Livestock’s potential effect on the environment is part of the U.S. National Research Council’s revised book on nutritional requirements for beef cattle.
The new guide attempts to balance environmental issues with animal nutrition requirements, performance and economics.
“Many of the environmental issues that are of potential concern can be affected by the nutrition or the management of the animals for feeding,” said Andy Cole of the U.S. Department of Agriculture during a July 12 webinar.
“Animal operations can potentially affect water and air quality, and there is an increasing amount of information in the literature on this,” said Karen Beauchemin of Agriculture Canada, who was the only Canadian scientist on the 10 member committee, which has worked on the new guide for three years.
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The last version of the nutrition guide was released in 1996.
Most of the information relates to intensive systems such as feedlots, although many of these operations work under strict environmental regulations, said Cole.
Water quality, atmospheric changes, dietary effects on nutrient excretion, total manure output, nitrogen and phosphorus excretion and runoff are addressed.
Research has shown that dry matter intake, feed processing and byproducts high in fibre can affect manure output.
It is known that animals excrete more nitrogen toward the end of the feeding period. The guide helps assess feces and urine excretions to calculate the amount of nitrogen and phosphorus excretion.
For example, the guide suggests that phosphorus supplements should not be used in most finishing diets, especially if the animals are receiving high phosphorus byproducts.
Hydrogen sulfide may occur for short periods of time and come mostly from the manure. This may be linked to feeding distillers grain and other byproducts with high sulfide concentrations.
Life cycle analyses of North American beef production show that enteric methane emission accounts for 55 to 65 percent of the total greenhouse gas emissions from cattle. Eighteen to 23 percent comes from manure and the rest is from feed production and the use of fossil fuels, said Beauchemin.
“Most of the emissions are from the cow-calf phase,” she said.
Eighty percent of a beef animal’s diet is forage based.
“The greater the forage concentration and the lower the quality, the greater the methane emission, often expressed as a percentage of gross energy intake on an energy basis,” she said.
Grain lowers emissions, but it also depends on how it is processed because of the way it is digested in the rumen.
For example, barley-based finishing diets are responsible for 20 to 30 percent more emissions than corn diets.
“Steam flaking of corn, for example, would reduce methane emissions by 20 percent,” she said.
The guide also talks about adding more fat to diets to decrease methane emissions. There is a 3.8 to 5.6 percent reduction in methane for each one percent increase in dietary lipid concentration in the diet.
New information also indicates that distillers grain and other coproducts can help lower methane emissions, but it depends on the fat content of the total diet.
“The net impact of feeding distillers grains has to be considered in the total greenhouse gas emissions because if distillers grains are added to the diet and the crude protein or the nitrogen content of the diet increases, there could be an increase in nitrous oxide or ammonia emissions,” she said.
“The net impact on emissions associated with beef production needs to be considered when using distillers grains as a mitigation strategy.”
Ammonia emissions are also discussed, and equations are provided to estimate what nutrients can be used to reduce it.
For example, removing supplemental crude protein in the last 45 to 56 days of feeding can lower ammonia emissions, but this has to be measured against animal performance.
Thirty to 70 percent of nitrogen consumed by feedlot cattle is released in the form of ammonia in the urine, although most of it is gone quickly. Output depends on temperature, animal activity and atmospheric stability.
“There is very little work that has been done with pastured cattle, so it is very difficult to determine the accuracy of this equation for grazing animals,” she said.
