The objective of this study was to investigate differences in yield and nutritive value of organically and conventionally grown winter wheat crops. Each cultivation system was carried out in 3 plots bordering each other to assure similar soil properties. Whole-plant (WP) yield was determined in May 2009, and grain and straw yields were determined at maturity in July 2009. Samples were dried and chemical composition and in vitro dry matter digestibility were determined. Samples (500 mg) of each substrate were incubated with 50 mL of buffered rumen fluid at 39°C, and gas production was measured at 3, 6, 9, 12, 16, 21, 26, 31, 36, 48, 60, 72, 96, 120 and 144 h to estimate fermentation kinetics. Mean yield in conventional plots was 3.12, 1.28 and 1.06 t DM/ ha for WP, grain and straw, respectively. Organic cultivation decreased the yield of WP, grain and straw to 74, 57 and 76% of that in the conventional cultivation, respectively (P > 0.24). No differences (P > 0.05) in organic matter, neutral detergent fiber and acid detergent fiber content of WP or grain were detected between cultivation systems, but crude protein content was lower (P 0.05) between cultivars were detected in chemical composition of straw. Organic and conventionally grown crops did not differ (P > 0.11) in their in vitro dry matter digestibility (43.6 vs. 45.2% for WP, 26.3 vs. 24.8% for straw and 79.6 vs. 78.2% for grains). The cultivation method did not affect (P > 0.26) either the potential gas production or the average production rate (calculated as mL of gas/h). The results indicate that organic cultivation reduced crop yield and protein content in WP and wheat grains, but no effects were observed on ruminal degradation.

1 Página.--Trabajo presentado al 2010 Annual Meeting Abstracts (Denver, Colorado, 11 al 15 de Julio del 2010).--J. Anim. Sci. Vol. 88, E-Suppl. 2/J. Dairy Sci. Vol. 93, E-Suppl. 1/Poult. Sci. Vol. 89, E-Suppl. 1

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