Submitted to: Journal of Animal Science
Publication Type: Peer reviewed journal
Publication Acceptance Date: 6/16/2004
Publication Date: 10/1/2004
Citation: Ralphs, M.H., Wiedmeier, R.D. 2004. Conditioning cattle to graze broom snakeweed (gutierrezia sarothrae). Journal of Animal Science. 82:3100-3106. Interpretive Summary: Broom snakeweed is the most wide-spread range weed in North America. We attempted to positively condition cattle to graze snakeweed as a biological tool to reduce its competitive ability in a plant community. Cattle were offered snakeweed and then were dosed with starch to provide a positive energy feedback. Heifers conditioned with starch consumed more snakeweed than did control heifers in the pen conditioning study. However, preference for snakeweed did not hold when they were taken to a field grazing trial. They preferred green bunchgrasses, forbs, and even dry cheatgrass to snakeweed. When the pasture sizes were restricted, the heifers quickly ran out of alternative feed and consumed snakeweed for up to 40% of their diets. Increasing grazing pressure in a short-duration grazing system may force cattle to graze snakeweed and provide a form of biological control.
Technical Abstract: Broom snakeweed (Gutierrezia sarothrae (Pursh) Britt. & Rusby) is the most wide-spread range weed in North America. We attempted to positively condition cattle to graze broom snakeweed to create a biological tool to reduce its competitive ability in a plant community. Fifteen yearling heifers were divided into 3 treatment groups receiving different supplements: corn starch, starch plus ground snakeweed, control. Heifers were fed fresh snakeweed, and then were gavaged with the respective supplements to provide positive feedback to enhance their acceptance of it. The starch group consumed more snakeweed in the pen conditioning trial (P = 0.02). The starch and control groups were then taken to the field for two grazing trials. In the spring grazing trial there was no snakeweed consumed in the free-ranging part of the trial. However, when the pasture size was reduced, the heifers started to consume snakeweed as they ran short of feed. In the second small pasture trial, heifers in the positively conditioned group consumed more snakeweed than those in the control group (16% vs. 4% of bites, P < 0.0001). In the fall grazing trial, little snakeweed was consumed in the free-ranging part of the trial. When the pasture size was reduced, both positively conditioned and control groups increased snakeweed consumption up to 35 - 40% of bites. Up to 88% of snakeweed plants in the small pastures were grazed. Cattle can be forced to graze snakeweed in a short-duration, high intensity