The 2008 Joint Meeting of the Society for Range Management and the America Forage and Grassland Council. |
Wednesday, January 30, 2008
15
Influence of Prior Exposure and Basal Diet Quality on Intake of Three Locoweed Species by Naïve Heifers
Jacob A. Martin1, Andres F. Cibils1, and John D. Graham2. (1) Department of Animal and Range Sciences, New Mexico State University, Las Cruces, NM 88003, (2) Cooperative Extension, New Mexico State University, Clayton, NM 88003
Cattle in NE New Mexico show increased preference for locoweeds (Oxytropis sp. and Astragalus sp.) during spring and fall when nutritional value of dominant warm season grasses declines. In addition, cattle preference for locoweeds increases over time. The relative role that each of these factors play in herd intoxications is unknown. We conducted a pen experiment with 18 yearling heifers that were naïve to locoweed to determine the effect of prior exposure and quality of basal diet on the intake of air-dried ground white locoweed (O. sericea), purple locoweed (O. lambertii), and wooly locoweed (A. mollissimus). Total locoweed offered was 7% of daily ration (1.7% body weight DM basis), which consisted of low (L: millet hay) and high (H: corn-hay mix) quality foods. We used a latin square design with two 5-day testing phases preceded by 7 days of adaptation to basal diets and locoweeds. Intake of locoweeds (g/kg LBW) was affected by quality of the basal ration and by a heifer’s prior exposure to this plant; however the influence of both these factors differed depending on the species of locoweed considered. Quality of basal ration influenced intake of both white (L=0.28±0.11, H=0.17±0.15) and purple locoweed (L=0.23±0.12, H=0.11±0.14) of naïve heifers. However, quality of basal ration ceased to influence intake after heifers had become familiar with this plant (white locoweed: L=0.27±0.11, H=0.30±0.11; purple locoweed: L=0.27±0.08; H=0.27±0.09). Conversely, quality of basal ration affected intake of wooly locoweed regardless of prior exposure (limited exposure L=0.17±0.15, H=0.11±0.15; with prior exposure L=0.26±0.12; H=0.20±0.14). Our results suggest that heifers that are exposed to white and purple locoweed for short periods of time will consume this plant regardless of the quality of alternative food choices. Ingestion of wooly locoweed, on the other hand, consistently increased with decreasing quality of basal ration.