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J. Anim. Sci. 2005. 83:2684-2695
© 2005 American Society of Animal Science

ANIMAL PRODUCTION

Effect of rotation frequency and weaning date on forage measurements and growth performance by cows and calves grazing endophyte-infected tall fescue pastures overseeded with crabgrass and legumes1

K. P. Coffey*,2, W. K. Coblentz*, D. A. Scarbrough3, J. B. Humphry4, B. C. McGinley5, J. E. Turner6, T. F. Smith{dagger}, D. S. Hubbell, III{dagger}, Z. B. Johnson*, D. H. Hellwig7, M. P. Popp{ddagger} and C. F. Rosenkrans, Jr.*

* Departments of Animal Science and and {ddagger} Agricultural Economics and Agri Business, University of Arkansas, Fayetteville 72701, and and {dagger} Livestock and Forestry Branch Experiment Station, Batesville, AR 72501


   Abstract
Top
 Abstract
Introduction
 Materials and Methods
 Results and Discussion
 Implications
 Literature Cited
 
A grazing study was initiated in April 2000 and continued through three calving and weaning cycles (ending July 2003) to investigate the effects of rotational grazing management (twice monthly [2M] vs. twice weekly [2W]) and weaning date (mid-April [EARLY] vs. early June [LATE]) on production of fall-calving cow-calf pairs (495 ± 9.6 kg initial BW) grazing Neotyphodium coenophialum-infected tall fescue (Festuca arundinacea Schreb.) overseeded with legumes and crabgrass. Secondary objectives of the experiment were to monitor differences in quantity and quality of available forage and to evaluate changes in forage species composition. Pastures were dominated by tall fescue throughout the study, and the proportion of basal cover was greater (P < 0.05) in 2M than in 2W pastures. The percentage of legumes was very low across all treatment combinations, but the percentage of crabgrass continued to increase (P < 0.05) linearly and quadratically across years for both summer and fall sampling periods, regardless of rotation or weaning program. In vitro DM disappearance and mineral concentrations varied minimally because of rotation frequency or weaning date. Rotation frequency did not substantially affect (P = 0.11 to 0.97) cow BW, hay offered, milk production, calving interval, calf birth weight, or actual or adjusted weaning weights; however, 2M cows had 0.3 units higher (P < 0.05) BCS at the time of breeding than 2W cows. Calves weaned late had greater (P < 0.05) actual weaning weight and weighed more (P < 0.05) on the LATE weaning date than on the EARLY weaning date, but 205-d adjusted weaning weights did not differ (P = 0.74) across weaning dates. Therefore, rotation frequency and/or weaning date had little effect on forage species composition or forage quality. In addition, the rapid rotation program offered little advantage with respect to animal performance, and weaning fall-born calves grazing endophyte-infected tall fescue pastures at approximately 189 d of age seemed to be detrimental to calf performance compared with delaying weaning until 243 d of age.

Key Words: Beef Cows • Fescue arundinacea • Forage • Legumes • Neotyphodium coenophialum • Tall Fescue


   Introduction
Top
 Abstract
 Introduction
Materials and Methods
 Results and Discussion
 Implications
 Literature Cited
 
Cattle consuming Neotyphodium coenophialum-infected tall fescue (Festuca arundinacea Schreb.; E+) have exhibited decreased DMI (Goetsch et al., 1987Go; Forcherio et al., 1995Go; Humphry et al., 2002Go) and fiber digestion (Hannah et al., 1990Go; Humphry et al., 2002Go), lower cow and calf BW gains (Gay et al., 1988Go; Peters et al., 1992Go), and lower milk production (Ashley et al., 1987Go; Peters et al., 1992Go) compared with those consuming noninfected fescue. Weight differential between steers grazing E+ (288 µg/kg of ergovaline) and those grazing fescue with a low infection (no detectable ergovaline) of N. coenophialum increased more during the period between mid-May and mid-June than the period between mid-April and mid-May (Coffey et al., 2001Go), likely because of increasing ergovaline concentrations during late spring (Rottinghaus et al., 1991Go). Therefore, weaning fall-born calves earlier in the spring should decrease their exposure to tall fescue toxins. Both cow (Holloway and Butts, 1984Go) and stocker cattle performances (Coffey et al., 1990Go; McMurphy et al., 1990Go) were improved by diluting fescue pastures with legumes. Rotational grazing systems have resulted in greater persistence of forages known to persist poorly under grazing conditions, such as endophyte-free tall fescue (Hoveland et al., 1997Go). These systems also have resulted in greater animal production per unit of land area (Walton et al., 1981Go), increased forage digestibility (Walton et al., 1981Go; Heitschmidt et al., 1987Go), and increased legume composition (Walton et al., 1981Go) in some studies, but not in others (Barker et al., 1999Go). Our objective was to investigate the effects of rotational management and weaning date on forage quantity and quality, species composition, and production of fall-calving cow-calf pairs grazing E+ over-seeded with legumes and crabgrass.


   Materials and Methods
Top
 Abstract
 Introduction
 Materials and Methods
Results and Discussion
 Implications
 Literature Cited
 
Pastures and Treatments
All animal procedures were approved by the University of Arkansas Institutional Animal Care and Use Committee Project No. 98010 and 01016. Sixty pregnant fall-calving cows and heifers (initial BW = 495 ± 9.6 kg; mean calving date = October 1) primarily of Angus breeding were stratified by age and BW and allocated randomly in early April 2000 to one of 11 pastures ranging in area between 4.0 and 6.5 ha that had been seeded previously with E+ in fall of 1997. The number of cows per group was determined to set an initial stocking rate of 1.0 cow/ha. Additional adjacent pasture area was established to E+ in fall of 2000 and was added to the existing grazing area in April 2002 to produce a total of 12 pastures of 6.5 ha each. Additional cows and heifers of comparable age and BW to those already grazing in the study were added in April 2002 to maintain a stocking rate of 1.0 cow/ha. Calves from these cows were weaned before adding them to the experimental pastures.

