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Effects of Phytase Inclusion in Broiler Breeder Diets During Early Lay on their Fecal and Egg Characteristics

ABSTRACT

This study investigated the effects of phytase inclusion in broiler breeder diets on fecal and egg characteristics. A total of 48 female broiler breeders were evaluated in this study from 21 to 31 weeks of age. The dietary treatments were fed from 30 to 31 wks of age, and included a Positive Control (PosCon) diet, containing 3.0% calcium and 0.50% available phosphorus (AvP); a Negative Control (NegCon) diet, with 3.0% calcium and 0.25% AvP; Negative Control diet + 275 FTU/kg phytase (NegCon+275), and Negative control diet + 550 FTU/kg phytase (NegCon+550). Egg, yolk, albumin, and eggshell weight, albumin height, and eggshell thickness were measured. Fecal parameters included fecal moisture, liquid portion, and mineral content. After 14 d on the experimental diets during the onset of lay, the NegCon+550 diet increased (p<0.01) fecal moisture content. In general, hens fed the highest enzyme level (NegCon+550) excreted fewer (p<0.05) divalent and trivalent cations, which included Al, Fe, Mg, Mn, and Zn. Fecal Na and K levels were not affected by dietary treatments. The NegCon+550 diet increased fecal P when compared with the NegCon and the NegCon+275 diets. The NegCon+550 and PosCon diets exhibited similar fecal P. No significant effects on egg characteristics were observed. It was concluded that during early lay, various signs of fecal changes would probably be observed at phytase dosages above approximately 500 FTU/kg characterized by increased fecal moisture content and excretion of P in broiler breeders.

Keywords:
Broiler breeders; fecal minerals; fecal moisture; liquid portion; phytase

INTRODUCTION

It has been long established that plant feed stuffs contain phytate, which is considered an anti-nutritional factor for poultry (Anderson, 1912Anderson RJ. Phytin and phosphoric acid esters of inosite. Journal of Biological Chemistry 1912;11:471-488.), as they do not produce sufficient endogenous phytase to fully utilize the phosphorus (P) trapped as phytic acid (Maenz & Classen, 1998Maenz DD, Classen HL. Phytase activity in the small intestinal brush border membrane of the chicken. Poultry Science 1998;77:557-563.). Therefore, P bioavailability in common feedstuffs, such as corn and soybean meal, is limited (NRC, 1994). Consequently, the addition of highly-bioavailable inorganic phosphorus (P) sources to poultry diets has become a common practice. However, excessive dietary P, which was not utilized by the body, is excreted in the feces causing environmental pollution (Foy & Withers, 1995Foy RH, Withers PJ. The contribution of agricultural phosphorus to eutrophication. Paris: International Fertilizer Association; 1995.). Several strategies have been employed to reduce this environmental impact. The PosCon birds (Ca:AvP ratio ~6) exhibited an intermediate P excretion, followed by the NegCon+550 hens. Such as genetic selection for reduced P requirement (Punna & Roland, 1999Punna S, Roland DA. Variation in phytate phosphorus utilization within the same broiler strain. Journal of Applied Poultry Research 1999;8:10-15.), reduced P safety margins in feed formulation, and the dietary inclusion of phytase enzymes to feed (Yi et al., 1996Yi Z, Kornegay ET, Ravindran V, Denbow DM. Improving phytate phosphorus availability in corn and soybean meal for broilers using microbial phytase and calculation of phosphorus equivalency values for phytase. Poultry Science 1996;75:240-249.; Selle & Ravindran, 2007Selle PH, Ravindran V. Microbial phytase in poultry nutrition. Animal Feed Science and Technology 2007;135:1-41.). These strategies have effectively reduced inorganic P levels in poultry diets and the environmental consequences of poultry production.

