Nutrient digestibility in sheep fed diets containing Roundup Ready or conventional fodder beet, sugar beet, and beet pulp1

Abstract

The objective of this digestibility assessment was to determine whether there are significant differences in the digestibility of Roundup Ready (glyphosate-tolerant) and conventional sugar beet, fodder beet, and beet pulp produced from sugar beet varieties when fed to sheep (seven wethers per treatment group). Three experiments were conducted in this assessment. Experiment 1 (35 wethers) compared one glyphosate-tolerant fodder beet variety with four conventional varieties, Exp. 2 (42 wethers) compared one glyphosate-tolerant sugar beet variety with five conventional varieties, and Exp. 3 (42 wethers) compared beet pulp derived from glyphosate-tolerant sugar beet with beet pulp from five European locations. The experimental phase consisted of a 2-wk preliminary period followed by a 1-wk collection period for Exp. 1 and 2, and a 1-wk preliminary period followed by a 1-wk digestibility collection period for Exp. 3. Diets were comprised of grass hay at 30, 30, and 20% of DM for Exp. 1, 2, and 3, respectively, with the balance being beet components. Urea and sodium sulfate were supplemented (8 and 2.9 g, respectively, for Exp. 1 and 2; and 6 g and 2.16 g, respectively, for Exp. 3) to supply sufficient dietary N and S. Each diet was fed to sheep (96 +/- 0.9 kg) in the three experiments to at or near maintenance energy levels. Treatment differences were considered significant at P < 0.05. Apparent digestibilities of DM, OM, CP, NDF, ADF, and DE for glyphosate-tolerant fodder and sugar beets did not differ from those for commercial fodder and sugar beets in Exp. 1 and 2. There were differences (P < 0.05) in DM, OM, CP, NDF, ADF, and DE digestibilities influenced by the different varieties of beet pulp in Exp. 3, but these were not unique to just the Roundup Ready sugar beet variety. Digestibilities and feeding values of Roundup Ready fodder beet, sugar beet, and beet pulp produced from Roundup Ready sugar beet varieties were not influenced by the introduction of the Roundup Ready trait compared with conventional varieties.