Chemical composition and in vitro fermentation characteristics of range species growing in Central Tunisia

Chemical composition and in vitro fermentation characteristics were determined on 15range(herbaceous and shrubby) species collected in a postural area from the region of Kairouan (Central Tunisia) during the grazing period (end of winter and spring). The in vitro fermentation parameters were determined using 100 ml glass syringes containing the plant material and inoculum and incubated for 96 hours. Correlations between chemical parameters, calculated in vitro organic matter digestibility (IVOMD24h) and metabolisable energy (ME) were determined. Crude protein (CP) content was highest in Rosedaalba (184 g per kg DM) and Medicago minima (175 g per kg DM) and the lowest in Rosemarinus officinalis (58 g per kg DM) and Globularia alypum (61 g per kg DM). The NDF contents varied widely between the studied species and ranged from 273 g per kg DM in Rosedaalba to 607 g per kg DM in Marrubium vulgare. The same wide variation was observed for ADF since it varied from 169 to 502 g per kg DM respectively in Rhus tripartita and Artemisia herba alba. Lignin content (ADL) was highest in Pistacia lentiscus (239 g per kg DM) and lowest in Calendula arvensis (49 g per kg DM). Asymptotic gas production (A) varied from 82.7 ml in Chrysanthemum coronarium to 26.7 ml in Artemisia herba alba. Positive correlations were found between CP content and IVOMD24h (r equal to 0.74, P less than 0.0001) and also ME (r equal to 0.76, P less than 0.0001). While, negative correlations were found between IVOMD24h and NDF (r equal to -0.58, P less than 0.0001), ADF (r equal to -0.65, P less than 0.0001) and ADL (r equal to -0.72, P less than 0.0001) contents. The same trend was noted with ME (r equal to -0.58, -0.63, -0.73, P less than 0.0001, respectively for NDF, ADF and ADL). It was concluded that the range species available in the studied area presented a wide nutritional variability, thus they could have a complementary role for small ruminants grazing. Considering the laborious in vivo approach in pasture conditions, the in vitro technique may considerably contribute into evaluating such diversity of resources. Secondary compounds should be considered in order to improve accuracy of predictive equations.