Mineral salt supplementation of cattle grazing tall larkspur-infested rangeland during drought.

Abstract

Mineral salt supplements are used in attempts to reduce cattle losses to tall larkspur (Delphinium spp.). We determined the effects of a mineral salt mix on larkspur consumption, ruminal fluid kinetics, and water intake during 4 periods in June, July, and August, 1988 (Trial 1), and during an 18-day grazing period in August, 1989 (Trial 2). In 1988, 12 ruminally cannulated heifers were divided into 3 treatment groups: control with no access to mineral (CONT), 0.5 g mineral (LOW), and 1.0 g mineral.kg body weight-1.day-1 (HIGH) dosed intraruminally. In 1989, 10 cows were allocated to either a control group or 0.75 g mineral.kg body weight-1.day-1. During Trials 1 and 2, consumption of larkspur peaked at 5 and 7% of cattle diets, respectively; these low levels were attributed to drought. There were no differences (P>0.1) in consumption of total larkspur or larkspur plant parts. Mineral supplement increased water consumption (P<0.05) during Trial 1, but not during Trial 2. The HIGH group averaged 0.1 liters.kg body weight-1.day-1 compared to 0.07 liters for the CONT and LOW groups. Ruminal fluid passage rate, turnover time, volume and fluid outflow rate (FOR) did not differ (P>0.05) among treatments during Trial 1, but FOR was increased by mineral treatment in Trial 2. Alkaloid concentration in larkspur declined with maturity, and was apparently elevated by drought in Trial 2. This study found little indication that mineral salt supplement altered the amount of larkspur consumed by grazing cattle. Increased water intake one summer did not alter ruminal fluid kinetics. If dietary minerals alter toxicity of larkspur to cattle, other mechanisms than those tested are responsible.