ARS | Publication request: Effects of supplemental flaxseed on site and extent of digestion in beef heifers grazing summer native pasture in the northern Great Plains

Submitted to: Flax Institute Proceedings
Publication Type: Proceedings
Publication Acceptance Date: March 1, 2008
Publication Date: March 26, 2008
Citation: Scholljegerdes, E.J., Kronberg, S.L. 2008. Effects of supplemental flaxseed on site and extent of digestion in beef heifers grazing summer native pasture in the northern Great Plains. Flax Institute Proceedings. p. 34-42 in Proc. 62nd Flax Inst. U.S., Fargo, ND.

Interpretive Summary: Six Angus heifers (367 ± 8.0 kg) fitted with ruminal and duodenal cannulas were used to determine the effect of ground flaxseed on the intake and digestibility of forage consumed by cattle grazing native range in the northern Great Plains. Starting on June 9, 2006 heifers were rotationally grazed on three 12 ha native pastures and were randomly allotted to one of three treatments being: no supplement (Control); a conventional cracked corn-soybean meal supplement fed at 0.32% of BW once daily; or a ground flaxseed supplement fed at 0.18% of BW once daily. Supplements were formulated to provide equal quantities of crude protein and energy with the major difference being the source of energy (carbohydrate versus fat). There were three experimental periods that were 28 d in length with 18 d for diet adaptation and 10 d for intensive sampling. Supplementation irrespective of source did not forage selectivity. Nor did it affect forage intake. There were no interactions between forage quality and supplement type. True ruminal and total tract organic matter digestibility (% of intake) did not differ between Control and supplemented treatments and total tract digestibility was greater corn-fed cattle than flax-fed cattle. Intestinal supply of crude protein did not differ across treatments. True ruminal crude protein digestibility was not affected by supplementation. Likewise, ruminal fiber digestibility also did not differ with supplementation and supplement type did not cause any differences. Therefore, ground flaxseed appears to be a suitable energy supplement for cattle grazing summer rangelands.

Technical Abstract: Six Angus heifers (367 ± 8.0 kg) fitted with ruminal and duodenal cannulas were used in a split-plot designed experiment to determine the effects of ground flaxseed or corn and advancing season on site and extent of digestion when beef heifers grazed summer range in the northern Great Plains. Starting on June 9, 2006 heifers were rotationally grazed on three 12 ha native pastures and were randomly allotted to one of three treatments being: no supplement (CON); a cracked corn-soybean meal supplement fed at 0.32% of BW once daily (CRN); or a ground flaxseed supplement fed at 0.18% of BW once daily (FLX). Supplements were formulated to be isonitrogenous and isocaloric. There were three experimental periods that were 28 d in length with 18 d for diet adaptation and 10 d for intensive sampling. Provision of supplement did not affect (P = 0.22) masticate in vitro organic matter digestibility, however, between supplemented treatments, cattle fed FLX tended (P = 0.08) to select a lower quality masticate than CRN. Forage OM intake was not affected (P = 0.12) by supplementation nor was there a difference (P = 0.49) between CRN and FLX. A quadratic (P = 0.001) response was observed for forage OM intake as the grazing season advanced. Duodenal and fecal OM flow was not different (P = 0.39) across treatments. Therefore, true ruminal and total tract OM digestibility (% of intake) did not differ (P = 0.37 to 0.56) between CON and supplemented treatments and total tract digestibility was greater (P = 0.01) for CRN than FLX. Total duodenal N flow did not differ (P = 0.16) across treatments but responded quadratically (P = 0.03) with advancing season. True ruminal N digestibility was not affected by supplementation (P = 0.16 to 0.26). Likewise, ruminal neutral detergent fiber digestibility also did not differ (P = 0.26) with supplementation and CRN was not different (P = 0.22) from FLX. Total ruminal volatile fatty acid decreased with supplementation (P = 0.04) and ruminal molar proportion of acetate was greater (P = 0.02) for FLX than CRN. Therefore, ground flaxseed appears to be a suitable energy supplement for cattle grazing summer rangelands.