Determination of threshold concentration for toxicity became possible when analytical assays were developed for ergovaline in tall fescue and perennial ryegrass (Craig et al., 1994; Duringer et al., 2005; Rottinghaus et al., 1993; Tor-Agbidye et al., 2001). From those investigations, a threshold for ergovaline in cattle was set at 0.35 to 0.50 mg/g at ambient temperatures. The colder the ambient temperature, the lower the threshold ergovaline level. The threshold was set at 0.50 mg/g for low temperatures for sheep since they appeared to be slightly more tolerant of ergovaline than cattle (Tor-Agbidye et al., 2001).

Determination of the threshold level of lolitrem B in ryegrass also became possible when an analytical assay for the molecule and pure standards became available (Gallagher et al., 1984; Hovermale and Craig, 2001; Miles et al., 1992). From studies conducted in pastures where cases of ryegrass staggers had been observed (diMenna et al., 1992; Galey et al., 1991; Tor-Agbidye et al., 2001), the toxic threshold level was set at 2.0 mg/g lolitrem B for cattle and sheep. This threshold level was used by a USDA Blue Ribbon Committee in 1999-2000 to determine which straw would be used for export to Asian countries.

Subsequently, reports of Japanese Black Cattle being affected by lolitrem B at concentrations lower than this threshold came to the attention of the grass straw industry (Miyazaki et al., 1999, 2001, 2004; Saiga, 1998; Saiga and Maejima, 1998). Feeding trials with cattle were conducted with endophyte infected perennial ryegrass straw having known levels of toxin. In the pilot study (Fisher et al., 2004), 72 Angus/Hereford crossbred cows were fed perennial ryegrass straw ad libitum and supplemented with soybean [Glycine max (L.) Merr.] meal during the last trimester of pregnancy. No signs were observed at 1.4 mg/g, but they were observed at 1.95 mg/g and greater concentrations. A second study (Blythe et al., 2007) confirmed these values with Angus and Angus crossbred cattle. Japanese Black Cattle did not develop ryegrass staggers at 1.4 mg/g lolitrem B for 28 d, indicating that this breed is not necessarily more susceptible to staggers than other breeds. Based on these results, the current threshold of toxicity of lolitrem B in straw and other feedstuffs is 1.8 to 2 mg/g. A later Japanese study has suggested that Japanese Wagyu cattle exhibit ryegrass staggers at 1.2 mg/g lolitrem B (Miyazaki et al., 2004). The authors also were concerned that residues of about 0.2 mg/g lolitrem B found in the fat might raise public health concerns (Miyazaki et al., 2004). Considering these and other studies, the USDA Blue Ribbon Committee set the toxicity threshold level at 2.0 mg/g lolitrem B for cattle and sheep (determined by Tor-Agbidye et al., 2001). This threshold level was used by USDA to determine which straw would be used for export to the Asian countries.

 

<--Previous     

 

 

 Next-->