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a Agric. Sci. Center at Tucumcari, New Mexico State Univ., 6502 Quay Road AM.5, Tucumcari, NM 88401
b Retired, Dep. of Anim. and Range Sci., Box 3003 MSC 3-I, New Mexico State Univ., Las Cruces, NM 88003
c Dep. of Anim. Sci., 2471 TAMU, College Station, TX 77843-2471
d Dep. of Agric. and Ext. Educ., Agric. Biometrics Service, P. O. Box 30003, MSC 3501, Las Cruces, NM 88003
* Corresponding author (lmlaur{at}nmsu.edu)
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ABSTRACT |
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 TOPNOTES ABSTRACT INTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSSIONCONCLUSIONSREFERENCES |
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Abbreviations: ADG, average daily gain • DM, dry matter • LW, live weight • PLS, pure live seed
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INTRODUCTION |
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TOPNOTESABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSSIONCONCLUSIONSREFERENCES |
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The objectives of this study were to compare pasture productivity and beef (Bos taurus L.) stocker performance on rotationally stocked alfalfa and tall wheatgrass monocultures and on rotationally and continuously stocked alfalfa–tall wheatgrass.
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MATERIALS AND METHODS |
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TOPNOTESABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSSIONCONCLUSIONSREFERENCES |
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Pasture Establishment and Construction
In 1997, a 14-ha block of irrigable cropland, previously in winter wheat (Triticum aestivum L.), was divided into two replicates of four pastures each. In July, the field was conventionally-tilled and formed into beds (101.6-cm centers) for furrow irrigation. The soils were Canez (fine-loamy, mixed, superactive, thermic Ustic Haplargids) fine sandy loam; Quay (fine-silty, mixed, superactive, thermic Ustic Haplocalcids) fine sandy loam; and Quay loam, having medium levels of P and K, based on initial soil test results. A preplant application of 34 kg N and 12 kg S ha–1 was broadcast over the field. The following pasture treatments were sown between 15 Aug. and 8 Sept. 1997: monoculture ‘Jose’ tall wheatgrass (20.8 kg PLS ha–1), monoculture ‘AmeriGraze 401+Z’ alfalfa (16.2 kg PLS ha–1), and AmeriGraze 401+Z alfalfa (5.1 kg PLS ha–1) + Jose tall wheatgrass (13.5 kg PLS ha–1). Each species was distributed from a different seed box. After seeding, each pasture was irrigated as needed until 8 Oct. 1997 to promote germination and establishment.
All pastures were sized to carry a minimum of six animals. Monoculture tall wheatgrass pastures were 2.43 ha and all other rotationally stocked pastures were 1.62 ha. The continuously stocked pastures were 1.3 ha. An alley was constructed at one end of each pasture to facilitate cattle movement and provide a centralized area for cattle watering. The rotationally stocked pastures were subdivided into five paddocks of equal size. The continuously stocked pastures were fenced in halves so that animals could be excluded from half of the pasture on the day that half was irrigated. Otherwise, the gates in the continuously stocked pastures remained open at all times and cattle in those pastures grazed as a group.
Animal Management
The New Mexico State University Institutional Animal Care and Use Committee approved the use of animals in this research project. The Clayton Livestock Research Center (CLRC) purchased animals through a buyer with instructions to form a uniform group. Animals were preconditioned at the CLRC for a minimum of 25 d before being delivered to Tucumcari. All animals were tagged with insecticide ear tags in June of each year.
Cattle on trial were provided ad libitum access to 12:12 Ca:P mineral block, white salt, and water. Animals on pastures with an alfalfa component were also provided ad libitum access to Bloat Guard (PM Ag Products, Homewood, IL) blocks containing 6.6% poloxalene. The rate of bloat block disappearance was determined by weight for each pasture in each year.
Pasture Management
Each year, irrigation of one paddock in each rotationally stocked pasture commenced when surface water became available in the spring (26 Apr. 1998, 14 Apr. 1999, 19 Apr. 2000, and 30 Apr. 2001). Subsequent paddock irrigations were applied in the week following grazing until approximately 1 September. Grazing was initiated on ALF/TW-C the same day as the rotationally stocked pastures. Irrigations were applied to ALF/TW-C every 5 wk to match the irrigation schedule of the rotationally stocked pastures. All irrigations were delivered through gated pipe and were of sufficient duration to completely wet the center of the beds for their full length. All pastures were watered an average of 3.8 times in 1998 (pretrial) and four times in 1999 and 2000. In 2001, ALF/TW-R pastures were irrigated four times and the rotationally stocked pastures were watered an average of 3.6 times. Historical irrigation flow rate data from this location indicated that approximately 200 mm was applied with each irrigation (Lauriault et al., 2002a). Water furrows were reopened each winter to alleviate siltation problems.
