Preference for Smooth Bromegrass Clones Is Affected by Divergent Selection for Nutritive Value

Abstract

Selective grazing by sheep (Ovis aries) leads to diet improvement. To learn whether animals select the most nutritious food available, differences in percent consumption were determined among smooth bromegrass (Bromus inermis Leyss.) clones selected for divergent levels of neutral detergent fiber (NDF) or in vitro dry matter disappearance (IVDMD). High‐ and low‐NDF clones from a single population and high‐ and low‐IVDMD clones from four populations were evaluated as spaced plants in separate replicated trials. Preference was determined by offering sheep grazing access to complete blocks comprised of both high and low selections. Pre‐ and post‐grazing plant height and weight were measured and the differences used to calculate percent consumption, which was used as an indicator of preference. Preference and forage nutritive value were determined at three grazing periods in each of 2 yr. High‐IVDMD clones (mean IVDMD = 700 g kg−1) were 12% more preferred (29 vs. 26% of height consumed) than low‐IVDMD clones (mean IVDMD = 690 g kg−1). Low‐NDF clones (mean NDF = 470 g kg−1) were 36% more preferred (34 vs. 25% of height consumed) than high‐NDF clones (mean NDF = 505 g kg−1). Preference was positively correlated with IVDMD in three of four populations and negatively correlated with NDF. Sheep discriminated between equally‐accessible, more‐ and less‐nutritious clones and preferentially selected the more nutritious clones.