Effect of the Lenght of Fasting on Intake, in Vitro Digestability and Chemical Composition of Forage Samples Collected by Esophageal Fistulated Sheep1

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Abstract
Four sheep wtih esophageal fistulae were used to measure the effect of different periods of fasting on the weight and chemical composition of samples collected from four pasture types. The four periods of fasting used were 0, 12, 24 and 36 hr arranged to occur in a latin square sequence; the four pasture types were native, improved, Phalaris tuberosa and chamise. Each sheep grazed for 1 hr and each sample was lyophilized, weighed, and in vitro digestibility, percentage nitrogen, ash, neutral and acid detergent fiber (NDF, ADF), lignin (ADL) and hemicellulose were measured. There were significant differences between pastures in all constituents measured. The results showed that fasting significantly affected sample size and ADF; however, within pastures the regression coefficient of some parameters against hours of fasting were significant. Notable among these were the significant negative coefficients for in vitro digestibility and ash for the native pasture and the positive coefficients for nitrogen for the Phalaris pasture and ADF and NDF for the chamise pasture. It was concluded that moderate fasting did not have a pronounced effect on the composition of samples collected, but the direction and magnitude of the effect of fasting was dependent on the pasture.