The pasture area was located at the University of Arkansas Livestock and Forestry Branch Experiment Station near Batesville. The pasture site was situated on Clarksville and Gepp very cherty silt loams characterized as being deep, somewhat excessively drained, and having 8 to 40% slopes. These are predominant soil types in the Ozark Highlands, and they are not adapted to tillage (Ferguson et al., 1982Go).

Broadcasting techniques (power take-off-driven broadcast seeder) were used to overseed all experimental pastures with a mixture/ha of 2.2 kg of ‘Advantage’ ladino clover (Trifolium repens L.), 6.7 kg of ‘Redland Graze’ red clover (Trifolium pretense L.), and 13.4 kg of ‘Marion’ lespedeza (Lespedeza stipulacea Maxim.) in late February and early March 2000. The pastures were grazed closely before initial legume seeding. Common crabgrass (Digitaria sanguinalis [L.] Scop.) seed was broadcast at a rate of 4.5 kg/ha in May. Legumes and crabgrass were overseeded again in March and May 2002, respectively, at the same seeding rates because of poor establishment and persistence.

The forage fertility program consisted of annual applications of 45 kg of N/ha in early June and late August. Phosphorus and potassium were applied annually as per soil test recommendations by the Arkansas Cooperative Extension Service in late August, and 2.2 kg of boron/ha were applied annually in the spring to enhance legume growth (Spooner and Huneycutt, 1978Go). Lime was applied as needed based on soil test recommendations for fescue-legume mixed pastures.

Pastures were allocated randomly to one of four pasture or calf weaning date treatments in a 2 x 2 factorial arrangement (Table 1Go). Pasture treatments were applied by dividing each experimental pasture into either two or eight paddocks and rotating cows to a new paddock either twice weekly (2W) or twice monthly (2M). This procedure was used in an attempt to evaluate whether increased rotational frequency would increase persistence of overseeded forages. Within each of the rotation schedules, calves were weaned either in mid-April (EARLY; average of 189 ± 14.9 [SD] d of age) or early June (LATE; average of 243 ± 15.7 [SD] d of age) to evaluate the effect of time of exposure to infected fescue on their long-term performance measurements.


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  		Table 1. Treatment structure used to evaluate the effect of rotation frequency and weaning date on cow-calf production and changes in forage species composition
 
Cattle and Forage Management
Once allocated, cows remained on their assigned pasture throughout the study and were replaced only if their calf died or they did not give birth to a live calf. A Gelbvieh bull that passed a breeding soundness examination was added to each pasture replicate in late November of each year and remained in the assigned pasture for the entire 60-d breeding season. Cows without calves were replaced with primaparous cows and their calves at the time bulls were added. Bulls were rotated annually to prevent them from mating the same group of cows during the study.

Cows received vaccinations against seven Clostridial strains (Alpha 7; Boehringer Ingelheim Animal Health, Inc., St. Joseph, MO) approximately 2 wk before the onset of calving and were vaccinated against infectious bovine rhinotracheitis, bovine virus diarrhea, parainfluenza, bovine respiratory syncytial virus, Haemophilus somnus, and five strains of Leptospira (Elite 9-HS; Boehringer Ingelheim Animal Health, Inc.) approximately 2 wk before adding bulls to the experimental pastures. Cows were treated for internal parasites with moxidectin (Cydectin; Fort Dodge Animal Health, Fort Dodge, IA) immediately before adding bulls to the experimental pastures. Cows also were treated with Permectin CDS (Boehringer Ingelheim Animal Health, Inc.) as needed to control external parasites.

Cows were offered fescue hay in their individual pasture groups when available forage dropped below 1,000 kg/ha as measured by disk meter (Bransby et al., 1977Go), and the quantity of hay offered was measured as a response variable. Hay was sampled before feeding, and supplemental corn and soybean meal were fed equally to each pasture group during the breeding season only, to meet NRC (1996)Go requirements and to maintain their current BCS. A representative number of bales was weighed (average = 461 ± 5.5 kg). This weight was used to estimate the quantity of hay offered. A commercial trace mineral salt (90 to 95% salt and a minimum of 0.03% Mg, 0.01% K, 100 mg of Co/kg, 300 mg of Cu/kg, 70 mg of I/kg, 6,500 mg of Fe/kg, 1,700 mg of Mn/kg, and 2,000 mg of Zn/kg) was provided free-choice throughout the year.

Milk production was estimated by a modified weigh-suckle-weigh procedure (Williams et al., 1979Go) when the average calf age was 2 mo. Cows and calves were removed from their respective pastures beginning at 0800, and calves were separated from their dams and placed in drylot pens without feed or water. Calves were allowed to nurse their dams at approximately 1600 to remove existing milk and to provide an initiation point for the milk production measurements, after which they were separated from their dams. Calves were weighed empty, allowed to nurse at approximately 1000, then weighed to estimate milk consumption. Calves were then held in drylot pens without feed or water until approximately 1600, when they were allowed to nurse their dams to remove existing milk and provide an initiation point for the second milk production measurement. The procedure was then repeated the following morning, and the values were extrapolated to a 24-h basis and averaged across both days. During the milk production measurement period, cows were maintained in a lot of approximately 1 ha adjacent to the holding pens, and hay was provided for ad libitum consumption.

Extra cows were added to the pastures in the spring of the first 2 yr to help control and utilize typical rapid spring forage growth. Extra cows were used in lieu of mowing hay because of the severity of slopes in most of the experimental pastures. The number of extra cows allocated to each pasture was based on available forage in each pasture at the time of allocation, and assignment of individual cows to groups was completely random. Historically, summer dry periods had resulted in very low forage production on the study site; therefore, fewer animals than might be deemed necessary were added. Allocations were based on allowing the extra cattle a 60-d grazing period to consume the available forage surplus in addition to that needed to maintain the experimental cows throughout the summer if no additional forage were produced. After the first 2 yr, it became evident that this practice was not beneficial because insect damage or more severe dry weather conditions decreased late-summer available forage below critical levels; hence, extra cows were not added during the spring of 2002 and 2003.

