Review: Aspects of digestibility and requirements for minerals and vitamin D by growing pigs and sows

Some of the biggest changes in mineral nutrition for pigs that have occurred due to recent research were caused by the understanding that there is a loss of endogenous Ca and P into the intestinal tract of pigs. This resulted in development of the concept of formulating diets based on standardized total tract digestibility (STTD) rather than apparent total tract digestibility because the values for STTD of these minerals are additive in mixed diets. There are, however, no recent summaries of research on digestibility and requirements of macro- and microminerals and vitamin D for pigs. Therefore, the objective of this review was to summarize selected results of research conducted over the last few decades to determine the digestibility and requirements of some minerals and vitamin D fed to sows and growing pigs. Benefits of microbial phytase in terms of increasing the digestibility of most minerals have been demonstrated. Negative effects on the growth performance of pigs of over-feeding Ca have also been demonstrated, and frequent analysis of Ca in complete diets and raw materials is, therefore, recommended. There is no evidence that current requirements for vitamin D for weanling or growing-finishing pigs are not accurate, but it is possible that gestating and lactating sows need more vitamin D than currently recommended. Vitamin D analogs and metabolites such as 1(OH)D3 and 25(OH)D3 have beneficial effects when added to diets for sows in combination with vitamin D3. Recent research on requirements for macrominerals other than Ca and P is scarce, but it is possible that Mg in diets containing low levels of soybean meal is marginal. Some of the chelated microminerals have increased digestibility compared with sulfate forms, and hydroxylated forms of Cu and Zn appear to be superior to sulfate or oxide forms. Likewise, dicopper oxide and Cu methionine hydroxy analog have a greater positive effect on the growth performance of growing pigs than copper sulfate. The requirement for Mn may need to be increased whereas there appears to be no benefits of providing Fe above current requirements. In conclusion, diets for pigs should be formulated based on values for STTD of Ca and P and there are negative effects of providing excess Ca in diets. It is possible vitamin D analogs and metabolites offer benefits over vitamin D3 in diets for sows. Likewise, chelated forms of microminerals or chemical forms of minerals other than sulfates or oxides may result in improved pig performance.

Effect of increasing dietary fermentable fiber on diet nutrient digestibility and estimation of endogenous phosphorus losses in growing pigs

Fermentable fiber may increase endogenous losses of phosphorus (EPL) and amino acids (AA), thereby reducing apparent nutrient digestibility. Acacia gum with medium-to-high fermentability and low viscosity was increasingly included in diets to investigate its effect on apparent ileal digestibility (AID) and apparent total tract digestibility (ATTD) of nutrients, gross energy (GE), and standardized total tract digestibility (STTD) of P in growing pigs. A control diet (49% cornstarch; 18% bovine plasma protein) was formulated to measure basal EPL. Three additional diets were formulated to include 2.5%, 5.0%, or 7.5% acacia gum at the expense of cornstarch. Diets contained 16.1% to 17.4% CP and 0.31% to 0.33% total P (DM-basis). The four diets were fed to eight ileal-cannulated barrows (initial BW, 54.6 kg) for four 9 d periods in a double 4 × 4 Latin square. Apparent hindgut fermentation (AHF) was calculated as ATTD minus AID. Feeding increasing acacia gum quadratically affected (P < 0.05) AID of DM, GE, linearly decreased (P < 0.05) ATTD of DM, crude protein (CP), GE, digestible (DE) and predicted net energy (NE) value of diets, and linearly increased (P < 0.001) AHF of DM and GE. Increasing acacia gum did not affect AID and standardized ileal digestibility (SID) of CP and AA. Basal EPL was 377 mg/kg DM intake (DMI) and increasing acacia gum linearly increased (P < 0.05) total tract EPL. Increasing acacia gum linearly decreased (P < 0.05) diet ATTD of P, and STTD of P based on either the calculated EPL or NRC (2012) recommended value (190 mg P/kg DMI). Increasing acacia gum did not affect AID and ATTD of Ca of diets. In conclusion, feeding increasing dietary fermentable, low-viscous acacia gum decreased diet AID and ATTD of DM and GE, but did not affect AID or SID of CP and AA. Increasing acacia gum decreased ATTD of P, which might have been due to increased specific endogenous losses of P in the total tract of growing pigs.

Effects of microbial phytase on standardized total tract digestibility of phosphorus in feed phosphates fed to growing pigs

An experiment was conducted to test the hypothesis that the apparent total tract digestibility (ATTD) and the standardized total tract digestibility (STTD) of P in feed phosphates are increased by microbial phytase when fed to growing pigs. Monocalcium phosphate (MCP), monosodium phosphate (MSP), and magnesium phosphate (MgP) from volcanic deposits were used in the experiment. Three corn-soybean meal based diets that contained 0, 500, or 4,000 units of microbial phytase (FTU), but no feed phosphates, were formulated. Nine additional diets were formulated by adding each of the three feed phosphates to the three basal diets. A P-free diet was also formulated to estimate the basal endogenous loss of P, and therefore, 13 diets were used in the experiment. A total of 117 growing barrows (initial body weight: 15.56 ± 1.68 kg) were allotted to the 13 diets with 9 pigs per diet. Pigs were housed individually in metabolism crates equipped with a feeder and a nipple drinker. Installation of a screen floor under the slatted floor allowed for collection of feces. Diets were fed for 10 d, with the initial 5 d being a period of adaptation to the diet followed by a collection period of 4 d. During the experiment, pigs were fed equal amounts of feed twice daily at 0800 and 1600 h. Results indicated that the ATTD and STTD of P in all diets increased with the inclusion of 500 or 4,000 FTU, but the ATTD and STTD of P in the feed phosphates were not affected by the inclusion of phytase. This indicates that the increases in ATTD and STTD of P that were observed in the mixed diets when phytase was used were due to the release of P from phytate in corn and soybean meal and not from an increase in digestibility of P in feed phosphates. However, MgP had a lower (P < 0.05) ATTD and STTD of P than MCP and MSP. In conclusion, microbial phytase does not increase the digestibility of P in MCP, MSP, or MGP, but the digestibility of P in MgP is less than in MCP and MSP.

Microbial phytase reduces basal endogenous loss of calcium in pigs fed diets containing phytate phosphorus at commercial levels

The objective of this experiment was to test the hypothesis that increasing dietary phytase reduces basal endogenous loss of Ca and increases P balance in pigs. Seventy barrows (initial body weight: 17.66 ± 1.69 kg) were allotted to seven Ca-free diets using a randomized complete block design with two blocks and five pigs per diet in each block. All diets were based on corn, potato protein concentrate, and full-fat rice bran. A positive control (PC) diet was formulated to contain P at the requirement for standardized total tract digestible (STTD) P by 11 to 25 kg pigs. Six negative control (NC) diets were formulated by reducing the provision of digestible P by 0.15% and adding 0, 250, 500, 1,000, 2,000, or 4,000 phytase units/kg diet. Pigs were housed individually in metabolism crates that allowed for total, but separate, collection of urine and feces. Daily feed allowance was 3.0 times the maintenance requirement for metabolizable energy and was divided into two equal meals. Diets were fed for 12 d with the first 5 d considered the adaptation period. Urine collections started on day 6 in the morning and ceased on day 10 in the morning. Fecal markers were also included in the morning meals on day 6 and day 10 and feces were collected according to the marker-to-marker procedure. Results indicated that the apparent total tract digestibility of dry matter was not affected by dietary P or phytase levels. The basal endogenous loss of Ca was not affected by dietary P, but exponentially decreased (P = 0.030) as phytase level increased in the diets. Phosphorus retention (g/d) and standardized total tract digestibility of phosphorus were greater (P < 0.05) in pigs fed the PC diet compared with pigs fed the NC diet with no phytase. The STTD of P exponentially (P < 0.001) increased as phytase level increased in the diets, but because of the lack of Ca, retention of P (% of absorbed) linearly decreased (P = 0.006) as phytase increased. In conclusion, basal endogenous loss of Ca decreased as dietary phytase increased demonstrating that endogenous Ca can be bound to phytate in the intestinal tract of pigs. However, STTD of P increased as phytase level in the diets increased.

Effect of dietary peNDF levels on digestibility and rumen fermentation, and microbial community in growing goats

Physically effective neutral detergent fiber (peNDF) is a concept that accounts for the particle length of NDF in diets, sustaining the normal chewing behavior and rumen fermentation of ruminants. Specifically, peNDF>1.18 is the commonest one that is calculated from NDF and the percentage of feed dry matter left on the 1.18, 8.00, and 19.00 mm sieves. This study aimed to investigate the effects of different levels of peNDF>1.18 on the rumen microbiome and its correlation with nutrient digestibility and rumen fermentation in goats. A total of 30 Lezhi black goats were randomized and blocked to five dietary treatments (n = 6). All the diets were identical in composition but varied in hay lengths, leading to the different peNDF>1.18 content of the diets: 32.97, 29.93, 28.14, 26.48, and 24.75%. The results revealed that the nutrient digestibility increased when dietary peNDF>1.18 levels decreased from 32.97% to 28.14%, with the highest digestibility at 28.14% peNDF>1.18 treatment, after which nutrient digestibility decreased with the decreasing of dietary peNDF levels. Ruminal NH3-N concentrations in the 29.93% and 28.14% groups were higher than that in the 24.75% group (p < 0.05). Ruminal microbial protein concentration was the highest in the 32.97% group (p < 0.05). Daily CH4 production in the 32.97% and 24.75% peNDF>1.18 treatments was lower than that in the 26.48% group (p < 0.05) and no differences were observed among other groups. The relative abundance of rumen fungi at the phylum and genus levels and archaea at the species were affected by dietary peNDF>1.18 content. In conclusion, decreasing dietary peNDF>1.18 levels within a certain range can improve nutrient digestibility and change the rumen microbial community structure of goats. Dietary peNDF>1.18 level should be 28.14% (roughage length around 1 cm) among the five levels for 4 months Lezhi black goats with the purpose of optimal nutrient digestibility.

