Phosphorus digestibility in low-phytate barley fed to finishing pigs

Allelic Variants of CRISPR/Cas9 Induced Mutation in an Inositol Trisphosphate 5/6 Kinase Gene Manifest Different Phenotypes in Barley

Inositol trisphosphate 5/6 kinases (ITPK) constitute a small group of enzymes participating in the sequential phosphorylation of inositol phosphate to inositol hexakisphosphate (IP6), which is a major storage form of phosphate in cereal grains. The development of lines with reduced IP6 content could enhance phosphate and mineral bioavailability. Moreover, plant ITPKs participate in abiotic stress signaling. To elucidate the role of HvITPK1 in IP6 synthesis and stress signaling, a barley itpk1 mutant was created using programmable nuclease Cas9. Homozygous single bp insertion and deletion mutant lines were obtained. The mutants contained altered levels of phosphate in the mature grains, ranging from 65% to 174% of the wild type (WT) content. Homozygous mutant lines were tested for their response to salinity during germination. Interestingly, insertion mutant lines revealed a higher tolerance to salinity stress than deletion mutants. Mature embryos of an insertion mutant itpk1-2 and deletion mutant itpk1-33 were cultivated in vitro on MS medium supplemented with NaCl at 50, 100, and 200 mM. While both mutants grew less well than WT on no or low salt concentrations, the itpk1-2 mutant was affected less than the WT and itpk33 when grown on the highest NaCl concentration. The expression of all ITPKs was induced in roots in response to salt stress. In shoots, the differential effect of high salt on IPTK expression in the two iptk1 mutants was consistent with their different sensitivities to salt stress. The results extend the evidence for the involvement of ITPK genes in phosphate storage and abiotic stress signaling.

Digestibility of phosphorous in cereals and co-products for animal feed

Feed ingredients used in swine diets contain various levels and availabilities of nutrients. Nutritional precision evaluation of each ingredient is necessary for formulating diets of pigs. Especially, phosphorous (P) is one of important nutrients for metabolism. However, current data of P digestibility were most apparent digestibility. Therefore, this study was aimed to estimate the coefficient of total tract standardized digestibility (CTTSD) of P in cereals and various co-products used in pig diet. Twelve barrows (initial BW ± SD, 46.70 ± 3.21 kg) were used in this experiment. The experimental design was a 12 × 8 incomplete Latin square with 12 diets and 8 periods. Experimental diets were consisted of barley, wheat, lupine kernel (LK), soybean meal (SBM), almond meal (AM), corn gluten meal (CGM), corn gluten feed from China (CGF-C), corn gluten feed from Korea (CGF-C), wheat bran (WB), rice bran (RB), lupine hull (LH) and P-free diet. The CTTAD of Ca was higher in AM than RB and CGF-K. The LK and CGM showed greater CTTSD of P than RB and LH. In conclusion, our results indicated that the cereals and co-products as P sources were the ideally used as an ingredient in mixed diets of the growing-finishing pigs.

Hulled and hull-less barley grains with the genetic trait for low-phytic acid increased the apparent total-tract digestibility of phosphorus and calcium in diets for young swine

A 35-d experiment was conducted using 63 crossbred pigs (35 barrows and 28 gilts) with an initial average BW of 7.0 kg and age of 28 d to evaluate the efficacy of the low-phytic acid (LPA) genetic trait in hulled or hull-less barley in isocaloric diets. Hulled barleys were the normal barley (NB) cultivar Harrington and the near-isogenic LPA mutant 955 (M955) with P availabilities of 36 and 95%, respectively. Hull-less lines were produced by crossing NB and the LPA mutant 422 line with a hull-less line, producing hull-less NB (HNB) and hull-less mutant 422 (HM422) with P availabilities of 41 and 66%, respectively. Pigs were in individual metabolism cages or pens for Phase 1 (d 0 to 14) and Phase 2 (d 14 to 35). Diets defined as NB, HNB, HM422, or M955 with no added inorganic P (iP) had available P (aP) concentrations of 0.27, 0.28, 0.35, and 0.40% for Phase 1 and 0.15, 0.17, 0.23, and 0.31% for Phase 2, respectively. Only diet M955 was adequate in aP. Therefore, iP was added to the P-deficient diets to make diets NB + iP, HNB + iP, and HM422 + iP with aP equal to that in diet M955. Overall (d 0 to 35), ADG and G:F were greater ( < 0.01) for pigs fed diet M955 or the diets with added iP than for pigs fed the NB diet. Serum tartrate-resistant acid phosphatase activity on d 34 was greater ( < 0.01) for pigs fed the NB or HNB diets than for pigs fed the other diets. Bone breaking strength and P absorption (g/d) were greater ( < 0.01) for pigs fed diet M955 or the diets with iP than for pigs fed the NB or HNB diets. Pigs fed diet M955 absorbed greater ( < 0.01) percentages of P and Ca and had less ( < 0.01) fecal excretion of P (g/d and %) and Ca (%) than pigs fed the other diets. In conclusion, the LPA genetic trait was effective in hulled and hull-less barley in isocaloric diets fed to young pigs. Pigs fed the diet with LPA M955 consumed 31% less P and excreted 78% less fecal P and 30% less fecal Ca than pigs fed the diet with NB + iP that was equal to diet M955 in aP. Therefore, LPA barley, especially M955 with 95% aP, will reduce the use of iP in swine diets, reduce P pollution from swine manure, and support the goal of achieving global P sustainability.

