Is UOM (Mediterranean Ovine Unit) a good reference for the evaluation of the production of mediterranean grazing areas ?

Abstract

PHILOETIOS, a group of mediterranean research workers, defined a standard unit, the UOM or Mediterranean Ovine Unit, to estimate and compare roughage production from pasture and bushy areas. The UOM is defined as the disposable energy ingested by a 45 kg ewe fed at maintenance on pasture. All other energetic expenditure is converted into UOM. In this work the UOM was used to compare the potential production of irrigated Crau meadows and « garrigue » rangelands grazed by sheep only, during 4 years. Mean values, respectively 37 and 2.3 UOM/ha/year, show clearly what could be obtained on such pastures. Moreover, this study shows the extreme variability of seasonal and annual results from garrigue rangeland, and their heterogeneity. Production values vary in the ratio of 2.5 to 1 among years for the same plot of land as well as among different plots for the same year. For irrigated meadows, there is less variation. Calculation of UOM is simple but requires the verification of several parameters : grazing schedule, regular weighing of ewes and lambs, breeding and body score. The use of corrective factors leads to consistent results for Crau irrigated meadows. On the contrary, for grazing in worse conditions on bushy areas such as « garrigue », it seems that the usual specific needs for living outdoors (i.e. 30 % of the maintenance needs) are underestimated. A further correction appears to be necessary for grazing in range conditions.