Beginning in 1999, all pastures received 25 and 117 kg ha–1 N and P, respectively, each spring before grazing. Additional applications of 84 N kg ha–1 were broadcast on all monoculture tall wheatgrass paddocks before they were irrigated the first time in the spring and before irrigation in July of each year.
The management goal for rotational stocking was to graze individual paddocks for 7 d followed by a 28-d rest period. To begin the rotational stocking sequence each year, the first three paddocks of each pasture were grazed for durations of 2 to 5 d. Thereafter, individual paddocks were grazed for approximately 7 d to leave stubble heights of approximately 7.5 or 20 cm for tall wheatgrass and alfalfa, respectively, even in the mixed pastures. Available herbage mass was visually assessed several times per week, and because paddock size was fixed, the duration of grazing period was lengthened or shortened to match grazing pressure and forage availability, maintaining a 6- to 8-d grazing period. If it became apparent from visual estimates that the current stocking density would force a significant deviation from the 7-d graze/28-d rest cycle, put-and-take animals were used to adjust stocking density of rotationally stocked pastures. Continuously stocked pastures were observed at the same frequency as the rotationally stocked pastures, but the stocking rate of those pastures remained constant throughout each growing season except for the beginning of 2001, when they received additional animals.
Both replicates of a treatment were moved within 24 h of each other. Animal movements were made in midmorning or early afternoon. Duration of the measured grazing season (167, 154, and 161 d for 1999 to 2001, respectively) was from turn-in until the animals reached an average weight of approximately 364 kg LW, at which time they were removed to a feedlot. Six animals in each pasture were designated as testers for each pasture and remained on that pasture throughout the season.
In 1998, the initiation of grazing was delayed until 6 May and all pastures were rotationally stocked to allow pasture establishment. Grazing ceased on 23 September. No measurements were taken in 1998.
On 14 Apr. 1999 (initial data collection year), 74 mixed-breed yearling steers (predominantly British x continental, 238 ± 1 kg) were allotted to pastures such that testers were of uniform weight across pastures. The initial stocking density for TW-R was 6.2 animals ha–1, while all other pastures were stocked with 6.9 animals ha–1. All paddocks of pastures containing tall wheatgrass were swathed at least once before 22 July, to remove tall wheatgrass reproductive tillers. Swathing and baling was done after the paddocks were grazed, but before irrigation. Grazing ceased on 28 Sept. 1999. All pastures were swathed to remove residual forage 6 Jan. 2000.
Grazing was initiated on 26 Apr. 2000, when 80 crossbred yearling heifers (predominantly British x continental, 228 ± 4 kg) were assigned to the pastures. Grazing was initiated on ALF/TW-C in 2000 with a fixed stocking rate of 6.2 animals ha–1. As with other pastures, six animals in each ALF/TW-C pasture were designated as testers. The animals were removed from the pastures on 27 Sept. 2000. Residual forage and regrowth was swathed on 31 Oct. 2000 and baled.
On 17 Apr. 2001, 84 yearling mixed-breed steers (predominantly British x continental, 183 ± 0.2 kg) were allotted to pastures and turned in to graze. Because these animals were of lighter weight than those of previous years, all pastures needed more animals. Eleven additional steers were received 30 d later. One additional animal was allotted to each ALF/TW-C pasture, increasing the stocking density from 6.2 to 6.9 animals ha–1, and the remainder were allotted to the rotationally stocked pastures as put-and-take animals. Grazing was terminated on 25 Sept. 2001.
Data Collection
Before initiation of grazing each year, and at 28-d intervals throughout the grazing season, animals were weighed after a 16-h fast with water available. All performance measures were based on data from the tester animals. Thus, stocking rate for each pasture was calculated as the number of animal days of grazing divided by the number of days in the measurement period and the area of the pasture. Season mean stocking rate is the average of measurement period stocking rates. Likewise, gain ha–1 was calculated by multiplying season total animal grazing days by the season mean ADG for each pasture.
