Project: MLMMI 03-01-20
To determine the solubility and reactivity of manure P from phytase amended diets in Manitoba soils.
To develop techniques that can be used to assess the environmental reactivity and mobility of manure P.
To obtain a better understanding of the relationship between increased dietary efficiency of feed P, animal performance and reduced environmental impact of manure.
KEYWORDS: Phosphorus sorption, phosphorus desorption, degree of phosphorus saturation, phosphorus sorption index, phosphorus index, phosphorus sorption maximum, phosphorus adsorption isotherm, single point isotherm
University of Manitoba
Funding Partners: who have contributed to MLMMI in support of this project:
SDIF - $25,000
MRAC - $12,007
Elite Swine - $2,000
Manitoba Pork Council and industry groups - $47,993
Amount Funded: $85,000.00
Performer Funded: $2,000.00
Total Cost: $87,000.00
First Progress Report received on July 2, 2004.
Second Progress Report received on January 6, 2005.
Third progress report received on October 7, 2005.
Final Report due on January 1, 2006. Extension granted until January 1, 2007.
Extension granted until March 31, 2007.
Final report received June 7, 2007.
1.0 Executive Summary
A multidisciplinary study was conducted to provide the swine industry in Manitoba with better information on the effect of phytase addition on animal performance, manure phosphorus characteristics, and behavior of manure phosphorus on addition to the soil. Three basal diets were formulated namely: a positive control, a negative control and a double negative control. Four more diets were obtained by adding 500 and 1000 phytase U/kg to the negative control, and 2000 and 4000 phytase U/kg to the double negative control. These seven diets were fed to 28 growing pigs and the animal performance during this period was monitored. Feces and urine from these animals were also collected and subjected to various chemical analyses. The manure was then added to representative Manitoba soils and changes in P with time was monitored. The objectives of this study were: To determine the solubility and reactivity of manure P from phytase amended diets in Manitoba soils. To develop techniques that can be used to assess the environmental reactivity and mobility of manure P. To obtain a better understanding of the relationship between increased dietary efficiency of feed P, animal performance and reduced environmental impact of manure.
1.2 Major Findings and Recommendations
1.2.1 Performance responses and nutrient utilization in growing pigs fed corn-barley soybean based diets supplemented with microbial phytase.
The effect of microbial phytase supplementation in diets of growing pigs was studied in a two weeks performance and nutrient digestibility trial involving 28 growing pigs. Seven corn-barley-soybean meal-based diets consisting of a positive control (PC) formulated to meet or exceed National Research Council (NRC, 1998) nutrient requirements; a negative control (NC) with non-phytate P reduced by 0.1 percentage unit from NC requirement and fed without or with 500 or 1000 U/kg; a doubled negative control (DNC) with no added inorganic P and fed without or with 2000 or 4000 U/kg. Chromic oxide was added as an indigestible marker and all diets were fed as mash. No differences were detected in ADG, ADFI and gain:feed ratio between pigs fed the PC diet and those fed the other diets. Addition of phytase to the NC diet had no effect on all the performance criteria measured. Supplementing DNC diet with phytase tended to improve ADG and gain:feed ratio. Pigs fed the PC diet had a higher P digestibility compared with those fed the NC and the DNC diets. Supplementing the NC diet with pyhtase tended to improve P digestibility. However, addition of phytase to the DNC diet resulted in linear and quadratic increases in P digestibility with an overall improvement of 8% and 121% at 4000 phytase U/kg of diet, respectively, compared with the PC and DNC diets. Increasing the levels of phytase supplementation in the NC and the DNC diets linearly decreased fecal P content by 45 and 42%, respectively. Adding phytase at 1000 or 4000 U/kg increased P retention by 14 or 16 percentage units, respectively, compared with the PC diet. Urinary P excretion was higher in the group fed the PC diet compared with those fed the NC and DNC diets. Urinary P output was not influenced by addition of phytase to P deficient diets. The results of this study show that complete removal of inorganic P from growing pig diets coupled with phytase supplementation improves digestibility and retention of P and N, thus reducing manure P excretion without any negative effect on pig performance.
1.2.2 Characterizing fecal and manure phosphorus from phytase amended swine diets
This study was conducted to characterize the amount and forms of P in feces and manure from phytase amended swine diets. A total of 28 growing pigs were fed seven different dietary treatments. The fecal material and urine were collected separately and a sub-sample of manure was formulated by mixing the feces and urine. Total P in feces, urine and manure was determined and both the feces and manure were fractionated using the modified sequential fractionation procedure. Total P in feces and manure were significantly reduced by 26% and 32% respectively, with phytase addition while urine total P increased by 33 – 73% with phytase addition. The labile P concentration (sum of H2O –P and NaHCO3-P) was about 71 – 89% of total P in both feces and manure. Phytase addition to the diets significantly reduced the labile P in feces; however, the reduction in labile P was not significant in the manure. Phytase addition beyond the 2000U kg-1 of diet tend to increase both the total and labile P. Overall, the addition of phytase to the diets of pigs reduced the total and labile P in the manure and feces and this may reduce the loss of P to the environment.