Furthermore, the chelation capacity of phytic acid for minerals such as calcium (Ca), P, and magnesium has been reported to reduce the bioavailability of these minerals (Nolan et al., 1987Nolan KB, Duffin PA, McWeeny DJ. Effects of phytate on mineral bioavailability. In vitro studies on Mg, Ca, Fe, Cu, and Zn solubilities in the presence of phytate. Journal of the Science of Food and Agriculture; 1987 [cited 2014 Jun 8]. Available from: http://onlinelibrary.wiley.com/doi/10.1002/jsfa.2740400110/epdf
http://onlinelibrary.wiley.com/doi/10.10...
; Karimi et al., 2013Karimi A, Min Y, Lu C, Coto C, Bedford MR, Waldroup PW. Assessment of potential enhancing effects of a carbohydrase mixture on phytase efficacy in male broiler chicks fed phosphorus-deficient diets from 1 to 18 days of age. Poultry Science 2013;92:192-198.). Over the past two decades, phytase enzymes have been introduced to increase the availability of P, Ca, and zinc bound by the phytate molecule (Adeola et al., 2004Adeola O, Sands JS, Simmins PH, Schulze H. The efficacy and equivalency of an Escherichia coli-derived phytase preparation. Journal of Animal Science 2004;82:2657-2666.; Dilger et al., 2004Dilger RN, Onyango EM, Sands JS, Adeola O. Evaluation of microbial phytase in broiler diets. Poultry Science 2004;83:962-970.).

According to Plumstead et al. (2007Plumstead PW, Romero-Sanchez H, Maguire RO, Gernat AG, Brake J. Effects of phosphorus level and phytase in broiler breeder rearing and laying diets on live performance and phosphorus excretion. Poultry Science 2007;86:225-231.), adding 300 FTU phytase/kg diet reduced fecal moisture (FM) of floor-reared broiler breeder pullets receiving diets with 0.85% Ca and either 0.35% or 0.45% AvP. However, during lay, FM increased when 500 FTU phytase/kg were included in diets with2.7% Ca and either 0.22% or 0.45% AvP. Differences in FM may be due to phytase inclusion level, dietary Ca offered, or the relative absence of P on slats versus floor rearing (Harms et al., 1984Harms RH, Bootwalla S, Wilson HR. Performance of broiler breeder hens on wire and litter floors. Poultry Science 1984;63:1003-1007.). It has also been reported that an inappropriate or imbalanced Ca to available P (Ca:AvP) ratio may negatively affect water intake (Leeson & Summers, 1987Leeson S, Summers JD. Effect of dietary calcium levels near the time of sexual maturity on water intake and excreta moisture content. Poultry Science 1987;66:1918-1923.) and water retention (Guo et al., 2008Guo X, Huang K, Chen F, Luo J, Pan C. High dietary calcium causes metabolic alkalosis in egg-type pullets. Poultry Science 2008;87:1353-1357.; Enting et al., 2009Enting H, Mozos J de los, Gutiérrez del Álamo A, Pérez de Ayala P. Influence of minerals on litter moisture. Proceedings of 17th European Symposium of Poultry Nutrition; 2009 Aug 23-27; Edinburgh: World's Poultry Science Association; 2009. p.23-27.). It has been suggested that dietary phytase changes effective Ca:AvP ratio (Selle & Ravindran, 2007Selle PH, Ravindran V. Microbial phytase in poultry nutrition. Animal Feed Science and Technology 2007;135:1-41.; Naves et al., 2016), which may result in increased FM (Bedford et al., 2007Bedford MR, Parr T, Persia ME, Batal A, Wyatt CL. Influence of dietary calcium and phytase source on litter moisture and mineral content. Poultry Science 2007;86 Suppl 1:673.). These data suggest that dietary mineral content and phytase activity in feed needs to be appropriately managed to prevent excessive FM, which may have detrimental effects on animal welfare (Francesch & Brufau, 2004Francesch M, Brufau J. Nutritional factors affecting excreta/litter moisture and quality. World's Poultry Science Journal 2004;60:64-74.) as well as contaminate eggs used to produce broiler chicks. Therefore, this trial aimed at determining the effect of the inclusion of phytase in broiler breeder diets during early lay on FM, mineral excretion, and egg quality.

MATERIALS AND METHODS

This experiment was designed and conducted in compliance with the Guide for Care and Use of Agricultural Animals in Research and Teaching (FASS, 2010FASS. Guide for the care and use of agricultural animals in research and teaching. 3rd ed. Champaign: Federation of Animal Science Society; 2010.).

A total of 48 female Ross 708 (Aviagen, Huntsville, AL) broiler breeder pullets were individually placed at 21 wks of age in 0.33 m x 0.46 m x 0.41 m (w x l x h) cages. The experimental diets were provided in individual PVC feeders, allowing minimal cross-contamination between cages. A lighting program of 14 h of light in 21 wk, 15 h of light 10 d after housing, 15.5 h at 5% lay (25 wk), and 16 h from 50% rate of lay to the end of the experiment. House temperature was maintained between 16°C and 27°C using curtains, heaters, and circulating fans.

