EFFECTS OF FLOURENSIA-CERNUA INGESTION ON NITROGEN-BALANCE OF SHEEP CONSUMING TOBOSA

Flourensia cernua DC. (tarbush) is a deciduous shrub with potential as a high-protein forage source for livestock. Twenty-four Polypay x Ram bouillet wethers housed in metabolism crates were used to evaluate tar bush as a N source for sheep fed a low quality grass diet. Treatments were 100% ground tobosa grass (Pleuraphis mutica Buckl.) or tobosa sub stituted with 10, 20, or 30% whole pre-bloom tarbush leaves (n = 5) or 26% ground alfalfa (n = 4, Medicago sativa L.) on a dry matter basis (dmb). Sheep were fed ad libitum for 11 days, after which feed was res tricted to 1% (dmb) of body weight for 11 days to seduce sorting and m aintain uniform intake. Apparent dry matter digestibility was not impr oved (P = 0.2646) with tarbush or alfalfa. Fecal N was similar (P = 0. 1626), but urinary N varied (P = 0.0008) among treatments. Apparent N digestibility differed (P = 0.0042) among treatments (43, 46, 50, 56, and 63% for sheep consuming 0, 10, 20, or 30% tarbush or alfalfa, resp ectively). All treatments resulted in similar (P = 0.1569) but negativ e N retentions (-2.4, -2.2, -2.8, -2.0, and -1.5 g day(-1) for sheep c onsuming 0, 10, 20, or 30% tarbush or alfalfa, respectively). Serum cl inical profiles (day 22) confirmed all sheep were nutritionally stress ed, but did not indicate toxicosis. Although neither tarbush nor alfal fa N compensated for the low quality basal diet, N from 30% tarbush wa s utilized with similar efficiency to alfalfa N. The major impediment for using tarbush as a N source appeared to be low palatability.