RED DEER ÑMany animals are fed more phosphorus than they can digest so it is excreted in their manure, said Rick Corbett of Alberta Agriculture.
The buildup of phosphorus in soil from heavy manure applications is considered an environmental hazard because of its potential to pollute water. Reducing levels in manure starts by adjusting livestock diets.
Animals have no mechanism to store phosphorus but nutritionists often increase levels to ensure poultry, pig and dairy diets do not cause deficiencies, Corbett told a manure management conference in Red Deer June 26-28.
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A survey from the United States said dairy cattle are fed 20 to 35 percent more than required and a Manitoba survey found dairy cattle there were fed 52 percent more phosphorus than required.
ÒAll that 52 percent ends up in the manure and we have to deal with it,Ó he said.
If provincial manure regulations switched the recommendations for nitrogen requirements to phosphorus needs, intensive livestock operators would need 2 % times more land to deal with the manure.
New information
Dairy rations are a good example of overfeeding because it was once believed the cows needed more phosphorus for improved fertility based on 50-year-old research. Nutritionists commonly use 20 to 40 percent more phosphorus than the animal requires.
More contemporary research says phosphorus does not have any reasonable effect on dairy production or reproduction.
Corbett said most dairy cows are fed the same mixed ration for their entire lactation and that increases phosphorus in the manure, compared to more selective diets for the high, medium and low producers. Adjusting their diets could reduce output by five to 10 percent.
Feedlot diets do not typically add phosphorus because normal rations already contain more than the animal can use. The cattle pass it in their feces. Most big feedlots do not have a large enough land base for the manure so phosphorus buildup grows.
ÒThe story looks bad and its gets worse,Ó he said.
Availability and digestibility of phosphorus are relatively poor among pigs and chickens so it is supplemented.
Phosphorus is a complex mineral and comes in many forms. The major form in plant-based feed is bound as phytate, which is digested by a family of enzymes called phytases produced by micro-organisms.
Phytase supplements have been designed for pig and poultry feed to make about half the phytate phosphorus available. This phytase supplementation cuts the amount of phosphorus in manure by 28 percent.
