Submitted to: Florida Cattleman
Publication Type: Trade Journal
Publication Acceptance Date: 4/23/2007
Publication Date: 4/23/2007
Citation: Coleman, S.W., Breman, J., Blount, A.S., Quesenberry, K.H. 2007. Nutritive value of Bahiagrass and other warm season perennials following a freeze. Florida Cattleman. 70(5);78-79. Interpretive Summary: Winter feed is the largest single cost for the cow-calf industry in most of the USA. With warmer temperatures, the southern part of the US should have a longer growing season, more winter pasture, and require less stored feed in the subtropical zone along the Gulf Coast, multiple frosts during the winter will freeze back bahiagrass, the staple forage grass. Quality is perceived to decline rapidly following a frost. The question is why cannot we use the residue from mature Bahiagrass as standing forage? One possibility is that the bahiagrass cells rupture, cell contents leak and sour so that cattle no longer would graze the residue. Pensacola, Argentine, and Tifton 9 varieties of Bahiagrass were evaluated for quality decline following a freeze and compared to the Midwestern native grasses switchgrass, big bluestem, and Indiangrass. Single plant yield and percent leaf were different among genotypes. Switchgrass had the highest yield and bahiagrass had the highest leaf percent. Leaf yield was more similar, but switchgrass produced more than twice as much leaf of any other cultivar. Crude protein content of the tall-grasses was marginal for supporting a beef cow whereas that for Bahiagrass approached levels that would support maintenance. This suggests that if Bahiagrass is not suitable for winter feed, then something other than chemical (CP) and nutritional (digestibility) composition is involved. It is possible that intake is not adequate, but we have no values for intake in this study. Tifton 9 showed the most resistance to freeze damage whereas the native grass cultivars and Argentine bahiagrass were completely damaged. Midwest native species can accumulate tremendous amounts of dry forage in the subtropical U.S.A. for stockpiling but are very low in CP and digestibility. Therefore, protein and possibly energy supplement would be required. While bahiagrass has the reputation of being very poor in quality after a freeze, this study suggests at least one variety (Tifton 9) maintains quality quite well following a freeze and may not require additional supplement for non-lactating cows.
Technical Abstract: The objective of this study was to investigate the processes that occur after a freeze in three ecotypes of Bahiagrass, along with the native species that are commonly grazed in the Midwest, namely big bluestem, Indiangrass and switchgrass.A randomized complete block design of 6 genotypes was established in north Florida in rows of eight single plants. Three bahiagrass cultivars (‘Argentine’, ‘Pensacola’ and ‘Tifton 9’), with Argentine being the commercial cold-sensitive cultivar, were compared to several native grasses. Plots were fertilized twice, staged on 1 July 2003 to 6.08 cm for bahiagrass and 15.24 cm for native grasses, and allowed to grow thereafter to stockpile dry matter until a killing frost would occur. Harvests included a pre-freeze event baseline (16 Nov 2003), freeze event -3.3C (30 Nov 2003) followed by harvest at 3, 7, 14, and 28 d post-freeze. Harvested material was dried at 80oC and separated into leaf and stem. Leaf tissue cold tolerance (LTCT) was rated after 28 d using the USDA G.R.I.N. scale (1= no damage or 100% green leaf, 9= total top growth damaged or 0% green leaf). Crude protein (CP) and neutral detergent fiber (NDF) were determined on all samples using NIRS calibrated with 20% of the samples. Single plant yield and percent leaf were different among genotypes. Switchgrass had the highest yield and bahiagrass had the highest leaf percent. Leaf yield was more similar, but switchgrass produced more than twice as much leaf of any other cultivar. Tifton 9 showed the most resistance to freeze damage whereas the native grass cultivars and Argentine bahiagrass were completely damaged. Crude protein of native grasses and Argentine declined dramatically following the freeze. Tifton 9 increased slightly in CP concentration and remained above 8%. At this level, Tifton 9 would provide maintenance protein for dry beef cows during the winter. Pensacola would be marginal. Neutral detergent fiber increased following the freeze for all grasses except Tifton 9, but more dramatically for switchgrass and Argentine.