Farm-Scape, Episode 2097

As livestock producers grapple with the prospects of new restrictions on the amounts of crop nutrients, primarily nitrogen and phosphorus, that can be applied to the soil as manure, scientists in Saskatchewan are offering a number of dietary strategies that can be used now and options that will be available down the road.

Phosphorus Loading Raises New Environmental Concerns

Although environmental concerns related to the application of livestock manure have traditionally revolved around nitrogen there is now growing concern in many jurisdictions over the gradual buildup of phosphorus in the soil and its potential migration into ground and surface waters.

“What happens is the manure contains a nitrogen to phosphorus ratio that is not the same ratio as the plants require so the phosphorus builds up in the soil,“ explains Dr. Denise Beaulieu, a research assistant in the nutrition program at the Prairie Swine Centre.

New Regulations on the Horizon to Address Phosphorus Concerns

She notes, “As we are seeing more and more concern with environmental issues due to phosphorus, producers themselves are realizing that [by] the spreading of the manure, depending on where they're doing it, they may be reaching soil phosphorus levels. And, of course, the government is legislating soil phosphorus levels in several areas. In Manitoba, it's going to happen, in the eastern provinces there is legislation and in Saskatchewan and Alberta phosphorus-based manure management will probably happen.“

A main contributor to manure phosphorus levels is the use of inorganic dietary supplements. Because phosphorus is a key component in the development of bone and teeth and is an important component of cell membranes and RNA and DNA molecules, it is important to ensure the pig has enough to meet its nutritional requirements. This commonly means the animals get more than they need.

Supplemental Phosphorus Added to Feed Contributes to Concern

Dr. Beaulieu explains, “We have used inorganic forms of phosphorus in the diet because a large amount, 40 to 50 percent if not more, of the phosphorus in feed stuffs is tied up in the form of phytate phosphorus and phytate phosphorus is not available to pigs. They can’t use it so it’s excreted into the manure. That causes two issues. Number one, we have to add inorganic phosphorus which is available but that’s a cost to the diet and the other factor is the phytate phosphorus that is not used is excreted into manure so the manure contains this phosphorus.“

She observes, “When this manure is spread on some lands, of course, the phosphorus in the soil can build up to levels that the soil can’t hold – the phosphorus goes into the groundwater and can reach surface waters which causes a problem.“

Phytase Offers Economic Alternative to Inorganic Supplements

One of the newest approaches to reducing the need for the use of these dietary supplements is the use of phytase, an enzyme that helps the pig break down and utilize more of that unavailable phosphorus. A number of companies, including BASF, Alltech Inc. and Roche, currently offer both dry and liquid formulations containing this enzyme.

Dr. Beaulieu notes, “Phytase has been used in the U.S. for several years, the enzyme itself, and producers are definitely aware of it.“

“This is a bacterial enzyme added to the feed and it breaks down the phytate phosphorus making the phosphorus in that molecule available to the animal. You can increase dietary phosphorus digestibility by 20 or 30 percent with the use of this enzyme, so decreasing phosphorus output immediately by 20 to 30 percent.“

She estimates, “Even depending upon the cost of dicalcium phosphate, or inorganic sources of phosphorus, diet costs can be reduced by the use of the enzyme so it’ll compete in a least cost formulation with inorganic sources of phosphorus.“

Other Strategies Also Effective

She adds, “There are other things that can be done. More closely watching the total phosphorus levels in the ration. Formulating on an available phosphorus basis, which means the phosphorus that you know is available to the pig. Phase feeding. Split-sex feeding. And there are some other dietary things that can be done, but phytase will see the biggest returns.“

Low Phytate Grains and Oilseeds Promise Additional Options Down the Road

Meanwhile another approach seeks to address the high proportion of unavailable phosphorus in the feed by going directly to the source of the problem through plant breeding.

Last month, at the annual meetings for variety registration in Banff, the University of Saskatchewan’s Crop Development Centre received support for the registration of a new strain of hulless variety barley, based on the variety CDC Freedom that incorporates a low phytate trait.

“By having a lower percent of the phosphorus in the barley tied up in this form we refer to as phytate, or phytic acid as another correct way to describe it, that phosphorus is not available to monogastric animals like pigs and so it’s unfortunate in two ways,“ explains Crop Development Centre oat and barley breeder Dr. Brian Rossnagel. “One is that you have to add phosphorus to the diet of the pig to make sure they get enough and so that’s an added cost for pork producers. But perhaps more importantly, in the long run, is that the phosphorus that is tied up in phytate ends up going in the front end of the pig and then comes out the back end and then is a potential pollutant concern in the effluent from swine operations.“

Low Phytate Grains Expected to Displace Dietary Supplements

Dr. Rossnagel says, “By having the low phytate barley, the phosphorus is in an available form in the barley so the pig can actually use it. Theoretically at least, you shouldn’t have to add as much to the pig diet reducing the diet cost and then, out the other end, you would have less phosphorus in the effluent.“

The Crop Development Centre began working on low phytate barley in 1999 using germplasm obtained through a germplasm exchange agreement with colleagues at the U.S. Department of Agriculture labs in Aberdeen, Idaho who were working on low phytate strains of various crops including corn, barley, soybeans and others. The new strain, which has yet to be named or registered, contains 75 percent less phytate than regular barley.

Dr. Rossnagel suggests, “What that means is, theoretically at least, about 80 percent of the phosphorus in that barley seed will be available to the pig as opposed to only some five to ten percent of it being available in regular barley if you will.“

This type of research offers producers in areas facing new restrictions based on the amount of phosphorus that can be applied annually to cropland another tool that can be used to help manage those restrictions.

Nitrogen No Longer the Only Concern

Dr. Rossnagel explains, “Until recently most of the concerns were all about nitrogen levels. But, as things have progressed on the concerns about contamination of ground water and so on around the world, and in particular in Europe, they’ve actually moved to more of a so called phosphorus standard as well as a nitrogen one. Everyone is really quite concerned about phosphorus levels.“

He notes, “Obviously for most of western Canada, this isn’t nearly as big an issue as it is in places in Europe and particularly in places like southeast Asia and so on.“

Although he hopes this will ameliorate the problem, he admits, “It won’t solve it all because, in this material, not all of the phosphorus is free. Some of it is still tied up as phytic acid and so on but at least it’s a step in the right direction in combination with enzyme treatments of the feed and so on that we hope will help.“

Additional Low Phytate Crops Now Under Development

Dr. Rossnagel indicates, “It would also be valuable to reduce the phytate level of other feed ingredients such as peas. Dr. Tom Warkentin, Crop Development Centre pea breeder, is working toward that goal.“

Commercial Availability Still Some Time Off

“We grew the first ‘Breeder’ seed last year,“ Dr. Rossnagel notes. “That means it needs to be increased as ‘Select’ and ‘Foundation’ seed over the next two years. I would think that, realistically, we would see ‘Certified’ seed available for commercial production in 2008-2009, not much in 2008.“

He adds “We’d like this [low phytate trait] to be in a higher performing variety with better disease resistance and all those good things and we’re coming along with those as well.“

He notes, “We do have what we think are even better [lines], from an agronomic point of view.“

Phosphorus Reduction in Feed-A Win Win Approach

Dr. Beaulieu considers the nutritional approach to reducing the level of phosphorus in swine manure to be a winning solution. “Using phytase enzymes, formulating rations more closely to match the pig’s phosphorus requirement, these will not cost producers anything. They will save money so that can be a win-win situation. Diet costs go down, the manure phosphorus goes down and so the manure nitrogen to phosphorus ratio becomes more favorable for plant growth.“

Staff Farmscape.Ca