Phosphorus nutrition of growing pigs

Phosphorus (P) is an essential nutrient for diverse biological processes, which aggregate to the animal's requirement for P, and nutritionists strive to meet this requirement accurately. The P demand for a growing pig comprises requirements for maintenance and tissue deposition. The P in feed ingredients, however, must be digested and absorbed before its ultimate partition between the 2 aforementioned requirement components. Phosphorus from various sources could behave differently during digestion and absorption, which results in their disparate bioavailability for pigs. The system of standardized total tract digestibility reflects true total tract digestibility of P and feed ingredient effects on specific endogenous P loss with relative ease of implementation, and this system guarantees satisfactory additivity in digestible P among the ingredients in a diet—the foundation for diet formulation. The basal endogenous P loss, which is much easier to measure than the specific endogenous P loss, is considered as part of the pig's maintenance requirement. With this arrangement, a digestibility framework is established both for measuring the P-providing capacity of various feed ingredients and for describing the pig's P requirement. This framework entails basic understanding of the function, digestion, absorption, excretion, and homeostasis of P as support pillars. Understanding the workings of this framework enables potential integration of factors such as environment conditions and disease status in future P requirement models. The current review discusses dietary sources, digestion, absorption, bioavailability and requirement of P for growing pigs to understand the status quo, revealing the points of consensus as well as those of debate, and to encourage further investigation to provide more clarity.

Effect of Microbial Phytase on Ileal Digestibility of Minerals, Plasma and Urine Metabolites, and Bone Mineral Concentrations in Growing-Finishing Pigs

The study was conducted to evaluate the effects of added phytase in the diet of pigs on utilization of minerals and to determine the essential levels of this supplement in compound feed. An additional aim of the study was a critical assessment of current recommendations regarding the level of phosphorus in the diet of pigs, taking into account the use of phytase. A total of 432 pigs were allotted to six dietary treatments, with nine replicate pens per treatment according to body weight (BW) and sex. The treatments included a negative control (NC) with reduced content of digestible phosphorus; the NC diet supplemented with 6-phytase produced by a genetically modified strain of Aspergillus oryzae in the amount of 250 (NC + 250), 500 (NC + 500), 1000 (NC + 1000), or 1500 (NC + 1500) FTU/kg of feed; and a positive control (PC) diet formulated to meet NCR nutrient requirements for pigs. The results showed that, the higher the phytase activity in the diet (NC+), the lower the concentration of P, Ca, and Mg in the chyme (p < 0.05). Pigs fed the PC and NC+ diets had higher plasma levels of P and Ca than group NC in both fattening periods (p < 0.05). The content of phosphorus in the femur of pigs increased with the level of phytase added to the diet (p < 0.05). The content of Cu and Zn in the femur of pigs in the growing period was higher in groups NC + 500 and NC + 1000 than in the remaining experimental groups (p < 0.001). The content of P and Ca in the feces was higher in pigs fed the PC diet in comparison to the remaining experimental groups in both fattening periods (p < 0.001). There was a decrease in the content of P, Ca, and Mg in the excreta of pigs fed NC+ diets in both fattening periods (p < 0.05). A linear decrease in excretion of zinc in the feces was noted in the case of high levels of phytase, i.e., 1000 and 1500 FTU (p < 0.001). Increasing the level of phytase decreased the Cu (p < 0.001) content in the urine of growing−finishing pigs. In conclusion, the analysis of the effects of the use of phytase in a range of 0−1500 FTU/kg in low-phosphorus diets for fattening pigs indicates that 1000 FTU is the most effective level of phytase for increasing utilization of minerals and reducing excretion of elements into the environment.

Dietary Phosphorus and Calcium Utilization in Growing Pigs: Requirements and Improvements

The sustainability of animal production relies on the judicious use of phosphorus (P). Phosphate, the mined source of agricultural phosphorus supplements, is a non-renewable resource, but phosphorus is essential for animal growth, health, and well-being. P must be provided by efficient and sustainable means that minimize the phosphorus footprint of livestock production by developing precise assessment of the bioavailability of dietary P using robust models. About 60% of the phosphorus in an animal's body occurs in bone at a fixed ratio with calcium (Ca) and the rest is found in muscle. The P and Ca requirements must be estimated together; they cannot be dissociated. While precise assessment of P and Ca requirements is important for animal well-being, it can also help to mitigate the environmental effects of pig farming. These strategies refer to multicriteria approaches of modeling, efficient use of the new generations of phytase, depletion and repletion strategies to prime the animal to be more efficient, and finally combining these strategies into a precision feeding model that provides daily tailored diets for individuals. The industry will need to use strategies such as these to ensure a sustainable plant–animal–soil system and an efficient P cycle.

Digestibility of phosphorus in growing pigs as influenced by source and concentration of dietary phosphorus and collection site

The current study examined the influence of source and concentration of dietary phosphorus (P) on the apparent ileal digestibility (AID) and apparent total tract digestibility (ATTD) of P in growing pigs. Eighteen cannulated barrows (25 ± 5 kg) were allotted to a triplicate 6 × 3 incomplete Latin square design with six diets and three periods. The diets comprised of soybean meal (SBM) or distillers' dried grain with solubles (DDGS) as sole sources of dietary P, and three concentrations of P (2.0, 2.5 or 3.0 g/kg) in a 2 × 3 factorial arrangement. The AID and ATTD of P were not different (p = 0.37) in all diets. Apparent digestibility of P was affected (p < 0.01) by source and concentration of P. There was no interaction between source and concentration of dietary P on the apparent digestibility of P. Determined by regression analysis, the true ileal digestibility of P was 58.3% or 57.6%, and true total tract digestibility of P was 56.0% or 62.6%, for SBM or DDGS, respectively. The regression-derived ileal endogenous P loss (EPL) was 0.61 or 0.13 g/kg DM intake, and total tract EPL was 0.53 or 0.35 g/kg DM intake, for SBM or DDGS, respectively. In conclusion, the study demonstrated that both the source and concentration of dietary P affect the digestibility of P in growing pigs.

Heat processing increased the digestibility of phosphorus in soybean expeller, canola meal, and canola expeller fed to growing pigs

It is hypothesized that heat processing may increase P digestibility in different protein sources fed to growing pigs. A study was conducted to determine the apparent total tract digestibility (ATTD) and standardized total tract digestibility (STTD) of P in soybean expeller (SBE) produced from oil extraction using dry extrusion and expelling and to investigate the effects of heat treatment on the ATTD and STTD of P in SBE, canola meal (CM), and canola expeller (CE) fed to growing pigs. Thirty-six growing barrows with an initial body weight of 19.0 ± 1.0 kg (mean ± SD) were assigned to 1 of 6 experimental diets in a completely randomized design to give 6 replicates per diet. The experimental design was a 3 × 2 factorial arrangement including three oilseed meals with or without heat treatment. The diets were formulated to contain non-autoclaved or autoclaved (at 121 °C for 60 min) SBE, CM, and CE as the sole source of P. Limestone was included in diets to maintain a Ca:total P ratio of 1.3:1 across diets. Pigs were individually housed in metabolism crates for 12 d, including 7 d for adaptation and 5 d for total collection of feces. Pigs were offered their daily ration at 2.8 times their maintenance energy requirement. Data were analyzed using the PROC MIXED of SAS. Heat treatment increased (P < 0.05) the ATTD and STTD of P. Pigs fed the SBE diets had greater (P < 0.05) ATTD and STTD of P than pigs fed CM and CE diets. For the autoclaved ingredients, the values of STTD of P were 49.4%, 23.2%, and 25.8% for SBE, CM, and CE, respectively, whereas STTD of P in non-autoclaved SBE, CM, and CE were 48.5%, 20.2%, and 22.5%. Heat treatment increased (P < 0.05) the ATTD of Ca. In conclusion, heat treatment increased ATTD and STTD of P and ATTD of Ca in SBE, CM, and CE fed to growing pigs. The ATTD and STTD of P in SBE determined in the current study were 41.0% and 48.5%, respectively.

