Effects of Grazing System on Performance of Cow-Calf Pairs Grazing Bermudagrass Pastures Interseeded with Wheat and Legumes1

The Professional Animal Scientist 16:169–174 Rotational vs Continuous Grazing of Bermudagrass

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Effects of Grazing System on Performance of Cow-Calf Pairs Grazing Bermudagrass Pastures Interseeded with Wheat and Legumes1 L. W. LOMAS*,2, PAS, J. L. MOYER*, G. A. MILLIKEN†, and K. P. COFFEY3, PAS *Southeast Agricultural Research Center, Kansas State University, Parsons, KS 67357 and †Department of Statistics, Kansas State University, Manhattan, KS 66506

Abstract

cows and calves grazing wheat, and gains of cows grazing bermudagrass A total of 96 fall-calving cows and 64 interseeded with legumes were meacalves grazed Hardie bermudagrass sured. Grazing system had no effect [Cynodon dactylon (L.) Pers.] interseeded (P>0.05) on legume cover, available with wheat (Triticum aestivum L.), red forage DM, BW gains of cows and calves clover (Trifolium pratense L.), ladino grazing wheat, or BW gains of cows white clover (Trifolium repens L.), and grazing bermudagrass interseeded with lespedeza (Lespedeza stipulacea Maxim.) legumes. However, rotationally grazed during 1996, 1997, and 1998 in either a pastures produced more (P<0.05) residual continuous or a rotational system stocked hay than those grazed continuously. at equal rates. Grazing of wheat was initiated in early spring with cows and (Key Words: Rotational Grazing, calves and terminated in late summer Continuous Grazing, Bermudagrass, with cows grazing bermudagrass. Wheat.) Rotationally grazed units were subdivided into eight paddocks that were grazed for 3.5-d (1996 and 1997) or 2-d Grazing studies comparing intervals (1998). Residual forage was continuous systems with rotational removed as hay in late July each year and credited to the corresponding grazing systems have reported no difference in ADG for native range (8, 12, 16, system. Legume cover, available forage 19, 20); bermudagrass grazed with 3DM, residual hay production, gains of and 5-paddock systems (15); bermudagrass sod-seeded with wheat and ryegrass (Lolium multiflorum 1Contribution No. 00-310-J from the Kansas Lam.) grazed with 3- and 11-paddock Agricultural Experiment Station. systems (1); bermudagrass sod-seeded 2To whom correspondence should be adwith endophyte-free tall fescue dressed: [email protected] (Festuca arundinacea Schreb.) grazed 3Current address: Animal Science Departwith a 12-paddock system (9); endoment, University of Arkansas, Fayetteville, AR phyte-infected and endophyte-free

Introduction

72701.

tall fescue grazed with a 10-paddock system (18); endophyte-infected tall fescue-clover grazed with a 7-paddock system (6); or an alfalfa (Medicago sativa L.), tall fescue, and orchardgrass (Dactylis glomerata L.) mixture grazed with 6- and 11paddock systems (3). However, rotational grazing may increase BW gain per unit of land area for improved pastures by allowing higher stocking rates (3, 8, 18). Aiken (1) reported that rotational stocking increased steer BW gain per unit of land area because of an increased stocking rate on wheat-ryegrass, but not on bermudagrass. Rotational grazing may be beneficial for maintenance of certain plants in mixed-species pastures. Hoveland et al. (9) reported that rotational stocking appeared to be useful in maintaining stands of endophyte-free tall fescue sod-seeded in bermudagrass pastures. Brink and Pederson (5) indicated that stolon survival of white clover interseeded into existing tall fescue pastures was greater under rotational stocking than under continuous stocking. Barker et al. (2) indicated that cattle grazing legume-grass mixtures may

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have increased BW gains compared with those grazing grass pastures because of higher forage quality. Stocking rate has been reported to have a greater effect than grazing system on ADG of grazing livestock and total gain per unit of land area (7, 11, 12). Several studies that have evaluated grazing systems have used higher stocking rates for rotational than for continuous systems, which makes it difficult to determine the cause of differences in grazing performance (3, 8, 9, 12, 13). Therefore, a grazing study was conducted to compare continuous and rotational grazing, with the same number of cattle on equivalent areas of pasture, by measuring legume presence, available forage, and performance of fall-calving cows and calves grazing bermudagrass pasture interseeded with legumes.

