Effects of calendar date and summer management on the in situ dry matter and fiber degradation of stockpiled forage from bermudagrass pastures

ABSTRACT Limited information is available that describes the disappearance kinetics of bermudagrass (Cynodon dactylon L. Pers.) during fall and early winter. Five ruminally cannulated, crossbred steers (387 ± 18.3 kg) were used to determine the effects of calendar date and previous summer management on the in situ degradation kinetics of DM and NDF for forage clipped from stockpiled `Greenfield' bermudagrass pastures. Forage was stockpiled at two sites following summer hay or pasture management, and samples were taken outside (GRAZED) and under caged exclosures (UNGRAZED) at 4-wk intervals beginning October 17, 1997, and ending January 9, 1998. No effort was made to remove or avoid contaminate species. Concentrations of NDF increased (P < 0.001) to a maximum for UNGRAZED forages at the hay site between October 17 and December 12, but sampling date had no effect (P = 0.627) on concentrations of NDF at the pasture site. Concentrations of ADF and lignin increased (P is less than or equal to 0.023) during at least one sampling interval in UNGRAZED forages at both sites. At the hay site, degradation rates of DM decreased (P < 0.001) by 0.013/h for UNGRAZED forage between October 17 and January 9, whereas the effective ruminal degradability of DM decreased (P < 0.001) by 33.5% during the same time period. Fractional degradation rates of NDF for UNGRAZED forages at the hay site decreased (P < 0.001) by 0.014/h between October 17 and November 14 but did not change (P is more than or equal to 0.077) throughout the remainder of the study. The effective ruminal degradability of NDF decreased (P < 0.001) by 33.8% between the first and last sampling date. At the pasture site, sampling date did not affect (P = 0.458) rates of DM degradation, but the effective degradability of DM for UNGRAZED forages decreased (P = 0.001) by 19.0% from October 17 to December 12. Rates of NDF degradation for UNGRAZED forages did not differ (P is more than or equal to 0.113) on the first three sampling dates, but the rate on January 9 was slower than that observed on October 17 (P = 0.025) and November 14 (P = 0.044). The effective degradability of NDF decreased (P < 0.001) by 19.2% between October 17 and December 12. These data indicate that stockpiled bermudagrass should be used during a limited window during the late fall; after this time, the nutritive value becomes very poor.

Implications

Degradation characteristics of DM and NDF indicate that significant losses in nutrient availability occurred as stockpiled bermudagrass aged or was grazed by cattle. Spring-calving beef cows grazing stockpiled bermudagrass may require supplementation with an energy source during the late fall or early winter to maintain BW and condition due to the poor DM and NDF degradation of this forage. Based on these data, stockpiled bermudagrass may be best used in northern Arkansas during a relatively short (60-d) window between mid-October and mid-December. After this time, the nutritive value of these forages seems to be very poor, especially if grazing pressure has been applied throughout the fall. Instead of attempting to use stockpiled bermudagrass beyond mid-December, producers should probably consider rotating cows to pastures of stockpiled, cool-season grasses, such as tall fescue, or maintaining these animals in drylot on stored forages.

Key Words: Degradation, Stockpiling

© 2001, by the American Society of Animal Science. All rights reserved.

J. Anim. Sci. 2001. 79:3158-3169