Effect of feeding acidified or fermented barley using Limosilactobacillus reuteri with or without supplemental phytase on diet nutrient digestibility in growing pigs

Fermentation of cereal grains may degrade myo-inositol 1,2,3,4,5,6-hexakis (dihydrogen phosphate) (InsP6) thereby increasing nutrient digestibility. Effects of chemical acidification or fermentation with Limosilactobacillus (L.) reuteri with or without phytase of high β-glucan hull-less barley grain on apparent ileal digestibility (AID) and apparent total tract digestibility (ATTD) of nutrients and gross energy (GE), standardized ileal digestibility (SID) of crude protein (CP) and amino acids (AAs), and standardized total tract digestibility (STTD) of P were assessed in growing pigs. Pigs were fed four mash barley-based diets balanced for water content: 1) unfermented barley (Control); 2) chemically acidified barley (ACD) with lactic acid and acidic acid (0.019 L/kg barley grain at a ratio of 4:1 [vol/vol]); 3) barley fermented with L. reuteri TMW 1.656 (Fermented without phytase); and 4) barley fermented with L. reuteri TMW 1.656 and phytase (Fermented with phytase; 500 FYT/kg barley grain). The acidification and fermentation treatments occurred for 24 h at 37 °C in a water bath. The four diets were fed to eight ileal-cannulated barrows (initial body weight [BW], 17.4 kg) for four 11-d periods in a double 4 × 4 Latin square. Barley grain InsP6 content of Control, ACD, Fermented without phytase, or Fermented with phytase was 1.12%, 0.59%, 0.52% dry matter (DM), or not detectable, respectively. Diet ATTD of DM, CP, Ca, and GE, digestible energy (DE), predicted net energy (NE) value, and urinary excretion of P were greater (P < 0.05) for ACD than Control. Diet ATTD of DM, CP, Ca, GE, DE and predicted NE value, urinary excretion of P was greater (P < 0.05), and diet AID of Ca and ATTD and STTD of P tended to be greater (P < 0.10) for Fermented without phytase than Control. Diet ATTD of GE was lower (P < 0.05) and diet ATTD and STTD of P, AID and ATTD of Ca was greater (P < 0.05) for Fermented with phytase than Fermented without phytase. Acidification or fermentation with/without phytase did not affect diet SID of CP and AA. In conclusion, ACD or Fermented without phytase partially degraded InsP6 in barley grain and increased diet ATTD of DM, CP, and GE, but not SID of CP and most AA in growing pigs. Fermentation with phytase entirely degraded InsP6 in barley grain and maximized P and Ca digestibility, thereby reducing the need to provide inorganic dietary P to meet P requirements of growing pigs.

Formulation of diets for pigs based on a ratio between digestible calcium and digestible phosphorus results in reduced excretion of calcium in urine without affecting retention of calcium and phosphorus compared with formulation based on values for total calcium

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 does not decrease Ca retention, but increases P utilization. Forty barrows (59.4 ± 3.8 kg) were individually housed in metabolism crates and allotted to four corn-soybean meal-based diets in a randomized complete block design with two blocks and five pigs per diet in each block. Diets were formulated using a 2 × 2 factorial design with two diet formulation principles (total Ca or STTD Ca) and two inclusion levels of microbial phytase (0 or 500 units per kg of feed). 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 or a ratio between STTD Ca and STTD P of 1.25:1. Diets were fed for 11 d and fecal and urine samples were collected from feed provided from day 6 to day 10. Interactions (P < 0.05) between diet formulation principle and phytase level were observed for Ca intake, Ca in feces, Ca absorbed, Ca retained, P digestibility, P absorbed, and P in urine. Phytase increased (P < 0.05) the digestibility of Ca in both total Ca and STTD Ca diets. Without phytase, Ca intake, Ca in feces, and Ca absorbed was greater (P < 0.05) from pigs fed total Ca diets than from pigs fed STTD Ca diets, but P absorbed, P digestibility, and P in urine was greater (P < 0.05) from pigs fed STTD Ca diets than from pigs fed total Ca diets. However, in the presence of phytase, no differences between diet formulation principles were observed in these variables. Regardless of phytase, Ca in urine was lower (P < 0.05) from pigs fed STTD Ca diets than from pigs fed total Ca diets. There were no differences in Ca retention between pigs fed STTD Ca diets and total Ca diets, but pigs fed total Ca diets retained less (P < 0.05) Ca if diets contained phytase. No differences in P retention were observed between diet formulation principles, but pigs fed non-phytase diets retained more (P < 0.05) P than pigs fed diets with phytase. In conclusion, because diets formulated based on STTD Ca contain less Ca than total Ca diets, pigs fed STTD Ca diets excreted less Ca in urine, but retention of Ca was not affected. Formulating non-phytase diets based on STTD Ca instead of total Ca increased P absorption, which confirms the detrimental effect of excess Ca on P digestibility. However, P retention was not improved if pigs were fed STTD Ca diets.

Nutritional value of a new source of fermented soybean meal fed to growing pigs

Three experiments were conducted to test the hypothesis that the standardized ileal digestibility (SID) of amino acids (AA), concentrations of digestible energy (DE) and metabolizable energy (ME), and the standardized total tract digestibility (STTD) of P in a new source of fermented soybean meal (Fermex 200) are greater than in conventional soybean meal (SBM-CV). In experiment 1, 9 barrows (initial body weight: 9.17 ± 1.03 kg) were surgically fitted with a T-cannula in the distal ileum and allotted to a triplicated 3 × 3 Latin square design. A nitrogen-free diet and 2 diets that contained cornstarch and SBM-CV or Fermex 200 as the sole source of crude protein (CP), and AA were formulated. Results indicated that there were no difference between SBM-CV and Fermex 200 for SID of CP and AA. In experiment 2, 24 growing pigs (initial body weight: 14.19 ± 1.18 kg) were housed individually in metabolism crates. Pigs were allotted to a corn-based diet or 2 diets that contained corn and SBM-CV or corn and Fermex 200. Feces and urine samples were collected using the marker-to-marker approach with 5-d adaptation and 4-d collection periods. Results indicated that the concentration of DE and ME in Fermex 200 were not different from DE and ME in SBM-CV. In experiment 3, 40 barrows (initial body weight: 11.01 ± 1.38 kg) were allotted to 1 of 4 diets with 10 replicate pigs per diet. Four diets were formulated to contain Fermex 200 or SBM-CV and either 0 or 1,000 units/kg of microbial phytase. Pigs were housed individually in metabolism crates. Fecal samples were collected as explained for experiment 2. Results indicated that the STTD of P in Fermex 200 was greater (P < 0.01) than in SBM-CV, but the addition of microbial phytase to the diets increased the ATTD and STTD of P in SBM-CV, but not in Fermex 200 (interaction; P < 0.01). In conclusion, the SID of AA and concentrations of DE and ME in Fermex 200 were not different from values determined for SBM-CV, but the STTD of P was greater in Fermex 200 than in SBM-CV if microbial phytase was not added to the diet.

Additivity of apparent and standardized ileal digestibility of phosphorus in mixed diets containing corn and soybean meal fed to broiler chickens

Phosphorus (P) is an integral part of diet formulation for broiler chickens as P is required for various biochemical processes essential to life. A study was designed to examine the additivity of apparent ileal digestibility (AID) and standardized ileal digestibility (SID) of P in mixed diets containing corn and soybean meal (SBM) with or without phytase supplementation. Birds were fed a commercial starter diet from day 0 to 21 after hatching and then allotted to 7 dietary treatments in a randomized complete block design with the BW as a blocking factor. Four semipurified diets were prepared to contain corn or SBM as the sole source of P with or without the addition of phytase at 1,000 phytase units/kg of diet. Two mixed diets were also prepared to contain corn and SBM with or without the addition of phytase at 1,000 phytase units/kg diet. A P-free diet (PFD) was formulated to determine the basal ileal endogenous loss of P. There were 16 replicate cages of the PFD and 8 replicate cages of the 6 experimental diets, with 8 birds per replicate cage for a total of 512 birds. Diets were fed for 3 d. The ileal digesta of birds were collected from the distal two-thirds of the ileum on day 24 after hatching. The SID of P in corn and SBM were 52.2 and 65.4%, respectively (SEM = 1.37). The addition of phytase improved (P < 0.05) both the AID and SID of P in the corn, SBM, and mixed diets. The determined AID or SID in the corn and SBM with or without phytase was used to predict the AID or SID in the mixed diets. There were no differences between the predicted and determined digestibility values in the mixed diets for either AID or SID of P and thus additive. Phytase supplementation of the mixed diet did not influence the additivity of AID or SID. In conclusion, the AID or SID of P in the corn and SBM was additive in the mixed diets containing corn and SBM with or without the addition of phytase.

Intrinsic phytase in hybrid rye increases the digestibility of phosphorus in corn and soybean meal in diets fed to growing pigs

An experiment was conducted to test the hypothesis that inclusion of hybrid rye in diets containing corn and soybean meal (SBM) without or with microbial phytase improves the apparent total tract digestibility (ATTD) and the standardized total tract digestibility (STTD) of P because of the intrinsic phytase activity in hybrid rye. Forty-eight growing barrows (initial body weight: 39.5 ± 7.7 kg) were allotted to six diets. A basal diet containing corn and SBM; a rye-based diet; and a diet containing corn, SBM, and rye were formulated. Each diet was formulated without and with microbial phytase (500 units/kg of diet) for a total of six diets. Fecal samples were collected for 4 d following a 5-d adaptation period according to the marker-to-marker procedure. Results indicated that no interactions between diets and concentration of phytase were observed for any of the response criteria measured. The ATTD and STTD of P and the ATTD of Ca differed (P < 0.05) among diets, but regardless of diet, the concentration of P in feces was reduced (P < 0.05) by adding microbial phytase to the diets. As a consequence, microbial phytase increased (P < 0.05) ATTD and STTD of P, and the ATTD of Ca was also increased (P < 0.05) by the use of microbial phytase. Measured values for the ATTD and STTD of P in the diets containing corn, SBM, and hybrid rye without or with phytase were greater (P < 0.05) than values that were predicted based on the ATTD and STTD of P for the corn-SBM and the hybrid rye diet. The observation that STTD predicted from the individual ingredients underestimated the STTD of P in the mixed diet indicates that the intrinsic phytase in hybrid rye resulted in increased digestibility of the P in the corn and SBM included in the corn-SBM-hybrid rye diet. In conclusion, microbial phytase increased the ATTD and STTD of P and the ATTD of Ca regardless of feed ingredients used in diets fed to pigs. In addition, the intrinsic phytase from hybrid rye increased the ATTD and STTD of P in corn and SBM.