Interaction of calcium and phytate in broiler diets. 1. Effects on apparent prececal digestibility and retention of phosphorus

Phytate P utilization from soybean meal (SBM) included in broiler diets has been shown to be poor and highly dependent on dietary Ca intake. However, the effect of Ca on P utilization and on the optimal ratio of Ca to nonphytate P (Ca:NPP) when diets contained varying levels of phytate has not been clearly shown and was the objective of this research. A factorial treatment structure was used with 4 dietary Ca levels from 0.47 to 1.16% and 3 levels of phytate P (0.28, 0.24, and 0.10%). Varying dietary phytate P levels were obtained by utilizing SBM produced from 3 varieties of soybeans with different phytate P concentrations. Ross 508 broiler chicks were fed 1 of 12 diets from 16 to 21 d of age. Excreta were collected from 16 to 17 d and from 19 to 20 d of age and ileal digesta was collected at 21 d of age. Apparent prececal P digestibility decreased when dietary Ca concentration increased and was higher when diets contained low-phytate SBM. The apparent digestibility of Ca and percentage of phytate P hydrolysis at the distal ileum were not reduced when dietary phytate P concentration increased. Including low-phytate SBM in diets reduced total P output in the excreta by 49% compared with conventional SBM. The optimum ratio of Ca:NPP that resulted in the highest P retention and lowest P excretion was 2.53:1, 2.40:1, and 2.34:1 for diets with 0.28, 0.24, and 0.10% phytate P. These data suggested that increased dietary Ca reduced the extent of phytate P hydrolysis and P digestibility and that the optimum Ca:NPP ratio at which P retention was maximized was reduced when diets contained less phytate P.

Effect of low-phytate barley or phytase supplementation to a barley-soybean meal diet on phosphorus retention and excretion by grower pigs

Two studies were conducted to determine the effect of diets containing low-phytate barley or supplemented with phytase on P balance and excretion in grower pigs. In Exp. 1, eight 32-kg barrows were assigned to a repeated, 4 x 4 Latin square design and fed 4 diets that contained 96% barley: normal-phytate hulled barley (HB), low-phytate hulled barley (LPHB), normal-phytate hull-less barley (HLB), and low-phytate hull-less barley (LPHLB). The barley cultivars contained 0.16, 0.05, 0.24, and 0.03% phytate, respectively. Inorganic P (iP) was added to the HB and HLB diets to meet the 1998 National Research Council recommendation of available P (aP, 0.23%), whereas LPHB and LPHLB contained sufficient aP. The diets were fed at 2.5 times the maintenance requirement for ME. The apparent total tract digestibilities (ATTD) of P did not differ between the hulled and hull-less barley diets, but P retention (%) and excretion were greater in pigs fed the hull-less barley diets (P < 0.05). The ATTD of P was greater and P excretion was 35% lower in pigs fed the low-phytate compared with the normal-phytate diets (P < 0.001). The amount of P retained (g/d) was greater (P < 0.001) in pigs fed low-phytate barley, reflecting an ATTD of P of 65 and 49% for low-phytate and normal-phytate barley, respectively (P < 0.001). In Exp. 2, eight 21-kg barrows were assigned to a repeated, 4 x 4 Latin square design and fed 4 diets based on barley and soybean meal (SBM): HB-SBM, HB-SBM + iP, HB-SBM + phytase, and LPHB-SBM. The HB-SBM and HB-SBM + phytase diets were deficient in aP, whereas the HB-SBM + iP and LPHB-SBM diets had adequate aP. The feeding regimen was similar to that of Exp. 1. Adding iP to the HB-SBM diet did not affect the ATTD but increased the amount of P retained (g/d) and excreted (P < 0.001). The ATTD and amount of P retained (g/d) did not differ among pigs fed the HB-SBM + iP, HB-SBM + phytase, and LPHB-SBM diets. However, pigs fed the HB-SBM + phytase and LPHB-SBM diets excreted 32 and 29% less P, respectively, than pigs fed the HB-SBM + iP diet (P < 0.05), confirming that low-phytate barley is as effective as supplemental phytase in improving P digestibility and utilization and decreasing P excretion in grower pigs.

