Cattle grazing tall larkspur on Utah mountain rangeland

Abstract

Ingestion of tall larkspur (Delphinium barbeyi L. Huth) is a major cause of cattle death on ranges where the plant occurs. The amount and timing of tall larkspur ingestion by grazing cattle was studied from 30 July to 2 September 1986 on high mountain rangeland in central Utah. Forbs dominated the vegetation and were also the major dietary item selected by cattle (>70% of total bites). There was a negative relationship (r=-0.62) between standing crop of other forbs and tall larkspur consumption. Cattle began eating substantial quantities (>10% of bites) of tall larkspur about 10 August, and consumption had increased to 20% when the study ended. Tall larkspur leaves and pods were the major parts selected. At the time of major consumption, leaves were relatively low and declining in total alkaloid concentration (TAC) (1.0-0.6%) while pods were approximately 1.0% TAC and increasing when the study ended. Time spent per feeding station (TFS) was influenced by the vegetation area where animals foraged. TFS in the grass-forb, currant (Ribes spp.), and larkspur areas were 11.2, 25.9, and 22.0 s, respectively. Cattle grazed most efficiently (bite rate:step rate) in the grass-forb areas, and least efficiently in the current areas. Cattle ate large quantities of tall larkspur during the study with no deaths, probably due to the low alkaloid levels in the tall larkspur. Larkspur consumption was not correlated with previous 12- or 24-h precipitation totals. However, cattle did begin major consumption of tall larkspur after 2 rain showers fell following a several week dry period.