A rat bioassay for screening tropical legume forages and seeds for palatability and toxicity

Abstract

A rapid evaluation of palatability and apparent toxicity of forage legumes, using a rat bioassay and requiring only 400 g of dried forage or 100 g of seed, is described. Vegetative material is included as 20%, or seed as 5%, of a nutritionally complete, 12% protein (casein) diet for rats. Voluntary intake and weight gain of rats on test diets are compared with results from standard diets given ad libitum and at restricted rates. It proved possible to distinguish toxicity from simple unpalatability by comparing the weight gain observed on test diets, with the expected weight gain estimated from the regression of weight gain on intake of the standard diet. The method is satisfactorily reproducible, and discriminated clearly between commercially acceptable forages and others known to be toxic, between young and old or between leaf and stem material of the same plant, and between raw and autoclaved seed. The method was used to screen forage from 340 accessions and seed from 110 accessions held in the Australian Tropical Forages Genetic Resources Centre of the CSIRO Division of Tropical Crops and Pastures. Of 150 species, mostly in the genera Cassia, Crotalaria, Indigofera and Tephrosia, only 40 could be classified as palatable and non-toxic to rats, though there was considerable variation between accessions of some other species. As the rat, which is the common laboratory test animal for plant compounds harmful to poultry, man and other monogastric animals, is likely to be more sensitive to ingested phytotoxins than ruminants in most cases, the technique provides a fast, cheap, conservative, preliminary screen of potential forages.

Harvest management and genotype effects on sunn hemp forage characteristics

“…Sunn hemp seeds and pods may contain pyrrolizidine alkaloids (van Wyk & Verdoorn, 1990) which can negatively affect animal performance. Several studies have shown animal intake of this legume without adverse effects if consumed in the vegetative stages with no inflorescence (Burke, Mosjidis, Miller, & Casey, 2011;Purseglove, 1981;Strickland, Lambourne, & Ratcliff, 1987).…”

The Facts about Sunn Hemp Toxicity

“…Many Crotalaria species have been found to be toxic to animals mainly because of high pyrrolizidine alkaloid content. Strickland et al (1987) established that about 50% of the Crotalaria species they tested had toxic plant tissue or seeds or both. For example, Ritchey et al (1941) determined that feeding C. spectabilis seed was toxic to cattle, chickens, and game birds, and C. retusa seeds were toxic to chickens.…”

“…In summary, there are two types of evidence indicating that C. juncea seeds do not cause acute toxicity as reported for other Crotalaria species, particularly some species introduced to the United States such as C. spectabilis and C. retusa (Ritchey et al, 1941; Hooper and Scanlan, 1977; Williams and Molyneux, 1987) (Table 1). The first set of evidence comes from the reports that found no or low pyrrolizidine alkaloids levels in seeds and other plant parts in a large number of populations developed in several countries (Adams and Gianturco, 1956; Pilbeam and Bell, 1979b; Strickland et al, 1987; Williams and Molyneux, 1987; Ji et al, 2005; Nurhayati and Ober, 2005). Second, toxicological studies conducted with animals, particularly chickens that are very susceptible to pyrrolizidine alkaloids, demonstrated lack of acute toxic effects (Williams and Molyneux, 1987; Hess and Mosjidis, 2008).…”

“…In fact, a recent study by Burke et al (2011) reported that goats and sheep that grazed the new sunn hemp cultivars developed by Mosjidis (2010) had good performance. A rat bioassay conducted by Strickland et al (1987) indicated that neither leaves nor stems of C. juncea were toxic. This was confirmed by Nurhayati and Ober (2005) who did not detect alkaloids in cotyledons, leaves, flowers, or roots of C. juncea .…”

Review: Dampak Negatif Indospicine dalam Indigofera sp. pada Ternak

“…Strictland et al (1987) menyatakan bahwa sekitar 50% spesies Indigofera dilaporkan dapat menyebabkan keracunan dan penurunan palatabilitas pada hewan. Namun demikian, laporan penelitian Strictland et al (1987) tersebut menggunakan tikus sebagai hewan coba sehingga sulit untuk disimpulkan pada ternak ruminansia dan lebih tepat pada hewan monogastrik. Dengan demikian hasil penelitian yang saling bertentangan tersebut masih membutuhkan kajian kajian dan penelitian untuk membuktikan seberapa jumlah spesies Indigofera yang dapat menimbulkan keracunan pada ternak ruminansia.…”