Submitted to: Arkansas Animal Scientist
Publication Type: Experiment Station
Publication Acceptance Date: December 9, 2002
Publication Date: July 29, 2003
Citation: Mcginley, B.C., Coffey, K.P., Humphry, J.B., Sauer, T.J., Goodwin, H.L. 2003. Mineral content of forages grown on poultry litter-amended soils. Journal of Animal Science. 81(2):106.
Interpretive Summary: In much of the mid-South U.S., poultry litter (manure with bedding material) is spread on pastures to supply nutrients for grass growth. Often, no other fertilizer is applied to the pastures so there is sometimes concern that the litter does not contain all the nutrients needed to make the grass grow well and keep the grazing animals healthy. This study analyzed grass samples from four farms over nearly two years to determine if and when beef cows eating the grass might have mineral deficiencies in their diets. It was found that there were times when the grass had too little magnesium or copper, which would put the cows in danger of developing a nutritional disease called grass tetany or to suffer from copper deficiency. It is recommended that the diets of beef cows grazing pastures receiving poultry litter be supplemented with magnesium and copper to prevent these nutritional disorders. This information is important to help beef producers maintain good herd health and production by avoiding grass tetany and copper deficiency in their animals.
Four farms in northwest Arkansas and northeastern Oklahoma were used to monitor mineral concentrations in forages grown on poultry litter-amended soils from April 2000 to March 2002. Mineral concentrations were compared to the requirements of beef cows in gestation and early lactation, and grass tetany ratios were calculated to determine the risk of grass tetany occurrence. For most of the grazing period, calcium, phosphorus (P), potassium (K), sulfur, and iron concentrations were adequate to meet the requirements of beef cows in gestation and early lactation. Forage magnesium (Mg) concentrations from all four farms were generally below the requirement for beef cows in early lactation during the winter months of 2001 and 2002. Forages from two farms surpassed the tetany ratio during the spring of 2000, indicating that grass tetany could be a potential problem in lactating cows during that period. In general, zinc concentrations were above requirements at three of the four farms, but barely met or were below beef cattle requirements during most of the fall and winter of 2000-2001 at Farm 1. With few exceptions copper (Cu) concentrations at all farms were at or below cow requirements, indicating that Cu supplementation would be necessary throughout much of the year. Pastures fertilized with broiler litter may meet some but not all mineral requirements of beef cattle; therefore, supplementation with specific minerals, such as Mg and Cu, may be warranted.