Proceedings, Western Section, American Society of Animal Science Vol. 55, 2004 EFFECTS OF LOCOWEED ON SERUM CONSTITUENTS AND RUMEN PROFILES OF SHEEP S B. S. Obeidat 1 , J. R. Strickland 2 , M. L. Vogt 1 , C. A. Löest 1 , J. E. Sawyer 3 , M. M. Reed 1 , C. R, Krehbiel 4 , J. B. Taylor 5 , R. A. Halalsheh 1 , and L. Chen 1 1 New Mexico State University, Las Cruces, NM 2 USDA-ARS, Forage-Animal Production Research Unit, Lexington, KY 3 Texas A & M University, College Station, TX 4 Oklahoma State University, Stillwater, OK 5 USDA-ARS, US Sheep Experiment Station, Dubois, ID S Research supported in part by a grant from the USDA Special Grants Program, in part by a grant from PHS-NIH (GM08136-27), and in part by the Agriculture Experiment Station, New Mexico State University. ABSTRACT: Thirteen mixed breed wethers (47.5 ± 9.3 kg), fitted with ruminal and duodenal cannula, were used in a randomized design experiment to evaluate the effects of locoweed on serum constituents and ruminal fermentation. Locoweed treatments supplied: 1) 0.2 mg, 2) 0.4 mg, and 3) 0.8 mg of swainsonine·kg BW -1 ·d -1 . Data were collected during 3 periods: pre-locoweed treatment (d -19 to d 0), locoweed treatment (d 1 to d 20), and post-locoweed treatment (d 21 to d 40). Blood and rumen samples were collected throughout each period; nutrient digestion (in situ) was assessed during the pre- and locoweed treatment periods. Serum swainsonine was detected in all treatments when locoweed was consumed, and was highest (P < 0.05) for the 0.8 mg treatment. Serum alkaline phosphatase activity was elevated (P < 0.05) due to locoweed treatment, but immediately returned to pre-locoweed values during the post-locoweed period (P = 0.13). Locoweed concentration and duration of exposure increased (P < 0.05) serum aspartate aminotransferase (AST). However, serum AST did not return to pre-locoweed values during the post- locoweed treatment period. Concentrations of blood urea N, NEFA, and AA were not affected by treatments (P > 0.11). Although not affected when locoweed was fed, propionate was elevated (P = 0.05) for the 0.2 mg treatment during the post-treatment period. Ammonia concentrations, ruminal pH, and DM digestion were not different (P > 0.13) among treatments. Extent of ruminal DM, OM, and ADF digestion during the treatment period was greatest (P = 0.01) in the 0.4 mg treatment. Wethers consuming locoweed exhibited subclinical toxicity. However, effects on nutrient metabolism were dependent upon the amount of locoweed consumed. Further, research is needed to fully determine the effects of swainsonine on nutrient metabolism. Key Words: Sheep, Locoweed, Rumen digestion Introduction Poisonous plants are a major detriment to livestock production worldwide. Several species of locoweed (e.g. those in the Oxytropis and Astragalus genuses) are toxic to livestock, resulting in production and economic losses to livestock producers (Nielsen et al., 1988). Locoweed intoxication generally occurs in animals having consumed the locoweed plants for 7 to 14 d (Taylor et al., 2000). The intoxication is characterized by slow growth rates, depression, emaciation, dull eyes, and reproductive problems (Broquist, 1986). Swainsonine, an indolizidine alkaloid, has been identified as the primary toxicant in locoweed (Molyneux and James, 1982). Limited data is available concerning the effects of locoweed consumption under range conditions on nutrient digestion and metabolism by livestock. Altered nutrient digestion and metabolic processes due to locoweed consumption is evident in studies by Stavanja et al. (1992) and Taylor et al. (2000), who reported that serum cholesterol and triglycerides were depressed in rats and sheep consuming locoweed, respectively. In a recent preliminary report by our laboratory, Reed et al. (2003) found minimal effects of consuming locoweed on ruminal VFA, ammonia, and nutrient digestion (i.e., OM, ADF, NDF, CP) when sheep were fed at either 0.2 mg or 1.6 mg of swainsonine·kg BW -1 ·d -1 . Given the mixed reports concerning the effects of swainsonine on nutrient metabolism, our objective was to further define the effects of feeding a forage-based diet containing different levels of locoweed on serum constituents and ruminal fermentation profiles of sheep. Materials and Methods Experimental protocols were approved by the New Mexico State University Institutional Animal Care and Use Committee. Thirteen mixed breed wethers (BW = 47.5 ± 9.3 kg) fitted with ruminal and duodenal cannula, were used in a randomized design and housed individually in metabolism crates. Data were collected during 3 periods: pre-locoweed treatment (d -19 to d 0), locoweed treatment (d 1 to d 20), and post-locoweed treatment (d 21 to d 40). Diets for all three periods were isocaloric/isonitrogenous and restricted to a DM intake of 1.84% of BW to minimize diet refusal. During the pre-locoweed treatment period, animals were fed a diet of blue grama and alfalfa hay 410