Growth at Low Temperatures Increases Alfalfa Leaf Cell Constituents Related to Pasture Bloat

The incidence of alfalfa ( Medicago sativa L.) pasture bloat appears to increase with growth at the low temperatures that prevail in the high‐altitude valleys of the Intermountain West. This study determined whether plant characteristics associated with bloat are more prevalent in the leaves of alfalfa plants grown at suboptimal (15/5°C) day/night temperatures than in plants grown at optimal (25/15°C) temperatures. We hypothesized that the larger leaves characteristic of alfalfa grown at low temperatures would contain more soluble protein and chlorophyll than leaves of plants of the same cultivars grown at higher temperatures, even though cell number per leaf remains constant. We also expected that the larger cells typical of alfalfa grown at low temperatures would rupture more easily than cells of alfalfa grown at warmer temperatures. Fresh leaves were ground with a mortar and pestle, or shaken in buffer with glass beads to simulate mechanical damage such as would occur with rumination. Leaves from growth chamber‐grown Ranger and Fortress alfalfa contained more chlorophyll and more than twice the soluble protein when grown at low than at optimal temperatures. Contrary to our expectations, susceptibility of cells and tissue to damage decreased by approximately 15% with growth at low temperatures. Soluble plant protein and chlorophyll have been implicated in alfalfa bloat, and the increased content of cellular components related to bloat with low temperature growth could increase the rate of their release into the rumen, resulting in bloat.