The effect of feeding low-phytate barley-soybean meal diets differing in protein content to growing pigs on the excretion of phosphorus and nitrogen

An experiment was conducted with growing pigs to determine the excretion of P and N in 4 barley-based diets formulated to contain 18 or 15% CP by using a normal barley (NB) or a low-phytate barley (LPB). The NB contained 0.31% total P and 0.19% phytate P; the LPB contained 0.32% total P and 0.01% phytate P. The diets were supplemented, when so required, with lysine, methionine, threonine, and tryptophan to meet their apparent ileal digestible supplies according to the NRC (1998). The diets containing NB were supplemented with inorganic P to meet the NRC (1998) recommendation for available P (0.23%). The diets containing LPB were not supplemented with inorganic P because these contained sufficient available P (0.27%). Eight barrows with an average BW of 20.9 kg were assigned to the 4 dietary treatments according to a repeated 4 x 4 Latin square design. The diets were fed at a rate of 2.5 times the ME requirement for maintenance. The barrows were fed twice daily, at 0800 and 1500, equal amounts each meal. Water was added to the feed at a ratio of 2.5:1. Each experimental period consisted of a 7-d adaptation period followed by a 5-d collection of feces and urine. The substitution of NB with LPB decreased (P < 0.001) the total P excretion by 38 and 43% for the 18 and 15% CP diets, respectively. Reducing the CP content from 18 to 15% decreased (P < 0.001) the N excretion by 29 and 32% for the NB and LPB diets, respectively. With the reduction in CP content, there was a decrease (P < 0.001) in the amount of N retained. The N:P ratio in manure of pigs fed the LPB diets was greater (P < 0.001) than from pigs fed the NB diets. These data indicate that P and N excretion can be greatly reduced by substitution of NB by LPB, and also by the reduction of the CP content, in diets for growing pigs.

Low-phytate barley cultivars improve the utilization of phosphorus, calcium, nitrogen, energy, and dry matter in diets fed to young swine

A 28-d experiment was conducted using 45 crossbred barrows with an average initial BW of 9.5 kg and age of 35 d to evaluate low-phytate barley (LPB) mutants (M) M422, M635, and M955, which were hulled, near-isogenic progeny of the normal barley (NB) Harrington and had 47, 66, and 80% less phytic acid, respectively, than NB. A hull-less LPB, M422-H, which was not near-isogenic to the other cultivars, was also evaluated. Apparent nutrient balance, bone measurements, and growth performance were the response criteria evaluated. The barrows were fed the diets to appetite in meal form in individual metabolism crates. Barley and soybean meal were the only sources of phytic acid. Dietary protein supplementation and ME/kg were equalized in all diets. The treatments were diets containing NB, M422, M635, or M422-H without or with added inorganic P (iP), or M955 without added iP. Diets with added iP contained 0.30% available P (aP), the same concentration of aP provided by the diet containing M955 without added iP. There were linear increases (P < or = 0.02) in ADG, G:F, metacarpal and radius bone strength, and fat-free dry weight, and in the absorption and retention (g/d and % of intake) of P and Ca with increasing dietary concentration of aP from the near-isogenic cultivars NB, M422, M635, or M955 without added iP. There were linear decreases in the grams (P < or = 0.02) and percentages (P < 0.001) of P and Ca excreted per day with increasing dietary concentration of aP without added iP. There were no responses for N or energy balance. Growth performance and bone response criteria did not differ for barrows fed the diet containing M955 or the near-isogenic diets containing NB, M422, or M635 with added iP. However, barrows fed the diet containing M955 had greater (P < or = 0.02) percentages of P, N, and energy absorption and retention, Ca absorption, and DM digestibility and had less (P < or = 0.02, g/d and %) excretion of P, N, energy, and Ca (g) per day than barrows fed the diets containing the near-isogenic NB or LPB cultivars with added iP. When dietary aP was equalized with iP, the excretion of P in feces plus urine (g/d) was reduced by 20.2, 27.9, and 44.6%, respectively, in barrows fed the diets containing M422 + iP, M635 + iP, or M955 compared with barrows fed the diet containing NB + iP. Energy utilization did not differ for barrows fed the diets containing hulled or hull-less LPB when ME/kg was equalized with lard. In conclusion, the apparent utilization of P and Ca, the bone strength and fat-free dry weight, and growth performance increased with increasing dietary concentration of aP provided by LPB, in association with linear decreases in P and Ca excretion. Barrows fed the diet containing M955 also had greater utilization and less excretion of P, Ca, N, energy, and DM than barrows fed the diets containing the near-isogenic NB or LPB cultivars with added iP to equalize aP at 0.30%.