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was estimated visually from the percentage of the disk circumference that was in contact with a portion of the canopy. Three readings were taken from each one-third of the pasture or paddock being sampled, and available forage DM was calculated using equations developed for wheat or bermudagrass during their respective grazing phases. Available forage of rotationally grazed pastures was the mean of that in the previous and next paddocks in the grazing cycle. Botanical composition of forage was estimated in pastures on July 11, 1996 and July 25, 1997. Three 0.1-m2 quadrats were clipped in each pasture or paddock from an exclosure that had been in place for about 4 wk, separated into legume, bermudagrass, and weedy components, dried, and weighed to express the percentage of each component on a DM basis. Eight fall-calving crossbred cows were allotted randomly to each Four 4.04-ha Hardie bermudagrass pasture on May 21, 1996, and eight pastures located at the Mound Valley fall-calving crossbred cow-calf pairs Unit of the Kansas State University were assigned randomly to each Southeast Agricultural Research pasture on March 21, 1997 and April Center on an Eram silty clay loam 7, 1998. Cattle were weighed on (fine, mixed, thermic, Aquic consecutive days, without prior Argiudoll) were used in a 3-yr experiremoval from pasture and water, and ment with a completely randomized stratified by weight and sex of calf. design containing two replications They were treated for internal and per grazing system. Jagger wheat was external parasites prior to being no-till-seeded into established turned out to pasture. Rotationally bermudagrass at the rate of 101 kg/ha grazed units were subdivided into on October 3, 1995; September 12, eight paddocks that were grazed for 1996; and September 18, 1997. 3.5-d (1996 and 1997) or 2-d intervals Pastures were interseeded on April 1, (1998). Continuous and rotational 1996 with 20 kg of Korean lespedeza, grazing were compared with the same 11 kg of Kenland red clover, and 3 kg number of cattle on an equivalent of Regal ladino clover per hectare and area of pasture. Rotationally stocked on March 10, 1997 with 19 kg of pastures were subdivided so that Korean lespedeza, 8 kg of Kenland cattle had access to only one-eighth red clover, and 2 kg of Regal ladino of the land area at any given time, clover per hectare. All pastures were whereas cattle grazing continuously fertilized with 56-45-45, 68-57-54, and stocked pastures had access to the 72-63-72 kg/ha of N-P2O5-K2O in mid- entire pasture area at all times. May of 1996, 1997, and 1998, respecStocking rates were based on the tively, and 56 kg/ha of N in late July previous grazing history of these of each year. pastures. Cows and calves in 1997 Available forage was determined at and 1998 initially grazed hard red the initiation of grazing and during winter wheat for 56 d. Calves were the season with a calibrated disk removed from the pastures on May meter (4). Legume canopy coverage 16, 1997 and June 2, 1998, and cows

Materials and Methods

grazed bermudagrass interseeded with legumes for the remainder of the summer. Wheat was not available for grazing in 1996, so grazing was initiated with cows at the beginning of the bermudagrass-legume phase. Cows grazed bermudagrass interseeded with legumes for 113, 88, and 91 d in 1996, 1997, and 1998, respectively. Grazing was terminated on September 11, 1996; August 12, 1997; and September 1, 1998. Cattle were weighed on consecutive days, without prior removal from pasture and water, at the beginning and end of the wheat and bermudagrass phases. During the wheat phase, access was provided ad libitum to a commercial loose mineral mix that contained 14.0% Ca, 6.0% P, 10.0% Mg, and 12% salt (guaranteed minimum of 0.007% I, 0.0022% Se, and 0.12% Cu), and during the bermudagrass phase, to commercial mineral blocks that contained 12% Ca, 12% P, and 12% salt (guaranteed minimums of 0.015% I, 0.001425% Se, 1.50% Mg, 1.10% S, 1.00% K, and 0.005% Cu). All pastures were mowed to a height of approximately 9 cm in late July of each year and harvested for hay in order to remove excess forage and maintain the bermudagrass in a vegetative state. Pasture means for available forage DM and canopy coverage were analyzed each year by SAS procedures for ANOVA (17) using a split plot in time with effects of Julian day, treatment, replicate, and their interaction in the model. Means were compared using Fisher’s protected LSD (17). Cattle performance data were analyzed using PROC MIXED (14). Pasture was used as the experimental unit. Mean comparisons were made using t-tests, with the correct degrees of freedom determined by the Satterthwaite option (17).

