no treatment differences (P>0.10) for bone density and bone mineral density between metacarpals, fibulas, and 2nd ribs. For 10th ribs, pigs fed industry levels of P had increased (P< 0.05) bone density compared with pigs fed NRC levels with phytase, with pigs fed deficient P, NRC P with no phytase, and excess vitamin D from HyD being intermediate. Pigs fed diets supplemented with HyD had increased bone mineral density in 10th ribs compared with pigs fed NRC levels of P with phytase, with pigs fed P deficient diets, industry P without HyD, and NRC P with monocalcium being intermediate. In summary, bone density and bone mineral content responses varied depending on the bone. Differences in bone density and mineral content in response to vitamin D and P were most apparent with the 10th ribs. [ABSTRACT FROM AUTHOR]

A total of 2,184 pigs (337 × 1,050, PIC; initially 12.4 ± 0.17 kg) were used in a 143-d study to evaluate the effects of feeding varying analyzed calcium to phosphorus ratios (Ca:P) at two standardized total tract digestible (STTD) phosphorus to net energy ratios (STTD P:NE). Pens of pigs (26 pigs per pen) were assigned to 1 of the 6 dietary treatments in a 2 × 3 factorial with main effects of STTD P:NE and Ca:P ratio. Diets consisted of two levels of STTD P:NE; High (1.80, 1.62, 1.43, 1.25, 1.10, and 0.99 g STTD P/Mcal NE from 11 to 22, 22 to 40, 40 to 58, 58 to 81, 81 to 104, and 104 to 129 kg, respectively); or Low (75% of the High levels), and three analyzed Ca:P ratios (0.90:1, 1.30:1, and 1.75:1). There were 14 pens per treatment. Diets were corn-soybean meal-based and contained a constant phytase concentration within each dietary phase with levels decreasing throughout the trial (phases 1 through 3, 500 FTU/kg, assumed release of 0.13% STTD P; phase 4, 400 FTU/kg, assumed release of 0.11% STTD P; phase 5, 290 FTU/kg, assumed release of 0.09% STTD P; and phase 6, 210 FTU/kg, assumed release of 0.07% STTD P). Overall, there was a Ca:P × STTD P:NE interaction (P < 0.05) observed for average daily gain (ADG), feed efficiency (G:F), final body weight (BW), hot carcass weight (HCW), bone mineral density, bone mineral content, and bone-breaking strength. When feeding Low STTD P:NE levels, increasing the analyzed Ca:P ratio decreased (linear, P < 0.001) ADG final BW, HCW, and tended to worsen G:F, bone mineral density, and bone mineral content (linear, P < 0.10). However, when feeding High STTD P:NE levels, increasing the analyzed Ca:P ratio significantly improved bone mineral content and bone mineral density (linear, P < 0.05), and tended to improve ADG and final BW (linear, P < 0.10) and G:F (quadratic P < 0.10). Additionally, increasing the analyzed Ca:P ratio worsened ADG, G:F, and bone mineralization with Low STTD P:NE but had marginal impacts when adequate STTD P:NE was fed., (© The Author(s) 2023. Published by Oxford University Press on behalf of the American Society of Animal Science. All rights reserved. For permissions, please e-mail: journals.permissions@oup.com.)