Estimation of true phosphorus digestibility and endogenous phosphorus loss in growing pigs fed conventional and low-phytate soybean meals

This study reevaluated the method of regressing of total P output against dietary P intake to simultaneously estimate true P digestibility and endogenous P loss in growing pigs fed either conventional or low-phytate soybean meal (SBM). Four isocaloric diets were formulated to contain increasing concentrations of each type of SBM (8 diets total), and therefore contained increasing concentrations of dietary P. Dietary P and Ca concentrations were deficient because they were supplied solely by SBM, and Ca:total P ratios were less than 1:1. Sixteen barrows (initial BW 17.7 +/- 1.8 kg) were surgically fitted with a simple T-cannula at the distal ileum, randomly assigned to metabolism crates, and fed the experimental diets in a replicated 8 x 8 Latin square design. Feed was provided at 90 g/kg of BW(0.75) and fed in 2 equally sized meals at 0800 and 2000, with diets containing Cr sesquioxide (3 g/kg) as an indigestible marker. As the P concentration increased from 0.9 to 3.9 g/kg of DM, the apparent prececal P digestibility increased for conventional SBM (P < 0.05), but no relationship was observed for low-phytate SBM. The output of total P [mg/(kg of BW(0.75).d)], either prececal or total tract, exhibited a linear relationship (P < 0.01) with increasing P intake. However, a quadratic response (P = 0.02) was also detected for total tract P output from pigs fed low-phytate SBM. True P digestibility was not different between prececal and total tract collection sites (P > 0.10), but was greater (P < 0.01) for low-phytate SBM (62.6%) compared with conventional SBM (44.5%). Endogenous P estimates were not different between the SBM varieties and averaged 4.83 mg/(kg of BW(0.75).d). However, endogenous P estimates were highly variable between individual animals and, therefore, were not significantly different from zero. In this study, estimates of endogenous P loss from pigs were relatively low compared with previously reported values, and evidence of nonlinearity in P output was observed. These results suggest that the difference in true P digestibility between conventional SBM and low-phytate SBM is influenced by dietary phytate content when growing pigs are fed P-deficient diets.

Phosphorus fractions in manure from growing pigs receiving diets containing micronized peas and supplemental enzymes

Different livestock feeds manipulations have been reported to reduce the total P concentration in manure. Information on the influence of these dietary manipulation strategies on the forms of P in manure is, however, limited. This study was, therefore, conducted to investigate the effect of diet manipulation through feed micronization and enzyme supplementation on the forms of P in swine manure. Eight growing pigs were fed four diets: barley-raw pea (BRP), barley-micronized pea (BMP), barley-raw pea with enzyme (BRPE), and barley-micronized pea with enzyme (BMPE) in a 4 x 4 Latin square design. Because we are interested in the effect of enzyme cocktail and pea micronization on manure P, we did not reduce the non-phytate P with enzyme addition in this study. The fecal material and urine were collected and analyzed for total P. Fecal material was fractionated to determine the total P in H2O-, NaHCO3-, NaOH-, and HCl-extractable fractions. The total P in the residual fractions was also determined. About 98% of the total P excreted by the pigs was found in the fecal material. Inclusion of micronized pea in pig diet did not have any significant effect (p > 0.1) on either the total P or the different P fractions in the manure. The labile P (the sum of H2O-P and NaHCO3-P) was significantly reduced (p < 0.05) by the addition of enzyme to swine diets. Pigs fed the BRPE and BMPE had 14 and 18% lower labile P, respectively, compared with pigs fed the BRP. Enzyme addition to pig diets reduced not only the total P in manure, but also the labile P fraction, which is of great environmental concern. Thus, the potential of P loss to runoff and the subsequent eutrophication can be reduced by enzyme addition to pig diets.