All calves received vaccinations against seven Clostridial strains (Alpha 7), infectious bovine rhinotracheitis, bovine virus diarrhea, parainfluenza, bovine respiratory syncytial virus, Haemophilus somnus, and five strains of Leptospira (Elite 9-HS) at 28 d before weaning and were revaccinated at 14 d before weaning. On the designated weaning date, calves were gathered beginning at approximately 0800, separated from their dams, and transported approximately 39 km to a local livestock auction facility. At the auction facility, calves were penned without feed or water until approximately 2000, at which time they were weighed and returned to a pen with water but no feed. Calves were returned to the research station by 1100 the following day, treated for internal parasites with moxidectin (Cydectin), placed in drylot pens, and fed alfalfa hay ad libitum along with 0.9 kg of cracked corn for a 21-d receiving period. At the end of the receiving period, calves were commingled and placed on bermudagrass pastures.

Sample Collection
Soil samples were taken at a 15-cm depth in 50 random locations within each pasture in July 2000 to 2003. The samples were mixed, and representative samples from each pasture were sent to the Arkansas Soil Testing Laboratory for routine analyses.

Unless cattle were being fed hay, pastures were evaluated monthly for quantity and quality of available forage by walking each pasture in a zigzag pattern to ensure random, but representative, sampling of each pasture (Sollenberger and Cherney, 1995Go). Available forage was estimated at 10 locations/ha using a disk meter (Bransby et al., 1977Go), and samples for forage quality analyses were gathered at five of those locations per hectare by clipping forage to a 2.5-cm stubble height with hand shears. Forage samples were dried under forced air at 50° C, ground to pass a 1-mm screen in a Wiley mill (Arthur H. Thomas, Philadelphia, PA), and analyzed for IVDMD by the batch-culture procedures outlined by Ankom Technology Corp. (Fairport, NY; Vogel et al., 1999Go) and for total N by rapid combustion (AOAC, 1998Go; Method 990.03; Elementar Americas, Inc., Mt. Laurel, NJ). Forage samples were composited across sampling dates within pasture and year and analyzed for selected mineral concentrations using a Model D inductively coupled plasma spectrophotometer (Spectro Analytical Instruments, Inc., Fritchburg, MA) as outlined by McGinley et al. (2004)Go. All values were corrected to a DM basis based on drying a subsample of the ground forage overnight at 100° C.

Separate pasture samples of fescue only were gathered in June of each year to assess total ergot alkaloid concentrations. Samples were gathered as just described, placed in plastic bags, and submerged in ice. Each hour during sample collection, samples were transported to a conventional freezer and stored for a minimum of 12 h. Samples were then transported on ice and placed in an ultra-low freezer (–80° C). The samples were subsequently lyophilized, ground to pass a 1-mm screen, and analyzed for total ergot alkaloids (Agrinostics, LLC, Athens, GA), using the procedures of Hill and Agee (1994)Go.

Forage species frequency and basal cover were determined in February, July, and October 2000; April, July, and October 2001 and 2002; and April and July 2003 by a modified step-point procedure (Owensby, 1973Go). Thirty-seven observations were recorded per hectare. The proportion of perennial forages, such as bermudagrass, orchardgrass, and knotroot foxtail (Setaria geniculata [Lam.] Beauv.), along with annual forages, such as cheat (Bromus secalinus L.), little barley (Hordeum pusillum Nutt.), and broadleaf signalgrass (Brachiaria platyphylla [Griseb.] Nash), were combined into a category designated as other grasses.

Statistical Aanalyses
Statistical analyses for all measurements were conducted using SAS (SAS Inst., Inc., Cary, NC) MIXED procedures for a repeated measures analysis of variance; year was considered the repeated measurement, and the individual pasture or group of cows was considered the experimental unit. The error term for treatment effects was pasture x rotational management x weaning date. When multiple forage measurements were made during a year, sampling date and associated interactions were added to the statistical model, and year x month was considered the repeated measurement. Sampling date and season were considered repeated measurements for forage species composition because the various forages grazed in this study were seasonal. When the year x season interaction was detected, orthogonal linear and quadratic contrasts were evaluated within season to determine how species composition changed over years within a season. Cow BW and BCS at calving, breeding, and weaning were analyzed independently; year was considered the repeated measurement. This approach of analyzing the production phases independently was taken because open cows were replaced with lactating heifers at the time bulls were added for breeding. Calf birth dates were analyzed using Julian dates. Calf weaning weights were analyzed both as actual and adjusted 205-d weaning weights. Adjusted weaning weights were adjusted for calf age but not for age of cow. Sex of calf and associated interactions were included in the model for cow and calf measurements. If sex of calf did not interact with main effects, those interactions were removed from the model. All data are reported as least squares means. Differences referred to as tendencies are those with a P-value between 0.05 and 0.10.


   Results and Discussion
Top
 Abstract
 Introduction
 Materials and Methods
 Results and Discussion
Implications
 Literature Cited
 
Monthly rainfall data during the grazing periods are shown in Table 2Go. Rainfalls from July through October 2000 and 2002 and from March to June 2001 were below the previous 30-yr average.