Results and Discussion Below-normal precipitation from September, 1995 through March, 1996 resulted in unavailability of wheat for grazing in the spring of

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nificant amounts by the end of the season. Legumes constituted a similar amount (P>0.10) of DM in pastures of the two systems, averaging 11% Year (data not shown). Red clover accounted for an average of about 42% 30-yr of legume DM, and lespedeza ac1997 1998 mean counted for most of the balance. In 1997, available forage DM in (cm) the wheat-grazing phase was similarly 1.88 7.52 3.96 low in both treatments (Fig. 2). 11.23 0.69 3.94 During the bermudagrass-grazing 5.08 15.16 9.14 phase, available forage DM increased 7.06 12.55 9.37 until d 195, when it was higher 16.31 7.06 14.25 (P<0.05) in the continuous grazing treatment than in the rotational 17.55 8.48 13.56 6.60 10.74 8.79 treatment. After haying, available 12.12 3.71 10.69 forage DM was reduced to similar 11.43 21.34 12.62 (P>0.05) amounts in the two treat9.96 32.66 9.73 ments, though DM increased in both 3.61 9.80 8.05 by the end of grazing. 10.29 4.55 4.70 Legume canopy coverage was 113.11 134.26 108.76 estimated in late winter of 1997 and averaged 16% with no difference in the rotational treatment than for (P>0.10) between treatments (data those in the continuous treatment. not shown). During the 1997 grazing After haying, available forage DM season, day-by-treatment interaction was reduced, especially in the rotawas again nonsignificant (P>0.10), so tional treatment, and similar legume coverage means during the amounts of DM were available for season are shown (Fig. 2). Legume the rest of the season. Season-long coverage, again, declined during the available DM was similar for grazing season, though not as quickly as in treatments. Overall means for 1996. Legumes constituted a similar legume canopy coverage during the amount (P>0.10) of DM in pastures season are shown, because no signifi- of the two systems, averaging about cant (P>0.10) day-by-treatment 17% (data not shown). Red clover interaction occurred in 1996. Legume accounted for an average of about coverage declined throughout the 79% of legume DM, with the balance season, particularly after pastures being mostly ladino clover. were cut for hay, and reached insigIn 1998, there was a nonsignificant day-by-treatment interaction

TABLE 1. Annual and long-term monthly rainfall at Southeast Agricultural Research Center (Mound Valley, KS).

Month

January February March April May June July August September October November December Total

1995

1996

2.74 0.86 1.68 14.27 25.02

1.88 0.56 2.84 12.57 8.43

25.65 9.58 17.40 3.51 1.07 0.36 5.79 107.92

8.48 8.56 7.80 15.80 8.36 12.47 0.89 88.65

1996 (Table 1). Monthly rainfall distribution within years and between years was generally more variable than annual rainfall. However, rainfall in 1996 was 20.11 cm below the long-term average. Available forage DM and legume canopy coverage in pastures are shown by year in Fig. 1 through 3. In 1996, available DM in the bermudagrass phase increased until d 197, the last day of measurement before pastures were cut for hay (Fig. 1). Available forage DM was similar (P>0.05) between treatments until d 197, when it was higher for pastures

Figure 1. Available forage DM in the rotational (Rot.) or the continuous (Cont.) system and mean legume canopy cover (Leg) in bermudagrass phase, 1996. LSD(0.05) for DM comparisons both within and between treatments = 600 kg/ha-1. LSD(0.05) for Leg comparisons = 3%.

Figure 2. Available forage DM in the rotational (Rot.) or the continuous (Cont.) system and mean legume canopy cover (Leg) in wheat and bermudagrass phases, 1997. LSD(0.05) for DM comparisons both within and between treatments = 810 kg/ha-1. LSD(0.05) for Leg comparisons = 3%.

Figure 3. Mean available forage DM and mean legume canopy cover (Leg) in wheat and bermudagrass phases, 1998. LSD(0.05) for DM comparisons = 930 kg/ha-1. LSD(0.05) for Leg comparisons = 13%.