A total of 360 pigs (DNA 600 × 241, DNA; initially 11.9 ± 0.56 kg) were used in a 28-d trial to evaluate the effects of different bones and analytical methods on the assessment of bone mineralization response to dietary P, vitamin D, and phytase in nursery pigs. Pens of pigs (six pigs per pen) were randomized to six dietary treatments in a randomized complete block design with 10 pens per treatment. Dietary treatments were designed to create differences in bone mineralization and included: (1) 0.19% standardized total tract digestibility (STTD) P (deficient), (2) 0.33% STTD P (NRC [2012] requirement) using monocalcium phosphate, (3) 0.33% STTD P including 0.14% release from phytase (Ronozyme HiPhos 2700, DSM Nutritional Products, Parsippany, NJ), (4) 0.44% STTD P using monocalcium phosphate, phytase, and no vitamin D, (5) diet 4 with vitamin D (1,653 IU/kg), and (6) diet 5 with an additional 50 µg/kg of 25(OH)D3 (HyD, DSM Nutritional Products, Parsippany, NJ) estimated to provide an additional 2,000 IU/kg of vitamin D3. After 28 d on feed, eight pigs per treatment were euthanized for bone (metacarpal, 2nd rib, 10th rib, and fibula), blood, and urine analysis. The response to treatment for bone density and ash was dependent upon the bone analyzed (treatment × bone interaction for bone density, P = 0.044; non-defatted bone ash, P = 0.060; defatted bone ash, P = 0.068). Thus, the response related to dietary treatment differed depending on which bone (metacarpal, fibula, 2nd rib, or 10th rib) was measured. Pigs fed 0.19% STTD P had decreased (P < 0.05) bone density and ash (non-defatted and defatted) for all bones compared to 0.44% STTD P, with 0.33% STTD P generally intermediate or similar to 0.44% STTD P. Pigs fed 0.44% STTD P with no vitamin D had greater (P < 0.05) non-defatted fibula ash compared to all treatments other than 0.44% STTD P with added 25(OH)D3. Pigs fed diets with 0.44% STTD P had greater (P < 0.05) defatted second rib ash compared to pigs fed 0.19% STTD P or 0.33% STTD P with no phytase. In summary, bone density and ash responses varied depending on bone analyzed. Differences in bone density and ash in response to P and vitamin D were most apparent with fibulas and second ribs. There were apparent differences in the bone ash percentage between defatted and non-defatted bone. However, differences between the treatments remain consistent regardless of the analytic procedure. For histopathology, 10th ribs were more sensitive than 2nd ribs or fibulas for the detection of lesions., (© The Author(s) 2023. Published by Oxford University Press on behalf of the American Society of Animal Science. All rights reserved. For permissions, please e-mail: journals.permissions@oup.com.)

Improving dietary P utilization without modifying pig performance is crucial for production sustainability. A feeding program comprising three 28-d phases (20 to 40, 40 to 70, and 70 to 100 kg) was used to feed 72 pigs with an initial BW of 20 kg. The ability of the pigs to modify the digestive and metabolic utilization of P when fed either a control (CON) diet or a low-P (LOW) diet providing 40% less digestible P with a constant Ca:digestible P was studied using different sequences of dietary P and Ca restriction (i.e., depletion [LOW]) and recovery (i.e., repletion [CON]), namely CON-CON-CON, CON-CON-LOW, CONLOW- LOW, LOW-CON-CON, LOW-LOW-CON, and LOW-LOW-LOW. Bone mineral content (BMC) was measured in the lumbar region (L2-L4) by dual-energy X-ray absorptiometry at the beginning and end of each feeding phase. Total feces and urine were collected during phases 2 and 3. At the end of phase 1, BMC was lower in the LOW pigs than in the C pigs (29%; P < 0.001). During phase 2, the BMC gain was greater in the LOW-CON pigs than in the CON-CON pigs (16%; P < 0.001 ). During phase 3, the LOW-LOW-CON pigs absorbed 26% more Ca (P < 0.001) and retained 56% more BMC {P < 0.001 ) than the CON-CON-CON pigs did. Digestive and metabolic adaptations allowed the LOW-LOW-CON and LOW-CON-CON pigs to reach BMC similar to that of the CON-CON-CON pigs. These metabolic adaptations are promising, but practical applications of these results requires a better understanding of the underlying mechanisms to fine-tune the degree of depletion, pig age, and the duration of P and Ca depletion and repletion periods. [ABSTRACT FROM AUTHOR]

Presents abstracts of several studies on poultry nutrition. "Gluconeogenesis and Krebs Cycle Metabolism in 2-Day-Old Fed and Fasted Chicks," by N. E. Sunny, S. W. El-Kadi, M. Oba, S. L. Owens, R. Angel and B. J. Bequette; "Dietary Glycine Needs of Broiler Chicks," by A. Corzo, M. T. Kidd, D. J. Burnham, S. L. Branton and B. J. Kerr; "Comparison of Methionine Requirements Between an Alternative Slow-Growing Genotype and a Commercial Genotype During the Starter Period," by A. C. Fanatico, P. B. Pillai and J. L. Emmert.

