Location: Poisonous Plant Research
Project Number: 2080-32630-014-006-R
Project Type: Reimbursable Cooperative Agreement
Start Date: May 1, 2020
End Date: Sep 30, 2021
The objective of this study is to graze larkspur-native and larkspur- naïve cattle on larkspur containing pastures and determine susceptibility of cattle to larkspur poisoning in an attempt to identify cattle that are resistant to larkspur poisoning. Larkspurs (Delphinium spp.) are native plants that grow on foothill and mountain rangelands of western North America and have a long history of poisoning grazing cattle. Ranches with large populations of toxic larkspur often have yearly herd mortalities up to 10%. These losses amount to millions of dollars. If herd numbers are to remain constant, lost animals must be replaced which adds to operating costs of grazing on these rangelands. The reason larkspur poisoning is a significant and re-occurring problem is that, larkspur grows on high quality ranges where stocker cattle can gain upwards of 1.1 kg per day. This incentivizes producers to graze cattle on these rangelands year after year even with the risk of losses due to poisonings. As a result, there is a costly cycle of animal loss and replacement which is not sustainable. Reducing cattle losses to larkspur would increase the sustainability of cattle production. Toxic larkspurs typically contain two main classes of alkaloids which are the highly toxic MSAL-type, and the less toxic non-MSAL type. The two classes act together in the form of a toxic mixture that poisons cattle. These toxic alkaloid mixtures and alkaloid concentrations change based upon growing season, plant growth stage, geographic location, and larkspur species. Just as there are differences in plant factors, there are animal factors which influence larkspur poisoning in cattle. These factors include; cattle breed, sex, age, and previous larkspur exposure. As a result of this complexity, each pasture containing larkspur, and the animals grazed on those pastures must be considered individually. Grazing plans must be continuously modified to reflect seasonal changes in plant growth and alkaloid concentrations, and changes in animals. This includes the proper selection of replacement animals. The proper selection of replacement animals for grazing on larkspur containing rangelands is extremely important. For example, ranchers have often described to the Poisonous Plant Research Lab (PPRL) that the greatest larkspur losses occur with replacement animals, and once the initial losses are over, larkspur poisoning is much less of a problem. What ranchers are describing is known as a selective sweep in genetics. We propose to take advantage of this natural experiment and compare replacement animals from a herd grazed on larkspur-containing pastures (larkspur-native) to replacements from a herd that has never been exposed to larkspur (larkspur-naive). We hypothesize that fewer larkspur-native replacement animals will be lost to larkspur poisoning than larkspur-naive replacement cattle. If our hypothesis is correct, the sourcing of replacement cattle from larkspur-native herds is a simple solution for reducing cattle losses. This would also add value to cattle being sold as replacements from larkspur-native regions of the western United States.
Grazing studies will be conducted during the summer months when larkspur is growing and toxic to cattle (May 1 to October 1). In year 1, Ten Angus steers from the US Meat Animal Research Center, Clay Center, Nebraska (USMARC), that have not been preselected, due to culling practices and are naïve to larkspur poisoning along with ten Angus Angus steers from ranches that have historically preselected animals, due to culling practices, that are more resistant to larkspur (native) poisoning will graze in year one (May 1, 2020 to October 1, 2020). Animals will be placed on a mountain rangeland infested with Delphinium occidentale near Cody, Wyoming (May 1, 2020 to October 1, 2020) on a private ranch. Six animals will be fitted with GPS collars. Collars have been successfully used to monitor grazing distribution and activity (Anderson et al., 2012). Current technology employs sensors within the collars that allows researchers to develop a decision tree that allows them to detect grazing bouts and foraging behavior (Augustine and Derner, 2013). Vegetation maps will be created using ArcGIS software so that the collar data can be overlaid onto the vegetation map to determine grazing patterns. Bite counts will be taken when cattle begin to consume larkspur. Past research has shown that this typically occurs when flowers are partially or fully open and may increase as larkspur moves into the pod stage (middle of July to middle of August; Green et al., 2014). Larkspur samples will be collected weekly during bite count collections to determine alkaloid content of larkspur. Cattle will be removed from the rangeland on October 1 and taken to the USDA-ARS Poisonous Plant Research Laboratory in Logan, UT. Cattle will be tested (phenotyped) for larkspur susceptibility by methods previously described (Green et al., 2014). Blood serum will also be collected at this time for genetic testing. In year 2, a new set of ten naïve and ten native Angus steers will graze the same larkspur infested rangeland. Research protocols will follow procedures described in year 1.