Increasing calcium from deficient to adequate concentration in diets for gestating sows decreases digestibility of phosphorus and reduces serum concentration of a bone resorption biomarker

The objective of this experiment was to test the hypothesis that the concentration of Ca in diets fed to late gestating sows affects the apparent total tract digestibility (ATTD) and retention of Ca and P, serum concentrations of Ca and P, hormones, and blood biomarkers for bone formation and resorption. Thirty-six sows (average parity = 2.8) were housed in metabolism crates from day 91 to day 104 of gestation and fed 1 of 4 experimental diets containing 25, 50, 75, or 100% of the requirement for Ca. All diets met the requirement for P. The initial 5 d of each period were the adaptation period, which was followed by 4 d of quantitative collection of feces and urine. At the end of the collection period, a blood sample was collected from all sows. Results indicated that feed intake, weights of dried fecal and urine samples, and the ATTD of DM were not affected by dietary Ca, but ATTD of Ca increased (quadratic, P < 0.05) as Ca in diets increased. Urine Ca output was not affected by dietary Ca, but Ca retention increased (quadratic, P < 0.05) as Ca intake increased. Fecal P output increased (linear, P < 0.001) as dietary Ca increased, which resulted in a linear decrease (P < 0.001) in the ATTD of P. Urine P output also decreased (linear, P < 0.001) as dietary Ca increased, but P retention increased (linear, P < 0.05). Regressing the apparent total tract digestible Ca against dietary Ca intake resulted in a regression line with a slope of 0.33, indicating that true total tract digestibility of Ca in calcium carbonate was 33%. Serum concentrations of Ca and P and estrogen, calcitonin, and parathyroid hormone were not affected by dietary Ca. Serum concentration of carboxyterminal cross-linked telopeptide of type I collagen (CTX-I) decreased (linear, P < 0.05) as dietary Ca increased, which is a result of reduced bone resorption as dietary Ca increased. Serum bone-specific alkaline phosphatase tended to decrease (linear, P < 0.10) as Ca in diets increased, but the concentration of osteocalcin (OC) in serum was not affected by dietary Ca. The ratio between OC and CTX-I tended to increase (P < 0.10) as dietary Ca increased, which indicated that there was more bone formation than resorption in sows as dietary Ca increased. In conclusion, P digestibility in late gestating sows decreased, but retention of P increased, as dietary Ca increased from inadequate to adequate levels and blood biomarkers for bone resorption changed as Ca and P retention increased.

Nutritional evaluation of different varieties of sorghum and the effects on nursery pig growth performance

Five experiments were conducted to determine the standardized total tract digestibility (STTD) of P, digestible energy (DE), metabolizable energy (ME), and standardized ileal digestibility (SID) of amino acids (AA) in three sorghum varieties compared with corn and to determine the effects of sorghum varieties on nursery pig growth. In exp. 1, 48 barrows (initially 18.6 kg) were housed individually in metabolism crates. Treatments were arranged in a 2 × 4 factorial evaluating two levels of microbial phytase (0 or 500 units/kg) and four grain sources (corn, high-lysine, red, or white sorghum). Added phytase improved (P < 0.05) STTD of P in all ingredients, but was not different among the grains. In exp. 2, the DE and ME in the three sorghum varieties were not different from corn. In exp. 3, 10 growing barrows (initially 25.9 kg) with a T-cannula in the terminal ileum were used. Standardized ileal digestible Lys, Met, Thr, and Val were greater (P < 0.05) in corn than in the sorghum-based diets with no differences among the sorghum varieties. In exp. 4, 160 pigs (initially 6.3 kg) were randomly allotted to one of four dietary treatments with five pigs per pen and eight replicate pens per treatment in a 20-d experiment. Dietary treatments included corn or the three sorghum varieties, where the varieties of sorghum replaced corn on an SID Lys basis. No differences among treatments were observed in any growth performance parameters. In exp. 5, treatments consisted of a corn-based diet, a diet based on conventional sorghum (a mixture of red and white sorghum), and four diets with high-lysine sorghum containing increasing amounts of feed-grade AA, replacing soybean meal. Overall, pigs fed the high-lysine sorghum diet with the greatest amount of added feed-grade AA had the poorest gain:feed ratio (G:F; P < 0.05) compared with pigs fed all the other experimental diets. Within those fed the high-lysine sorghum and feed-grade AA, average daily gain, final body weight (linear, P < 0.10), and G:F (linear, P < 0.01) decreased as feed-grade AA increased. In summary, no differences in STTD of P or in DE and ME were observed among the grain sources. The SID AA values for the three sorghum varieties were not different; however, they were all lower than for corn. These results indicate that these varieties of sorghum can successfully replace corn in nursery pig diets if diets are formulated to account for differences in AA digestibility.

Comparative digestibility of polysaccharide-complexed zinc and zinc sulfate in diets for gestating and lactating sows

We hypothesized that the digestibility of a zinc polysaccharide complex is greater than zinc sulfate when sows consume high fiber diets containing corn dried distillers grains with solubles (DDGS). Gilts and sows (n = 32) were blocked according to parity and assigned randomly to one of four dietary treatments (n = 8 sows per treatments). Dietary treatments consisted of: 1) Control (ConZnSO4)-corn-soybean meal-based diet + 100 ppm supplemental Zn from ZnSO4; 2) Control PSZn (ConPSZn)-corn-soybean meal-based diet + 100 ppm supplemental Zn from Zn polysaccharide complex; 3) DDGS/ZnSO4-corn-soybean meal-40% DDGS gestation diet and a 30% DDGS lactation diet, with each containing 100 ppm supplemental Zn from ZnSO4; 4) DDGS/PSZn-corn-soybean meal-40% DDGS gestation diet and a 30% DDGS lactation diet, with each containing 100 ppm supplemental Zn from Zn polysaccharide complex. A fifth dietary treatment was imposed using a subset of sows (n = 20) to determine basal Zn losses in gestating and lactating sows fed corn-soybean meal-based diets containing no supplemental Zn. Nutrient balance experiments were conducted in both gestation and lactation to evaluate the digestibility of Zn sources of the four dietary treatments and to determine basal Zn losses when no supplemental Zn was provided. The statistical model included fixed effects of diet, Zn source, and their interaction, and random effects of parity. Estimated endogenous losses of Zn were used to adjust apparent total tract digestibility (ATTD) to true total tract digestibility (TTTD) of Zn in the four dietary treatment balance periods. There were no differences in Zn concentrations of urine, plasma, colostrum, or milk samples among treatments at any time of the experiment (P > 0.05). Gestating sows fed DDGS/PSZn had improved (P < 0.05) ATTD, TTTD, and overall retention of Zn compared with both Control treatments, with the DDGS/ZnSO4 treatment responses being intermediate. Lactating sows consuming diets without DDGS and supplemented with Zn polysaccharide complex had the greatest (P < 0.05) ATTD, TTTD, and retention of Zn, which were opposite to responses observed in gestation. Furthermore, ATTD, TTTD, and Zn retention for lactating sows consuming DDGS/PSZn were less (P < 0.05) than all other treatments. Overall, zinc digestibility of ZnSO4 and PSZn appears to be differentially influenced by the stage of the reproductive cycle and presence of dietary fiber from DDGS.

Standardized total tract digestible phosphorus requirement of 24- to 130-kg pigs1,2

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.

Effect of microbial phytase supplementation on P digestibility in pigs: a meta-analysis

The objectives of this meta-analysis were to determine to which extent phosphorus (P) digestibility and digestible P concentration in pig diets were increased by phytase supplementation and to quantify factors that potentially influence effects of phytase supplementation. A data set with a total of 547 data lines was compiled from 88 experiments published in 74 peer-reviewed papers between 2007 and April 2019. An exponential model was determined as more suitable to describe the response of P digestibility to phytase supplementation than a polynomial model. Phytase supplementation increased P digestibility by 25.6 percentage points (standard error (SE) = 1.54) to a plateau at 64.9% (SE = 1.82). The digestible P concentration was increased by phytase supplementation in the order of 1.01 g/kg (SE = 0.102) to a plateau at 2.62 g/kg (SE = 0.122). Goodness-of-fit criteria were R² = 0.780 and root mean square error = 7.55% for P digestibility, and R² = 0.691 and root mean square error = 0.48 g/kg for digestible P concentration. Consideration of further factors such as mineral P supplementation (yes or no), ad libitum vs. restrictive feeding, mixed diets vs. single feed ingredients, sex and age of pigs did not increase the accuracy of prediction in this data set. Some of these traits exhibited responses, but they likely are artefacts generated through the imbalanced structure of the data set. Effects of dietary total P, phytate (InsP₆), InsP₆-P to total P ratio, and Ca on the effect of supplemented phytase were not quantifiable. The present meta-analysis showed that responses to phytase supplementation can be well predicted although variation in P digestibility and digestible P concentration in the data set was high. Overall, predicted effects of phytase on P digestibility well corresponded to predictions made 25 years ago.