Individual aluminum pans were fitted to each cage in order to collect feces. A 250-mL beaker was attached to collect the liquid portion (LP) that drained from feces daily (Figure 1). This setup allowed for the separation of the LP and feces for purposes of measuring amount of liquid. The aluminum fecal collection pans were installed in a manner that avoided water and feed contamination of the feces. Additionally, an empty cage was left between birds to prevent any cross-contamination. A graduated cylinder was used to daily measure the LP separately from the fecal material. The feces and LP from each individual hen were then mixed and homogenized in duly-identified bag to ensure the analysis of total nutrients present in both LP and feces. A sub-sample was collected and dried in an oven at 95°C for 24 h for the determination of FM and dry matter content (AOAC, 2006). Dried feces were then ground, and a sample was analyzed for mineral content.

Figure 1
Aluminum trays used for feces collection. Hanging beaker used to collect liquid portion (LP) of the feces. Trays are placed within sufficient distance from the drinkers and feeders, and an empty cage was left between birds to prevent sample and treatment cross-contamination.

A broiler breeder grower diet (0.9% Ca, 0.45% AvP) was fed from 21 to 28 wks of age, after which each birds was fed 154 g of feed/d of a standard broiler breeder layer diet (2.7% Ca, 0.37% AvP) for an additional 7 d before the experimental period began (Table 1). For the following 14 d (30 to 31 wks of age), the experimental diets were fed. A basal diet was formulated to contain 3.0% Ca, to which appropriate amounts of dicalcium phosphate, limestone, filler, and phytase were added. The dietary treatments (Table 2) included: positive control with 0.50% AvP (PosCon); negative control with 0.25% AvP (NegCon); NegCon with the addition of 275 FTU phytase/kg (NegCon+275); and NegCon with the addition of 550 FTU phytase/kg (NegCon+550). Diets were offered in coarse mash form. The phytase enzyme product was an Escherichia coli-derived 6-phytase added “on top” of the basal diet without using a matrix value.

Table 1
Ingredient composition and calculated analysis of initial layer diet fed to 28-wk-old broiler breeders prior to the experimental period.
Table 2
Ingredient composition and calculated analysis of diets fed to 30 to 31-wk-old broiler breeders.

After feeding the 48 females the standard layer diet (Table 1) for 7 d, hens were classified in three blocks based on LP production (high, average, and low LP). Four hens per LP block were assigned to each of the four dietary treatments (Table 2). Fecal LP and FM were determined on d 0 (pretreatment) and d 14 feeding the four experimental diets. The change in percentage FM (∆%FM) while consuming the 4 experimental diets was calculated as follows: ∆%FM = %FM@14 d - %FM@0 d. Positive values indicate wetter feces with respect to d 0 d FM base value. Egg weight, eggshell weight, eggshell thickness, yolk weight, and albumen weight and height were determinedin two eggs per hen at 31 wks of age.

A randomized block design with 12 replicate hens per dietary treatment and four replicate hens per LP block (low, average, and high LP producers) was employed. The general linear model of SAS (2011) was used to analyze the variables. The LSMEANS command of SAS was used to partition differences among the means. Statistical significance was set at p≤0.05.

RESULTS AND DISCUSSION

Egg weight and egg quality parameter results are presented in Table 3, and no influence of dietary treatments were detected p>0.05), suggesting that all diets contained adequate nutrient levels. No differences were observed due to the dietary treatments in the production of LP volume (Figure 2) during the entire experimental period. However, LP differences were verified during the first period (d 0-1), when dietary Ca level wasincreased to 3.0% and AvP content was altered. The PosCon group exhibited the greatest transient increase in LP while NegCon+550 exhibited the least change. Previous research in commercial layers demonstrated that increasing dietary Ca caused a temporary increase in water intake and FM (Leeson & Summers, 1987Leeson S, Summers JD. Effect of dietary calcium levels near the time of sexual maturity on water intake and excreta moisture content. Poultry Science 1987;66:1918-1923.). Moreover, Smith et al. (2000Smith A, Rose SP, Wells RG, Pirgozliev V. Effect of excess dietary sodium, potassium, calcium and phosphorus on excreta moisture of laying hens. British Poultry Science 2000;41:598-607.) found that increasing dietary AvP levels in commercial layer diets caused a significant linear increase in water intake that consequently increased FM. Indeed, PosCon diet, containing the highest inorganic P level, resulted in the most pronounced transient increase in LP. There was considerable sensitivity to altered Ca:AvP ratios in these laying birds, which may affect the contamination of hatching eggs. The hens fed the NegCon+550diet, which contained the greatest amount of enzyme, exhibited greater FM (Figure 3) on d 14 when compared to the other three dietary treatments (p<0.05). Therefore, theLP and FM of the evaluated broiler breeder hens dynamically responded to altered Ca:AvP, either with or without phytase.

