Effect of drying method on estimated nutritive value of browse species using an in vitro gas production technique

Abstract

Browse species in the Mediterranean area are an important feed source, especially during the summer/autumn period when herbaceous species senesce and do not meet animal nutrient requirements. The effect of laboratory drying method on estimated nutritive value of Arbutus andrachne, an evergreen shrub, Gleditsia triacanthos (acanthos), a deciduous leguminous shrub, and Medicago arborea, an evergreen leguminous shrub, was determined. Hand-plucked samples collected during the rapid growth period in May, and later when growth had ceased in August, were dried in either an oven or freeze-drier. The nutritive value of the samples was determined by standard laboratory techniques and an in vitro gas production technique after incubation for 3, 6, 12, 24, 48, 72 and 96 h by determining the kinetics of fermentation with the equation p = a + b(1 − e − ct ). Crude protein (CP) was higher ( P<0.01) in legumes (154 g/kg DM for G. triacanthos and 216 g/kg DM for M. arborea) than in the evergreen species (84 g/kg DM for A. andrachne). As a result of maturation, CP decreased while neutral detergent fibre (NDF) and acid detergent lignin (ADL) increased in all species. Freeze-drying had no effect on CP content, but it reduced ( P<0.05) concentrations of NDF and ADL. Oven drying depressed in vitro organic matter (OM) digestibility (IVOMD) in all species ( P<0.01). Drying method had no effect on gas production from A. andrachne samples. However, freeze-dried G. triacanthos and M. arborea samples produced more ( P<0.05) gas at both stages of maturity compared to oven dried ones. Drying method affected a and potential gas a + b ( P<0.01), but b and c were not affected. The three species had similar c rates, but different potential gas production (i.e., a + b). Sample drying technique affected leguminous species and their in vitro fermentation, but there was no affect in a non-leguminous species.