Seasonal changes in forage nutrient and toxicity levels on California central coast rangelands: a preliminary study

Authors: LARSEN, ROYCE - University Of California; COOK, DANIEL - US Department Of Agriculture (USDA); GARDNER, DALE - US Department Of Agriculture (USDA); LEE, STEPHEN - US Department Of Agriculture (USDA); SHAPERO, MATTHEW - University Of California; ALTHOUSE, LYNNEDEE - Althouse And Meade, Inc; DENNIS, MICHAEL - University Of California; FORERO, LARRY - University Of California Agriculture And Natural Resources (UCANR); DAVY, JOSH - University Of California; RAO, DEVII - University Of California; HORNEY, MARC - California Polytechnic State University; BROWN, KATIE - Althouse And Meade, Inc; Rigby, Craig; Jensen, Kevin

Submitted to: Grasslands
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/1/2020
Publication Date: 1/1/2021
Citation: Larsen, R.E., Cook, D., Gardner, D.R., Lee, S.T., Shapero, M., Althouse, L., Dennis, M., Forero, L.C., Davy, J.S., Rao, D.R., Horney, M., Brown, K., Rigby, C.W., Jensen, K.B. 2021. Seasonal changes in forage nutrient and toxicity levels on California central coast rangelands: a preliminary study. Grasslands. 31(1):15-24.

Interpretive Summary: Poisonous plants are a major cause of economic loss to the livestock industry, adversely effecting 3 to 5 percent of the cattle, sheep, goats, and horses that graze western rangelands. California rangelands represent an estimated 60% of the state’s land area. Forage available to livestock on California rangelands mostly consists of annual grasses and forbs. Over half the rangelands in California are used for livestock grazing. However, some rangeland forages that are high in nutrients may also contain toxins. This paper provides an organized source of information on the nutrient values and levels of toxins found in many plants that are common on California Central Coast rangelands. The reduction in nutrient levels happens quickly as the forage dries, especially for annual grasses. Leaching from rainfall can occur anytime the forage is dry, normally this occurs during the fall. During our study, a spring (mid-May) rainfall caused significant reductions in nutrient values. The late summer growing plants we studied were found to have high nutritional levels, with protein values remaining higher than 15% for some species, late into the summer months. Some of these plants could potentially be used by livestock to help maintain their nutritional needs during the long summer period, while others are toxic and need to be avoided.

Technical Abstract: Poisonous plants are a major cause of economic loss to the livestock industry, adversely effecting 3 to 5 percent of the cattle, sheep, goats, and horses that graze western rangelands. California rangelands represent an estimated 60% of the state’s land area. Studies looking at toxin levels as plants age, and especially the seeds, would be helpful to better understand livestock poisonings. We found that as winter and spring forage (both grasses and forbs) senesces, and dries, it no longer meets the nutritional needs of livestock. This reduction in nutrient levels happens quickly as the forage dries, especially for annual grasses. Leaching from rainfall can occur anytime the forage is dry, normally this occurs during the fall. During our study, a spring (mid-May) rainfall caused significant reductions in nutrient values. The late summer growing plants we studied were found to have high nutritional levels, with CP values remaining higher than 15% for some species, late into the summer months. Some of these plants could potentially be used by livestock to help maintain their nutritional needs during the long summer period, while others are toxic and need to be avoided. Good livestock management is necessary to keep livestock away from harmful and deadly plants found on rangelands. In general, ranchers can mitigate potential losses due to poisonous plants through good range management, especially making sure that livestock can meet their dietary requirements with enough forage or supplementation. Ranchers should be attentive to changes in selection and diet of their livestock as the plants mature and the forage availability changes. The poisonous plants we surveyed all contain sufficient toxin concentrations to pose a risk to livestock if consumed in sufficient quantities.