Forage samples were collected every 28 d from mid-May to late September 1999 to 2001. In the rotationally stocked pastures, three exclosures (1.55-m diam.) were erected in the paddock that was to be grazed during the week before sampling dates, which were concurrent with animal weigh dates. Exclosures were distributed across the paddock at regular intervals away from the alley. Placement of each exclosure was such that it encompassed two furrows and the bed between them.
When animals were rotated out of those paddocks, 35-d regrowth was collected from inside the exclosures, and postgrazing herbage mass was collected nearby the exclosures and from the same bed. Exclosures in ALF/TW-C pastures were erected before the onset of grazing. These pastures were sampled on the same day as rotationally stocked pastures. Forage collected from exclosures in ALF/TW-C represented 28-d regrowth. For each sample (regrowth and postgrazing herbage mass), all forage within a 30.5- by 101.6-cm quadrat was hand-clipped to ground level with manual grass shears. Placement of the quadrats inside and outside the exclosures was such that each sample provided a representative cross-section of the furrow-bed continuum and the surrounding area. For mixtures, the harvested material was separated by species. Weeds were negligible and not collected. After sampling, exclosures in ALF/TW-C were moved to a previously unsampled area in the same general part of the pasture. All samples were dried for 48 h at 65°C to determine the DM production of each component species. Total regrowth and postgrazing herbage mass for each quadrat was calculated as the sum of the component species (alfalfa and tall wheatgrass).
Statistical Analyses
The test was analyzed as a split-split plot across time with pasture, date, and year as the whole, subplots, and sub-subplots, respectively. Pasture was the experimental unit, so samples within each pasture on each sample date were averaged for that date. Component and total regrowth and postgrazing herbage mass variables, stocking rate, ADG, and cumulative gain ha–1 were subjected to SAS PROC MIXED ANOVA (Version 8.1, SAS Inst., Inc., Cary, NC, 2000) to test the main effects of pasture, date, and year and all possible interactions. Rep x pasture, rep x pasture x date, and residual mean squares were considered random and used as denominators for tests of significance (Littell et al., 1996). All differences reported are significant at P 
0.05. When an interaction was significant, sequential analysis by year and date was conducted until no interaction involving pasture treatment remained. Protected least significant differences were used to determine where differences occurred between pastures within dates and years and for experiment means.
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RESULTS AND DISCUSSION |
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TOPNOTESABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSSIONCONCLUSIONSREFERENCES |
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Seasonal distribution of alfalfa regrowth in ALF-R (Fig. 2) was similar to that measured in other tests at this location (Lauriault et al., 2002b). Unlike that observed elsewhere under rainfed conditions (Bertelsen et al., 1993; Sleugh et al., 2000), alfalfa productivity in the region is generally characterized by higher production for the midseason harvests than for early- and late-season harvests and is much more uniform than tall wheatgrass (Fig. 1 and Lauriault et al., 2002a) or other perennial cool-season grasses (Sleugh et al., 2000). The alfalfa variety used in the present study had a fall dormancy rating of 4, and generally begins active growth in early to mid-March at Tucumcari. Low early-season yields are attributed to insufficient precipitation and the unavailability of irrigation water from November to April (Table 1) at this location.
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The year x date x pasture interaction for total regrowth (Fig. 3) was likely related more to changes in tall wheatgrass productivity across the growing season, as previously discussed (Fig. 1), than to alfalfa productivity (Fig. 2). Cooper (1973) mentioned that seasonal imbalance in forage productivity may be a major problem in irrigated pasture systems. Lauriault et al. (2003) found that production of binary legume (including alfalfa) and tall fescue mixtures was highly correlated with the yield of the legume component. Although total regrowth of ALF/TW-R was somewhat affected by the grass component (Fig. 1), the data in Fig. 3 still shows the effectiveness of using alfalfa to overcome forage deficits during the summer months (Sleugh et al., 2000; Lauriault et al., 2003). Additionally, the tall wheatgrass and alfalfa in the mixtures complemented each other very well in stabilizing growth across the growing season (Fig. 1, 2, and 3).
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Postgrazing Herbage Mass
Tall wheatgrass herbage after grazing was different among pastures such that TW-R and ALF/TW-C were different from one another and ALF/TW-R was intermediate [2.8, 1.9, and 1.3 Mg ha–1 for TW-R, ALF/TW-R, and ALF/TW-C, respectively; LSD (0.05) = 1.3 Mg ha–1]. For postgrazing alfalfa herbage, the ALF/TW-C was intermediate to the ALF-R and ALF/TW-R, which were different [2.5, 1.3, and 1.9 Mg ha–1 for ALF-R, ALF/TW-R, and ALF/TW-C, respectively; LSD (0.05) = 0.8 Mg ha–1]. There was no difference between pastures in total postgrazing herbage mass (3.0 Mg ha–1) and no interaction involving postgrazing herbage mass variables, indicating that all pastures were grazed equally to the desired level.