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(P>0.10), and grazing system had no effect (P>0.10) on available forage DM, so the overall means during the season are shown (Fig. 3). Available forage DM was relatively low but uniform (P>0.05) during the wheatgrazing phase. During the bermudagrass-grazing phase, available forage DM increased until d 176 and remained at that level until haying, when it declined to intermediate levels that lasted for the remainder of the season. Legume canopy coverage declined less dramatically during the wheat-grazing phase in 1998 than in 1997. However, during the bermudagrass phase the decline was more rapid, until practically no coverage remained by the end of the grazing season. Average legume cover and available forage DM did not differ (P>0.05) between grazing systems during either the wheat or the bermudagrass phase (Table 2). However, residual hay production was higher (P<0.05) from rotationally grazed pastures than from pastures grazed continuously. Brink and Pederson (5) indicated that stolon survival of white clover interseeded into existing tall fescue pastures was greater under rotational than under continuous stocking. Hull et al. (10) reported that a higher proportion of legumes was maintained in continuously grazed pastures with a mixture of orchardgrass, ryegrass, fescue, ladino clover, and strawberry clover (Trifolium fragiferum) than in those grazed rotationally. Available forage was utilized more uniformly throughout the grazing season, and the swards were maintained in a more vegetative condition, with continuous than with rotational grazing. A summary of grazing performance as influenced by grazing system is presented in Table 2. No significant (P>0.05) year-by-treatment interactions were observed. Grazing system had no effect (P>0.05) on BW gains of cows and calves grazing wheat or gains of cows grazing bermudagrass interseeded with legumes. Grazing cattle performance, BW gain per hectare, legume cover,

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TABLE 2. Effect of grazing system on performance of cow-calf pairs grazing bermudagrass pastures interseeded with wheat and legumes. Grazing System Item Wheat phase No. of cow-calf pairs No. of days Stocking rate, cow-calf pairs/ha Calf initial wt., kg Calf final wt., kg Calf gain, kg Calf ADG, kg Cow initial wt., kg Cow final wt., kg Cow gain, kg Cow ADG, kg Cow + calf gain, kg/ha Legume cover, % Average available DM, kg/ha Bermudagrass phase No. of cows No. of days Stocking rate, cows/ha Cow initial wt., kg Cow final wt., kg Cow gain, kg Cow ADG, kg Cow gain, kg/ha Legume cover, % Average available DM, kg/ha Hay DM production, kg/ha Total cow + calf gain, kg/hac

Continuous

Rotation

SEM

32 56 1.98 231.1 302.9 71.8 1.28 609.7 643.0 33.3 0.60 208.2 19.9 1825.6

32 56 1.98 231.4 301.1 69.6 1.24 610.6 642.8 32.2 0.58 201.6 18.8 1741.6

– – – 1.24 3.76 2.99 0.05 0.75 4.01 3.71 0.07 12.81 4.31 25.81

48 97 1.98 593.9 663.3 69.4 0.71 137.4 7.0 4106.7 1934.8a 276.2

48 97 1.98 590.9 667.2 76.2 0.77 151.0 10.0 4332.5 3443.9b 285.4

– – – 3.13 3.79 4.99 0.06 9.89 1.71 276.15 297.99 10.82

a,bMeans within a row followed by the same letter are not significantly different at P<0.05. cSum of BW gain per hectare during wheat and bermudagrass phases does not equal total BW gain per hectare because wheat was not grazed in 1996.

and available forage DM were similar between grazing systems during both the wheat and bermudagrass phases, and total cow + calf BW gains were similar. Similar gains between rotationally and continuously stocked pastures also have been reported by others (1, 3, 6, 8, 9, 12, 15, 16, 18, 19, 20). Aiken (1) reported similar grazing steer performances on rotationally and continuously stocked bermudagrass pastures sodseeded with wheat and ryegrass. However, rotational stocking increased steer BW gain per unit of land area because of an increased stocking rate on wheat-ryegrass, but

not on bermudagrass. Chestnut et al. (6) observed no differences in animal performance or quantity of forage available in a study comparing continuous and rotational stocking of endophyte-infected [Neotyphodium coenophialum Glen, Bacon, Price, and Hanlin (formerly Acremonium coenophialum Morgan-Jones and Gams)] tall fescue-clover pastures with cow-calf pairs stocked at equal rates. Although stocking rates and gain per hectare were similar for continuously and rotationally stocked pastures in this study, several researchers have reported increased gain per unit of land area using

Rotational vs Continuous Grazing of Bermudagrass

TABLE 3. Effect of year on performance of cow-calf pairs grazing bermudagrass pastures interseeded with wheat and legumes. Year

