Seasonal Fluctuations in Nutrient Content of Feral Burro Forages, Lower Colorado River Valley, Arizona

Hanley, Thomas; Brady, Ward

Determining carrying capacity of desert ranges for feral burros is a concern of land managers in the southwestern United States. Forage quality has a direct bearing on the quantity of forage consumed to meet the animal’s nutritional requirements. In this study, the authors studied the seasonal fluctuation in nutrient content of four major forage species for feral burros. The species studied were Plantago insularis (wooly Indianwheat), Ambrosia dumosa (white bursage), Lycium andersonii (desertthorn), and Cercidium microphyllum (foothills paloverde). The study was conducted in 1974 and 1975 in the Havasu Resource Area, California-Arizona. Nutrient contents were determined at the end of February, May, August and November. Results showed gross energy content was the least variable on a seasonal basis. Crude protein, phosphorus and beta-carotene contents tended to follow the pattern generally expected with nutritional quality increasing following the pulse of growth produced by winter precipitation then slowly declining. Plantago insularis appears to be an excellent forage plant being rich in protein, phosphorus, and beta-carotene and makes up the bulk of the burros’ diet between January and May. Cercidium microphyllum and Lycium andersonii may be sources of phosphorus and beta-carotene in late summer and fall. Ambrosia dumosa has the highest nutrient value in the spring but is less nutritional than the other species in the fall. Since burros occupy riparian habitat during the summer, mesquite and arrowweed are major forage species at that time. Riparian vegetation’s role in meeting the nutritional requirements of feral burros is still to be investigated.

Seasonal Fluctuations in Nutrient Content of Feral Burro Forages, Lower Colorado River Valley, Arizona

Series