In vitrodigestibility and nutrient concentration of bermudagrass under rotational stocking, continuous stocking, and clipping

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Abstract
Grazing method effects on bermudagrass [Cynodon dactylon (L.) Pers.] nutritive value have received little attention. To examine the effects of three grazing methods and a hay system on herbage digestibility, nitrogen (N), and mineral concentration, a 2-yr study was conducted using '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 stocking with short grazing periods (1.5 to 2.5 d per paddock), ii) rotational stocking with long grazing periods (10 to 14 d per paddock), and iii) continuous stocking. Herbage samples (above a 15 cm height) were collected from all pastures and hay areas on four sampling dates per year (26 to 28 d of regrowth). Despite differences in leaf percentage as great as 18 units, in vitro digestible organic matter concentration averaged 565 g/kg OM and did not differ among managements by more than 32 g/kg OM in either year. Greater N, potassium (K), and sulfur (S) concentrations were observed in grazed than hay swards during the second year. For phosphorus (P), calcium (Ca), magnesium (Mg), and the micronutrients there generally was little effect of grazing method and when differences occurred they were small in magnitude. Mineral concentrations were or tended to be greater during the summer rainy season than in dry periods of late spring or early summer. Zinc (Zn) and copper (Cu) concentrations were lower than those required by growing cattle. We conclude that nutritive value varied relatively little among defoliation methods evaluated and that management variables other than defoliation method are likely to have greater impact on animal performance.

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