Table 3
Effect of inclusion of phytase in diets fed to 30 to 31-wk-old broiler breeders on egg quality variables measured at 31wks of age.

These results demonstrated that higher phytase inclusion levels resulted in greater enzymatic digestion of phytate, as expected. However, only the birds fed the diet with the highest enzyme inclusion (NegCon+550) exhibited greater fecal moisture (FM) on d 14 (Figure 3). The NegCon+550 hens exhibited approximately 10% greater FM when d 0 and d 14 were compared. Presumably, this was due to greater digestion of the phytate molecule. It is known that phytate has the capacity to chelate positively-charged cations, and form complexes with starch and proteins/aminoacids (Humer et al., 2015Humer E, Schwarz C, Schedle K. Phytate in pig and poultry nutrition. Journal of Animal Physiology and Animal Nutrition 2015;99:605-625.). As a consequence, phytase may release these potentially hygroscopic organic macromolecules (Hori et al., 2001Hori G, Wang MF, Chan YC, Komatsu T, Wong Y, Chen TH, et al. Soy protein hydrolyzate with bound phospholipids reduces serum cholesterol levels in hypercholesterolemic adult male volunteers. Bioscience, Biotechnology, and Biochemistry 2001;65:72-78.; Castro-Freitas, 2005Castro-Freitas DDG. Barras de cereais elaboradas com proteína de soja e gérmen de trigo, características físico-químicas e textura durante armazenamento. Archivos Latinoamericanos de Nutrición 2005;55:299-304.; Selle et al., 2000Selle PH, Ravindran V, Caldwell RA, Bryden WL. Phytate and phytase:consequences for protein utilization. Nutrition Research Reviews 2000;13:255-278.), contributing to increase FM.

Figure 2
Daily fecal liquid portion (LP) volume produced during the first 14 d on dietary treatments. The four dietary treatments consisted of PosCon = 0.50% AvP (diamond), NegCon = 0.25% AvP (circle), NegCon+275 = NegCon plus 275 FTU/kg feed (triangle), and NegCon+550 = NegCon plus 550 FTU/kg feed (dot). Standard error of the mean (SEM) for n=12 hens per diet. There was a significant effect of time (p<0.01), but no dietary treatment effect.

Figure 3
Effect of inclusion of phytase in low available phosphorus broiler breeder diets on the absolute change in percentage fecal moisture (FM) after 14 d of dietary treatments. The four dietary treatments consisted of PosCon = 0.50% AvP, NegCon = 0.25% AvP, NegCon+275 = NegCon plus 275 FTU/kg feed, and NegCon+550 = NegCon plus 550 FTU/kg feed. Standard error of the mean (SEM) for n=12 hens per diet. A,BMeans with different superscripts are significantly different at p<0.01.

A clear relationship between FM and LP volume was not evident in this study. Greater LP volume values did not result in greater FM. Other researchers have reported that this maybe explained by a difference in water-holding capacity of the feces. Previously, Kalmar et al. (2007Kalmar ID, Werquin G, Jenssen GPJ. Apparent nutrient digestibility and excreta quality in African grey parrots fed two pelleted diets based on coarsely or finely ground ingredients. Journal of Animal Physiology and Animal Nutrition 2007;91:210-216.) observed that African gray parrots fed fine or coarse particle-size pelleted feed produced similar FM (~72%). However, they also found that excreta texture was significantly different. They attributed their observations to the differential release of non-starch polysaccharides due to feed particle size (i.e., surface area) and microbial action upon them. It has been reported that these factors could influence fecal water-holding capacity (Francesch & Brufau, 2004Francesch M, Brufau J. Nutritional factors affecting excreta/litter moisture and quality. World's Poultry Science Journal 2004;60:64-74.).