Item

1996

Wheat phase No. of cow-calf pairs – No. of days – Stocking rate, cow-calf pairs per ha – Calf initial wt, kg – Calf final wt, kg – Calf gain, kg – Calf ADG, kg – Cow initial wt, kg – Cow final wt, kg – Cow gain, kg – Cow ADG, kg – Cow + calf gain, kg/ha – Legume cover, % – Average available DM, kg per ha – Bermudagrass phase No. of cows 32 No. of days 113 Stocking rate, cows/ha 1.98 Cow initial wt, kg 491.2a Cow final wt, kg 585.9a Cow gain, kg 94.7a Cow ADG, kg 0.84 Cow gain, kg/ha 187.5a Legume cover, % 6.5a,b Average available DM, kg/ha 4312.0 Hay DM production, kg/ha 2464.3a,b Total cow + calf gain, kg/ha 187.5a

1997

1998

SEM

32 56 1.98 212.8a 285.4a 72.5 1.30 578.3a 610.8a 32.5 0.58 208.0 23.2 1559.6a

32 56 1.98 249.7b 318.6b 68.9 1.23 642.0b 675.0b 33.0 0.59 201.8 15.5 2007.6b

– – – 1.24 4.35 3.94 0.07 0.94 4.01 3.71 0.07 14.34 4.31 25.81

32 88 1.98 611.1b 689.2b 78.1a,b 0.89 154.7a,b 16.2a 4289.6 3456.8a 362.7b

32 91 1.98 675.0c 720.7c 45.6b 0.50 90.4b 2.9b 4057.2 2146.8b 292.2b

– – – 3.59 5.99 6.94 0.08 13.74 2.11 338.21 364.96 17.01

a-cMeans within the same row followed by the same letter are not significantly different at P<0.05.

higher stocking rates with rotational compared with continuous grazing (3, 8, 18). Bertelsen et al. (3) observed similar gains by heifers grazing pastures containing a mixture of alfalfa, tall fescue, and orchardgrass that were rotationally or continuously stocked; however, rotationally stocked pastures produced more kilograms of gain per hectare, because they were stocked at a higher rate. Significantly more residual forage remained at the end of the grazing season on the continuously stocked pastures than on the rotationally stocked pastures in that study, which suggests that the former were understocked. Stocking rate has been

reported to have a greater effect on ADG of grazing livestock and total BW gain per unit of land area than grazing system (7, 11, 12). In the current study, when continuous and rotational grazing systems were compared, with the same number of cattle on equivalent areas of pasture, cattle BW gains and gain per hectare were similar between systems. Hull et al. (10) reported higher steer gains with continuously stocked than with rotationally stocked improved pastures at equal stocking rates. However, gain per hectare was similar between grazing systems, because rotationally stocked pastures provided more days of grazing.

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A summary of grazing performance as influenced by year is presented in Table 3. Gains during the wheat-grazing phases were similar in 1997 and 1998. Available forage DM during the wheat phase was lower (P<0.05) in 1997 than in 1998, likely because of the below-normal precipitation that occurred from October, 1996 through May, 1997. Legume cover did not differ (P>0.05) during the wheat phases in 1997 and 1998. Although there were differences (P<0.05) in cattle BW gain between years, cow ADG was not significantly different (P>0.05) between years in the bermudagrass phase because of differing length of grazing season between years. However, the ADG of cows grazing bermudagrass in 1998 tended to be lower (P=0.08) than the ADG of those that grazed in 1996, and lower (P=0.06) than the ADG of those that grazed in 1997. Gain per hectare was higher (P<0.05) in 1996 than in 1998, which may be attributed to higher available forage DM at the beginning of the bermudagrass phase as a result of the unavailability of wheat for grazing in 1996, and the low rainfall (69.4% of normal) during June, July, and August of 1998. Legume cover, hay production, and gain per hectare were higher (P<0.05) during the bermudagrass phase in 1997 than in 1998, which likely was due to total precipitation during June, July, and August being higher in 1997 (109.8% of the longterm average).

Implications The results of this study indicate that with equal stocking at the optimum rate, gain per hectare and weight gains by cow-calf pairs grazing bermudagrass pastures sod-seeded with wheat and legumes were similar for continuous and rotational stocking systems. Legume cover was not affected by grazing system. Continuous stocking at the optimum rate would be more resource-efficient than rotational stocking, because additional fencing and water systems

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for pasture subdivision and labor to move cattle from one pasture to the next would not be required. The results of this research, coupled with those of previous studies, imply that stocking rate has a greater effect on animal performance and weight gain per hectare than grazing system. Additional research is needed to compare continuous and rotational grazing systems for other forages stocked with the same number of cattle on equivalent areas of pasture.