Standardized total tract digestibility of calcium varies among sources of calcium carbonate, but not among sources of dicalcium phosphate, but microbial phytase increases calcium digestibility in calcium carbonate1

Two experiments were conducted to test the hypothesis that standardized total tract digestibility (STTD) of Ca and the response to microbial phytase is constant among different sources of Ca carbonate and that the STTD of Ca is constant among different sources of dicalcium phosphate (DCP) when fed to growing pigs. In Exp. 1, 80 pigs (initial BW: 19.0 ± 1.9 kg) were randomly allotted to 10 diets and 2 blocks with 4 pigs per diet in each block. Four sources of Ca carbonate were used, and each source was included in a diet without microbial phytase and a diet with microbial phytase (500 units/kg diet). Two Ca-free diets without or with microbial phytase were also formulated. Feed allowance was 2.7 times the maintenance energy requirement for ME and daily feed allotments were divided into 2 equal meals. The initial 4 d of each period were considered the adaptation period to the diets followed by 4 d of fecal collection using the marker-to-marker procedure. Pigs fed diets containing exogenous phytase had lower (P < 0.05) basal endogenous loss of Ca compared with pigs fed diets containing no phytase. There were no interactions between phytase and source of Ca carbonate. Values for STTD of Ca were greater (P < 0.05) for diets containing microbial phytase (77.3% to 85.4%) compared with diets without exogenous phytase (70.6% to 75.2%), and values for STTD of Ca differed (P < 0.05) among the 4 sources of Ca carbonate. In Exp. 2, 40 pigs (initial BW: 14.9 ± 1.3 kg) were allotted to a completely randomized design with 5 diets and 8 replicate pigs per diet. A basal diet in which all Ca was supplied by Ca carbonate was formulated. Three diets were formulated by adding 3 sources of DCP to the basal diet and a Ca-free diet was also used. Feeding and collection methods were as described for Exp. 1. Results indicated that values for STTD of Ca and ATTD of P were not different among diets, indicating that under the conditions of this experiment, the digestibility of Ca and P in DCP appears to be constant regardless of origin of DCP. In conclusion, use of microbial phytase reduces the basal endogenous loss of Ca and increases Ca digestibility in Ca carbonate. The STTD of Ca varies among sources of Ca carbonate, regardless of phytase inclusion, but that appears not to be the case for the STTD of Ca in different sources of DCP.

Effects of standardized total tract digestible phosphorus on growth performance of 11- to 23-kg pigs fed diets with or without phytase1,2

Two experiments were conducted to determine the standardized total tract digestible phosphorus (STTD P) requirement for 11- to 23-kg nursery pigs fed diets with or without phytase. A total of 1,080 and 2,140 pigs (PIC 359 × Camborough, Hendersonville, TN; initially 11.4 ± 0.29 and 11.1 ± 0.24 kg) were used in Exp. 1 and Exp. 2, respectively. There were 23 to 27 pigs per pen with 6 and 12 replicate pens per treatment in Exp. 1 and Exp. 2, respectively. After weaning, pigs were fed a common pelleted diet with 0.45% STTD P for 7 d, and a common phase 2 meal diet with 0.40% STTD P for 14 d in Exp. 1 and 18 d in Exp. 2. Pens of pigs were then allotted to dietary treatments in a randomized complete block design with body weight (BW) as the blocking factor. In Exp. 1, dietary treatments consisted of 0.26%, 0.30%, 0.33%, 0.38%, 0.43%, 0.48%, and 0.53% STTD P. Treatments were achieved with the inclusion of monocalcium phosphate at the expense of corn. In Exp. 2, diets contained 1,000 phytase units (FYT; Ronozyme Hiphos 2500, DSM Nutritional Products, Inc., Parsippany, NJ) with assumed release value 0.132% STTD P, and treatments consisted of 0.30%, 0.33%, 0.38%, 0.43%, 0.48%, 0.53%, and 0.58% STTD P. These STTD P concentrations included the expected phytase release of 0.132% STTD P. In both experiments, a similar 1.17:1 Ca:P ratio was maintained across treatments. Statistical models included linear model (LM), quadratic polynomial (QP), broken-line linear (BLL), and broken-line quadratic (BLQ). In Exp. 1, increasing STTD P increased (linear, P < 0.001) ADG, ADFI, G:F, final BW, and grams of STTD P intake per day and per kilogram of gain. There was also a marginal quadratic response for G:F (P < 0.066). In Exp. 2, ADG and G:F increased quadratically (P < 0.05), whereas ADFI increased linearly (P = 0.060) with increasing STTD P. The BLL and QP model provided similar fit to G:F in Exp. 1, estimating the requirement for maximum G:F at 0.34% and 0.42%, respectively. The BLL was the best fitting model for ADG and G:F in Exp. 2, estimating the breakpoint at 0.40% and 0.37% STTD P, respectively. The BLL and BLQ models estimated the breakpoint for ADG as a function of STTD P intake in grams per day at 2.92 and 3.02 g/d, respectively. These data provide empirical evidence that for 11- to 23-kg pigs, the NRC (2012) accurately estimates the STTD P requirement on a g/d basis. As a percentage of the diet, the STTD P requirement for diets without or with 1,000 FYT added phytase ranged from 0.34% to 0.42%.

Effects of microbial phytase on standardized total tract digestibility of phosphorus in hybrid rye, barley, wheat, corn, and sorghum fed to growing pigs

An experiment was conducted to determine the apparent total tract digestibility (ATTD) and the standardized total tract digestibility (STTD) of P in three varieties of hybrid rye and in one source of barley, wheat, corn, and sorghum. The STTD of P in each cereal grain was determined both without and with addition of microbial phytase. In total, 112 growing barrows (13.7 ± 1.3 kg initial BW) were allotted to a randomized complete block design with four blocks of 28 pigs. Pigs were randomly allotted to 14 diets with two replicate pigs per diet in each block, resulting in a total of eight replicate pigs per diet for the four blocks. Each diet contained one of the cereal grains as the sole source of P. There were two diets with each cereal grain with one diet containing no microbial phytase and the other diet containing 1,000 units of microbial phytase per kilogram of diet. In each period, fecal output was collected for 5 d following a 5-d adaptation period according to the marker-to-marker procedure. Among the diets that did not include microbial phytase, one hybrid of rye had greater (P < 0.05) STTD of P than wheat, corn, and sorghum, which is likely a result of the greater intrinsic phytase activity in rye than in the other cereal grains. Without microbial phytase, there was no difference in the STTD of P in the three hybrids of rye and barley. Among the diets containing microbial phytase, there was no difference in STTD of P among the three hybrids of rye, barley, and corn. The STTD of P in the three hybrids of rye with microbial phytase was 61.9%, 70.8%, and 63.0%, respectively. Overall, microbial phytase improved (P < 0.05) the STTD of P in all cereal grains, although the magnitude of the increase in STTD of P differed among the grains.

Basal endogenous loss, standardized total tract digestibility of calcium in calcium carbonate, and retention of calcium in gestating sows change during gestation, but microbial phytase reduces basal endogenous loss of calcium1

The objective was to test the hypothesis that the standardized total tract digestibility (STTD) of Ca and the response to microbial phytase on STTD of Ca and apparent total tract digestibility (ATTD) of P in diets fed to gestating sows are constant throughout gestation. The second objective was to test the hypothesis that retention of Ca and P does not change during gestation. Thirty-six gestating sows (parity = 3.3 ± 1.5; d of gestation = 7 d) were allotted to 4 diets. Two diets containing 0 or 500 units of microbial phytase per kilogram were based on corn, potato protein concentrate, and calcium carbonate. Two Ca-free diets were also formulated without or with microbial phytase to estimate basal endogenous loss of Ca. Daily feed allowance was 1.5 times the maintenance energy requirement. Sows were housed individually in gestation stalls and fed a common gestation diet, but they were moved to metabolism crates from days 7 to 20 (early gestation), days 49 to 62 (midgestation), and again from days 91 to 104 (late gestation). When sows were in metabolism crates, they were fed experimental diets and feces and urine were quantitatively collected for 4 d after 4 d of adaptation. Results indicated that outcomes were not influenced by the interaction between period of gestation and dietary phytase. The basal endogenous loss of Ca was greater (P < 0.05) by sows in early gestation than by sows in mid- or late-gestation, but supplementation of microbial phytase to the Ca-free diet decreased (P < 0.01) the basal endogenous loss of Ca and tended (P = 0.099) to increase ATTD of P. Supplementation of microbial phytase did not affect ATTD of DM, STTD of Ca, Ca retention, ATTD of P, or P retention in sows fed the calcium carbonate-containing diet. The ATTD of DM was not affected by period of gestation, but the ATTD of Ca, the ATTD of P, and the retention of Ca were least (P < 0.05) in midgestation, followed by early and late gestation, respectively, and the STTD of Ca in midgestation was also reduced (P < 0.05) compared with sows in early or late gestation. Phosphorus retention was greater (P < 0.05) in late gestation than in the earlier periods. In conclusion, Ca retention was less negative and ATTD of P tended to increase with supplementation of microbial phytase to the Ca-free diet regardless of gestation period. The basal endogenous loss, STTD of Ca, ATTD of P, and retention of Ca and P in gestating sows change during gestation with the greatest digestibility values observed in late gestation.