The lack of differences in total postgrazing herbage mass between the TW-R and ALF-R is not well-understood. Seman et al. (1999) stated that yield distribution throughout the canopy structures of tall fescue and alfalfa were different and that mixtures containing different proportions of the components would have a structural yield distribution more similar to that of the dominant component. In this study, postgrazing canopy heights were approximately 7.5 and 20 cm for TW-R and ALF-R, respectively. According to Seman et al. (1999), the 0- to 10-cm layer of ungrazed tall fescue had the highest density of forage mass compared with other strata in the canopy. Both Dougherty et al. (1990) and Seman et al. (1999) found that the 10- to 20-cm stratum of an ungrazed alfalfa canopy was most dense. Arias et al. (1990) found that animals grazing tall fescue would utilize forage above a 10-cm horizon, avoiding pseudostems in the horizon below. Density of each stratum in grazed pastures including alfalfa would be much less because, as in the case of the present study, alfalfa mass of rotationally stocked pastures was composed of erect, defoliated stems. So, one of the least dense strata (0–10 cm) of rotationally stocked pastures containing alfalfa remained ungrazed, and the most dense portion of the tall wheatgrass was left, but there was no difference in postgrazing herbage mass.
Postgrazing alfalfa mass of ALF/TW-C was shorter or decumbent stems that still had many leaves (Smith et al., 2000). The first alfalfa dormancy-inducing temperatures (<–2.2°C) occurred on 2 Nov. 1999, 7 Nov. 2000, and 27 Nov. 2001, permitting a fall rest period of at least 4 wk every year. Maintenance of photosynthetic surfaces by the alfalfa in ALF/TW-C compared with ALF/TW-R, combined with a fall rest period, provided sufficient root reserves for initiation of spring growth with no yield reduction in ALF/TW-C (Fig. 2).
A 1:2 ratio of alfalfa and tall wheatgrass seed by weight was projected to establish a 50:50 mixture of harvested forage (Cabanillas-Cruz, 1999). The actual ratio used in the present study, calculated as the difference between seed weight before and after planting was 1:2.5 alfalfa–tall wheatgrass. Regrowth of the mixtures in the present study was approximately 40% grass and 60% alfalfa. Each component was approximately 50% of the total postgrazing herbage mass (calculated from Fig. 1–6) . Average disappearance of component species was similar for both mixed pastures at 0.2 and 0.3 Mg ha–1 of tall wheatgrass and 1.3 and 1.1 Mg ha–1 of alfalfa for ALF/TW-R and ALF/TW-C, respectively (calculated from Fig. 1–6).
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All pastures had been rotationally stocked in 1998 and 1999. A death occurred on 22 June 1998, in an alfalfa–tall wheatgrass pasture. Subacute bloat occurred in another steer in that same pasture on 23 June, and 5 and 13 August 1998. In 1999, death losses occurred on 6 May and 21 September in an ALF-R pasture, and on 26 September in an alfalfa–tall wheatgrass pasture. One animal died in each event. There were no death losses due to bloat in 2000. However, on the night of 15 August, a put-and-take animal crossed from a nontest pasture that had been continuously stocked for 26 d into a paddock that had been allowed to regrow for 22 d. The next morning, the animal was returned to its original pasture where it drank and bloated. Two animals died of bloat in 2001, one each on 6 and 25 September, in the same ALF-R pasture in which the deaths occurred in 1999.
Bloat usually is caused by a combination of several factors, including animal species, genetics, and management; plant species, soil factors, and changes in ambient environment (Berg et al., 2000; Hall et al., 1984).
Since all animals in the present study had access to bloat preventative, it is assumed that, when conditions are favorable for bloat, some animals are more likely to bloat than others (Berg et al., 2000; Hall et al., 1984) even if poloxalene is consumed. One animal that bloated in 1998 appears to have been a chronic bloater, experiencing it at subacute levels three times. It was observed, however, in 1998 that disappearance of the bloat block from the only pasture where bloat occurred was less than the other pastures until after the animal died on 22 June. It may that some animals are unwilling to consume poloxalene block due to its unpalatability (Dougherty et al., 1992). Majak et al. (1995) administered the poloxalene intraruminally to cannulated animals, which certainly would overcome this problem but is not feasible on a large scale.
