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Superintendent
David Davis
21262 Genoa Road
Linneus, MO 64653
Phone: 660 895-5121
FAX: 660 895=5122
Email: DavisDK@missouri.edu

Results and Discussion

Steer performance: As in the first four years of the study, steer ADG in 2000 declined linearly with increasing stocking rate but was largely unaffected by grazing method (Figure 2). There has been no statistically significant difference in season ADG due to grazing method in any year, although differences have been noted in individual weigh periods. Five-year mean ADG is shown in Figure 3 and shows the consistency of the performance trend across all years. In each year, there has been about a one tenth pound/day numeric advantage to rotational grazing at the 900 and 1200 pound/acre stocking rates. In four out of five years, the same numeric advantage has been present at the 300 pound/acre stocking rate. The consistently superior performance of steers continuously grazing at 600 pound stocking rate is not consistent with the usual theoretical linear model of declining animal performance with increasing stocking rate. The response at this stocking rate may be an effect of the characteristics of the two specific pastures where the 600 pound stocking rate was located rather than a true effect of the treatment. By random assignment, that particular treatment fell on two superior sites based on soil type and past performance.

The similar ADG across grazing method may reflect the high condition of the continuously grazed pastures at the outset of this study. Pastures were well established and had been under rotational management for six years prior to this study. Legume component in these pastures was well above what is typically seen in pastures in this region that have been under long term continuous grazing. However, legume composition of continuously grazed pastures declined during the 1998 season and were quite low through 1999 but rebounded somewhat in 2000. Another factor to consider in assessing animal performance in a study of this nature is that the steers were weighed every 21 days creating a stress on the animals that is typically not present in a commercial production system. While every attempt was made to handle the cattle in a relatively gentle manner, research at University of Hawaii has shown depressed performance by cattle put through a handling chute to last in excess of six weeks (Smith, B. 1998. A guide to low stress animal handling. The Graziers Hui, Kamuela, HI, p5). Handling stress may be an overriding factor in determining steer performance.

Figure 2. Steer average daily gain on continuously and rotationally grazed pastures at four stocking rates in 2000.

Figure 3. Four year mean steer average daily gain for continuously and rotationally grazed pastures at four stocking rates.

The shade issue must also be considered in light of the treatments and the possible confounding effect noted in the weather discussion. Recent research at University of Kentucky has shown a benefit to yearling cattle allowed access to shade on high-endophyte pastures. Pastures used in this study were mixed grass-legume pastures with low endophyte fescue. At the beginning of this study we did not consider shade to be an issue and no provision was made to provide equal shade opportunity for the different grazing treatments. There is no way of knowing whether or not the lack of shade played a role in this study but it is a possible confounding factor that we should be aware of. Steers in all of the continuously grazed pasture had access to shade every day of the grazing season, while cattle in five of eight of the rotationally grazed pastures had shade access only on two days out of each 24 day grazing cycle. In two of the remaining rotationally grazed pastures, shade was available perhaps 50% of the time while the final pasture had shade available until solar noon on almost all days.

Figure 4. Change in steer liveweight through the 2000 grazing season for steers grazing at four stocking rates on continuously grazed pastures.

For most of the 2000 season, little difference existed in rate of gain due to grazing management (Figures 4 & 5). Steers in all treatments gained steadily for the first 100 days of the season and then rate of gain in all treatments slowed significantly during the hot period in July-August. Continuously grazed steers at 1200 lb/acre stocking rate in one block lost weight from June 31 until August 3, resulting in their removal from the study. During most of the month of July, we experienced difficulties with the pump and water distribution system and cattle were frequently without water for periods from 4 to 24 hours. Weights for eleven out of the sixteen treatment groups on July 12 indicated weight loss. During the next 21-day period all herds except the one continuously grazed 1200 lb/acre had positive weight change.

In 1996, 1998, 1999, and 2000, rotationally grazed steers gained more than continuously grazed steers in the last 6 weeks of the grazing season, but not in 1997. One of the claims that has been made for rotational grazing is that it will maintain ADG later in the summer than continuous grazing. While that trend was apparent in this study, the measured increased rate of gain by itself would not be adequate justification for implementing a rotational grazing system. Rate of gain declined much more rapidly at higher stocking rates earlier in the grazing season (Figures 6 and 7).

There are several negative effects associated with maintaining cattle on pasture after cattle growth rate significantly slows. Two major factors affecting profitability of the grazing enterprise are very little additional salable gain being produced from the forage resource and delayed marketing in late summer or early fall usually results in lower prices received. The land and pasture cost for the steer gaining 2.5 lb/hd/day in May and June is essentially the same for a steer gaining only 1 lb/hd/day in August. Obviously, the pound produced in June is much more profitable than the pound produced in August. The seasonal price for cattle typically steadily declines from mid-July through early winter. Maintaining cattle on pasture past midsummer usually results in lower price per pound. Combined with higher cost of production for late summer gains, the producer gains very little from late summer grazing of stockers.

Figure 5. Change in steer liveweight through the 2000 grazing season for steers grazing at four stocking rates on rotationally grazed pastures.

Figure 6. Five-year pattern of net liveweight accumulation for continuously grazed steers at four stocking rates.

From an environmental perspective, late summer grazing often results in very low forage residuals remaining after grazing resulting in loss of plant species diversity, vegetative ground cover, and potential increase in water runoff and soil erosion. These factors will be discussed later in this report.

Figure 7. Five-year pattern of net liveweight accumulation for rotationally grazed steers at four stocking rates.

We have identified dates by which 85% of the seasonal gain was achieved for the different treatments in this study (Table 3). Most of the profit in a stocker operation will be made on the early season gain. Heavier stocking rates require earlier removal of cattle from the system, but this strategy would allow a longer recovery period for the pasture. This approach is termed early-intensive double stocking and is used widely in the Kansas Flint Hills as a management practice to maintain health and vigor of native tallgrass range in that environment. This may be a useful management tool to maintain pasture ground cover, particularly in more fragile south Missouri environments.