Location: Range and Livestock ResearchTitle: In Situ Digestibility of Grass Hay after Heifer Diets were Abruptly Switched from 35 or 70% Concentrate to 100% Forage Author
Submitted to: Meeting Proceedings
Publication Type: Proceedings
Publication Acceptance Date: 5/1/2010
Publication Date: 7/15/2010
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 or 70% Concentrate to 100% Forage. Meeting Proceedings. Western Section of American Society of Animal Science. 61:266270 Interpretive Summary: There is an abundance of literature pertaining to changing cattle diets from forage to concentrates. Research has summarized that cattle consuming high grain diets have lower ruminal pH levels, higher total VFA concentrations, and higher propionate levels compared to acetate and butyrate. Also, the effects of cereal grain supplementation are widely known. Researchers have reported that as supplemental ground corn increased, there was a linear decrease in digestibility of cellulose and hemicellulose in low quality grass hay. On the other hand, corn did not affect OM digestibility in steers grazing summer pastures . Others have found no significant effects on DMD when cows grazing winter range were fed supplemental energy(cracked barley). However, little is known about the changes that may occur when ruminants are abruptly switched from a concentrate-containing diet to one of all forage. This situation might be common where heifers or bulls are developed in confinement, then turned out to pasture for the breeding season. Research has found that steers limit-fed high concentrate diets were able to adapt to pasture as well as steers fed hay-based diets. Conversely, reports indicate that steers and heifers lost weight in the first 2 wk after being switched from a high energy diet to a low energy diet. Therefore, objectives for the present experiment were to characterize ruminal function in heifers after an abrupt diet switch from diets containing 35 or 70% corn to a diet containing forage only compared to animals that were maintained on a forage diet alone. Results indicate that forage digestibility was depressed when heifers were fed a high-concentrate diet; however, this effect disappeared within 96 h of feeding an all-forage diet. Future research where in situ sampling hours are timed more immediately after the diet switch could target the precise timing of rumen adaptation. It appears that the rumen can adapt quickly when diets are switched from concentrate-containing to all-forage.
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 0, 3, 6, 9, 12, 15, 18, 21) 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 × 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 52.8 ± 2.5%; 96-h: 76.3, 75.2, and 61.4 ±0.7% for CONTROL, 35%, and 70 % respectively) A comparable pattern was observed for NDF digestibility; 48-h: 67.7, 65.6, and 48.9 ± 3.1%; 96-h: 77.0, 75.9, and 58.6 ±0.9% for CONTROL, 35%, and 70%, respectively. In contrast, after the diet switch (d 0), OM digestibility of grass hay was similar for all diets (P = 0.10; 48-h: 66.5,66.0, and 68.7 ± 2.5%; 96-h: 75.9, 76.1, and 76.0 ± 0.7%for CONTROL, 35%, and 70%, respectively). Digestibility of NDF exhibited a similar pattern for 70% than 35% or CONTROL; 48-h: 65.5, 64.4, and 68.0 ± 3.1%; 96-h: 76.2,76.3, and 77.1 ± 0.9% 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 = 0.65; avg 4.3 ±0.2%/h). Forage digestibility was depressed when heifers were fed a high-concentrate diet; however, this effect disappeared within 96 h of feeding an all forage diet.