| Abstrakt: |
Intake, digestibility and mineral balance trails were conducted with two warm-season grasses, switchgrass and big bluestem, harvested at different cutting dates in 2 yr. Switchgrass was grown in Pennsylvania, New York, New Jersey, Kentucky and Iowa, and big bluestem in Pennsylvania. The hays were fed ad libitum to mature beef cows and mature wether sheep and intake and digestibilities of dry matter, neutral detergent fiber (NDF) and protein were determined. Composition of the hays was characterized by high levels of NDF (67.6 to 83.8%) and relatively low concentrations of crude protein (4.8 to 13.6%) and certain elements (P, S, Zn). Dry matter, NDF and protein digestibility by cattle and sheep declined (P<.05) with advancing maturity of the grasses. Mean dry matter digestibility (DMD) by beef cows decreased from 70.8 to 56.6% between the late vegetative and early heading harvest stages, and from 60.2 to 52.1% by sheep. For switchgrass, no consistent differences due to cultivar or location were noted. Dry matter and NDF digestibilities of the hays by beef cows (means of 60.2 and 63.9%) were higher (P<.05) than by sheep (means of 53.2 and 55.2%). Mean apparent protein digestibilities by cattle and sheep were not different (52.5 vs 52.4%). Ad libitum dry matter intake, in g/kg body weight (BW).75, was higher (P<.001) by cows than by sheep, with mean values of 92.3 vs 67.8 g, respectively; species differences were not significant at the BW.9power. Intake decreased with stage of maturity, with no effects (P>.05) of cultivar or location. Intake was associated with DMD percentage in a linear fashion for both cattle and sheep, with correlation coefficients of .80 and .62, respectively. Cattle showed significant positive retentions of Ca, P and Mg from hay at the late vegetative harvest stage, with slightly negative values for Ca and P at later stages. Sheep remained in positive balance of P and Mg at all harvest stages, with negative Ca retention at the earlier cutting dates. Cultivar effects were noted (P<.05) in the apparent retention of Mg and P by sheep. |