Effects of microbial phytase on mucin synthesis, gastric protein hydrolysis, and degradation of phytate along the gastrointestinal tract of growing pigs

An experiment was conducted to test the hypothesis that pigs fed diets supplemented with exogenous phytase reduce mucin synthesis in the small intestine, increase protein hydrolysis in the stomach, increase breakdown of phytate along the gastrointestinal tract, and increase mineral and AA digestibility. A diet based on corn, soybean meal, and canola meal was formulated to meet requirements for growing pigs except for Ca and P, which were lower than requirements. Three additional diets were formulated by adding 750, 1,500, or 3,000 units of phytase (FTU) per kilogram to the basal diet. Eight growing barrows (38.45 ± 3.06 kg) were prepared with a T-cannula in the duodenum and another T-cannula in the distal ileum. Pigs were housed individually and allotted to a replicated 4 × 4 Latin square design with four pigs and four periods in each square. Each period lasted 14 d with the initial 7 d being the adaptation period to the diets. Pigs were fed twice daily in combined amounts equal to 3.2 times the estimated requirement for maintenance energy. Results indicated that the apparent ileal digestibility (AID) and the apparent total tract digestibility (ATTD) of Ca and P increased (linear and quadratic, P ≤ 0.05) as phytase inclusion increased. However, values for AID of Ca and P were not different from values for ATTD of Ca and P, indicating that there is no net absorption of Ca and P in the hindgut. The apparent duodenal digestibility (ADD) of Ca and P was ~30% and 10% to 20%, respectively, indicating some digestion in the stomach of both Ca and P. A quadratic increase (P < 0.05) of the AID of GE was observed with the breakpoint around 1,500 FTU, but there was a negative linear (P ≤ 0.001) effect of dietary phytase on the ATTD of GE. Phytase did not affect mucin synthesis in the small intestine, protein hydrolysis in the stomach, or ileal digestibility of dispensable and indispensable AA. However, degradation of higher phytate esters (IP6 and IP5) into lower phytate esters (IP4 and IP3) and inositol increased as dietary phytase increased, indicating that it is possible to completely degrade dietary phytate if microbial phytase is included by at least 3,000 FTU in the diet. In conclusion, supplementing diets with phytase resulted in increased degradation of phytate and phytate esters and improved digestibility of Ca and P, but phytase did not change intestinal mucin synthesis, gastric protein hydrolysis, or the AID of AA.

Estimation of standardized mineral availabilities in feedstuffs for broilers

Two experiments were conducted to estimate standardized mineral (Ca, P, Cu, Fe, Mn, and Zn) availabilities (SMA) in commonly used feedstuffs and verify the additivity of SMA for diet formulation of broilers. In Exp. 1, after 3 d of acclimation, a total of 96 22-d-old Arbor Acres male broilers were fasted for 24 h. Then the broilers were fed a mineral-free, corn, soybean meal (SBM), or corn-soybean meal (C-SBM) diet for 4 h and the excreta samples were collected for 48 h after feed withdrawal (totally 52 h). The results showed that the endogenous losses of Ca, P, Cu, Fe, Mn, and Zn for chickens fed the mineral-free diet were 13.7, 113, 0.064, 0.593, 0.094, and 0.132 mg/52 h per bird, respectively. The standardized availability values of Ca, P, Cu, Fe, Mn, and Zn were 20.8%, 39.6%, 37.8%, 47.4%, 10.7%, and 45.2% in corn as well as 54.3%, 51.1%, 39.7%, 27.6%, 26.1%, and 51.0% in SBM, respectively. The determined values of SMA in C-SBM diet were close (P > 0.09) to the predicted summations of SMA from corn and SBM (Ca, 48.6% vs. 48.1%; P, 44.9% vs. 46.0%; Cu, 41.7% vs. 39.1%; Fe, 35.3% vs. 33.2%; Mn, 22.7% vs. 22.2%; Zn, 46.2% vs. 48.4%). In Exp. 2, a total of 144 22-d-old Arbor Acres male broilers were used to estimate the SMA values in 6 feedstuffs by using the above procedure. The results showed that the standardized availability values in wheat, wheat bran, corn distillers dried grains with solubles, cottonseed meal, rapeseed meal, and corn gluten meal diets were 24.7% to 55.8% for Ca, 35.6% to 46.6% for P, 24.5% to 45.7% for Cu, 21.6% to 43.5% for Fe, 9.3% to 34.5% for Mn, and 22.9% to 52.9% for Zn, respectively. The results from the present study indicated that the mineral-free diet could be used for estimating the endogenous losses of the above minerals and SMA values of feedstuffs for broilers, and the estimates of SMA in feedstuffs for the C-SBM diet formulation were additive.

Additivity of values for phosphorus digestibility in corn, soybean meal, and canola meal in diets fed to growing pigs

OBJECTIVE

This study was conducted to determine the apparent and standardized total tract digestibility (ATTD and STTD) of phosphorus (P) in corn, soybean meal (SBM), and canola meal (CM), and additivity of values for ATTD and STTD of P in corn, SBM, and CM in diets fed to growing pigs.

METHODS

Thirty-six growing barrows (initial body weight of 21.6±1.7 kg) were placed in metabolism crates and allotted to a completely randomized design with 6 diets and 6 pigs per diet. Six diets were formulated using corn, SBM or CM as the sole source of P, or corn and SBM, or corn and CM, or corn, SBM, and CM as the P source in each diet, respectively. Fecal samples were collected for 5 d following a 7 d adaptation period to the diets.

RESULTS

Values for ATTD and STTD of P in corn, SBM, and CM in growing pigs were 33.12% and 37.76%, 50.19% and 56.62%, 34.93% and 39.45%, respectively. The ATTD and STTD of P in SBM were greater (p<0.05) than those in corn and CM. However, there were no differences in the ATTD or STTD of P between corn and CM. The determined STTD of P in the mixture of corn and SBM, corn and CM, and corn, SBM, and CM is not different from the calculated STTD values.

CONCLUSION

Values for STTD of P in corn, SBM, and CM are additive in their mixture fed to growing pigs.

Effects of extrusion and microbial phytase on the apparent and standardized total tract digestibility of phosphorus in hemp hulls fed to growing pigs

An experiment was carried out to determine the apparent total tract digestibility (ATTD) and the standardized total tract digestibility (STTD) of P and the effects of extrusion and microbial phytase on ATTD and STTD of P in hemp hulls (HH). Thirty-six pigs (30.3 ± 2.7 kg) were randomly allotted to 1 of 6 experimental diets in a complete randomized design with 6 replicates per diet. A corn-soybean meal (SBM)-based basal diet was formulated. Two additional diets were formulated by replacing 40% of corn and SBM (on a 100% of total diet basis) with HH or extruded HH (EHH). The test ingredients, corn, and SBM were the only sources of P in the diets. Three additional diets were also prepared by supplementing 500 unit/kg of microbial phytase to the initial 3 diets (the corn-SBM basal diet and diets containing test ingredients). Pigs were fed experimental diets at 3 times the maintenance energy requirement (197 kcal ME/kg BW0.60). Results indicated that fecal P concentration and daily P output were reduced (P < 0.05) from pigs fed diets with dietary phytase compared with pigs fed diets without dietary phytase. The ATTD and STTD of P in experimental diets were not different. However, the ATTD and STTD of P in experimental diets supplemented with dietary phytase were increased (P < 0.05) compared with the diets without phytase. The ATTD and STTD of P in HH were 18.8% and 22.0%, respectively, whereas respective values for EHH were 22.5% and 26.3%. Extrusion had no effects on ATTD and STTD of P in HH. However, the ATTD and STTD of P in HH and EHH increased (P < 0.05) when dietary phytase was added to the diets. The concentration of Ca in feces and daily Ca output were reduced (P < 0.05) as a result of phytase supplementation. Addition of dietary phytase increased (P < 0.05) the ATTD of Ca in all experimental diets. In conclusion, the ATTD and STTD of P in HH fed to growing pigs were 18.8% and 22.0%, respectively. Respective values for EHH were 22.5% and 26.3%. Extrusion did not affect the ATTD and STTD of P in HH. However, the addition of microbial phytase to experimental diets increased the ATTD and STTD of P in diets and test ingredients and decreased fecal P output from pigs fed experimental diets. There was no interaction between extrusion and dietary phytase supplementation.

Tail-end dehulling of canola meal improves apparent and standardized total tract digestibility of phosphorus when fed to growing pigs

Tail-end dehulling of canola meal (CM) has been shown to reduce dietary fiber and increase crude protein content in the dehulled meal. The application of this procedure also increased the total and non-phytate P content in the dehulled meal. However, it is unclear if dehulling affects P digestibility in the different fractions (i.e., the dehulled meal and the coarse fraction) and if it differs when fed to growing pigs at two different BW. Therefore, two experiments were conducted to determine the apparent (ATTD) and standardized (STTD) total tract digestibility of P in dehulled CM fed to growing pigs. Diets containing non-dehulled regular canola meal (RCM), and two fractions produced using sieve size of 355 µm: a low-fiber high-protein fraction (dehulled canola meal [DCM]) and a high-fiber low-protein fraction (coarse canola meal [CCM]) as the only source of P were fed to growing pigs at two different BW. A total of 48 pigs were used for the two experiments. In experiment 1, 24 barrows [(Yorkshire × Landrace) × Duroc] with initial BW of 24.5 ± 1.68 kg were individually housed in metabolism crates and fed the experimental diets for 10 d for total fecal collection. In experiment 2, 24 barrows with an average initial BW of 73.8 ± 4.93 kg were used; experimental diets and fecal collection procedures were the same as in experiment 1. Each experiment used six replicates per treatment. A P-free diet was used to determine basal endogenous losses of P (139.6 ± 10.7 and 150.89 ± 20.1 mg/kg of DMI for experiments 1 and 2, respectively). Data were analyzed as a completely randomized design. In experiment 1, the ATTD and STTD of P were greater (P < 0.05) for DCM (42.4% and 46.1%) than for the RCM (32.0% and 35.7%) and CCM (24.5% and 28.4%) diets. In experiment 2, the ATTD and STTD of P were greater (P < 0.05) for DCM (38.7% and 42.8%) than for the CCM diet (22.6% and 26.8%); whereas the values for RCM diet were intermediate (31.0% and 35.0%) and not different from the DCM and CCM. In conclusion, dehulling canola meal increased ATTD and STTD of P in growing pigs of different BW; however, there was no effect of BW.