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  		Table 2. Precipitation (mm) during the grazing seasons of 2000 through 2003
 
Soil and Species Composition
Year effects were detected (P < 0.05) for certain soil measurements (Table 3Go), but the two-and three-way interactions involving year were not detected (P = 0.24 to 0.99). Soil pH tended (P = 0.06) to be greater from 2M than from 2W pastures, but soil OM did not differ (P = 0.16 to 0.97) among treatments. Soil P tended (P = 0.06) to be higher from EARLY than from LATE pastures; however, soils were generally above the threshold of 50 mg of P/kg, below which 67 kg of P2O5/ha is recommended. Soil K and Ca concentrations were greater (P < 0.05), and soil Mg concentrations tended (P = 0.05) to be greater, from 2M than from 2W pastures. The quantity of P fertilization based on soil test recommendations from the University of Arkansas Cooperative Extension Service did not differ (P = 0.64 to 0.95) between rotation or weaning date treatments, and K fertilization was numerically (P = 0.11) greater on 2W than on 2M pastures. Lime application was greater (P < 0.05) on 2W pastures than on 2M pastures. Others have reported greater soil OM (Wood and Blackburn, 1984Go) and available soil K and Mg (Bryan et al., 1987Go) from pastures grazed rotationally compared with those grazed continuously. However, pastures grazed rotationally in those studies were only grazed one to four times annually, whereas, in our study, individual paddocks were grazed 8 to 10 times annually.


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  		Table 3. Soil chemical components (air-dry basis) from tall fescue pastures managed in a twice monthly (2M) or twice weekly (2W) rotation schedule with calves weaned in mid-April (EARLY) or early June (LATE)a
 
A three-way interaction involving year, rotation frequency, and weaning date was detected (P < 0.05) for available forage (Table 4Go); however, when analyzed within years, EARLY pastures tended (P = 0.10) to have greater available forage than LATE pastures in 2003, and main effects and interactions did not differ (P = 0.22 to 0.98) in the other years. Other research has demonstrated similar available forage between rotationally and continually stocked E+/clover mixed pastures (Chestnut et al., 1992Go) and bahiagrass pastures managed within similar methodologies (Williams et al., 2002Go); however, some investigators have reported greater hay harvest (Lomas et al., 2000Go) or higher stocking rates (Bertelsen et al., 1993Go; Mathews et al., 1994Go; Hoveland et al., 1997Go) by using rotational grazing compared with continuous grazing.


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  		Table 4. Available forage (kg of DM/ha) and forage species composition of tall fescue pastures managed in a twice monthly (2M) or twice weekly (2W) rotation schedule with calves weaned in mid-April (EARLY) or early June (LATE)
 
Interactions of year, rotation frequency, and/or weaning date were not detected (P = 0.26 to 0.99) for basal forage cover or forage species composition. Similarly, no rotation frequency x weaning date interactions were detected (P = 0.16 to 0.55) for those observations. The proportion of basal cover was greater (P < 0.05) on 2M pastures than on 2W pastures (37.2 vs. 34.5%, respectively) and tended (P = 0.07) to be greater in EARLY compared with LATE pastures when averaged across sampling dates and years. Pastures were dominated by tall fescue throughout the study, averaging 60% fescue across all sampling dates and years, and effects of rotation frequency and weaning date were not observed (P = 0.23 and 0.70, respectively). Pastures contained very low proportions of red and ladino clovers (≤ 1.1%), and those proportions were not affected substantially by rotation frequency (P = 0.34 to 0.35) or weaning date (P = 0.22 to 0.42). Lespedeza percentages also were less than desirable (≤ 5.3%) across treatments and did not differ because of rotation frequency (P = 0.63) or weaning date (P = 0.39). Summer 2000 was extremely dry, possibly contributing to the low survival of clover in the pastures. The study site also was located on drought-prone soil (Ferguson et al., 1982Go), thereby contributing further to the poor clover persistence. Others have reported advantages of rotational grazing on measures of white clover growth and persistence, such as single leaf area, stolon dry weight, and stolon growing point densities that were much more evident during a dry year than during a wet year (Brink and Pederson, 1993Go). Similarly, the proportion of alfalfa (Medicago sativa L.) in a mixture with bromegrass (Bromus L.) and creeping red fescue (Festuca rubra L.) increased with rotational grazing (Walton et al., 1981Go). Lomas et al. (2000)Go, however, reported no difference in legume cover for rotationally grazed bermudagrass pastures compared with those grazed continuously that were overseeded with red clover, white clover, and lespedeza.

Average proportions of crabgrass did not differ across rotation frequency (P = 0.37) or weaning date (P = 0.27) and averaged 9.7% across sampling dates and years. The proportion of other grasses was not affected by rotation frequency (P = 0.27) or weaning date (P = 0.16), and they comprised 17.2% across treatments, seasons, and years. The pastures also contained an average of 7.9% broadleaf weeds, but the proportion of these weeds was not affected by rotation frequency (P = 0.30) or weaning date (P = 0.54).

A year x season interaction was detected (P < 0.05) for basal cover and for each forage species. Therefore, data are presented by year and season in Table 5Go. Basal forage cover decreased in a linear and quadratic manner (P < 0.05) across years in the spring, but basal forage cover increased linearly (P < 0.05) in the summer and linearly and quadratically (P < 0.05) across years in the fall.


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  		Table 5. Forage species composition of tall fescue pastures managed in a twice weekly or twice monthly rotation schedule with calves weaned in mid-April or early Junea
 
Percentages of tall fescue decreased both linearly (P < 0.05) and quadratically (P < 0.05) across years during the spring and fall, and only linearly (P < 0.01) during the summer. Statistical trends (linear and quadratic decreases during summer sampling periods, P < 0.05) also were detected for the percentages of red and white clover, but the magnitude of these changes was minimal and of little significance to grazing animals.

Pastures contained their greatest percentage of lespedeza in July 2002 and 2003, averaging 10.9 and 15%, respectively. Percentage of lespedeza increased both linearly and quadratically (P < 0.05) during the summer sampling periods. These increases in lespedeza were promising, but still did not reflect a substantial diluting effect on the tall fescue.

The percentage of crabgrass in the forage canopy showed the most promise for diluting tall fescue at this research site. The percentage of crabgrass increased linearly and quadratically (P < 0.05) across years in both the summer and fall, reaching a peak of 28.9% in October 2001 and reaching approximately 24% in July and October 2002. At this percentage, crabgrass should significantly dilute some of the toxic effects of E+. The percentage of other grasses increased linearly and quadratically (P < 0.05) during the spring and increased linearly (P < 0.05) during the summer and fall, thereby indicating that fescue was becoming less competitive with other forages as the study progressed.

