Estimation of Organic Matter Digestibility and Intake from Faecal Organic Matter and Daily N Excretion and Concentration

Estimation of Organic Matter Digestibility and Intake from Faecal Organic Matter and Daily N Excretion and Concentration

This study was performed with grazing sheep, to establish: a) if the amount of total faecal N (C; in g 100g^-1 of organic matter intake (OMI)) remains constant at three feeding levels, in four utilisation periods of deferred Panicum coloratum cv. Verde; b) the relationship between C and faecal N fractions, and c) the relationship between faecal daily excretion of OM and N, and OMI. Intake increased (P< 0.01) with utilisation period, and was related (r = - 0.82; P< 0.01) to the protein content of food, the insoluble N fraction (r = -0.49; P< 0.01) and the soluble:insoluble N ratio (r = 0.41; P< 0.01) in faeces. No relation with total N concentration (r = -0.22; P> 0.05) or soluble N fraction (r = -0.02; P> 0.05) in faeces could be found. Daily excretion of OM and N were positively related (R² = 0.93 and 0.96, respectively; P< 0.01) to OMI. The slopes of regression lines, but not the intercepts, were different (P< 0.01) between evaluation periods. The digestibility can be estimated from OMI and faecal N whenever time of the year is taken into consideration.