Dietary sources of phosphorus affect postileal phosphorus digestion in growing pigs

The present study was conducted to investigate the postileal P digestion response of growing pigs to dietary P concentrations and sources. Twenty-four pigs (57.3 ± 1.9 kg initial BW) fitted with T-cannulas at the distal ileum were assigned to a duplicated 12 × 4 incomplete Latin square design with 12 diets and 4 periods. The 12 experimental diets consisted of 9 cornstarch-based diets using soybean meal (SBM), corn distiller's dried grains with solubles (DDGS), and canola meal (CM) as assay ingredients at 3 levels and 3 corn-SBM-based practical diets with 3 levels of dicalcium phosphate (DCP). Chromic oxide was included as an indigestible marker to calculate apparent ileal digestibility (AID), apparent total tract digestibility (ATTD), and apparent postileal digestibility (APID) of P. Each period consisted of 5 d of adaption period, 2 d of fecal samples collection, and 2 d of ileal digesta collection. The results showed that ileal P output, fecal P output, ileal digested P, total tract digested P, and the AID and ATTD of P were affected by the interaction of P concentrations and sources ( < 0.01). When pigs were fed the semipurified diets containing SBM and corn-SBM-based practical diets, the AID and ATTD of P increased with increasing dietary P level (linear, < 0.01). However, there were no linear or quadratic responses in the AID and ATTD of P for pigs fed diets containing increasing levels of CM and corn DDGS. Postileal digested P, the proportion of ileal digested P to total tract digested P, the proportion of postileal digested P to total tract digested P, APID of P, and hindgut disappearance of P were affected by dietary sources of P ( < 0.01). When pigs were fed the semipurified diets containing SBM and CM, there were no differences between the AID and ATTD of P. In contrast, the ATTD of P were greater than the AID of P for pigs fed diets containing corn DDGS and corn-SBM-based practical diets with DCP supplementation. In summary, postileal P digestion response of growing pigs was affected by dietary P sources.

Techniques for evaluating digestibility of energy, amino acids, phosphorus, and calcium in feed ingredients for pigs

Sound feed formulation is dependent upon precise evaluation of energy and nutrients values in feed ingredients. Hence the methodology to determine the digestibility of energy and nutrients in feedstuffs should be chosen carefully before conducting experiments. The direct and difference procedures are widely used to determine the digestibility of energy and nutrients in feedstuffs. The direct procedure is normally considered when the test feedstuff can be formulated as the sole source of the component of interest in the test diet. However, in some cases where test ingredients can only be formulated to replace a portion of the basal diet to provide the component of interest, the difference procedure can be applied to get equally robust values. Based on components of interest, ileal digesta or feces can be collected, and different sample collection processes can be used. For example, for amino acids (AA), to avoid the interference of fermentation in the hind gut, ileal digesta samples are collected to determine the ileal digestibility and simple T-cannula and index method are commonly used techniques for AA digestibility analysis. For energy, phosphorus, and calcium, normally fecal samples will be collected to determine the total tract digestibility, and therefore the total collection method is recommended to obtain more accurate estimates. Concerns with the use of apparent digestibility values include different estimated values from different inclusion level and non-additivity in mixtures of feed ingredients. These concerns can be overcome by using standardized digestibility, or true digestibility, by correcting endogenous losses of components from apparent digestibility values. In this review, methodologies used to determine energy and nutrients digestibility in pigs are discussed. It is suggested that the methodology should be carefully selected based on the component of interest, feed ingredients, and available experimental facilities.

Processing of ingredients and diets and effects on nutritional value for pigs

A conventional diet based on corn and soybean meal fed to pigs is usually provided in a mash form and in most cases, processing other than grinding and mixing is not used. However, due to the high cost of energy in pig diets, use of high fiber ingredients such as soybean hulls, distillers dried grains with solubles, and wheat middlings has increased. High fiber concentrations in the diet usually results in reduced energy and nutrient digestibility due to the low capacity of pigs to digest fiber, which negatively impacts growth performance and carcass composition of the pigs. Feed processing technologies such as changes in grinding procedures, expansion, extrusion, pelleting, use of enzymes or chemical treatments may, however, be used to solubilize some of the cellulose and hemicellulose fractions that form the cell wall of plants in the ingredients, and therefore, increase nutrient availability. This may have a positive effect on energy digestibility, and therefore, also on pig growth performance and carcass composition, but effects of different feed technologies on the nutritional value of feed ingredients and diets fed to pigs are not fully understood. It has however, been demonstrated that reduced particle size of cereal grains usually results in increased digestibility of energy, primarily due to increased digestibility of starch. Extrusion or expansion of ingredients or diets may also increase energy digestibility and it appears that the increase is greater in high fiber diets than in diets with lower concentrations of fiber. Chemical treatments have not consistently improved energy or nutrient digestibility, but a number of different enzymes may be used to increase the digestibility of phosphorus, calcium, or energy. Thus, there are several opportunities for using feed technology to improve the nutritional value of diets fed to pigs.

Methodological aspects of determining phosphorus digestibility in swine: A review

The role of phosphorus (P) in swine nutrition has been taken on new significance in recent years. Methods to determine the available phosphorus (AP) content of swine feeds include relative bioavailability (RBV), apparent total tract digestibility (ATTD), standardized total tract digestibility (STTD), and true total tract digestibility (TTTD). The RBV of P is determined by measuring bone ash or bone P, whereas the ATTD of P is determined by calculating the difference between P intake and P excretion in feces. Recent research has shown that the use of ATTD of P underestimates the AP due to the existence of endogenous P in feces and digesta. The STTD can be calculated from ATTD by taking basal endogenous phosphorus losses (EPL) into consideration. The basal EPL in pigs can be measured by feeding a P-free diet. Values for STTD of P are believed to be additive in mixed diets but not for ATTD of P. The regression method is a common approach to determine total EPL and TTTD of P, which measures the linear relationship between fecal P excretion and the dietary intake of total P. In addition, in vitro methods such as the bionic enzymatic method are being increasingly utilized because they can be done quickly and simply. Several dietary factors such as P and Ca concentrations, phytate, Ca to P ratio and vitamin D may affect AP. This review summarizes the evolution of methods to measure AP and factors that can affect AP, which may provide information to formulate swine diet more accurately. Moreover, the knowledge about AP may help to reduce the P waste in swine production and thus decrease its impact on the environment.

Endogenous phosphorus losses in growing-finishing pigs and gestating sows

An experiment was conducted to determine the effects of diet composition, feeding level (FL), and BW on endogenous phosphorous losses (EPL) using growing-finishing (GF) pigs and sows. After an adaptation period, 48 GF pigs (initial BW 90.5 kg) and 48 just-weaned sows (initial BW 195 kg), both individually housed, were allotted to 12 dietary treatments in a 2 × 3 × 2 factorial arrangement. Treatments were animal type (GF pigs or sows), diet composition (a semipurified starch (STA), inulin (INU), or lignocellulose (CEL) based low-P diet), and FL (2.0 or 3.0 kg/d). Digestibility of DM, OM, CP, crude fat, and carbohydrates (COH), and fecal P excretion (in g/d, mg/kg DMI, and g/(kg BW·d)) were determined using TiO as indigestible marker. Digestibility of OM and COH differed among diets ( < 0.001) and was greatest in both types of pigs fed the STA diet and lowest in those fed the CEL diet. While digestibility of OM and COH was similar in sows and GF pigs that were fed the STA diet and the CEL diet, on the INU diet, sows had, compared with GF pigs, a greater digestibility of OM (92.2 vs. 87.2%) and COH (92.5 vs. 88.4%), respectively. Both BW and FL increased fecal P excretion (g/d). When expressed in mg/kg DMI, P excretion was higher in sows than in GF pigs on the STA diet (498 versus 236 mg/kg DMI), the INU diet (526 vs. 316 mg/kg DMI), and the CEL diet (928 vs. 342 mg/kg DMI). When expressed in mg/(kg BW·d), however, P excretion was similar in GF pigs and sows that were fed the STA diet and in those that were fed the INU diet, whereas it was greater in sows than in GF pigs that were fed the CEL diet (11.6 vs. 7.3 mg/(kg BW·d)). The results of this study indicate that EPL (mg/kg DMI) in pigs substantially increase with increasing BW. Application of EPL (mg/kg DMI) determined in GF pigs may underestimate EPL and therefore P requirements in gestating sows. Moreover, EPL is diet dependent and increases with an increasing content of dietary nonstarch polysaccharides (NSP). The degree of this increase may differ between sows and GF pigs and seems to depend on properties of dietary fiber.