Presents abstracts of several studies on pig diet and nutrition. "Response of Pigs to Dietary Phytase and Calcium-to-Phosphorus Ratio," by J. A. Jendza, R. N. Dilger, M. R. Bedford and O. Adeola; "Performance of Pigs Fed Grain Sorghum-Based Diets Supplemented With Phytase," by M. Cervantes and colleagues; "Effects of Dietary Antibiotics on Growth Performance in Pigs," by J. W. Hong et al.

There are several Cu sources in the market that have different effects on pigs. We hypothesized that supplementing therapeutic doses of Cu(I)oxide (Cu2O) in diets for growing pigs improves body weight (BW), bone mineralization, and reduces Cu accumulation in liver than supplementing pigs with Cu sulfate (CuSO4). Two-hundred growing pigs (initial BW: 11.5 ± 0.98 kg) were randomly allotted to 5 dietary treatments. Dietary treatments included the negative control (NC) diet without Cu supplementation, and 4 diets in which 125 or 250 mg/kg of Cu from CuSO4 or Cu2O were added to the NC diet. The experiment was divided into 4 phases. Pig weights were recorded on d 1 and at the end of each phase. Eight pigs per treatment were sacrificed last d of phases 1 and 4 to obtain samples of liver, spleen, and the right metacarpal. Pigs fed diets containing 250 mg/kg of Cu2O had greater (P < 0.05) BW at the end of phases 1 and 2 than pigs fed the NC diet, and tended (P < 0.10) to have greater BW at the end of phases 3 and 4 than pigs fed the other diets. Copper accumulation in liver and spleen increased with Cu dose, but at the end of phase 1, pigs fed 250 mg/kg CuSO4 had greater (P < 0.05) Cu concentration in liver and spleen than pigs fed 250 mg/kg Cu2O. Pigs fed diets containing 250 mg/kg Cu2O had greater (P < 0.05) quantities of bone ash and greater (P < 0.05) concentrations of Ca, P, and Cu in bone ash than pigs fed the NC diets or diets containing CuSO4. Therefore, supplementing diets for growing pigs with therapeutic doses of Cu2O improves BW and bone mineralization with less Cu accumulation in liver compared with pigs fed diets containing CuSO4. [ABSTRACT FROM AUTHOR]

DON has been shown to induce anorexia, oxidative stress, and more recently, alterations in calcium (Ca) and phosphorus (P) metabolism. It was thus hypothesized that vitamin D3 or 25-OH-D3 can counteract the effects of DON in piglets. The objectives were to confirm the DON effect and to evaluate the impact of a vitamin D supplementation on growth performance and Ca and P metabolism on piglets receiving a DON contaminated feed. A total of 66 piglets received one of the 6 treatments in 2 x 3 factorial design: control treatments (CON) or DON unsupplemented or supplemented with VitD3 or 25-OH-D3. After 21 days, piglets were weighted and feed intake was measured. Bone mineral content of each piglet was measured with dualintensity X-ray absorptiometry at 21 days. Blood samples were taken to assess concentrations for VitD, P and Ca. Results showed that, DON reduced average daily feed intake and average daily gain (P < 0.001). DON increased BMC per kg live body weight (P < 0.001). Piglets fed DON diet had lower plasma concentrations of 25-OH-D3, 1,25-(OH)2-D3 and phosphate (P < 0.001). The sodium-dependent phosphate transporter 1 (SLC20A2; P < 0.050), sodium/calcium exchanger 1 (SLC8A1; P < 0.032) and Klotho (P < 0.014) gene expression was downregulated by DON contamination in intestinal mucosae. The calbindin d28K (CALB-1) (P < 0.042), SLC8A1 (P < 0.026), TRPV5 (P < 0.041), calbindin d9K (S100G) (P < 0.029) and Klotho (P < 0.013) gene expression was downregulated by DON contamination in the kidney. The 1α-hydroxylase gene expression tended to be downregulated by DON contamination in the kidney as well. The VitD3 and 25-OH-D3 supplementation upregulated vitamin D receptor (VDR, DON x VitD, P < 0.014), SLC8A1 (DON x VitD, P < 0.036) and Klotho (DON x VitD, P < 0.025) in intestinal mucosae, although those gene expressions were downregulated by DON contamination. Thus, DON induced an alteration of vitamin D-calcium-phosphorus metabolism by modifying Ca utilization from mechanisms still under investigation. [ABSTRACT FROM AUTHOR]

