Submitted to: Journal of Dairy Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/28/2007
Publication Date: 6/15/2007
Citation: Flores, R., Coblentz, W.K., Ogden, R.K., Coffey, K.P., Looper, M.L., West, C.P., Rosenkrans, C.F. 2007. Effects of Fescue Type and Sampling Date on the Ruminal Disappearance Kinetics of Autumn-Stockpiled Tall Fescue. Journal of Dairy Science. 90:2883-2896. Interpretive Summary: Recently, there has been increased interest in autumn-stockpiling of tall fescue for grazing during the winter months. However, intensive assessment of nutritive characteristics (including ruminal kinetics of digestion) have not been evaluated. Properly managed, autumn-stockpiled tall fescue forages exhibited good nutritive value and associated kinetic characteristics of ruminal disappearance for dry matter and fiber that suggest it can be incorporated easily into diets of developing dairy heifers. Energy densities for ungrazed, autumn-stockpiled tall fescue forages ranged from about 68% down to 62% during the utilization period between early December and late February. Based on these estimates, it should be possible to meet the energy requirements for developing dairy heifers targeted at a 0.8 kg rate of daily gain with little or no energy supplementation. In addition, nutritive traits exhibited by stockpiled forages are likely to be superior to those of hays made from fully-headed tall fescue that is often used as supplemental forage during winter months. Based on the results of this trial, the endophyte status of stockpiled tall fescue forages had little practical effect on forage nutritive value or kinetics of ruminal disappearance. This suggests that any differences in performance by grazing livestock are more likely related to toxin loads produced by the fungal endophyte than by inherent differences in the nutritional composition of the forages. Furthermore, the nutritional characteristics of stockpiled tall fescue forages exhibited little practical deterioration throughout the winter months; however, it remains unclear whether this resistance to deterioration occurs as a result of physical or biochemical limitations to deterioration of older leaves, generation of new growth at relatively low temperatures, or both. Overall, autumn-stockpiled tall fescue forage would appear to be a legitimate and lower-cost alternative to harvested forages that is suitable for developing dairy heifers in the southern Ozark Highlands.
Technical Abstract: Two tall fescue [Lolium arundinaceum (Schreb.) Darbysh] forages, one an experimental host plant/endophyte association containing a novel endophyte (HM4) that produces low or nil concentrations of ergot alkaloids, and the other a typical association of Kentucky 31 tall fescue and the wild-type endophyte (Neotyphodium coenophialum; E+), were autumn-stockpiled following late-summer clipping and fertilization with 56 kg/ha of N in order to assess the nutritive value and ruminal disappearance kinetics of autumn-stockpiled tall fescue forages. Beginning on 4 December 2003, sixteen 361 ± 56.4-kg replacement dairy heifers were stratified by weight and breeding and assigned to one of four 1.6-ha pastures (two each of E+ and HM4) that were strip-grazed throughout the winter. Pastures were sampled before grazing was initiated (4 December), each time heifers were allowed access to a fresh strip (26 December, 15 January, and 4 February), and when the study was terminated (26 February). For fiber components, there were no interactions between fescue type and sampling date for either ungrazed or grazed forages. Over sampling dates, NDF (56.5 to 67.8%), ADF (27.7 to 34.9%), hemicellulose (28.8 to 34.0%), cellulose (25.0 to 28.1%), and lignin (3.61 to 10.05%) varied with sampling date, but patterns were almost exclusively curvilinear with time. Ruminal disappearance rate of DM was not affected by any treatment factor (overall mean for both ungrazed and grazed forages = 0.050/h); similar responses were observed for NDF disappearance (overall mean = 0.048/h). Interactions of fescue type and sampling date were observed for both ungrazed and grazed forages with respect to effective ruminal disappearance of DM; however, estimates were relatively high for all forages (overall range = 59.5 to 70.0%). Effective disappearance of NDF also was relatively extensive for all forages (overall range = 51.3 to 58.4% of NDF). Based on the results of this trial, the endophyte status of stockpiled tall fescue forages had little practical effect on forage nutritive value and kinetics of ruminal DM or NDF disappearance. Overall, autumn-stockpiled tall fescue forages would appear to be a legitimate and lower-cost alternative to harvested forages, and appear to possess suitable nutritional characteristics for developing dairy heifers in the Ozark Highlands.