IN-VITRO DIGESTIBILITY AND NUTRIENT CONCENTRATION OF BERMUDAGRASS UNDER ROTATIONAL STOCKING, CONTINUOUS STOCKING, AND CLIPPING

Grazing method effects on bermudagrass [Cynodon dactylon (L.) Pers.] n utritive value have received little attention. To examine the effects of three grazing methods and a hay system on herbage digestibility, ni trogen (N), and mineral concentration, a 2-yr study was conducted usin g 'Callie' bermuda-grass pastures growing on a Florida flatwoods soil with a seasonally high water table. Grazed pastures were stocked with Holstein heifers (Bos taurus) and grazing methods were i) rotational s tocking with short grazing periods (1.5 to 2.5 d per paddock), ii) rot ational stocking with long grazing periods (10 to 14 d per paddock), a nd iii) continuous stocking. Herbage samples (above a 15 cm height) we re collected from all pastures and hay areas on four sampling dates pe r year (26 to 28 d of regrowth). Despite differences in leaf percentag e as great as 18 units, in vitro digestible organic matter concentrati on averaged 565 g/kg OM and did not differ among managements by more t han 32 g/kg OM in either year. Greater N, potassium (K), and sulfur (S ) concentrations were observed in grazed than hay swards during the se cond year. For phosphorus (P), calcium (Ca), magnesium (Mg), and the m icronutrients there generally was little effect of grazing method and when differences occurred they were small in magnitude. Mineral concen trations were or tended to be greater during the summer rainy season t han in dry periods of late spring or early summer. Zinc (Zn) and coppe r (Cu) concentrations were lower than those required by growing cattle . We conclude that nutritive value varied relatively little among defo liation methods evaluated and that management variables other than def oliation method are likely to have greater impact on animal performanc e.