An experiment was conducted to test the hypothesis that inclusion of Cu oxide (Cu2O) in diets for growing-finishing pigs improves body weight (BW) and bone mineralization, and reduces accumulation of Cu in the liver compared with pigs fed diets containing Cu sulfate (CuSO4). Two hundred growing pigs (initial BW: 11.5 ± 0.98 kg) were allotted to a randomized complete block design with 2 blocks of 100 pigs, 5 dietary treatments, 5 pigs per pen, and a total of 8 pens per treatment. Treatments included the negative control (NC) diet that contained 20 mg Cu/kg, and 4 diets in which 125 or 250 mg Cu/kg from CuSO4 or Cu2O were added to the NC diet. The experiment was divided into 4 phases and concluded when pigs reached market weight. Pig weights were recorded on day 1 and at the end of each phase and feed provisions were recorded throughout the experiment. On the last day of phases 1 and 4, 1 pig per pen was sacrificed to obtain samples of liver and spleen tissue, and the right metacarpal was collected. Results indicated that pigs fed diets containing 250 mg Cu/kg from CuSO4 had greater BW at the end of phases 1 and 2 than pigs fed NC diets. Pigs fed diets containing 250 mg Cu/kg from Cu2O had greater (P < 0.05) BW at the end of phases 1, 2, 3, and 4 compared with pigs fed NC diets, and these pigs also had greater BW at the end of phases 3 and 4 than pigs fed all other diets. Pigs fed the diets with 250 mg Cu/kg tended to have greater (P < 0.10) feed intake than pigs fed the NC diet at the end of phase 2, and for the overall experimental period, pigs fed diets containing 250 mg Cu/kg from Cu2O had greater (P < 0.05) feed intake than pigs on all other treatments. However, no differences in gain:feed ratio were observed among treatments. Copper accumulation in liver and spleen increased with Cu dose, but at the end of phase 1, pigs fed 250 mg Cu/kg from CuSO4 had greater (P < 0.05) Cu concentration in liver and spleen than pigs fed 250 mg Cu/kg from Cu2O. Pigs fed diets containing 250 mg Cu/kg from Cu2O had greater (P < 0.05) quantities of bone ash and greater (P < 0.05) concentrations of Ca, P, and Cu in bone ash than pigs fed NC diets or the 2 diets containing CuSO4, but Zn concentration in bone ash was less (P < 0.05) in pigs fed diets containing 250 mg Cu/kg from Cu2O. To conclude, supplementing diets for growing pigs with Cu2O improves growth performance and bone mineralization with less Cu accumulation in liver compared with pigs fed diets containing CuSO4., (© The Author(s) 2021. Published by Oxford University Press on behalf of the American Society of Animal Science. All rights reserved. For permissions, please e-mail: journals.permissions@oup.com.)