Forage Alkaloid and Nutrient Composition
Total ergot alkaloids differed (P < 0.01) across years, but did not differ among rotation (P = 0.41) and weaning date (P = 0.93) combinations. Interactions involving year were not detected (P = 0.45 to 0.84), and average total ergot alkaloid concentrations were 1,122, 1,172, 982, and 971 µg/kg (DM basis) for EARLY–2M, LATE–2M, EARLY–2W, and LATE–2W, respectively, across the 4 years of sampling. These values are somewhat lower than those reported in Georgia in late June from E+ pastures, but are comparable with those reported in mid-July (Stuedemann et al., 1998Go).

Two-way interactions of year, rotation, and weaning date with month of sampling were detected (P < 0.05) for IVDMD; therefore, IVDMD data were analyzed within sampling date. Effects of rotation, weaning, or their interaction were detected (P < 0.05) for IVDMD on only five of 30 sampling dates, and a tendency for rotation or weaning effects was detected (0.05 < P < 0.10) on another seven sampling dates (Table 6Go). The dates on which differences were detected seemed to be distributed randomly across sampling dates. Because of this, as well as a lack of consistency in the ranking of treatment responses, we concluded that weaning date and rotational management had little effect on forage IVDMD. Others have reported similar concentrations of IVDMD (Hoveland et al., 1997Go; Aiken, 1998Go) or apparent total tract digestibility (Bertelsen et al., 1993Go) for comparisons between continuous and rotationally grazed cool-season pastures.


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  		Table 6. In vitro dry matter disappearance (%) of tall fescue pastures managed in a twice monthly (2M) or twice weekly (2W) rotation schedule with calves weaned in mid-April (EARLY) or early June (LATE)a
 
Year and month of sampling effects and their interaction were detected (P < 0.05) for forage N concentration (Table 7Go), but overall main effects of rotation frequency or weaning date or their interaction were not detected (P = 0.33 to 0.55). Hoveland et al. (1997)Go reported no difference in forage CP concentrations between continuous and rotationally grazed pastures. In contrast, Bertelsen et al. (1993)Go reported increased forage CP concentrations in rotationally grazed paddocks immediately before grazing compared with continuously grazed pastures. It is possible that differences in forage CP actually occurred in our study but that they were masked by sampling equally across all paddocks within a pasture. Forage samples from the paddock cattle were grazing at the times of sampling that had been grazed selectively were combined with those from paddocks with varied stages of higher-quality regrowth.


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  		Table 7. Forage N and mineral concentrations (DM basis) from tall fescue pastures managed in a twice monthly (2M) or twice weekly (2W) rotation schedule with calves weaned in mid-April (EARLY) or early June (LATE)a
 
All forage mineral concentrations varied by year (P < 0.05), but interactions with year were limited (Table 7Go). Forage P concentrations were lower (P < 0.05) from EARLY–2W pastures than from the other treatment combinations. Forage Mg and Cu tended (P = 0.10) to be greater from LATE than from EARLY weaning. Forage Fe concentrations tended (P = 0.07) to be greater from EARLY–2M pastures than from EARLY–2W pastures. Iron concentrations from both LATE pasture treatments were intermediate and did not differ (P = 0.13 to 0.38) from those from either of the EARLY pasture treatments. The remaining forage mineral concentrations were not affected (P ≥ 0.15) by rotation or weaning date. Concentrations of most minerals were at or above NRC (1996)Go requirements for lactating beef cows, but both Cu and Zn were present at approximately one-half of the requirement.

Cow and Calf Growth Performance
Sex of calf and associated interactions were included originally in the overall statistical model evaluating cow BW and BCS but were not significant (P = 0.11 to 0.97); hence, these effects were removed from the model for cow measurements. Cow BW at calving, breeding, and actual weaning date did not differ (P = 0.11 to 0.51) across treatments across the three calving seasons (Table 8Go); however, cow BW on the EARLY weaning date was greater (P < 0.05) from 2M than from 2W. This result is likely a function of decreased available forage for 2W because of the restricted grazing area during the early days of the tall fescue growing season. Cow BW on the LATE weaning date tended to be greater for the 2M pastures than for the 2W pastures (P = 0.08) and from the EARLY than from the LATE weaning (P = 0.07). Various interactions between year and treatments were observed (P < 0.05) for cow BW change between different production phases; however, BW changes were averaged across years because those interactions were not consistent across production phases. When averaged across years, BW change between calving and breeding did not differ between main effects of rotation frequency (P = 0.69) or weaning date (P = 0.28). Weight change between breeding and weaning was greater (P < 0.05), and the overall BW change between calving and weaning was less negative (P < 0.05), from LATE cows than from EARLY cows. However, BW change between the EARLY and LATE weaning dates was less (P < 0.05) from LATE than from EARLY cows. Body condition scores at breeding were higher (P < 0.05) and loss of BCS between calving and breeding were lower (P < 0.05) for 2M cows than for 2W cows. Body condition scores did not differ (P = 0.16 to 0.82) among treatments at calving or either weaning date, and the small differences in BCS at breeding did not affect calving interval (P = 0.61 to 0.97). These findings are similar to those reported previously (Hoveland et al., 1997Go; Lomas et al., 2000Go), in which rotational and continuous grazing systems were compared; however, weaning spring-born calves at 150 d compared with either 210 or 270 d of age resulted in heavier cow BW and BCS postweaning (Story et al., 2000Go). Similarly, Myers et al. (1999b)Go reported that cow BW at 215 d postpartum decreased linearly as weaning age increased from 90 to 215 d.


