Straw Analyses and Diagnostics
The Oregon production and annual export of thousands of containers of grass straw is an important industry. The seed and straw exporters work with the Endophyte Testing Laboratory at Oregon State University to determine levels of lolitrem B and ergovaline in straw to be exported. The laboratory provides exporters a certificate that lists toxin levels. This is a voluntary testing program. Since not all exporters use it, some shipments of tall fescue and perennial ryegrass straw with above-threshold levels of ergovaline or lolitrem B are delivered to their destinations. Many samples are received from veterinarians, ranchers, managers, and extension agents to ascertain potential toxicity risk in tall fescue and perennial ryegrass feed in North America.
A definitive diagnosis of tall fescue toxicosis or ryegrass staggers depends on quantification of alkaloid levels in the suspected feed. In the ergovaline assay, straw is ground to 0.5 mm, partitioned into chloroform by shaking for 24 h, purified with a solid-phase extraction (SPE) column, and quantified with a high-performance liquid chromatography (HPLC) fluorescence assay (Rottinghaus et al., 1993; Craig et al., 1994). For the lolitrem B assay, straw also is ground to a 0.5-mm size and partitioned into a chloroform-methanol mixture. After shaking for 18 h, the mixture is evaporated to dryness, reconstituted into a chloroform-acetonitrile mixture, and quantified with an HPLC fluorescence assay (Craig et al., 1994; Hovermale and Craig, 2001).
Sampling of Straw Bales for Toxin Analyses
Proper sampling methods must be used to ensure that analyses accurately quantify toxin concentrations. To obtain a representative sample from stacks of baled straw, a forage core sampler, available from farm supply sources, must be used. Core samplers often are attached to a manual (Fig. 18-3) or an electric hand drill for easy penetration. The sample corer should have an external diameter of 1.27 cm (0.5 in) and a core length of at least 30 cm. A bale can be sampled best by centering the core sampler in the end of the bale and drilling horizontally (Fig. 18-4). A minimum of 20 cores per stack and not more than one per bale should be obtained for each lot.
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Fig. 18-3. Hay corer attached to a manual hand
drill. (photo: The Samuel Roberts Noble Foundation).
Fig. 18-4. Core sampling a bale in a straw
stack. (photo: Steve Van Mouwerik, Anderson Hay and Grain Co.)
A sampled lot should comprise only one cultivar, harvested from one field. If there are two or more lots in a stack, each lot should be sampled separately. A truckload of straw may be considered a lot if there is no information about its cultivar or field source. Bales within a lot should be sampled at random to guard against bias. Every fourth or fifth bale should be sampled, going around the stack or truck, taking at least five random samples from each of the four sides of the stack. Each set of samples from a sampled lot should be placed in a polyethylene freezer bag and sealed tightly. Each bag should be labeled carefully with the name and telephone number of the sender, the lot identification, and the name of the assay desired. Samples should be sent to a reputable laboratory with expertise in conducting toxin analyses. The author is connected with the Endophyte Service Laboratory at Oregon State University, which has a long history of competence in this area of analytical toxicology.
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