Another factor that may have affected FM and LP was the fact that no Ca matrix value was assigned to the phytase. This resulted in slightly different Ca:AvP ratios among the treatments. Previous research showed that altered Ca:AvP ratio resulted in wet litter when phytase was used (Pos et al., 2003Pos J, Enting H, Veldman A. Effect of phytase and dietary calcium level on litter quality and broiler performance. Proceedings of 14th European Symposium of Poultry Nutrition; 2003 Aug 10-14; Lillehammer: World's Poultry Science Association, 2003. p.7-18.). This could be mechanistically similar to the present data, but increased FM was only evident when the higher enzyme dosage was used.

Table 4 shows the effect of feed treatments on the fecal concentration of minerals on d 14. Birds fed the greatest amount of enzyme (NegCon+550 diet) excreted less divalent and trivalent cations and more P. Thus, a significant phytase effect was demonstrated at the greater dosage only. It has been previously proposed that the breakdown of the phytate molecule by phytase also releases chelated cations (Sebastian et al., 1998Sebastian S, Touchburn SP, Chávez ER. Implications of phytic acid and supplemental microbial phytase in poultry nutrition:a review. World's Poultry Science Journal 1998;54:17-47.). The present data suggest that only the greatest dosage (NegCon+550) sufficiently disrupted the phytate molecule to release several trapped cations.

Table 4
Effect of inclusion of phytase in diets fed to 30 to 31-wk-old broiler breeders on fecal mineral excretion at 31wks of age.

Furtermore, Table 4 clearly shows the resemblance in the response of NegCon and NegCon+275 birds with regards to fecal Ca and P content. This suggests that a low level of phytase activity or that a Ca:AvP ratio of around 12 caused increased Ca and reduced P excretion. It must be remembered that all diets, except for the positive control, had the same total P content. Thus, it could be suggested that the fecal P of PosCon was inorganic while that of NegCon+550 (greatest enzyme) was phytate-derived.

In conclusion, this study demonstrated the effects of adding stepwise doses of phytase on FM of broiler breeder hens during the early laying period. The use of the greater enzyme dose increased FM. A greater enzyme dosage or altered Ca:AvP ratio appeared to either increase water intake anddecrease the water-holding capacity of the feces. Thus, it was concluded that the addition of phytase at 550 FTU/kg to a broiler breeder layer diet increased FM during the onset of lay. Also, some ions and molecules with different electrochemical and hygroscopic properties were released only at the greatest phytase dosage. These data also demonstrated that broiler breeder hens required time to adapt to altered dietary Ca and AvP during early lay. This was observed irrespective of the presence or absence of dietary phytase. These results suggest that various signs of fecal changes may probably be observed at phytase dosages above approximately 500 FTU/kg.

