The hypothesis that the standardized ileal digestibility (SID) of AA, concentration of ME, and the standardized total tract digestibility (STTD) of P in an enhanced torula yeast (ETY; Arbiom, Raleigh, NC) are not different from values obtained in Menhaden fish meal (FM) was tested. In Exp. 1, 6 ileal cannulated barrows (11.7 ± 0.4 kg) were allotted to a replicated 3 × 3 Latin square with 3 diets (ETY, FM, and N-free) and 3 7-d periods. Ileal digesta were collected on d 6 and 7 of each period. Data were analyzed using the Proc Mixed with diet as main effect and pig as random effect. The SID of AA was greater (P < 0.05) in ETY than in FM (Table 1). In Exp. 2, 24 barrows (14.4 ± 1.1 kg) were individually housed in metabolism crates and allotted to a corn diet or diets based on corn and ETY or corn and FM. Feces and urine were collected for 5 d. Data were analyzed as in Exp. 1. No difference in ME between ETY (3,636 kcal/kg DM) and FM (3,611 kcal/kg DM) was observed. In Exp. 3, 32 barrows (11.9 ± 1.1 kg) were allotted to 4 diets in a 2 × 2 factorial with 2 ingredients (ETY and FM) and 0 or 500 units/kg of phytase. Housing and fecal sample collection was as in Exp. 2. Data were analyzed as in Exp. 1 with diet and phytase as main effects. Phytase did not influence STTD of P, but the STTD of P in the ETY (91%) was greater (P < 0.05) than in FM (68%). In conclusion, the SID of AA and the STTD of P in ETY is greater than in FM, but the ME in ETY is not different from FM.
An experiment was conducted to test the hypothesis that formulating diets for pigs based on a ratio between standardized total tract digestible (STTD) Ca and STTD P instead of total Ca and STTD P increases the efficiency of Ca and P utilization. Forty barrows (59.4 ± 3.8 kg) were individually housed in metabolism crates and allotted to 4 corn-soybean meal diets and 2 periods of 11 d in a randomized complete block design. Diets were formulated using a 2 × 2 factorial design with 2 Ca requirement estimates (total Ca or STTD Ca) and 2 inclusion levels of microbial phytase (0 or 500 units/kg). Phytase was assumed to release 0.11% STTD P and 0.16% total Ca. Diets were formulated based on requirements for total Ca and STTD P and the ratio between STTD Ca and STTD P was 1.25:1 in diets formulated based on STTD Ca. Fecal and urine samples were collected from feed provided from d 6 to 9. Data for Ca and P balance were analyzed using a model that included the main effects of diet formulation and phytase level, the interaction between main effects, and the random effect of period. Interactions (P < 0.05) between diet formulation and phytase level were observed for Ca intake, Ca in feces, Ca digestibility, Ca retained as a percentage of intake, P digestibility, P absorbed, and P in urine (Table 1). Despite being provided less (P < 0.05) Ca, pigs fed diets formulated based on STTD Ca did not absorb or retain less Ca than pigs fed total Ca diets, but they absorbed more (P < 0.05) P than pigs fed diets formulated based on total Ca. In conclusion, by formulating diets based on values for STTD Ca, P absorption was increased confirming detrimental effects of oversupplying Ca.
A 126-d experiment was conducted to test the hypothesis that the requirement for Ca expressed as a ratio between standardized total tract digestible (STTD) Ca and STTD P obtained in short-term experiments may be applied to pigs fed diets without or with microbial phytase from 11 to 130 kg. In a 5-phase program, 160 pigs (11.2 ± 1.8 kg) were randomly allotted to 32 pens and 4 corn-soybean meal diets in a 2 × 2 factorial design with 2 formulation strategies (total Ca or STTD Ca), and 2 phytase levels (0 or 500 units/kg) assuming phytase released 0.11% STTD P and 0.16% total Ca. The STTD Ca:STTD P ratios were 1.40:1, 1.35:1, 1.25:1, 1.18:1, and 1.10:1 for phases 1 to 5. At the conclusion of each phase, weights of pigs and feed left in feeders were recorded and a blood sample from 1 pig per pen was collected. At the end of phases 1 (d 24) and 5, the right femur of 1 pig per pen was collected. Data were analyzed as main effects of formulation strategy and phytase level and their interaction. Phase effect was analyzed by repeated measures. No interactions were observed and formulation strategy and phytase did not impact growth performance, bone ash, or plasma Ca and P on d 24 (Table 1). On d 126, an interaction (P < 0.05) between main effects was observed. Without phytase, pigs fed diets based on total Ca had greater bone ash than STTD Ca pigs, but with phytase, no differences were observed. A negative quadratic effect (P < 0.05) of phase for plasma Ca and P was observed. In conclusion, STTD Ca:STTD P ratios can be used in diet formulation for growing-finishing pigs without affecting growth performance. Phytase ameliorates bone resorption caused by low Ca in STTD Ca diets.