Literature Cited 1. Aiken, G. E. 1998. Steer performance and nutritive values for continuously and rotationally stocked bermudagrass sod-seeded with wheat and ryegrass. J. Prod. Agric. 11:185. 2. Barker, J. M., D. D. Buskirk, H. D. Ritchie, S. R. Rust, R. H. Leep, and D. J. Barclay. 1999. Intensive grazing management of smooth bromegrass with or without alfalfa or birdsfoot trefoil: Heifer performance and sward characteristics. Prof. Anim. Sci. 15:130. 3. Bertelsen, B. S., D. B. Faulkner, D. D. Buskirk, and J. W. Castree. 1993. Beef cattle performance and forage characteristics of continuous, 6-paddock, and 11-paddock grazing systems. J. Anim. Sci. 71:1381.

4. Bransby, D. I., A. G. Matches, and G. F. Krause. 1977. Disk meter for rapid estimation of herbage yield in grazing trials. Agron. J. 69:393.

12. Knight, J. C., M. M. Kothmann, G. W. Mathis, and R. T. Hinnant. 1990. Cow-calf production with alternative grazing systems. J. Prod. Agric. 3:407.

5. Brink, G. E., and G. A. Pederson. 1993. White clover response to grazing method. Agron. J. 85:791.

13. Kuykendall, H. A., C. S. Hoveland, M. A. McCann, and M. L. Cabrera. 1999. Continuous vs. rotational stocking of steers on mixed endophyte-infected tall fescue-bermudagrass pastures fertilized with broiler litter. J. Prod. Agric. 12:472.

6. Chestnut, A. B., H. A. Fribourg, D. O. Onks, J. B. McLaren, K. W. Gwinn, and M. A. Mueller. 1992. Performance of cows and calves with continuous or rotational stocking of endophyte-infested tall fescue-clover pastures. J. Prod. Agric. 5:405. 7. Heitschmidt, R. K., J. R. Conner, S. K. Canon, W. E. Pinchak, J. W. Walker, and S. L. Dowhower. 1990. Cow/calf production and economic returns from yearlong continuous, deferred rotation and rotational grazing treatments. J. Prod. Agric. 3:92. 8. Heitschmidt, R. K., J. R. Frasure, D. L. Price, and L. R. Rittenhouse. 1982. Short duration grazing at the Texas Experimental Ranch: Weight gains of growing heifers. J. Range Manage. 35:375. 9. Hoveland, C. S., M. A. McCann, and N. S. Hill. 1997. Rotational vs. continuous stocking of beef cows and calves on mixed endophyte-free tall fescue-bermudagrass pasture. J. Prod. Agric. 10:245. 10. Hull, J. L., J. H. Meyer, and C. A. Raguse. 1967. Rotation and continuous grazing on irrigated pasture using beef steers. J. Anim. Sci. 26:1160. 11. Kee, D. D., D. I. Bransby, B. E. Gamble, and W. E. Ivey. 1991. Continuous versus rapid rotational grazing of ‘Tifton-44’ bermudagrass steers at varying stocking rates. In Proceedings of the Forage and Grassland Conference. p 198. American Forage and Grassland Council, Georgetown, TX.

14. Littell, R. C., G. A. Milliken, W. W. Stroup, and R. D. Wolfinger. 1996. SAS System for Mixed Models. SAS Institute Inc., Cary, NC. 15. Matthews, B. W., L. E. Sollenberger, and C. R. Staples. 1994. Dairy heifer and bermudagrass pasture responses to rotational and continuous stocking. J. Dairy Sci. 77:244. 16. Nelson, M. L., J. W. Finley, D. L. Scarnecchia, and S. M. Parish. 1989. Diet and forage quality of intermediate wheatgrass managed under continuous and shortduration grazing. J. Range Manage. 42:474. 17. SAS Institute Inc. 1989. SAS/STAT User’s Guide: Statistics. (Version 6, 4th Ed.). SAS Institute Inc., Cary, NC. 18. Tharel, L. M., and M. A. Brown. 1989. Rotational grazing of three tall fescue varieties. p 43. Arkansas Exp. Stn. Spec. Rep. 140, Fayetteville, AR. 19. Volesky, J. D., J. K. Lewis, and C. H. Butterfield. 1990. High-performance shortduration and repeated-seasonal grazing systems: Effect on diets and performance of calves and lambs. J. Range Manage. 43:310. 20. Walker, J. W., R. K. Heitschmidt, E. A. De Moraes, M. M. Kothmann, and S. L. Dowhower. 1989. Quality and botanical composition of cattle diets under rotational and continuous grazing treatments. J. Range Manage. 42:239.