Poisonous Plants and Fungi

Goats, by their curiosity, browsing habits, and inhabitation of some environments where food is very scarce, are exposed to a myriad of plants containing toxic compounds. Often these compounds are secondary metabolites that have evolved in perennial plants for protection against her­bivores, especially insects.

For a plant to be called poisonous for goats, it needs to cause toxicity under natural settings, not just in laboratory experiments. The goat must eat enough of the plant to become ill when raised in the environment where the plant grows. Without proof from experimental feedings, a plant likewise cannot be firmly said to be toxic to goats. The absence of many species from the list of species toxic to goats in Table 19.7 represents, in part, a paucity of litera­ture documenting plant poisonings in goats. Where infor­mation is largely limited to experimental studies, this is indicated by “exp” in the table. Other plants with reports of just spontaneous or experimental toxicity have been sum­marized by Dobereiner et al.

Because the same toxic compounds are often present in multiple members of a genus or family of plants, practi­tioners in all countries should be suspicious of plants closely related to those in Table 19.7. However, even though this table omits some species names, not all members of a genus are equally or invariably toxic. A computer database on poisonous plants in the United States has been estab­lished and can be searched for information relative to goats (Wagstaff et al. 1989), but has not been updated since 2007.

When plants cause well-recognized clinical signs, they are discussed further and more references are supplied under the appropriate body system. Texts by other authors should also be consulted (Kingsbury 1964; Howard 1986; Dobereiner et al. 1987; Tokarnia et al. 2000; Frohne and Pfander 2005; Kellerman et al. 2005; Burrows and Tyrl 2013). Cyanide and nitrate poisoning are discussed in Chapter 9 and plants causing oxalate poisoning in Chapter 12. When the identity of a suspect poisonous plant or its toxic principle is unknown, oral dosing of the sick goat with activated charcoal is appropriate.

Even the partial listing of poisonous species given here could confuse the veterinarian searching for an etiology for an undiagnosed illness. It is guaranteed to terrify the aver­age goat owner. Dozens of species of plants that contain toxic principles are found on most pastures and ranges. The quantity consumed is a critical factor in determining if poisoning occurs, but both the quantity required for signs to occur and the amount eaten by an individual animal are usually imprecisely known. The stage of growth and the

Table 19.7 Plants poisonous to goats.

(Continued)

exp, evidence largely limited to experimental studies.

availability of alternative forage are other important fac­tors. In general, most plant toxicoses can be avoided by supplying supplemental hay and grain in times of drought, not overstocking pastures (Taylor and Ralphs 1992), not turning hungry animals out to forage, and preventing access of goats to ornamental plants (including trees and shrubs) and their clippings. Overgrazed pastures, snow coverage of more desirable forages, and unsanctioned entry into a garden or planted field are common situations in which poisoning occurs. Goats used for weed or brush control (Popay and Field 1996) or handfed potentially toxic plants in a cut-and-carry system are also at risk.

Mycotoxins from fungi growing on forage plants or grains present a special problem, as some pathogenic fungi are endophytic (growing within the live plant) where they cannot be seen. Other fungi grow in grains either in the field or during storage, especially under condi­tions of increased heat and humidity. Their presence may not be grossly detectable in purchased grain products. Deoxynivalenol (DON, vomitoxin) is a mycotoxin of great concern to swine producers, but little is known about its effects on goats other than that a first clinical sign would be feed refusal. A suggested safe concentration for DON in the total goat diet is 5 ppm, on a DM basis (Neary 2009). The estrogenic mycotoxin zearalenone probably would have adverse effects on reproduction in goats as it does in sheep, and the same authors suggest a maximum of 0.5 ppm zearalenone pre breeding and 5 ppm for pregnant goats.