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  		Table 8. Performance of cows grazing endophyte-infected tall fescue pastures managed as a twice monthly (2M) or twice weekly (2W) rotation with calves weaned in mid-April (EARLY) or early June (LATE)a
 
Milk production and the quantity of hay offered during the winter did not differ (P = 0.33 to 0.86) among treatments. Hoveland et al. (1997)Go reported less hay fed per cow from rotationally grazed than from continuously grazed fescue bermudagrass mixtures. Lomas et al. (2000)Go reported more hay produced in rotationally grazed compared with continuously grazed bermudagrass pastures overseeded with wheat and legumes. However, fall forage production was limited each year of the study by insufficient late summer and early fall rainfall and the inability of the soil at the study site to retain water.

A three-way interaction was detected (P = 0.02) among year, rotation frequency, and weaning date for calving rate. During yr 1, calving rates were higher (P < 0.05) from EARLY–2M than from LATE–2M or EARLY–2W cows. Calving rate from LATE–2W cows was greater (P = 0.03) than that from LATE–2M cows; however, calving rates averaged > 92% over the three calving seasons for all treatment combinations, and overall differences represent a difference of only one open cow per treatment in most instances. Hoveland et al. (1997)Go also reported no difference in pregnancy rate between rotationally and continuously grazed cows. The effect of early weaning on cow reproductive performance has been somewhat variable and seems to be related to the effect of weaning date on cow BCS. Early weaning had no effect on pregnancy rates when BCS were maintained > 5 across weaning treatments (Story et al., 2000Go), but pregnancy rates were decreased when BCS were < 5 on early and normal weaned groups (Myers et al., 1999aGo,bGo). In the present study, BCS were > 6 at calving for cows from all treatment combinations. It also should be noted that the calving rates observed in this study (average of 93.4%) were considerably higher than those reported previously from spring-calving cows grazing E+ (Gay et al., 1988Go; Tucker et al., 1989Go; Waller et al., 1989Go) and similar to those of cows grazing noninfected forages (Gay et al., 1988Go; Tucker et al., 1989Go). These high reproductive rates were likely caused by a number of factors, including decreased ergot alkaloid concentrations in fescue throughout the fall (Rottinghaus et al., 1991Go), decreased ergot alkaloid concentrations in hay compared with the growing forage (Garner et al., 1993Go), and further dilution of ergot alkaloids from supplementation to correct nutrient deficiencies in the hay (Tucker et al., 1989Go).

Extra grazing days by cows added during the spring did not differ across rotation frequencies (P = 0.65) or weaning dates (P = 0.93). Others have reported improved carrying capacity or production per hectare from rotational grazing systems (Bertelsen et al., 1993Go; Hoveland et al., 1997Go). It is possible that our conservative approach in using the more abundant available spring forage negated potential benefits of more rapid rotation in this study, or that benefits of more intensive rotational grazing on animal carrying capacity would require a longer period to manifest themselves on a site, such as this one, with harsh terrain. These scenarios are unlikely, however, because available forage did not differ across treatments.

Calf birth date and birth weight did not differ (P = 0.51 to 0.96) among rotation and weaning treatments (Table 9Go). The EARLY calves weighed 59 kg less (P < 0.05) at the time they were weaned than the LATE calves, but pasture rotation frequency did not affect (P = 0.78) actual weaning weights. A tendency for a rotation frequency x weaning date interaction was detected (P = 0.08) for actual calf BW measured on the April weaning date. On that date, BW of EARLY–2M calves was heavier (P = 0.09) than that of EARLY–2W calves. Actual calf BW on the June weaning date was 34 kg heavier (P < 0.01) from LATE calves than from EARLY calves. This difference was influenced substantially by the post-weaning feeding management used in this experiment. Adjusted 205-d weaning weights did not differ across rotation schedules (P = 0.78) or weaning dates (P = 0.74). A tendency (P < 0.08) for a year x weaning date x rotation frequency interaction was observed for gain during the period between the April and June weaning dates. Overall, however, BW gain during this period was greater (P < 0.05) from LATE compared with EARLY weaning. Hoveland et al. (1997)Go and Lomas et al. (2000)Go reported no advantage in weaning weights from rotational grazing compared with continuous grazing. In contrast, Hoveland et al. (1997)Go reported greater calf production per hectare, and Bertelsen et al. (1993)Go reported greater heifer gain per hectare, from rotationally grazed pastures because of increased forage availability and the resulting increased carrying capacity. Similarly, Lomas et al. (2000)Go reported that more hay was harvested from rotationally grazed pastures. In the present study, few sampling periods exhibited differences in available forage in response to grazing management treatments; thus, additional cattle likely would not have differentiated between rotational frequencies.


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  		Table 9. Performance of calves grazing endophyte-infected tall fescue pastures managed as a twice monthly (2M) or twice weekly (2W) rotation with calves weaned in mid-April (EARLY) or early June (LATE)a
 
In conclusion, the effect of rotational frequency or weaning date on soil chemical components was minimal and of little biological significance. Likewise, these treatments had little effect on available forage, forage species composition, or forage quality measurements. Possibly the most significant forage information gathered was the increase in the proportion of crabgrass over years during the summer and fall sampling periods. Although this increase occurred independently of rotation or weaning date, the increase in proportion of crabgrass over years offers producers with marginal land the opportunity to provide alternative forage of greater quality than dormant fescue during the summer months. Weaning fall-born calves in mid-April as opposed to early June allowed those cows to gain BW more rapidly during the period between mid-April and early June, but those differences in cow BW were negated by the subsequent time of calving. As expected, weaning fall-born calves in mid-April as opposed to early June resulted in lower actual weaning weights. Weaning in mid-April also resulted in lower weights at the June weaning time, but this weight is also influenced heavily by postweaning nutrition and management.


   Implications
Top
 Abstract
 Introduction
 Materials and Methods
 Results and Discussion
 Implications
Literature Cited
 
Producers interested in reaping quick returns from additional fencing costs incurred with intensive rotational grazing might be discouraged from investing in extra fencing if they wish to wean fall-born calves early. Weaning late led to greater calf weights and might be the preferred method for producers selling their calves at weaning in the cash market, especially because grazing of additional forage using extra cows was not a viable management option under the conditions encountered in this study. Therefore, it is likely that if improvements in beneficial plant species, carrying capacity, and forage quality resulting from weaning date or more frequent pasture rotation are to be realized, they will require more than 3 yr to become evident on sites such as the one used in the present study that have steep slopes and poor soil characteristics.