A 21-d experiment was conducted to test the hypothesis that the Ca requirement to maximize growth performance expressed as the standardized total tract digestible (STTD) Ca to STTD P ratio is less than 1.40:1. The second hypothesis was that increasing dietary Ca increases plasma Ca and downregulates abundance of genes related to Ca absorption (TRPV6 and S100G) and tight junction proteins (OCLN, CLDN1, and ZO1). Twenty corn-soybean meal diets were formulated using a 4 5 factorial design (0.16, 0.33, 0.42, or 0.50% STTD P and 0.14, 0.29, 0.44, 0.59, or 0.74% STTD Ca), and 640 pigs (11.1 ± 1.4 kg) were allotted to the 20 diets in a randomized complete block design. On d 21, weights of pigs and feed left in feeders were recorded and blood, duodenal tissue, ileal mucosa, and the right femur were collected from 1 pig per pen. Abundance of mRNA was determined in duodenum and ileum via quantitative RT-PCR. Data were analyzed using a response surface model by removing the terms in the model that were not significant. Interactions (P < 0.01) between dietary Ca and P for average daily gain (ADG), gain to feed ratio (G:F), and bone ash were observed (Table 1). The predicted maximum ADG (614 g), G:F (0.65), and bone ash (11.68 g) at 0.33% STTD P was obtained at STTD Ca:STTD P ratios of 1.39:1, 1.25:1, and 1.66:1, respectively. There was a linear negative effect (P < 0.05) of Ca on the abundance of S100G, TRPV6, OCLN, and Z01 in the duodenum and on CLDN and ZO1 in the ileum. In conclusion, the STTD Ca:STTD P ratio needed to maximize growth performance of 11- to 25-kg pigs is less than 1.40:1, if P is at the requirement. Increasing dietary Ca reduces transcellular but increases paracellular absorption of Ca.
An experiment was conducted to test the hypothesis that lowering dietary Ca and P reduces gastric pH and diarrhea of weanling pigs, but microbial phytase overcomes negative effects of low Ca and P on growth performance and bone ash. A total of 320 weanling pigs (6.35 ± 0.87 kg) were allotted to 8 corn-soybean meal-based diets in a randomized complete block design with 5 pigs/pen. Two phase 1 (d 1 to 14) control diets contained 100 or 50% of total Ca and digestible P relative to the requirement, and 6 diets in which 500, 2,000, or 16,000 units/kg of phytase was added to each control diet were formulated. Common diets were fed in phases 2 (d 15 to 27) and 3 (d 28 to 42). Fecal scores were recorded in phase 1 and growth performance data were recorded within each phase. Gastric pH was measured in 1 pig/pen on d 14; on d 14 and 42, the right femur of 1 pig/pen was collected. Data were analyzed using contrast statements in SAS. Results indicated that during phase 1, lowering Ca and P did not reduce gastric pH or fecal score, but the 50%-diets reduced (P < 0.05) average daily gain and average daily feed intake of pigs compared with the 100%-diets (Table 1). Phytase above 500 units/kg increased (P < 0.05) gain:feed ratio and tended (P < 0.10) to decrease gastric pH. Pigs fed the 50%-diets had reduced (P < 0.05) bone ash at d 14 and 42 compared with pigs fed the 100%-diets regardless of phytase inclusion level. In conclusion, reducing Ca and P in diets for weanling pigs does not decrease gastric pH or fecal score, but compromises growth performance and bone mineralization. However, super-dosing of phytase increases G:F of pigs regardless of dietary Ca and P concentration.
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