Chemical composition of Flourensia cernua at four growth stages

Tarbush (Flourensia cernua DC) is an abundant Chihuahuan Desert shrub but is used sparingly by livestock. Leaves were removed from forty tarbush plants harvested in each of 3 years during four growth stages: (1) early, (2) mid-point, (3) late and (4) curtailed growth (ten plants per growth stage each year). Plants were air dried and all leaves were removed. In vitro dry-matter (DM) disappearance was greater for the early growth stage than other stages (P < 0.05). The fibrous fraction increased with maturity, with neutral detergent fibre (NDF), acid detergent fibre (ADF) and acid detergent lignin (ADL) contents all less for the early growth stage (P < 0.05) than other stages. The latter three growth stages did not differ in NDF Or ADF content, but ADL content was lower for the mid-point growth stage than for the two later stages (P < 0.05). Calcium content increased with advancing season (P < 0.05), whereas phosphorus concentration exhibited an inverse pattern (P < 0.05). Nitrogen (N) content of tarbush was greatest in the early growth stage (P < 0.05) and declined substantially thereafter. Soluble N content was greater and acid detergent insoluble N (ADIN) content was lower for early growth (P < 0.05) than other stages. Insoluble N concentration followed a pattern similar to N, declining with advancing season (P < 0.05). When expressed as a fraction of total N, insoluble N decreased and soluble N increased with maturity (P < 0.05). Condensed tannin concentration tended (P < 0.10) to increase with advancing season. Total phenolic content was lowest for early growth (P < 0.05), and did not differ among the other stages. Chemical analysis revealed tarbush to be relatively high in N concentration. Fibre fractions, ADIN, ADL and condensed tannins were all generally low whereas total phenolic content of tarbush was quite high. Early use by livestock would be most advantageous in terms of nutrient availability (N, P and in vitro digestibility) and lowest total phenolic concentration. Year-to-year variability in chemical composition of tarbush appears to be substantial. It remains to be seen whether overriding intake deterrents would be beneficial to livestock, given the high phenolic concentration in tarbush. Tarbush has several characteristics that make it a suitable model for studying plant-animal interactions of desert shrubs.