Exploring the Fermentation Kinetics of Medusahead Treated with Glyphosate at Different Particle Lengths

Glyphosate-treated medusahead (Taeniantherum caput-medusae (L.) Nevski) has been shown to increase livestock grazing preference for an otherwise unpalatable plant. This response could be the consequence of changes in the plant's digestion kinetics induced by the herbicide. Thus, the objective of this study was to determine the in vitro digestion kinetics of medusahead treated with different herbicide concentrations (788 g ae/ha-1 (High), 394 g ae/ha-1 (Low), and 0 g ae/ha-1 (Control)) at different particle lengths (1, 20, 30, and 40 mm). Medusahead was treated with glyphosate during the late vegetative to early reproductive stage of the plant at two locations, Mantua, UT and Ritzville, WA. In vitro gas production was measured at 2, 4, 6, 8, 12, 18, 24, 36, 48, 72, 96, and 120 h of incubation, and gas production kinetics was adjusted using a single phasic model with three parameters. Apparent digestible organic matter (DOM) and ash content of the substrates were also measured after incubation. The experimental design was a completely randomized block design with herbicide treatment, particle length and location as fixed factors and four runs as replicates. The smallest particle length, Low herbicide treatment and Ritzville location showed the greatest DOM and lowest Ash content (Table 1; P