Effects of Carbachol Administration in Cattle Grazing Tall Larkspur-Infested Range

Abstract

Tall larkspur (Delphinium barbeyi L. Huth.) toxicosis of cattle is a serious problem on western USA mountain rangelands. Manipulating the ruminal environment may decrease the susceptibility of cattle to larkspur intoxication. The cholinergic drug carbachol can greatly increase salivary flow and fluid passage rate in ruminants. Our objectives were to: (1) determine if chronic administration of carbachol altered ruminal fluid passage rate, ruminal pH, or water intake in grazing cattle, and (2) evaluate mineral salt supplementation as a prophylactic procedure for cattle grazing larkspur-infested rangelands. The study was conducted during summer of 1990 and 1991 near Yampa, Colo. Twelve heifers were divided randomly into 3 treatment groups: (1) carbachol administered at 0.01 mg.kg-1.day-1 via subcutaneous osmotic minipumps; (2) mineral-salt supplement dosed intraruminally at 0.25 g.kg-1.day-1; and (3) controls. Administration of carbachol either had no effect or a negative effect on ruminal fluid passage rate, ruminal pH, saliva production, and water intake compared with the controls. Carbachol had few consistent effects on serum electrolyte concentrations compared to the controls. Treatments did not influence cattle diet selection; cattle ate no larkspur during 1990, but selected larkspur for 16% of their diets during August, 1991. There was no indication that supplementation with mineral salt would attenuate larkspur toxicosis through increased dilution rates, or decreased larkspur consumption. Our results indicate that neither carbachol nor mineral supplementation will reduce animal susceptibility to larkspur toxicosis.