Effects of nutrient supplementation in beef cows of poor body condition fed snakeweed (Gutierrezia spp)

Two replicate trials determined the effects of dietary supplementation on snakeweed toxicity in beef cows of poor condition. Cows were stratified by weight and randomly assigned to 3 dietary treatments. Dietary treatments were control (n = 3/trial; medium quality hay, 9.49% crude protein), corn supplementation (n = 3/trial; control diet + 628 g cracked corn), and protein supplementation (n = 3/trial; control diet + 800 g 42% protein supplement). Corn and protein dietary treatments were fed to be isocaloric. Each trial consisted of 2 phases (68 days/phase). Phase 1 consisted of dietary treatments without snakeweed. In phase 2 dietary treatments contained snakeweed as 10% of the dry matter. Phase 1 and 2 dietary treatments were isocaloric/isonitrogenous. Dry matter intake of the control diet was limited to 1.3% of body weight/d. Body condition score and back fat were measured on days 0, 21 and 68 of each phase. Serum samples were collected at the onset of each trial and on days 28, 42 and 56 of each phase. Serum bromosulphthalein (BSP) elimination half life (t1/2) was estimated during week 6 of each phase. Serum BSP elimination t1/2 was higher for the control diet versus corn and protein treatments. Increased blood urea nitrogen (BUN) was found by day 28 of phase 2. Serum total bilirubin increased by day 28 in phase 2 compared to baseline for the control and corn dietary treatments. Additionally, serum indirect bilirubin was higher by day 28 in phase 2. Likewise, serum direct bilirubin increased during phase 2 on day 28 in the corn diet, but decreased by day 28 for the protein diet. Alkaline phosphatase levels were higher (P < 0.05) in the controls by day 28, but lower in the protein treatment by day 28 in phase 2. Changes were noted during phase 2 for some of the serum clinical profiles; however, these changes appear due to dietary restriction. In contrast, changes during phase 2 point to possible hepatotoxic and renal toxic effects of snakeweed. Phase 2 data suggest a benefit of protein supplementation for improving animal tolerance to snakeweed.