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Title: Effects of Tall Fescue Forage Mass on Steer Ingestive Behavior and Performance

item Burns, Joseph
item Fisher, Dwight
item POND, K - Texas Tech University

Submitted to: Crop Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/5/2010
Publication Date: 5/10/2011
Citation: Burns, J.C., Fisher, D.S., Pond, K.R. 2011. Effects of Tall Fescue Forage Mass on Steer Ingestive Behavior and Performance. Crop Science. 51:1850-1864.

Interpretive Summary: Tall Fescue is the major cool-season perennial forage grown across the upper southern USA. In this humid transition zone tall fescue provides forage as both pasture and hay in ruminant production systems. Much of the past research has focused on fungal endophyte issues, N fertilizations, cutting or defoliation frequencies, time of defoliation, and height of defoliation whether grazed or stockpiled, or harvested as hay. Little attention, however, has been directed to the relationship between forage mass (FM) and animal daily responses and pasture productivity, especially after identifying and clarifying the role of toxic- and not-toxic endophytes on animal and plant metabolism. It is well established that throughout the transition zone supplemental N is a key to maintaining productive stands of pure tall fescue for pasture or generating acceptable stockpile. Recommended annual applications of N, depending on stand use, can be upwards of 224 kg ha-1. This expensive input, coupled with the removal of the toxic endophyte (seeding cultivars that are either endophyte free or carrying a novel endophyte), warrants forage management strategies that assure efficient utilization that favors stand longevity. An experiment was conduct to determine the importance of FM on steer daily gain and pasture productivity as well as on dry matter intake (DMI), digesta kinetics and grazing behavior of endophyte free tall fescue. In general, steer daily gain was similar among FM treatments in the spring averaging 0.88 kg, but steers were able to select a different diet from among the FM treatments, with nutritive value (NV) declining with increasing FM. Stocking rate was less at the greater FM. In the fall, steers selected a diet from among the FM treatments that was similar in NV. Grazing periods were not adequate to estimate steer daily gains. In general, tall fescue provided a leafy canopy structure that permits some selective grazing providing a diet of desirable NV. However, selective consumption was not altered by FM. Spring growth generally provides forage of adequate NV that permits a wide range of management strategies dealing with FM for application in production management schemes. Furthermore, fall growth, although considerably reduced compared with spring growth, is very leafy and supports a diet of very acceptable NV. Tall fescue that is free of endophyte, or contains a nontoxic endophyte, provides excellent forage to serve as a component of animal production systems across the north-south transition zone.

Technical Abstract: Tall fescue [Lolium arundinaceum (Schreb.) Darbysh] is a well adapted perennial pasture species utilized across the north-south transition zone of the United States and in similar environments worldwide. This 3-yr trial evaluated the influence of three forage masses (FM) on steer and pasture responses for spring (April to July) and fall (October) growths. Spring FM averaged 1450 kg ha-1 (Short), 3032 kg ha-1 (Medium) and 3812 kg ha-1 (Tall) in the three treatments. Canopy in vitro true organic matter disappearance (ITOD) decreased linearly from Short (797 g kg-1) to Tall (771 g kg-1). Steer daily gains (0.88 kg) and gains ha-1 (392 kg ha-1 yr-1) were not altered by FM, but the mean number of steers ha-1 increased linearly from Tall (6.1 steers ha-1) to Short (8.2 steers ha-1) as did effective feed units ha-1 (1712 to 2256 kg ha-1 yr-1). Canopies were predominately leaf (527 g kg-1) and averaged 847 g kg-1 ITOD with estimates similar among FM treatments. Diet ITOD declined linearly from Short (870 g kg-1) to Tall (839 g kg-1) as did CP (from 235 to 192 g kg-1). In the fall, FM averaged 1556, 3228 and 3494 kg ha-1 for the three FM treatments. Canopy ITOD averaged 774 g kg-1 and was not altered by FM. The canopies averaged 597 g kg-1 leaf and 864 g kg-1 ITOD, 91 g kg-1 stem and 857 g kg-1 ITOD and 312 g kg-1 dead and 584 g kg-1 ITOD and were similar among FM treatments. In addition, diets selected averaged 834 g kg-1 ITOD and 233 g kg-1 CP and were not altered by FM. Tall fescue free of toxic endophyte provides forage that can be managed flexibly in animal production systems.