Altitudinal and seasonal variation in herbage composition and energy and protein content of grasslands on Mt Varnoudas, NW Greece

This study was conducted to determine the flora of Mount Varnoudas pastures in NW Greece and to evaluate the seasonal and altitudinal variations in the chemical composition and energy content of herbage, during the years 2004 and 2005. Mt Varnoudas was divided into three altitudinal zones (lower zone: 900–1300 m, middle zone: 1301–1700 m, upper zone: 1701–2334 m) depending on the type of the dominant vegetation and floristic characteristics. 758 different taxa belonging to 84 families and 341 different genera were collected. In order to study the effect of the season and the altitudinal zone on the nutritive components of herbage, 24 experimental cages sized 4 m × 5 m in the three altitudinal zones (8 cages per zone) were placed. Crude protein (CP) decreased from 106.65 to 72.03 g/kg dry matter (DM) in the lowlands, from 133.95 to 80.38 g/kg DM in the middle zone and from 127.13 to 74.47 g/kg DM in sub-alpine grasslands. Metabolizable energy (ME) content of the herbage decreased as the growing season progressed about 19%, 32% and 23% in the lower, middle and upper altitudinal zone, respectively. Herbage quality was sufficient to meet maintenance CP and ME requirements of both, beef cattle and sheep, only during spring, while only in summer for beef cattle. CP and ME contents were affected (P<0.001) by season and altitudinal zone. Neutral detergent fibre assayed with a heat stable amylase and expressed inclusive residual ash (aNDF) and acid detergent fibre expressed inclusive residual ash (ADF) content increased as plants matured, showing peak values at the end of grazing period. Gross energy (GE) content also increased showing peak values during autumn. Both aNDF and ADF were affected (P<0.001) by the season as well as by the altitudinal zone (P≤0.05), while GE was affected (P<0.001) by the season and the altitudinal zone. The findings of this study suggested that additional protein and energy sources should be supplied in order to meet the maintenance requirements of grazing sheep and beef cattle after mid-summer. Furthermore, the movement of these animals from the lowlands in the upperlands during summer seems to be a proper practice for better utilization of grasslands because of the availability of herbage of higher quantity and better quality.