   Footnotes
 
1 This project was funded in part by Grant # 2001-35209-10079 from the USDA National Research Initiatives Competitive Grants Agri-Systems Program. Back

3 Former research specialist. Current address: 126 Jessie Dunn, Northwestern Oklahoma State University, Alva 73717. Back

4 Former research specialist. Current address: Humphry Environmental, Inc., Fayetteville, AR 72702. Back

5 Former graduate assistant. Current address: Stone Co. Extension Bldg., Mountain View, AR 72560. Back

6 Extension asst. prof. and extension specialist, Mountain Res. Stn., Dep. Anim. Sci., 239 Test Farm Rd., Waynesville, NC 28786. Back

7 Current address: Berea College, Berea, KY 40404. Back

2 Correspondence: B106E AFLS Bldg. (phone: 479-575-2112; fax: 479-575-7294; e-mail: kcoffey{at}uark.edu).

Received for publication February 22, 2005. Accepted for publication July 15, 2005.


   Literature Cited
Top
 Abstract
 Introduction
 Materials and Methods
 Results and Discussion
 Implications
 Literature Cited
 


Aiken, G. E. 1998. Steer performance and nutritive values for continuously and rotationally stocked bermudagrass sod-seeded with wheat and ryegrass. J. Prod. Agric. 11:185–190.

AOAC. 1998. Official Methods of Analysis. 16th ed. Assoc. Offic. Anal. Chem., Gaithersburg, MD.

Ashley, T. L., D. G. Keltner, J. B. McLaren, H. A. Fribourg, and D. Onks. 1987. Performance of crossbred cows and calves grazing fescue pastures with varying levels of Acremonium coenophialum infection. J. Anim. Sci. 65(Suppl. 1):49. (Abstr.)

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. 15:130–135.

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. 71:1381–1389.[Abstract]

Bransby, D. I., A. G. Matches, and G. F. Krause. 1977. Disk meter for rapid estimation of herbage yield in grazing trials. Agron. J. 69:393–396.[Abstract/Free Full Text]

Brink, G. E., and G. A. Pederson. 1993. White clover response to grazing method. Agron. J. 85:791–794.[Abstract/Free Full Text]

Bryan, W. B., T. A. Mills, and F. X. Rosica. 1987. Effects of grazing management and soil amendment on hill land pasture botanical composition. Appl. Agric. Res. 1:297–302.

Chestnut, A. B., H. A. Fribourg, D. O. Onks, J. B. McLaren, K. D. 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. 5:405–408.

Coffey, K. P., W. K. Coblentz, J. B. Humphry, E. L. Piper, C. F. Rosenkrans, Jr., D. S. Hubbell, III, K. F. Harrison, T. M. Denard, F. W. Pohlman, D. H. Hellwig, L. B. Daniels, and L. J. McBeth. 2001. Growth performance and serum prolactin concentrations of stocker steers implanted with trenbolone acetate while grazing endophyte-infected fescue in the spring. Prof. Anim. Sci. 17:166–173.

Coffey, K. P., L. W. Lomas, and J. L. Moyer. 1990. Grazing and subsequent feedlot performance by steers that grazed different types of fescue pasture. J. Prod. Agric. 3:415–420.

Ferguson, D. V., J. S. Lowrance, C. E. McFadden. 1982. Soil survey of Independence Co., AR. USDA, Soil Conservation Service, Washington, DC.

Forcherio, J. C., G. E. Catlett, J. A. Paterson, M. S. Kerley, and M. R. Ellersieck. 1995. Supplemental protein and energy for beef cows consuming endophyte-infected tall fescue. J. Anim. Sci. 73:3427–3436.[Abstract]

Garner, G. B., G. E. Rottinghaus, C. N. Cornell, and H. Testereci. 1993. Chemistry of compounds associated with endophyte/grass interaction: Ergovaline- and ergopeptine-related alkaloids. Agric. Ecosyst. Environ. 44:65–80.

Gay, N., J. A. Boling, R. Dew, and D. E. Miksch. 1988. Effects of endophyte-infected tall fescue on beef cow-calf performance. Appl. Agric. Res. 3:182–186.

Goetsch, A. L., A. L. Jones, S. R. Stokes, K. W. Beers, and E. L. Piper. 1987. Intake, digestion, passage rate and serum prolactin in growing dairy steers fed endophyte-infected fescue with noninfected fescue, clover or wheat straw. J. Anim. Sci. 64:1759–1768.

Hannah, S. M., J. A. Paterson, J. E. Williams, M. S. Kerley, and J. L. Miner. 1990. Effects of increasing dietary levels of endophyte-infected tall fescue seed on diet digestibility and ruminal kinetics in sheep. J. Anim. Sci. 68:1693–1701.[Abstract]

Heitschmidt, R. K., S. L. Dowhower, and J. W. Walker. 1987. Some effects of a rotational grazing treatment on quantity and quality of available forage and amount of ground litter. J. Range Manage. 40:318–321.

Hill, N. S., and C. S. Agee. 1994. Detection of ergoline alkaloids in endophyte-infected tall fescue by immunoassay. Crop Sci. 34:530–534.[Abstract/Free Full Text]

Holloway, J. W., and W. T. Butts, Jr. 1984. Influence of cow frame size and fatness on seasonal patterns of forage intake, performance and efficiency of Angus cow-calf pairs grazing fescue-legume or fescue pastures. J. Anim. Sci. 59:1411–1422.[Abstract/Free Full Text]

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. 10:245–250.

