Reproductive losses to poisonous plants: Influence of management strategies

Abstract

Poisonous plants that impair normal reproductive functions in livestock include Veratrum californicum Durand, lupines, ponderosa pine (Pinus ponderosa Dougl.), broom snakeweed (Gutierrezia sarothrae (Pursh) Britt. Rusby), locoweeds (Astragalus and Oxytropis spp.), selenium-containing forages, phytoestrogenic plants, endophyte-infected grasses and others. In this review we focus on lupines, locoweeds and ponderosa pine needles to demonstrate the broad and diverse effects that poisonous plants have on reproduction. Certain lupines (Lupinus spp.) contain quinolizidine and piperidine alkaloids that are fetotoxic and when grazed by pregnant cattle during specific stages of gestation induce skeletal birth defects and cleft palate, "crooked calf disease". Poison-hemlock (Conium maculatum) and some Nicotiana spp. contain similar alkaloids and induce identical birth defects in cattle, pigs, goats and sheep when ingested at certain stages of gestation. Locoweeds (species of the Astragalus and Oxytropis genera containing the indolizidine alkaloid swainsonine) interfere with most processes of reproduction when grazed for prolonged periods of time. Animals can recover normal reproductive function if withdrawn from locoweed grazing before severe poisoning occurs. While most animals may recover reproductive function, permanent neurological deficits may preclude normal reproductive behavior. Ponderosa and lodgepole pine needles (Pinus spp.) cause abortion in cattle when grazed during the last trimester of gestation. The specific chemical constituents responsible for the abortions belong to a class of compounds called labdane resin acids, including isocupressic acid (ICA), succinyl ICA, and acetyl ICA. Basic management recommendations to reduce reproductive losses to poisonous plants include: (1) keep good records; (2) know what poisonous plants grow on ranges and understand their effects; (3) develop a management plan to provide for alternate grazing in poisonous plant-free pastures during critical times; (4) provide for balanced nutrition, including protein, energy, minerals and vitamins; (5) maintain a good herd health program; (6) integrate an herbicide treatment program to reduce poisonous plant populations or to maintain clean pastures for alternate grazing; and, (7) manage the range for maximum forage production.