Yield and Quality Trends of Tall Fescue Grazed with Different Subdivisions of Pasture1
- E. W. Vartha,
- A. G. Matches and
- G. B. Thompson2
Subsequent to a grazing experiment which showed average daily gains of growing cattle on N-fertilized tall rescue (Festura arundinaceas, Schreb.) to be similar whether grazed continuously or in a two-paddock grazing round baled hay aftermath system, a study was done to determine short-term changes in the quantity and quality of herbage-on-offer for pastures with 0, 2, or 4 subdivisions of grazing. The objective of this experiment was to provide possible explanations for the lack of differences in rate of gain in the on-going grazing trial. Six groups of three weaner calves grazed replicated pastures of N-fertilized tall rescue (0.256 ha/group) for 80 days in spring-summer and 40 days in fall. Cattle were used as defoliators, and animal performance data are not presented. During each grazing cycle, cattle were continuously grazed on pastures with no subdivisions, rotated every 20 days with 2 subdivisions and every 10 days on pastures with 4-subdivisions. At 5-day intervals, herbage samples (10 × 0.26 m2) were cut to ground level from each subdivision under grazing. These samples were later analyzed for in vitro dry matter disappearance (IVDMD), N, and mineral composition. Residual herbage samples were also obtained following the completion of the second and third grazing cycles.
In the spring and summer (20 May to 7 August), subdivision treatments did not differ in average amount of herbage-on-offer/ha. On removal of cattle on 7 August when the no-subdivision treatment was fully grazed, amount of residual herbage among treatments was nearly the same. Percent IVDMD declined curvilinearly in all treatments from an average of 64% in May to 49% in mid-July, followed by a 2.5 percentage unit increase in August.
In the fall (17 September to 27 October), average amount of herbage-on-offer/ha ranged from 800 to 1,000 kg/ha higher with 4 subdivisions than with the other treatments. Fall digestibilities ranged from 62 to 43% IVDMD. Low values occurred at the end of the grazing cycle, especially in the 4 subdivision treatment where the most residue (trampled herbage) was observed.
Composited herbage samples from the no- and 4-subdivision treatments showed little difference between the spring-summer and fall grazing cycles in range of concentrations for N and eight minerals.
The results indicate that subdividing pastures for rotational grazing did not have a marked effect on average quantity and quality of tall rescue during the spring and summer. However, pastures with 4 subdivisions did provide more herbage growth in the fall. These findings may partially explain why cattle daily gains in another on-going grazing trial have not been different.Please view the pdf by using the Full Text (PDF) link under 'View' to the left.
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