ARS | Publication request: In Situ Digestibility of Grass Hay after Heifer Diets were Abruptly Switched from 35 to 70% Concentrate to 100% Forage

Submitted to: Meeting Abstract
Publication Type: Abstract Only
Publication Acceptance Date: May 1, 2010
Publication Date: July 15, 2010
Citation: Voigt, L.A., Endecott, R.L., Paterson, J.A., Waterman, R.C. 2010. In situ digestibility of grass hay after heifer diets were abruptly switched from 35 to 70% concentrate to 100% forage. Western Section American Society of Animal Science 88(E. Suppl. 2)838. Abstract #1042.

Technical Abstract: Twelve ruminally-cannulated Hereford-cross heifers (non-pregnant, 2-yr-old, 508 ± 2 kg) were randomly assigned to 3 individually-fed, pre-experiment diets (4 heifers/diet). Diets were: 1) all forage, (CONTROL); 2) 35% concentrate, (35%), and 3) 70% concentrate (70%). Heifers were fed the diets for ~100 d before the start of the trial. Pre-experiment diets consisted of grass-alfalfa hay (11.8% CP) and corn (9.8% CP), with soybean meal-urea supplement added to make the diets isonitrogenous at 13% CP. On d 0, diets were abruptly switched to grass hay (6.2% CP, fed at 2% BW). In situ digestibility runs were conducted starting on d -8 and ran continuously (d 1, 4, 7, 10, 13, 16, 19, 22) after the diet switch. Duplicate sample bags filled with 5 g of grass hay and a blank bag were incubated for 0, 24, 48, and 96 h. Pre-experiment diet x in situ run interactions occurred (P = 0.04) for OM and NDF digestibility. Organic matter digestibility of grass hay before the diet switch (d -8) was lower (P = 0.10) for 70% than for 35% or CONTROL; 48-h: 68.5, 66.7, and 53.0 ± 2.3%; 96-h: 76.3, 75.2, and 61.6 ± 1.0% for CONTROL, 35%, and 70%, respectively. A comparable pattern was observed for NDF digestibility; 48-h: 67.7, 65.6, and 48.8 ± 2.8%; 96-h: 77.0, 75.9, and 58.9 ± 1.1% for CONTROL, 35%, and 70%, respectively. In contrast, after the diet switch (d 1), OM digestibility of grass hay was higher for 70% than for 35% or CONTROL (P = 0.10; 48-h: 66.5, 66.0, and 69.0 ± 1.7%; 96-h: 75.9, 76.1, and 77.6 ± 0.7% for CONTROL, 35%, and 70%, respectively). Digestibility of NDF was also higher for 70% than 35% or CONTROL; 48-h: 65.5, 64.4, and 67.8 ± 2.2%; 96-h: 76.2, 76.3, and 78.1 ± 0.8% for CONTROL, 35%, and 70%, respectively. Organic matter and NDF digestibilities in subsequent in situ runs were similar (P > 0.10), regardless of pre-experiment diet. Rate of digestion was not influenced by pre-experiment diet (P = 0.74; avg 4.3 ± 0.002%/h). Forage digestibility was depressed when heifers were fed a high-concentrate diet; however, this effect disappeared within 48 h of feeding an all-forage diet.