Browsing Journal of Range Management, Volume 40, Number 6 (November 1987) by Subjects
Now showing items 1-3 of 3
Potential for hydrocyanic acid poisoning of livestock by indiangrassHydrocyanic acid or prussic acid poisoning of livestock by sorghums [Sorghum bicolor (L.) Moench] and sudangrasses [Sorghum sudanese (Piper) Stapf] is caused by the digestive liberation of hydrocyanic acid (HCN) from the cyanogenic compound, dhurrin [(S)-p-hydroxymandelonitrile β-D-glucopyranoside] found in tissue of these plants. Recent research documented that dhurrin is also present in indiangrass [Sorghastrum nutans (L.) Nash] seedlings. The purpose of this study was to determine the hydrocyanic acid potential (HCN-p) of forage from established stands of indiangrass. Five cultivars representative of indiangrass germplasm of the Great Plains were sampled during the growing season for 2 years from 2 sites in eastern Nebraska. The HCN-p of the indiangrass sampled in this study exceeded 750 mg-1 kg dry wt. (dangerous level) only in spring when new growth was 20 cm tall or less. Levels were less than 500 mg-1 kg (safe) when new growth was at least 40 cm tall and were very low (<200 mg-1 kg) or not detected when the forage was over 1 m tall. Pure stands of indiangrass that are grazed when the new growth is less than 20 cm tall could be lethal to livestock.
Seasonal diets of herded sheep grazing Douglas-fir plantationsUse of livestock for biological weed control in timber plantations is gaining popularity in the United States and elsewhere. Efficient use of livestock to control unwanted brush relies upon knowledge of livestock feeding habits. A study was conducted during 1981 and 1982 to determine seasonal diets of herded sheep grazing cutover Douglas-fir (Pseudotsuga menziesii) forests in the Coast Range of Oregon. Study sites included both 4- to 6-year-old non-grass-seeded and 2-year-old grass-seeded plantations. Sheep grazing was monitored in spring, summer, and late summer. Forage on offer ranged from 764 to 2,459 kg/ha. Vegetational composition of sheep diets varied by year, season, and plantation age class. Averaged over the 2 years of grazing, graminoids and forbs were nearly equal, at approximately 40% each, in sheep diets in older plantations. In contrast, diets of sheep in young grass-seeded plantations averaged 70% graminoids and only 16% forbs. Ferns were a minor component (<2%) of sheep diets in both plantation age classes. Browse averaged 15 and 12% of sheep diets in old and young plantations, respectively. Douglas-fir was most palatable to sheep in spring soon after bud break. It was generally avoided, however, and never comprised more than 3% of sheep diets. Our data suggest that sheep can be most effectively used for biological control of unwanted brush species during summer and late summer when differences in relative preference indices for target brush species and Douglas-fir are greatest.
Seasonal dynamics of minerals in forages at the Texas Experimental RanchRange livestock derive the bulk of their dietary mineral intake from forages that are often deficient in one or more essential minerals. The objective of this study was to quantify the seasonal dynamics of phosphorus (P), potassium (K), calcium (Ca), and magnesium (Mg) concentrations in the dominant native forages at the Texas Experimental Ranch. Concentrations were estimated by class of tissue (live and dead) for 5 species/species groups: sideoats grama (Bouteloua curtipendula Michx.), Texas wintergrass (Stipa leucotricha Trin. and Rupr.), annual grasses, other warm-season grasses, and forbs. The study spanned a period of 2 years and included 16 sample dates. Although P, Mg, and K concentrations varied significantly among species and date, they varied primarily as a function of class of tissue. Averaged across dates and species, concentrations of P, Mg, and K in live tissue averaged 0.12, 0.13, and 2.02%, respectively, while concentrations in dead tissue averaged 0.04, 0.09, 0.57%, respectively. As a result, seasonal differences in whole plant concentrations of P, Mg, and K were closely linked to seasonal growth dynamics as they affect live/dead ratios. Ca concentrations were affected more by species than class of tissue. Averaged across dates, Ca concentrations in live tissue averaged 0.55, 0.40, 0.42, 0.35, and 1.80% in annual grasses, Texas wintergrass, sideoats grama, other warm-season grasses and forbs, respectively, while concentrations in dead tissue averaged 0.41, 0.40, 0.41, 0.36, and 0.96%, respectively. It is concluded that considerations must be given to the potential effect that a given treatment may have on plant growth dynamics to properly interpret its effect on whole plant concentrations of minerals.