August, 1999 . Volume 22, Number 7 
NCSU Extension Swine Husbandry
August, 1999 . Volume 22, Number 7
Phosphorus (P) from animal manure is becoming an increasing environmental
concern. Nutritional strategies to reduce P excretion have been
investigated in the past and continue to be a priority research
focus of many research institutions. Particularly the use of phytase
enzyme has been reported to reduce the excretion of P in swine
manure by 30 to 50%. Phytase is an enzyme that can not be produced
by the pig, but is necessary to release P bound by phytic acid
(or phytate). A large proportion of the P in feedstuffs of plant
origin is bound in the form of phytate-P. For example, approximately
90% of the P in corn is present as phytate P and is therefore
not available to the pig. Grain companies are currently working
on corn varieties that contain less phytate bound P and have identified
the lpa1 gene that causes a large reduction in phytic acid
production in corn seeds. Lines of hybrid corn containing this
gene (low phytate corn) have been tested in swine experiments
to determine the availability of P in the corn and subsequent
pig performance.
The NRC (1998) lists a total P value for corn of 0.28%. The amount
of P that the pig can actually use (bioavailability) is only 14%,
or in other words 86% of this amount is excreted in the manure.
The bioavailability of low phytate corn is much higher as determined
in recent experiments (Table 1). On average, P in regular corn
was 18% available, whereas P in low phytate corn was 73% available.
| Bone strength, Ash | Cromwell et al., 1998 | ||||||
| Bone strength | Spencer et al., 1998a | ||||||
| Bone strength, Ash | Pierce and Cromwell, 1999a | ||||||
| 1 LPC is low phytate corn 2MSP is mono-sodium phosphate. The availability of P in MSP is set as 100%. | |||||||
The effect of replacing regular corn with low phytate corn based on total P was evaluated by Pierce et al. (1998a). The total P levels in the final diets ranged from 0.33% up to 0.59% and two of those levels were below the total P requirement of 0.50% suggested by the NRC (1998). However, as mentioned before, the amount of P available to the pig is higher for low phytate corn, and therefore, the available P content is greater in the low phytate corn diets (Table 2). The NRC (1998) lists an available P requirement for growing pigs of 0.23%, which means that the lowest P diet when low phytate corn was used was only marginally deficient in P (it contained 0.20% available P). In fact, the greater availability of P in low phytate corn resulted in an improvement in daily gain of 25% compared to regular corn pigs fed the diets with the lowest level of P. Other studies have reported improved performance ranging from 8 to 23% (Pierce et al., 1998b; Spencer et al., 1998b). The magnitude of performance improvement would likely depend on the design of the trial, particularly the level of dietary P used and how it compares to the pigs' requirement.
| Total P, % Available P, % | ||||||||
| Daily Gain, lbs | ||||||||
| Feed/Gain | ||||||||
| Bone Strength | ||||||||
| Bone Ash, % | 1 Each mean represent 5 pens of 2 pigs per pen.
Initial and final pig weights were 50 and 112 lbs, respectively for the 37 day trial.
Bone strength and bone ash are average values for the metacarpals and metatarsals | |||||||
Because more P from the low phytate corn is utilized by the pig,
P excretion can be reduced by feeding low phytate corn. Research
has demonstrated that P excretion can be reduced from 13 to 50%
(Pierce et al., 1998a; Pierce and Cromwell, 1999b; Veum et al.,
1998). When diets were formulated based on available P (rather
than total P) using low phytate corn, P excretion was reduced
by 35 to 40% (Pierce and Cromwell, 1999b). Collectively these
data show that total dietary P can be reduced by 0.1% when low
phytate corn is used and that P excretion can be reduced by appoximately
40%.
An interesting question is what effect phytase would have in diets
that contain low phytate corn. There is still potential for phytase
to improve P digestibility because other components of pig diets,
such as soybean meal contain significant amounts of phytate bound
phosphorus. Cromwell (1999) reported that phytase addition to
diets with low phytate corn decreased P excretion by 25% (Table
3). The reduction in P excretion by using phytase and low phytate
corn diets compared to control diets with regular corn and without
phytase was 51%.
|
| ||||
| Total P, % Available P, % |
||||
| Bone Strength, kg | ||||
| P Excretion, g/day | ||||
| Reduction in P Excretion, % | ||||
There is a great potential for low phytate corn and phytase in
reducing P excretion in swine. The feasibility of applying these
technologies in practice depend on the cost of inclusion versus
the economic benefits and the ability to identity preserve different
types of corn.
Literature Cited
Cromwell, G. L. 1999. Modifying manure by modifying diets. Nebraska Pork Expo, Feb. 3, 1999, Columbus, NE.
Cromwell, G. L., J. L. Pierce, T. E. Sauber, D. W. Rice, D. S. Ertl, and V. Raboy. 1998. Bioavailability of phosphorus in low-phytic acid corn for growing pigs. Midwestern Section Meeting of the American Society of Animal Science, Des Moines, IA:58.
NRC. 1998. Nutrient requirements of swine. 10th revised ed. National academic press, Washington, DC.
Pierce, J. L., and G. L. Cromwell. 1999a. Effects of phytase on bioavailability of phosphorus in normal and low-phytic acid corn. Midwestern Section Meeting of the American Society of Animal Science, Des Moines, IA:36.
Pierce, J. L., and G. L. Cromwell. 1999b. Performance and phosphorus excretion of growing-finishing pigs fed low-phytic acid corn. Midwestern Section Meeting of the American Society of Animal Science, Des Moines, IA:35.
Pierce, J. L., G. L. Cromwell, and V. Raboy. 1998b. Nutritional value of low-phytic acid corn for finishing pigs. J. Anim. Sci. 76 (Suppl. 1):177(Abstr.).
Pierce, J. L., G. L. Cromwell, T. E. Sauber, D. W. Rice, D. S. Ertl, and V. Raboy. 1998a. Phosphorus digestibility and nutritional value of low-phytic acid corn for growing pigs. Midwestern Section Meeting of the American Society of Animal Science, Des Moines, IA:58.
Spencer, J. D., G. L. Allee, T. E. Sauber, D. S. Ertl, and V. Raboy. 1998a. Digestibility and relative bioavailability of normal and genetically modified low phytate corn (LP) for pigs. Midwestern Section Meeting of the American Society of Animal Science, Des Moines, IA:58.
Spencer, J. D., G. L. Allee, T. E. Sauber, D. S. Ertl, and V. Raboy. 1998b. Grow-finish performance of high lean-growth pigs fed normal and genetically modified low phytate (LP) corn. Midwestern Section Meeting of the American Society of Animal Science, Des Moines, IA:58.
Veum, T. V. Raboy, D. Ertl, and D. Ledoux. 1998. Low phytic acid
corn improves calcium and phosphorus utilization for growing pigs.
J. Anim. Sci. 76 (Suppl. 1):177(Abstr.).
Currently, 16 herds remain under quarantine for PRV. This includeds: one breeding herd,
4 nurseries, and 4 finishers of Carrolls Foods; one independent producer who culled all
positives on June 18, 1999; and Prestage Farms that has 4 finishers and 2 nurseries.
A whole herd test of the independent producer is scheduled for July 19, 1999, and the one
breeding herd of Carrolls Foods is scheduled for a whole herd test on July 16, 1999.
| HERDS | SWINE | Breeding | 2 | 1,203 |
| Finishing | 8 | 35,620 |
| Nurseries | 6 | 25,776 |
| TOTAL | 16 | 62,599 |