Humphry, J. B., K. P. Coffey, J. L. Moyer, F. K. Brazle, and L. W. Lomas. 2002. Intake, digestion, and digestive characteristics of Neotyphodium coenophialum-infected and uninfected fescue by heifers offered hay diets supplemented with Aspergillus oryzae fermentation extract or laidlomycin propionate. J. Anim. Sci. 80:225–234.[Abstract/Free Full Text]

Lomas, L. W., J. L. Moyer, G. A. Milliken, and K. P. Coffey. 2000. Effects of grazing system on performance of cow-calf pairs grazing bermudagrass pastures interseeded with wheat and legumes. Prof. Anim. Sci. 16:169–174.

Mathews, B. W., L. E. Sollenberger, and C. R. Staples. 1994. Dairy heifer and bermudagrass pasture responses to rotational and continuous stocking. J. Dairy Sci. 77:244–252.[Abstract]

McGinley, B. C., K. P. Coffey, T. J. Sauer, H. L. Goodwin, J. B. Humphry, W. K. Coblentz, and L. J. McBeth. 2004. Case study: Mineral content of forages grown on poultry litter-amended soils. Prof. Anim. Sci. 20:136–145.

McMurphy, W. E., K. S. Lusby, S. C. Smith, S. H. Muntz, and C. A. Strasia. 1990. Steer performance on tall fescue pasture. J. Prod. Agric. 3:100–102.

Myers, S. E., D. B. Faulkner, F. A. Ireland, L. L. Berger, and D. F. Parrett. 1999a. Production systems comparing early weaning to normal weaning with or without creep feeding for beef steers. J. Anim. Sci. 77:300–310.[Abstract/Free Full Text]

Myers, S. E., D. B. Faulkner, F. A. Ireland, and D. F. Parrett. 1999b. Comparison of three weaning ages on cow-calf performance and steer carcass traits. J. Anim. Sci. 77:323–329.[Abstract/Free Full Text]

NOAA. 2003. Climatography of the United States No. 81, Monthly Station Normals of Temperature, Precipitation, and Heating and Cooling Degree Days. National Oceanic and Atmospheric Administration. Natl. Climatic Data Center. Arkansas, Asheville, NC.

NRC. 1996. Nutrient Requirements of Beef Cattle. 7th ed. Natl. Acad. Press, Washington, DC.

Owensby, C. E. 1973. Modified step-point system for botanical composition and basal cover estimates. J. Range Manage. 26:302–303.

Peters, C. W., K. N. Grigsby, C. G. Aldrich, J. A. Paterson, R. J. Lipsey, M. S. Kerley, and G. B. Garner. 1992. Performance, forage utilization, and ergovaline consumption by beef cows grazing endophyte fungus-infected tall fescue, endophyte fungus-free tall fescue, or orchardgrass pastures. J. Anim. Sci. 70:1550–1561.[Abstract]

Rottinghaus, G. E., G. B. Garner, C. N. Cornell, and J. L. Ellis. 1991. HPLC method for quantitating ergovaline in endophyte-infested tall fescue: Seasonal variation of ergovaline levels in stems with leaf sheaths, leaf blades, and seed heads. J. Agric. Food Chem. 39:112–115.

Sollenberger, L. E., and D. J. R. Cherney. 1995. Evaluating forage production and quality. Page 100 in Forages: The Science of Grassland Agriculture, Vol. II. 5th ed. R. F. Barnes, D. A. Miller, and C. J. Nelson, eds. Iowa State Univ. Press, Ames.

Spooner, A. E., and H. Huneycutt. 1978. Effects of boron on white clover. Arkansas Farm Res. 27(6):10. Arkansas Agric. Exp. Stn., Fayetteville.

Story, C. E., R. J. Rasby, R. T. Clark, and C. T. Milton. 2000. Age of calf at weaning of spring-calving beef cows and the effect on cow and calf performance and production economics. J. Anim. Sci. 78:1403–1413.[Abstract/Free Full Text]

Stuedemann, J. A., N. S. Hill, F. N. Thompson, R. A. Fayrer-Hosken, W. P. Hay, D. L. Dawe, D. H. Seman, and S. A. Martin. 1998. Urinary and biliary excretion of ergot alkaloids from steers that grazed endophyte-infected tall fescue. J. Anim. Sci. 76:2146–2154.[Abstract/Free Full Text]

Tucker, C. A., R. E. Morrow, J. R. Gerrish, C. J. Nelson, G. B. Garner, V. E. Jacobs, W. G. Hires, J. J. Shinkle, and J. R. Forwood. 1989. Forage systems for beef cattle: Effect of winter supplementation and forage system on reproductive performance of cows. J. Prod. Agric. 2:217–221.

Vogel, K. P., J. F. Pedersen, S. D. Masterson, and J. J. Toy. 1999. Evaluation of a filter bag system for NDF, ADF and IVDMD forage analysis. Crop Sci. 39:276–279.[Abstract/Free Full Text]

Waller, J. C., J. B. McLaren, H. A. Fribourg, A. B. Chestnut, and D. G. Keltner. 1989. Effect of Acremonium coenophialum infected Festuca arundinacea on cow-calf production. Pages 1193–1194 in Proc. XVI Int. Grassland Cong., Nice, France.

Walton, P. D., R. Martinez, and A. W. Bailey. 1981. A comparison of continuous and rotational grazing. J. Range Manage. 34:19–21.

Williams, J. H., D. C. Anderson, and D. D. Kress. 1979. Milk production in Hereford cattle. I. Effects of separation interval on weigh-suckle-weigh milk production estimates. J. Anim. Sci. 49:1438–1442.[Abstract/Free Full Text]

Williams, M. J., C. C. Chase, Jr., and A. C. Hammond. 2002. Diet quality and performance of heifers in the subtropics. Agron. J. 94:88–95.[Abstract/Free Full Text]

Wood, M. K., and W. H. Blackburn. 1984. Vegetation and soil responses to cattle grazing systems in the Texas rolling plains. J. Range Manage. 37:303–308.


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