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Many Sandhills ranches have two distinctly different forage resource bases: native upland range and subirrigated meadow. These two sites have different grass species composition and different plant growth characteristics. Familiarity with the nutritional composition of these sites is a valuable management tool for cattle producers in the Sandhills. The grazing animal has the ability to select a diet that is higher in nutritive value than would be obtained by analyzing clipped samples of the same pasture. The use of esophageally-fistulated animals to sample pastures gives the best estimate of the animal's diet.
A metabolizable protein system (NRC, 1985) expresses protein requirements on a degradable intake protein (DIP) and a metabolizable protein (MP) basis. Degradable intake protein is the protein which is degradable in the rumen and available to the microorganisms present in the rumen. Metabolizable protein is the sum of the digestible microbial protein flowing to the small intestine and the digestible escape protein flowing to the small intestine. Metabolizable protein is the protein which the animal uses for maintenance, growth, lactation, and gestation. Expressing protein requirements in this manner should enable producers to more precisely estimate type and amount of supplemental protein needed compared to simply using the crude protein system.
The objectives of this research were to characterize the seasonal changes in forage quality and protein degradability of diet samples and to use a metabolizable protein system to predict deficiencies in energy, degradable protein, and metabolizable protein.