Reporting Scientist: Roselina Angel, University of Maryland
Objective 4, Task 1:

Reporting Scientists: Roselina Angel (Univ. of Maryland), Wendy Powers (Iowa State Univ.) and Todd Applegate (Purdue University)
Objective:  Determine the effects of dietary phytase on manure soluble phosphorus

The use of phytase in poultry and swine diets, to increase phytin phosphorus availability, is becoming more common. Yet, controversy exists on the potential impact of dietary phytase on water-soluble phosphorus content in poultry litter.  A series of studies was done to determine the impact of phytase use in broiler, turkey and swine diets on total and soluble phosphorus content in excreta. Three trials were done with broiler chicks, one with turkey poults and one with growing swine.  When phosphorus level was reduced to account for the phytin phosphorus made available when phytase was used and the diets were formulated close to phosphorus requirement levels, phytase decreased (P<0.05) both total and water soluble phosphorus in excreta.  The ratio of water soluble to total phosphorus content in excreta was not affected by the use of phytase.  Holding excreta, at excreted moisture, at 37 C for 24 and 48 h post-excretion, resulted in a large increase (P<0.05) in water-soluble phosphorus.  Addition of antibiotics to the excreta at the time of excretion minimized post-excretion changes in water-soluble phosphorus content regardless of phytase inclusion in the diet.  This work demonstrates that the correct use of phytase decreases total and water-soluble phosphorus and that changes in phosphorus solubility post-excretion are mediated by bacterial activity.

Usefulness & Impacts:  The positive impact of the use of phytase in improving dietary phytin phosphorus availability and decreasing excreta phosphorus has been proven repeatedly and is currently being implemented commercially.  The usefulness of this approach is being challenged due to the controversy that exists on the impact of the use of phytase on levels of water-soluble phosphorus in excreta.  This work demonstrates that the correct use of phytase decreases total and water-soluble phosphorus and that changes in phosphorus solubility post-excretion are mediated by bacterial activity.

Reporting Scientists: Roselina Angel (Univ. of Maryland), Wendy Powers (Iowa State Univ.) and Todd Applegate (Purdue University)

Objective:  Determine the actual excretion of phosphorus and nitrogen in broilers fed commercial type diets in a balance study and compare these values with existing estimates.

In the absence of actual biological data on total excreted nutrients, development of models is needed to predict these values.  Models are usually constructed based on relationships that have been determined biologically and that allow for estimation of values.  Estimation of nutrient excretion has become necessary due to the recent emphasis on environmental management and regulation of animal feeding operations.  Because of the impact that new environmental regulations will have on animal production it is important to determine if model estimates are accurately predicting biological nutrient excretion rates.  A broiler chick total excreta collection by age period trial was conducted to determine actual excretion of dry matter (DM), nitrogen (N) and phosphorus (P).  Values obtained in this trial were compared to existing estimates.  The current American Society of Agricultural Engineers (ASAE, 1999) estimate for broilers consistently overestimates by approximately 65% both N and P excretion.  The most recent estimate by the National Research Council (NRC, 2003) overestimates N excretion by 50%.  The new proposed ASAE model overestimates DM, N and P excretion by 19.4, 14 and 13%, respectively as compared to numbers obtained from a total collection trial in broiler chicks up to 2.36 kg of body weight fed an average industry diet.  The apparent overestimation in nutrient excretion levels in the proposed ASAE model reflects variability inherent at the commercial production level.  These overestimations are within what would be expected when average production levels (variable) are being used compared to levels obtained from one controlled battery trial.

Usefulness & Impacts:  Excretion estimates are used routinely by regulatory agencies to determine baselines for regulations.  Having accurate and current excretion levels for N, P and DM improves the ability of regulatory agencies to set minimums as well as for producers to meet new regulations.
 

Planned work for 2003-2004

Work will continue on balance trials to determine N, P and micromineral excretion in laying hens and turkeys.  Validation/challenges of existing prediction models will be done.

Floor pen work will be done to further decrease P levels in diets.  Work will focus on changes early in the life of the bird and the consequences of this in the final stages of growth.

Publications

Angel, R., N.M. Tamim, T.J. Applegate, A.S.  Dhandu, and L.E. Ellestad.  2002.  Phytic acid chemistry: Influence on phytin-phosphorus availability and phytase efficacy.  J. Appl. Poult. Res. 11: 471-480

Applegate, T.J., B.C. Joern, D.L. Nussbaum-Wagler, and R. Angel.  2003.  Water soluble phosphorus in fresh broiler litter is dependent upon phosphorus concentration fed but not on fungal phytate supplementation. Poult. Sci. 82:1024-1029.

Applegate, T.J., R. Angel, and H.L. Classen.  2003.  Dietary calcium concentration but not source, 25-hydroxycholecalciferol or bird strain affects small intestinal phytase activity in broiler chickens.  Poult. Sci. 82:1140-1148.
 
Tamim, N.M., and R. Angel.  (2003).  Phytate phosphorus hydrolysis as influenced by dietary calcium and micro-mineral source in broiler diets.  J. Agric. Food Chem. 51:4687-4693.

Dhandu, A.S. and R. Angel. 2003.  Broiler non-phytin phosphorus requirement in the finisher and withdrawal phases of a commercial four-phase feeding system.  Poult. Sci. 82:1257-1265.

Maguire, R.O., J.T. Sims, J.M. McGrath, and C.R. Angel. 2003.  Phytase and 25-hydroxycholecalciferol in turkey diets affects phosphorus solubility in manure amended soils.  Soil Sci. 168:421-433.