1.2.3 Solubility of manure phosphorus from phytase amended diets in Manitoba soils.
Dietary manipulation to reduce P losses from manure and manure amended soils has become one of the ways to address environmental concerns arising from intensive animal production. Therefore, we investigated the solubility of manure P, produced from phytase amended swine diets, in Manitoba soils. Seven composite manures generated from replicates of seven dietary treatments: PC (A positive control that contains P at NRC (1998) recommendations), NC (a negative control containing 0.1 percentage units reduction, about 33% in available P from 1998 NRC recommendations), NC+P1 (control plus 500U of phytase kg-1 of diet), NC+P2 (negative control plus 1000U of phytase kg-1of diet), DNC (a double negative control with no added inorganic P), DNC+P3 (negative control plus 2000U of phytase kg-1 of diet), DNC+P4 (a double negative control plus 4000U of phytase kg-1 of diet) were applied at a rate of 75 kg of total P ha-1 of soil to four surface Manitoba soils (0-15 cm). The soils used were; Osborne (heavy textured and calcareous), Red River (heavy textured and non-calcareous), Ladywood (light textured and calcareous), and Glenhope (light textured and non-calcareous). The soils were incubated for 1 wk, 4 wk and 16 wk after which they were extracted using either Mehlich-3 (M3-P), Modified Kelowna (MK-P), Olsen (O-P) or water (W-P). The different methods extracted varying amounts of P depending on the period of incubation. The order of extracted P using Mehlich-3 was: Osborne > Red river > Ladywood = Glenhope.
The absence of inorganic P supplementation in swine diets increased the solubility of P in amended calcareous soils. The solubility of P as extracted using water increased at the end of 4 wk by 2 - 35% and then decreased between 4 wk and 16 wk by 2 – 25% in heavy textured soils. In light textured soils, W-P, decreased at week 4 by 54 – 91% and then increased between week 4 and week 16 of incubation by 52 – 93%. We conclude that the addition of phytase to swine diets had no effect on the solubility of P in manure amended soils and that the absence of Ca in the swine diet increased manure P solubility in amended calcareous soils. Therefore, caution should be exercised in modifying diets to reduce P excretion in manure.
1.3 Overall Conclusion
We have demonstrated in this study that it is possible to completely remove inorganic P from animal diet and have no negative impact on the performance of the animal if the diet is supplemented with adequate amounts of phytase. The digestibility and retention of N and P improved with phytase supplementation leading to reduced manure P content.
Overall, the addition of phytase to swine diets reduced the total and labile P in the manure and feces and this will reduce P loading when manure from phytase mended diets is added to the soil. This management practice has the potential to reduce the loss of P from soil to surface water, as such, swine producers in Manitoba should be encouraged to use this technology as part of their manure management strategies.
This study also shows that phytase supplementation had no effect on the solubility of manure P in representative Manitoba soils. However, in the absence of inorganic P, solubility of manure P increased in calcareous soil mainly due to a lack of calcium in the manure. It may not be environmentally prudent to eliminate all the inorganic P from swine diets due to its possible impact on increased manure P solubility in certain soils.
1.4 Need For Further Studies
The following items are recommended for further studies based on the results from this study.
- The mechanism for the increased solubility of manure phosphorus in calcareous soils.
- The effect of lime and varying manure Ca:P ratios on the solubility of manure P in soils.
- Field study to determine the solubility of manure P from pyhtase fed animals in different soil and establish the manure P buffer capacity of different soils i.e., by how much will soil test P change with the addition of manure.
- The mechanism of the effect of soil texture on the changes in water extractable P of manured soils with incubation time.
- The minimum level of supplemental inorganic P that is required for optimum productivity at different stages of swine production cycle.
1.5 List of Abbreviations
1. ADG = Average Daily Gain
2. ADFI = Average Daily Feed Intake
3. G:F ratio = Gain to Feed ratio
4. ATTD = Apparent Total Tract Digestibility
5. DE = Digestible Energy
6. CP = Crude Protein
7. OM = Organic Matter
8. DM = Dry Matter
9. P = Phosphorus
10. Ca = Calcium
11. N = Nitrogen
12. WSP = Water Soluble Phosphorus
13. TP = Total Phosphorus
14. NRC = National Research Council
15. NPP = None Phytase Phosphorus
16. PC = Postive Control
17. NC = Negative Control
18. DNC = Double Negative Control
The Department of Soil Science gratefully acknowledges the financial support provided by the Manitoba Livestock Manure Management Initiatives (MLMMI). Several technical and other personnel in the Department of Soil Science participated in the studies reported herein. Their expertise, patience and diligent work is hereby acknowledged.