Phosphorus composition of manure from swine fed low-phytate grains: evidence for hydrolysis in the animal

Including low-phytic-acid grains in swine diets can reduce P concentrations in manure, but the influence on manure P composition is relatively unknown. To address this we analyzed manure from swine fed one of four barley (Hordeum vulgare L.) varieties. The barley types consisted of wild-type barley (CDC bold, normal barley diet) and three low-phytic-acid mutant barleys that contained similar amounts of total P but less phytic acid. The phytic acid concentrations in the mutant barleys were reduced by 32% (M422), 59% (M635), and 97% (M955) compared with that in the wild-type barley, respectively. Phosphorus concentrations were approximately one-third less in manures from animals fed low-phytic-acid barleys compared with those fed the wild-type variety. Phytic acid constituted up to 55% of the P in feed, but only trace concentrations were detected in NaOH-EDTA extracts of all manures by solution (31)P nuclear magnetic resonance (NMR) spectroscopy. Phosphate was the major P fraction in the manures (86-94% extracted P), with small concentrations of pyrophosphate and simple phosphate monoesters also present. The latter originated mainly from the hydrolysis of phospholipids during extraction and analysis. These results suggest that phytic acid is hydrolyzed in swine, possibly in the hind gut by intestinal microflora before being excreted in feces, even though the animals have little phytase activity in the gut and derive little nutritional benefit from phytate P. We conclude that feeding low-phytic-acid grains reduces total manure P concentrations and the manure P is no more soluble than P generated from normal barley diets.

Effect of phytase supplementation on phosphorus digestibility in low-phytate barley fed to finishing pigs

Forty crossbred barrows (Camborough 15 Line female x Canabred sire) weighing an average of 79.6 +/- 8.0 kg were used in a factorial design experiment (5 barleys x 2 enzyme levels) conducted to determine the effects of phytase supplementation on nutrient digestibility in low-phytate barleys fed to finishing pigs. The pigs were assigned to one of 10 dietary treatments comprised of a normal 2-rowed, hulled variety of barley (CDC Fleet, 0.26% phytate) or 2 low-phytate hulled genotypes designated as LP422 (0.14% phytate) and LP635 (0.09% phytate). A normal, hulless barley (CDC Dawn, 0.26% phytate) and a hulless genotype designated as LP422H (0.14% phytate) were also included. All barleys were fed with and without phytase (Natuphos 5000 FTU/kg). The diets fed contained 98% barley, 0.5% vitamin premix, 0.5% trace mineral premix, 0.5% NaCl and 0.5% chromic oxide but no supplemental phosphorus. The marked feed was provided for a 7-day acclimatization period, followed by a 3-day faecal collection. In the absence of phytase, phosphorus digestibility increased substantially (P < 0.05) as the level of phytate in the barley declined. For the hulled varieties, phosphorus digestibility increased from 12.9% for the normal barley (0.26% phytate) to 35.3 and 39.8% for the two low-phytate genotypes (0.14 and 0.09% phytate respectively). For the hulless varieties, phosphorus digestibility increased from 9.2% for the normal barley (0.26% phytate) to 34.7% for the hulless variety with 54% of the normal level of phytate (0.14% phytate). In contrast, when phytase was added to the diet, there was little difference in phosphorus digestibility between pigs fed normal barley and those fed the low-phytate genotypes (significant barley x enzyme interaction, P = 0.01). For the hulled varieties, phosphorus digestibility was 50.1% for the barley with the normal level of phytate (0.26% phytate) compared with 51.1 and 52.4% for the varieties with 54 and 35% of the normal level of phytate (0.14 and 0.09% phytate respectively). For the hulless varieties, phosphorus digestibility increased from 47.1% for the normal barley (0.26% phytate) to 54.4% for the hulless variety with 54% of the normal level of phytate (0.14% phytate). In conclusion, both supplementation with phytase and selection for low-phytate genotypes of barley were successful in increasing the digestibility of phosphorus for pigs. Unfortunately, the effects did not appear to be additive. Whether or not swine producers will choose low-phytate barley or supplementation with phytase as a means to improve phosphorus utilization, will likely depend on the yield potential of low-phytate barley and the additional costs associated with supplementation with phytase.