|Shewmaker, G - UNIVERSITY OF IDAHO|
Submitted to: Agronomy Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: July 3, 2000
Publication Date: N/A
Interpretive Summary: Grazing animals eat a variety of plants, but often show a liking for some and a disliking for others. These preferences or aversions depend in part on chemical and physical factors that affect the animal's smell, vision, feel or taste of plants. We found that cattle preferred those tall fescue cultivars containing the highest concentrations of soluble sugars. Agronomic management should maximize soluble sugar concentrations in forages grazed by cattle. This information is important in forage breeding and selection strategies and grazing and harvest management decisions.
Technical Abstract: Grazing animals prefer some plants more than others. These choices are likely related to physical and chemical factors like energy-dense carbohydrates contained in herbage. This study quantified the nonstructural carbohydrate fractions in each of eight endophyte-free tall fescue cultivars (Festuca arundinacea Schreb.) and related the concentrations of these nonstructural carbohydrates to animal grazing preference determined in a previous study. The experimental area consisted of eight cultivar plots replicated three times in each of three pastures. Within each pasture, vegetative forage was sampled between 0830 and 1000 h MDT before pastures were successively grazed for 48-h by cattle (stocking rate of 11 AU/ha). The study was conducted during May, June, Aug. and Sept. in each of two years. Grazing preference scores were visual estimates of utilization 48 h after initiating grazing. Forage samples were extracted with hot water and with an amylase (Clarase) solution. Sugars were quantified colorimetrically using potassium ferricyanide and glucose oxidase methods. Data were expressed on nonstructural-carbohydrate free basis. Preferences were related to total nonstructural carbohydrates (r squared = 0.49, P < 0.05) and the sum of fructose, glucose and sucrose (r squared = 0.45, P < 0.05) concentrations. Other sugar fractions were not significantly related to preference in this study. Nonstructural carbohydrates averaged over the entire study were glucose, 14.5; fructose, 4.2; sucrose, 40; fructan, 24; insoluble starch, 24; and total nonstructural carbohydrates, 129 g/kg. When expressed on dry matter basis these average values were glucose, 12.6; fructose, 3.6; sucrose,