干旱区生态环境知识资源中心

Tarbush (Flourensia cernua DC.) contributes substantially to the Chihuahuan Desert shrub biomass, but is browsed sparingly by livestock. This study was designed to assess nutritional benefits and/or toxicosis of ingestion of pre-bloom tarbush leaves by sheep fed a low quality native grass diet. Sixteen ruminally cannulated sheep (46 kg) housed in individual pens were randomly assigned to 1 of 4 treatments for 28 days. Treatments were ground tobosa grass (Pleuraphis mutica Buckl.) substituted with 0, 10, 20, or 30% (dry matter basis) whole tarbush leaves (19% CP). At 20 and 30% of the diet, tarbush increased (P = 0.0049) dry matter intake during week 3, and sheep consuming 30% tarbush tended to increase dry matter intake during week 2 (P = 0.0559). Dietary tarbush did not affect any variable associated with ruminal fluid kinetics, particulate digesta kinetics, or in situ degradation rates of tobosa dry matter or neutral detergent fiber (P > 0.05). Molar butyrate proportions (P = 0.0032) and total volatile fatty acid concentrations (P = 0.0064) were greater for the 30% tarbush treatments. Ruminal ammonia was greater (P < 0.0029) at 6, 8, and 12 hours postfeeding for the 30% tarbrush treatment. Sheep lost body weight regardless of treatment; however, sheep not fed tarbush tended (P = 0.0945) to lose more weight. Serum clinical profiles (day 0, 7, 15, and 21) confirmed nutritional stress but did not suggest toxicosis.