Bloat can be more prevalent in drier years, even under irrigated conditions, and might be related to soil moisture status as it affects forage quality (Hall et al., 1984). In the present study, all years but 1999 were warmer and drier than average (Table 1). All incidences of bloat occurred within a 3.25-ha (114 x 287 m) area where ALF-R was observed to have greater soil moisture stress than any other part of the 14-ha field. Alfalfa forage having low concentrations of Na+ and high concentrations of K+, Mg+2, and Ca+2 also has been associated with bloat (Hall et al., 1984; Majak et al., 1995). There was very little change from year to year or between pastures in soil concentrations of Na+, K+, Mg+2, and Ca+2, which averaged 96, 240, 225, and 2387 ppm, respectively. However, soil moisture status in the area where bloat occurred might have exacerbated soil cation imbalances in the forage (Hall et al., 1984; Majak et al., 1995).
A reduction in companion species due to soil moisture status also could be a factor in bloat incidence (Hall et al., 1984). Ball et al. (1991) stated that the likelihood of bloat was greatly reduced when pastures contained >50% grass because the bloat-causing agents in the legume are diluted. Tall wheatgrass is characterized by a summer slump in production, while alfalfa production is higher in midseason than early or late (Lauriault et al., 2002a, 2002b; Undersander and Naylor, 1987). In the present study, the legume component of ALF/TW-R was <50% alfalfa in both available and residual forage early in the season when less bloat was observed (Fig. 1 and 2). During August and September, there was no difference between ALF/TW-R and ALF/TW-C in alfalfa regrowth (Fig. 1 and 2). But, the alfalfa component of postgrazing herbage mass of ALF/TW-R was much less, indicating an increase in dietary alfalfa, possibly leading to the increased incidence of bloat at that time (Fig. 1 and 2).
Turning hungry animals into a fresh alfalfa pasture has been consistently associated with the likelihood of bloat (Ball et al., 1991; Berg et al., 2000). In the present study, animals were always rotated soon after their morning grazing session to avoid this. When cattle are rotated to a new alfalfa paddock, they first select the upper 10 cm of the stems, which are higher in quality and more palatable than the postgrazing herbage mass in their previous paddock (Dougherty et al., 1990). Seman et al. (1999) found that forage quality declined over 5 d, and cattle must resort to selective grazing to maintain a diet quality. Bertelsen et al. (1993) found that animals grazing continuously stocked pastures were more selective graziers than those on rotationally stocked pastures. Once the decline in overall pasture quality and change in grazing behavior occurs, an appropriate stocking density on continuously stocked pastures will permit season-long grazing, most likely without any further change in diet quality that might lead to bloat.
Majak et al. (1995) found that the risk of bloat was substantially reduced under continuous stocking compared with when grazing was interrupted, as is the case of rotational stocking. Seman et al. (1999) stated that, in a rotational stocking context, cattle should be moved when quality begins to decline. Berg et al. (2000) reported that the incidence of bloat was greatly reduced after 7 to 10 d of continuous grazing, attributing it to a reduction in forage availability. A reduction in forage quality may also have been a factor (Dougherty et al., 1989). If the pasture in a study described by Berg et al. (2002) had been stocked with fewer animals for continuous occupation, quality of the forage may have declined in 5 d similarly to that described by Seman et al. (1999) and then equilibrated. Smith et al. (2000) said that grazing-tolerant varieties of alfalfa, such as that used in the present study had the ability to produce leaves even below a grazing horizon of 2.5 cm. This would allow those varieties to maintain a higher level of quality in the grazing horizon than traditional hay types because of a higher leaf-to-stem ratio. Bertelsen et al. (1993) found that forage quality in continuously stocked pastures was similar before and after grazing while that of rotationally stocked pastures was much higher at the onset of grazing than after grazing. They also found no difference between pasture systems in the quality of postgrazing herbage mass.
Changes in weather also have been implicated in the incidence of bloat (Hall et al., 1984). Weather conditions were favorable for bloat in forty percent of the occurrences in the present study. However, conditions also were favorable for bloat in 35% of the rotations when bloat was not observed.