Two experiments were conducted to determine the effects of calcium to phosphorus (Ca:P) ratio in diets adequate in standardized total tract digestible (STTD) P on performance of 26- to 127-kg pigs fed diets with or without phytase. Pens of pigs (n = 1,134 in Exp. 1 and n = 1,215 in Exp. 2, initially 26.3 and 25.3 kg) were blocked by body weight (BW) and allotted to treatments in a randomized complete block design. There were 27 pigs per pen with 7 and 9 replicates per treatment in Exp. 1 and Exp. 2, respectively. Treatments were formulated to contain 0.75:1, 1.00:1, 1.25:1, 1.50:1, 1.75:1, and 2.00:1 analyzed Ca:P ratios in Exp. 1, and 0.75:1, 1.00:1, 1.25:1, 1.50:1, and 2.00:1 analyzed Ca:P ratios in Exp. 2. These correspond to a range of 0.96:1 to 2.67:1 and 0.95:1 to 2.07:1 STTD Ca:STTD P ratios in Exp. 1 and Exp. 2, respectively. Experiment 2 diets contained 1,000 phytase units of Ronozyme HiPhos 2500 (DSM Nutritional Products, Inc., Parsippany, NJ) with release values of 0.132% STTD P, 0.144% total Ca, and 0.096% STTD Ca. Diets contained 122% of NRC (2012) STTD P estimates for the weight range across 4 phases. In Exp. 1, increasing Ca:P ratio increased (quadratic, P < 0.05) average daily gain (ADG) and average daily feed intake (ADFI). Feed efficiency (G:F) worsened (quadratic, P < 0.05) at the highest ratio. Hot carcass weight (HCW) and bone ash increased (quadratic, P < 0.05) while carcass yield decreased (linear, P < 0.10) with increasing Ca:P ratio. The maximum responses in ADG, HCW, and bone ash were estimated at 1.38:1, 1.25:1, and 1.93:1 analyzed Ca:P and at 1.82:1, 1.64:1, and 2.57:1 STTD Ca:STTD P, respectively. In Exp. 2, increasing Ca:P ratio increased (quadratic, P < 0.05) ADG and bone ash, and improved G:F (linear, P < 0.05). There was a quadratic increase (P < 0.05) in HCW and decrease in carcass yield (P < 0.10). The maximum responses in ADG, HCW, and bone ash were estimated at 1.63:1, 1.11:1 to 1.60:1, and 1.25:1 analyzed Ca:P and at 1.75:1, 1.28:1 to 1.71:1, and 1.40:1 STTD Ca:STTD P, respectively. Expressing ADG on a STTD Ca:STTD P basis provided a more consistent estimate of the ideal Ca:P ratio among the 2 studies than analyzed Ca to analyzed P ratio. A STTD Ca:STTD P ratio between 1.75:1 to 1.82:1 can be used for 26- to 127-kg pigs that are fed diets adequate in STTD P with or without added phytase to maximize growth rate without reducing bone ash., (© The Author(s) 2019. Published by Oxford University Press on behalf of the American Society of Animal Science. All rights reserved. For permissions, please e-mail: journals.permissions@oup.com.)

A study was conducted to determine the standardized total tract digestible phosphorus (STTD P) requirement for 24- to 130-kg finishing pigs housed under commercial conditions. A total of 1,130 barrows and gilts (PIC 359 × 1050, Hendersonville, TN; initially 24.2 kg) were used, with 26 to 27 pigs per pen with 7 replicates per treatment. Pens of pigs were allotted to treatments in a randomized complete block design with body weight (BW) as the blocking factor. The dietary treatments were fed in 4 phases and were formulated to contain 80%, 90%, 100%, 115%, 130%, and 150% of the National Research Council (NRC) requirement estimate for finishing pigs within each phase. Weight ranges for each phase were: 27 to 49, 49 to 76, 76 to 90, and 90 to 130 kg. Treatments were achieved by increasing the amount of monocalcium phosphate at the expense of corn in the diet with no added phytase. All diets were formulated to contain a similar 1.14:1 to 1.16:1 total Ca:P ratio across treatments in all phases. Increasing STTD P resulted in a quadratic response (P < 0.05) in average daily gain (ADG), gain-to-feed ratio (G:F), and final BW. The greatest improvement was observed with STTD P at 130% of NRC for ADG and final BW and at 115% STTD P for G:F. Average daily feed intake increased linearly (linear, P < 0.05) with the inclusion of STTD P. Increasing STTD P resulted in an increase (quadratic, P < 0.05) in hot carcass weight (HCW) and carcass ADG with the greatest response observed with STTD P at 130% of NRC. There was a marginally significant response (quadratic, P < 0.10) in carcass G:F, with the greatest improvement with STTD P at 115% of NRC. Carcass yield decreased (linear, P < 0.05) with increasing STTD P, while there was a marginally significant (linear, P < 0.10) decrease in backfat and increase in fat-free lean. At the end of the study, a metacarpal was collected and analyzed for bone ash. Increasing STTD P resulted in an increase (linear, P < 0.05) in bone ash weight and percentage ash. For ADG and G:F, the quadratic model demonstrated the best fit. The maximum response in ADG and G:F was estimated at 122% and 116% of NRC STTD P, respectively. The broken-line linear model best fit the data for percentage bone ash, with a plateau achieved at 131% of the NRC STTD P. In conclusion, the estimated STTD P requirement of 24 to 130 kg ranged from 116% to 131% of the NRC publication (2012) requirement estimate., (© The Author(s) 2019. Published by Oxford University Press on behalf of the American Society of Animal Science. All rights reserved. For permissions, please e-mail: journals.permissions@oup.com.)