Effects of graded levels of microbial phytase on apparent total tract digestibility of calcium and phosphorus and standardized total tract digestibility of phosphorus in four sources of canola meal and in soybean meal fed to growing pigs

One hundred twenty pigs were used to determine effects of graded levels of microbial phytase on the apparent total tract digestibility (ATTD) of P and Ca and the standardized total tract digestibility (STTD) of P in 4 sources of canola meal and in 1 source of soybean meal (SBM) fed to growing pigs. The 4 sources of canola meal were produced from 1 source of high-protein canola seeds and 2 sources of conventional canola seeds with 1 of the conventional canola seeds being divided into 2 separate batches before crushing. Pigs (16.2 ± 5.3 kg initial BW) were individually housed in metabolism crates and were randomly allotted to 1 of 20 diets in a 5 × 4 factorial arrangement of treatments with 5 ingredients and 4 levels of phytase. There were 6 replicate pigs per diet. Five basal diets based on high-protein canola meal (CM-HP), high-temperature processed canola meal (CM-HT), low-temperature processed canola meal (CM-LT), conventional canola meal (CM-CV), or SBM were formulated. The basal diets contained no phytase. Fifteen additional diets were prepared by adding approximately 500, 1,500, or 2,500 phytase units/kg to each of the 5 basal diets. Feces were quantitatively collected for 5 d based on the marker-to-marker approach after a 7-d adaptation period. Results indicated that supplementation of microbial phytase increased (linear, < 0.05) the ATTD of Ca in diets containing CM-HP, CM-HT, CM-CV, and SBM but not in diets containing CM-LT. Microbial phytase also increased (linear and quadratic, < 0.05) the ATTD and STTD of P in all 5 ingredients. Compared with the CM-CV diets, the CM-HP diets had greater ( < 0.05) ATTD of Ca. The ATTD of Ca in the SBM diet was greater ( < 0.05) than in all canola meal diets, but no differences were observed in ATTD of Ca between CM-HT and CM-LT diets. The ATTD and the STTD of P were less ( < 0.05) in CM-HP, CM-HT, CM-LT, or CM-CV than in SBM if no microbial phytase was added, but no differences were observed in the ATTD and STTD of P in SBM, CM-HP, CM-HT, or CM-CV if the highest amount of phytase were added (interaction, < 0.05). Regression equations were developed to calculate the response to microbial phytase on the STTD of P in CM-HP, CM-HT, CM-LT, CM-CV, and SBM. In conclusion, inclusion of graded levels of microbial phytase increased the ATTD and STTD of P in CM-HP, CM-HT, CM-LT, CM-CV, and SBM and the response to microbial phytase added to each ingredient can be predicted by regression equations.

Effects of tallow, choice white grease, palm oil, corn oil, or soybean oil on apparent total tract digestibility of minerals in diets fed to growing pigs

An experiment was conducted to determine the effect of supplementing diets fed to growing pigs with fat sources differing in their composition of fatty acids on the apparent total tract digestibility (ATTD) of minerals. A diet based on corn, potato protein isolate, and 7% sucrose was formulated. Five additional diets that were similar to the previous diet with the exception that sucrose was replaced by 7% tallow, choice white grease, palm oil, corn oil, or soybean oil were also formulated. Diets were formulated to contain 0.70% Ca and 0.33% standardized total tract digestible P. Growing barrows ( = 60; 15.99 ± 1.48 kg initial BW) were allotted to a randomized complete block design with 2 blocks of 30 pigs, 6 dietary treatments, and 10 replicate pigs per treatment. Experimental diets were provided for 12 d with the initial 5 d being the adaptation period. Total feces were collected for a 5-d collection period using the marker-to-marker approach, and the ATTD of minerals, ether extract, and acid hydrolyzed ether extract was calculated for all diets. Digestibility of DM was greater ( < 0.05) in the diet containing soybean oil compared with the diet containing choice white grease or the basal diet, with all other diets being intermediate. The ATTD of Ca, S, and P was greater ( < 0.05) for pigs fed diets containing soybean oil, corn oil, palm oil, or tallow than for pigs fed the basal diet or the diet containing choice white grease. The ATTD of Mg, Zn, Mn, Na, and K were not different among dietary treatments. The ATTD of ether extract was greater ( < 0.05) in diets containing palm oil, corn oil, or soybean oil compared with the diet containing choice white grease, and the ATTD of acid hydrolyzed ether extract in the diet containing soybean oil was also greater ( < 0.05) than in the diet containing choice white grease. In conclusion, supplementation of a basal diet with tallow, palm oil, corn oil, or soybean oil may increase the ATTD of some macrominerals, but that appears not to be the case if choice white grease is used. There was no evidence of negative effects of the fat sources used in this experiment on the ATTD of any minerals.

Standardized total tract digestibility of phosphorus in various inorganic phosphates fed to growing pigs

An experiment was conducted to determine the standardized total tract digestibility (STTD) of phosphorus (P) in five sources of inorganic phosphate fed to growing pigs, including dicalcium phosphate (DCP), monodicalcium phosphate (MDCP), monocalcium phosphate (MCP), tricalcium phosphate (TCP) and monosodium phosphate (MSP, reagent grade). Six barrows (42.4 ± 1.1 kg) individually housed in metabolism crates were allotted to a 6 × 6 Latin square design with six dietary treatments and six periods. Each experimental period consisted of a 4 day adaptation period and a 5 day collection period. The five experimental diets contained 0.24 to 0.34% of P from each inorganic phosphate as a sole source of P. A P-free diet was also prepared to estimate the basal endogenous loss of P. The STTD of P in MSP (94.9%) was not different from the STTD of P in MCP (93.0%), but was greater (P < 0.05) than that in DCP, MDCP and TCP (87.0, 86.5 and 71.3%, respectively). In conclusion, digestibility of P in reagent-grade MSP was greater than that in feed-grade inorganic phosphates such as DCP, MDCP and TCP, and digestibility of P in DCP and MDCP was greater than that in the TCP.

Dose-dependent effects of a microbial phytase on phosphorus digestibility of common feedstuffs in pigs

Objective

The objective of this study was to evaluate increasing doses of a novel microbial phytase (Cibenza Phytaverse, Novus International, St. Charles, MO, USA) on standardized total tract digestibility (STTD) of P in canola meal (CM), corn, corn-derived distiller’s dried grains with solubles (DDGS), rice bran (RB), sorghum, soybean meal (SBM), sunflower meal (SFM), and wheat.

Methods

Two cohorts of 36 pigs each (initial body weight = 78.5±3.7 kg) were randomly assigned to 2 rooms, each housing 36 pigs, and then allotted to 6 diets with 6 replicates per diet in a randomized complete block design. Test ingredient was the only dietary source of P and diets contained 6 concentrations of phytase (0, 125, 250, 500, 1,000, or 2,000 phytase units [FTU]/kg) with 0.4% of TiO₂ as a digestibility marker. Feeding schedule for each ingredient was 5 d acclimation, 5 d fecal collection, and 4 d washout. The STTD of P increased (linear or exponential p≤0.001) with the inclusion of phytase for all ingredients.

Results

Basal STTD of P was 37.6% for CM, 37.6% for corn, 68.6% for DDGS, 10.3% for RB, 41.2% for sorghum, 36.7% for SBM, 26.2% for SFM, and 55.1% for wheat. The efficiency of this novel phytase to hydrolyze phytate is best described with a broken-line model for corn, an exponential model for CM, RB, SBM, SFM, and wheat, and a linear model for DDGS and sorghum. Based on best-fit model the phytase dose (FTU/kg) needed for highest STTD of P (%), respectively, was 735 for 64.3% in CM, 550 for 69.4% in corn, 160 for 55.5% in SBM, 1,219 for 57.8% in SFM, and 881 for 64.0% in wheat, whereas a maximum response was not obtained for sorghum, DDGS and RB within the evaluated phytase range of 0 to 2,000 FTU/kg. These differences in the phytase concentration needed to maximize the STTD of P clearly indicate that the enzyme does not have the same hydrolysis efficiency among the evaluated ingredients.

Conclusion

Variations in enzyme efficacy to release P from phytate in various feedstuffs need to be taken into consideration when determining the matrix value for phytase in a mixed diet, which likely depends on the type and inclusion concentration of ingredients used in mixed diets for pigs. The use of a fixed P matrix value across different diet types for a given phytase concentration is discouraged as it may result in inaccurate diet formulation.

Methodologies for the Determination of Endogenous Phosphorus Losses in Growing Pigs

A study was conducted to compare the endogenous basal losses of phosphorus (EBLP) in pigs fed diets containing gelatin (GEL) or spray-dried porcine plasma (SDPP) as protein sources and to determine the standardized total tract digestibility (STTD) of phosphorus (P) in SDPP. The trial was carried out at the Federal University of Santa Maria, Brazil. Twelve castrated pigs with an initial body weight of 55 kg were individually allotted in metabolic crates during two 12-day periods, each with 7 days of adaptation and 5 days of total fecal collection. The beginning and the end of the collecting periods were determined according to the marker-to-marker approach, using ferric oxide as an indigestible marker. Pigs were submitted to four semi-purified diets, one being a P-free diet with 30% of GEL as the protein source and three were diets with 10%, 20%, and 30% inclusion of SDPP respectively. Data were subjected to analysis of variance and the model included the effects of period, animal and treatments; the results of the three diets with increased levels of SDPP were subjected to linear regression analysis. The intercept of the relation of between ingested P and absorbed P represented the EBLP, while the slope indicated the STTD of P in SDPP. The EBLP means obtained by P-free diet and regression method were compared with the Student t test. The EBLP were 128.95 mg/kg dry matter intake (DMI) and 153.63 mg/kg DMI (standard error = 77.0; p<0.06) using the P-free diet with GEL as the protein source and the regression method, obtained with diets containing increased levels of SDPP, respectively. The apparent digestibility of P was 87.9%, 94.2%, and 92.9% for the treatments containing 10%, 20%, and 30% inclusion of SDPP, respectively. The estimated STTD of P obtained with the linear regression was 97.4%. When the EBLP estimated by the P-free diet was used to corrected the apparent digestibility of P in diets containing SDPP, the STTD of P in SDPP was 96.9%, 98.8%, and 95.9% for 10%, 20%, and 30% SDPP, respectively. Therefore, it can be concluded that SDPP can replace GEL to estimate the endogenous losses of P. In addition, the STTD of P in SDPP estimated with the P-free diet was 97.2% and it was 97.4% by the regression method, utilizing SDPP.