WATER QUALITY AND THE GRAZING ANIMAL

Authors: Hubbard, Robert; NEWTON, G. - U. OF GA; HILL, GARY - U. OF GA

Submitted to: Journal of Animal Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/1/2003
Publication Date: 6/1/2004
Citation: Hubbard, R.K., Newton, G.L., Hill, G. 2004. Water quality and the grazing animal. Journal of Animal Science. 82(E.Suppl.):E255-E263.

Interpretive Summary: Contamination of surface or groundwater from wastes associated with grazing animals is an environmental concern. Water quality of streams, lakes, or other water bodies may be degraded by excessive amounts of nitrogen, phosphorus, pathogens, or organic materials from animal wastes. Excess N in surface water bodies may contribute to eutrophication. Elevated nitrate concentrations in drinking water have caused infant death from the disease methemoglobinemia. Excess P in surface water bodies is a major cause of eutrophication. Pathogen contamination of either surface or ground waters from wastes from grazing animals may pose a serious health problem for both humans and animals. Organic matter from animal feces can contribute to oxygen depletion in surface waters and hence negative effects on fish populations. The impacts of grazing animals on water quality must be evaluated at both field and watershed scales. Management to prevent environmental contamination centers around having good forage stands and a proper animal density, i.e. not having more grazing animals than the carrying capacity of the land. It is also important for animals to be fenced out of water bodies and to maintain or reestablish riparian buffers which assimilate or filter materials in runoff from grazed areas. This paper prevents an overview of water quality findings and concerns relating to grazing animals. The information is of use to animal producers, land managers, and technical personnel involved in preventing or reducing environmental degradation.

Technical Abstract: Grazing animals and pasture production impact water quality both through urine and feces dropped by the animals and through fertility practices associated with production of high quality pasture. The two nutrients of primary concern relating to animal production are nitrogen (N) and phosphorus (P). Nitrogen is of concern because high concentrations in drinking water in the nitrate form cause methemoglobinemia (blue baby disease) while other forms of N (primarily nitrite) are considered to be potentially carcinogenic. Phosphorus in the orthophosphate form is of concern because it causes eutrophication of surface water bodies. The impact of grazing animals on soil and water quality is best evaluated at the watershed scale. Such evaluation must include both direct input of animal wastes from the grazing animal and also applications of inorganic fertilizers to produce quality pastures. Watershed scale studies have primarily used the approach of nutrient loadings per land area and nutrient removals as livestock harvest. A number of studies have measured nutrient loads in surface runoff from grazed land and compared loads with other land uses. Concentrations in discharge have been regressed against standard grazing animal units per land area. Watersheds with concentrated livestock populations have been shown to discharge 5 to 10 times more nutrients than watersheds with other land uses. Another major concern with animal production including grazing animals is pathogens which may move from the wastes into surface water bodies. Major surface water quality problems associated with pathogens have been associated with grazing animals, particularly when they are not fenced out from the streams and farm ponds. This paper presents an overview of water quality findings and concerns relating to grazing animals.