Stocking Rate
There was a date x pasture interaction for stocking rate (Fig. 4). Stocking rate for pastures containing alfalfa was twice that for TW-R, with only small differences in stocking rates among the pastures containing alfalfa. The lack of difference in stocking rate between ALF/TW-R and ALF/TW-C is contrary to the report by Bertelsen et al. (1993), who found that rotationally stocked pastures could carry 42% more animals than continuously stocked pastures. But, in light of when their research was conducted, it is likely that Bertelsen et al. (1993) were not using a grazing-tolerant alfalfa variety with a deep-set crown that could avoid hoof damage, or could maintain greater carbohydrate reserves by producing leaves below the stubble height, even under continuous stocking (Smith et al., 2000).
Except for an increase of 0.7 animals ha–1 on 18 May 2001, stocking density of ALF/TW-C was held constant. Adjustments in the stocking density of rotationally stocked pastures throughout the season were due to fixed paddock size and target grazing duration. The interaction between years, dates, and pastures for stocking rate resulted from the use of put-and-take animals to maximize forage utilization in pastures. Changing paddock size or grazing duration would have affected stocking density similarly to changing animal numbers, but not season-mean stocking rate. Thus, the interaction may not have occurred if paddock size and/or grazing duration had been adjusted instead of stocking density, which is more likely the practice used by producers.
Individual Animal Performance
The year x date x pasture interaction for ADG (Fig. 5) was probably due in part to differences between 2000 and the other 2 yr. The cause of this interaction is not well-understood, particularly as it relates to total forage regrowth (Fig. 3) or stocking rate (Fig. 4). The use of put-and-take animals in rotationally stocked pastures should have moderated forage mass differences and it appears to have done so for ALF/TW-R (Fig. 3, 4, and 5).
It is not surprising that performance was not as good for animals grazing TW-R compared with animals grazing monoculture alfalfa or alfalfa–tall wheatgrass mixtures, particularly during late summer when nutritive value and forage mass of the grass declines (Fig. 1; Cabanillas-Cruz, 1999). Though not measured, there was a noticeable difference in the amount of reproductive tillers produced by tall wheatgrass with TW-R and ALF/TW-R having more than ALF/TW-C.
Bertelsen et al. (1993) found that forage nutritive value of continuously stocked pastures was similar before and after grazing and that there was no difference between pasture systems in the nutritive value of postgrazing herbage. In the present study, there was a 20% difference in legume proportion of total regrowth and postgrazing herbage mass in ALF/TW-R, but only a 9% difference in ALF/TW-C (calculated from Fig. 2 and 3), indicating a more consistent nutritive value of the diet in ALF/TW-C.
Cumulative Gain per Hectare
Without regard to stocking system, pastures containing alfalfa, as a group, produced more than twice as much total gain ha–1 than TW-R (Fig. 6). Differences in total regrowth (Fig. 3), stocking rate (Fig. 4), and ADG (Fig. 5) led to a date x pasture interaction for cumulative gain ha–1 (Fig. 6).
Bertelsen et al. (1993) compared continuous and rotational stocking systems using an alfalfa–grass mixture of similar proportions to that used in the present study and did not observe any interaction between treatment and year for either pasture productivity or animal performance. Seman et al. (1999) found that steers in alfalfa grazing pastures, including alfalfa–grass mixtures, selected diets of similar nutritive value, which should lead to similar individual animal performance and gain ha–1 provided forage availability was not limited. In the present study, diet quality of ALF/TW-C was high enough to support rates (ADG) and total seasonal gain ha–1 equivalent to rotationally stocked pastures containing alfalfa (Fig. 5 and 6).
Schlegel et al. (2000) also concluded that optimum stocking density is determined by the amount of forage produced. Forage production is difficult to predict in many situations because of variations between years in precipitation. In the irrigated semiarid West, pasture productivity is more uniform between years, but seasonal variation still occurs. Modifications in management of rotationally stocked pastures between years in the present study were successful in maintaining gain ha–1 across years. Success also was achieved with continuous stocking when careful attention was paid to carrying capacity and pasture health, as indicated by the lack of differences between ALF/TW-R and ALF/TW-C.
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CONCLUSIONS |
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TOPNOTESABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSSIONCONCLUSIONSREFERENCES |
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ACKNOWLEDGMENTS |
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NOTES |
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TOPNOTESABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSSIONCONCLUSIONSREFERENCES |
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Received for publication January 13, 2004.
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TOPNOTESABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSSIONCONCLUSIONSREFERENCES |
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