REFERENCES

  • Adeola O, Sands JS, Simmins PH, Schulze H. The efficacy and equivalency of an Escherichia coli-derived phytase preparation. Journal of Animal Science 2004;82:2657-2666.
  • Anderson RJ. Phytin and phosphoric acid esters of inosite. Journal of Biological Chemistry 1912;11:471-488.
  • AOAC - Association of Official Agricultural Chemists. Official methods of analysis of AOAC International. 17th ed. Gaithersburg; 2006.
  • Bedford MR, Parr T, Persia ME, Batal A, Wyatt CL. Influence of dietary calcium and phytase source on litter moisture and mineral content. Poultry Science 2007;86 Suppl 1:673.
  • Castro-Freitas DDG. Barras de cereais elaboradas com proteína de soja e gérmen de trigo, características físico-químicas e textura durante armazenamento. Archivos Latinoamericanos de Nutrición 2005;55:299-304.
  • Dilger RN, Onyango EM, Sands JS, Adeola O. Evaluation of microbial phytase in broiler diets. Poultry Science 2004;83:962-970.
  • Enting H, Mozos J de los, Gutiérrez del Álamo A, Pérez de Ayala P. Influence of minerals on litter moisture. Proceedings of 17th European Symposium of Poultry Nutrition; 2009 Aug 23-27; Edinburgh: World's Poultry Science Association; 2009. p.23-27.
  • FASS. Guide for the care and use of agricultural animals in research and teaching. 3rd ed. Champaign: Federation of Animal Science Society; 2010.
  • Foy RH, Withers PJ. The contribution of agricultural phosphorus to eutrophication. Paris: International Fertilizer Association; 1995.
  • Francesch M, Brufau J. Nutritional factors affecting excreta/litter moisture and quality. World's Poultry Science Journal 2004;60:64-74.
  • Guo X, Huang K, Chen F, Luo J, Pan C. High dietary calcium causes metabolic alkalosis in egg-type pullets. Poultry Science 2008;87:1353-1357.
  • Harms RH, Bootwalla S, Wilson HR. Performance of broiler breeder hens on wire and litter floors. Poultry Science 1984;63:1003-1007.
  • Hori G, Wang MF, Chan YC, Komatsu T, Wong Y, Chen TH, et al. Soy protein hydrolyzate with bound phospholipids reduces serum cholesterol levels in hypercholesterolemic adult male volunteers. Bioscience, Biotechnology, and Biochemistry 2001;65:72-78.
  • Humer E, Schwarz C, Schedle K. Phytate in pig and poultry nutrition. Journal of Animal Physiology and Animal Nutrition 2015;99:605-625.
  • Kalmar ID, Werquin G, Jenssen GPJ. Apparent nutrient digestibility and excreta quality in African grey parrots fed two pelleted diets based on coarsely or finely ground ingredients. Journal of Animal Physiology and Animal Nutrition 2007;91:210-216.
  • Karimi A, Min Y, Lu C, Coto C, Bedford MR, Waldroup PW. Assessment of potential enhancing effects of a carbohydrase mixture on phytase efficacy in male broiler chicks fed phosphorus-deficient diets from 1 to 18 days of age. Poultry Science 2013;92:192-198.
  • Leeson S, Summers JD. Effect of dietary calcium levels near the time of sexual maturity on water intake and excreta moisture content. Poultry Science 1987;66:1918-1923.
  • Maenz DD, Classen HL. Phytase activity in the small intestinal brush border membrane of the chicken. Poultry Science 1998;77:557-563.
  • Naves L de P, Rodrigues PB, Meneghetti C, Pereira Bernardino VM, Oliveira DH de, et al . Efficiency of microbial phytases in diets formulated with different calcium:phosphorus ratios supplied to broilers from 35 to 42 days of age. Journal of Applied Animal Research 2016;44:446-453.
  • Nolan KB, Duffin PA, McWeeny DJ. Effects of phytate on mineral bioavailability. In vitro studies on Mg, Ca, Fe, Cu, and Zn solubilities in the presence of phytate. Journal of the Science of Food and Agriculture; 1987 [cited 2014 Jun 8]. Available from: http://onlinelibrary.wiley.com/doi/10.1002/jsfa.2740400110/epdf
    » http://onlinelibrary.wiley.com/doi/10.1002/jsfa.2740400110/epdf
  • NRC - National Research Council. Nutrient requirements of poultry. 9th ed. Washington: National Academies Press; 1994.
  • Plumstead PW, Romero-Sanchez H, Maguire RO, Gernat AG, Brake J. Effects of phosphorus level and phytase in broiler breeder rearing and laying diets on live performance and phosphorus excretion. Poultry Science 2007;86:225-231.
  • Pos J, Enting H, Veldman A. Effect of phytase and dietary calcium level on litter quality and broiler performance. Proceedings of 14th European Symposium of Poultry Nutrition; 2003 Aug 10-14; Lillehammer: World's Poultry Science Association, 2003. p.7-18.
  • Punna S, Roland DA. Variation in phytate phosphorus utilization within the same broiler strain. Journal of Applied Poultry Research 1999;8:10-15.
  • SAS. SAS user's guide. The SAS system for windows 7. Version 9.3. Cary; 2011.
  • Sebastian S, Touchburn SP, Chávez ER. Implications of phytic acid and supplemental microbial phytase in poultry nutrition:a review. World's Poultry Science Journal 1998;54:17-47.
  • Selle PH, Ravindran V, Caldwell RA, Bryden WL. Phytate and phytase:consequences for protein utilization. Nutrition Research Reviews 2000;13:255-278.
  • Selle PH, Ravindran V. Microbial phytase in poultry nutrition. Animal Feed Science and Technology 2007;135:1-41.
  • Smith A, Rose SP, Wells RG, Pirgozliev V. Effect of excess dietary sodium, potassium, calcium and phosphorus on excreta moisture of laying hens. British Poultry Science 2000;41:598-607.
  • Yi Z, Kornegay ET, Ravindran V, Denbow DM. Improving phytate phosphorus availability in corn and soybean meal for broilers using microbial phytase and calculation of phosphorus equivalency values for phytase. Poultry Science 1996;75:240-249.

Publication Dates

  • Publication in this collection
    05 June 2020
  • Date of issue
    2020

History

  • Received
    25 Mar 2019
  • Accepted
    23 Dec 2019
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