Intensive Grazing Management of Smooth Bromegrass With or Without Alfalfa or Birdsfoot Trefoil: Heifer Performance and Sward Characteristics

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Barker etScientist al. The Professional Animal 15:130–135

Grazing Management of Intensive Smooth Bromegrass With or Without Alfalfa or Birdsfoot Trefoil: Heifer Performance and Sward Characteristics J. M. BARKER*, D. D. BUSKIRK, PAS*,1, H. D. RITCHIE, PAS*, S. R. RUST*, R. H. LEEP†, and D. J. BARCLAY2 *Department of Animal Science and †Department of Crop and Soil Sciences, Michigan State University, East Lansing, MI 48824

Abstract

10.04 vs 9.14 metric tons/ha). The ALFBR and BFT-BR pastures, when comOver 3 yr, 324 (n=108 per yr) Holstein pared to BR pastures, supported greater heifers (226±26 kg; ±SD) ranging in age animal average daily gain (0.93 and 0.97 vs 0.83 kg/d) and increased animal from 5 to 7 mo were assigned to a 3×2 gain per hectare (497.8 and 516.4 vs factorial arrangement of treatments to 443.3 kg/d). Legume-grass pastures also determine the effects of forage and had lower neutral detergent fiber content grazing management system on animal than BR pastures. There were no differperformance, forage availability, and ences in either animal gain or gain per forage quality. The forage treatments were: 1) alfalfa and smooth bromegrass hectare due to grazing system. Three (ALF-BR), 2) birdsfoot trefoil and smooth years after seeding, BFT-BR and ALF-BR had a similar percentage of legume bromegrass (BFT-BR), or 3) smooth present within their respective pastures. bromegrass plus nitrogen (BR). The Birdsfoot trefoil appears to be an acceptgrazing management systems were: 1) a four-paddock system in which cattle were able substitute for alfalfa in properly managed grass-legume mixed pastures. rotated based on time (4-p) or 2) a 12paddock system in which cattle were (Key Words: Rotational Grazing, rotated based on forage availability (12Stocking Density, Legume, Alfalfa, p). Stocking rate was held constant at Birdsfoot Trefoil.) 3.75 animals per hectare. The ALF-BR and BR pastures yielded more available forage than BFT-BR pastures (9.86 and

Introduction Rotational grazing is a recognized means of increasing beef production 1To whom correspondence should be adper unit of land area (12, 16). Also, dressed: [email protected] the addition of a legume into grass 2Current address: 10418 Evergreen Rd., Evart, pastures will increase animal perforMI 49631. mance (2, 17, 19). In order to optimize production, the grazing manReviewed by R. S. Adams and G. Hartnell.

agement system and forage species must be effectively matched with soil and environmental conditions. Alfalfa (Medicago sativa L.) is often incorporated into grass pastures because it is a palatable, high quality forage with high yield potential. However, it is intolerant of wet, poorly drained soils and does not thrive when soil pH falls below 6.5 (29). It may also cause bloat in ruminants (18). Birdsfoot trefoil (Lotus corniculatus) may be an acceptable substitute for alfalfa in grass-legume mixtures. It is a high quality, nonbloating legume that is adapted to poorly drained, acidic soils (29, 30). Digestibility of birdsfoot trefoil has been shown to be greater than or equal to that of alfalfa (3, 4, 22). Although birdsfoot trefoil may be lower yielding than alfalfa, it has not been extensively evaluated under rotational grazing management in the U.S. The objectives of this study were: 1) to compare animal performance and forage productivity of grasslegume mixtures and N-fertilized grass pastures; 2) to compare forage and animal productivity and forage quality when birdsfoot trefoil was

Intensive Grazing of Bromegrass With or Without Legume

prior to grazing and the other in the fall following the grazing season. Urea was first applied in May, 1993, 1 yr prior to the beginning of the grazing trial. Additionally, each year prior to grazing, all pastures were fertilized (P and K) and lime was applied according to soil test recommendations. Forage was harvested from all pastures in July, 1993, with animals first grazing the pastures in 1994. Prior to the first grazing season, the perimeter of each pasture was fenced Vegetation on 29.2 ha of land at with three strand, electrified high the Lake City Experiment Station, tensile fence. Pastures were subdiLake City, MI (44:20:07°N; vided into paddocks using a single 85:12:54°W), was cleared using electrified polywire attached to stepRoundup® (1.9 L/ha; Monsanto Co., in posts. Over 3-yr (1994–1996; yr 1, St. Louis, MO) in May, 1992. The yr 2, yr 3), 324 (n=108 per yr) Holland was cultivated and then seeded stein heifers (226±26 kg; ±SD) rangin late July, 1992. The soil was composed primarily of Nester sandy loam. ing in age from 5 to 7 mo were used in a 3×2 factorial arrangement of Prior to seeding, fertilizer (N, P, and treatments to determine the effects of K) was applied according to soil test forage and grazing management recommendations and lime was system on animal performance, applied so that soil pH was 6.5. forage availability, and forage qualThe area was partitioned into 18 ity. Heifers were allotted by weight 1.6-ha pastures that were randomly and randomly assigned to treatment assigned to a 3×2 factorial arrangewith six animals per pasture. Beginment of treatments replicated three ning and ending animal weights were times. The forage treatments asthe average of two full weights taken signed were: 1) alfalfa and smooth bromegrass (Bromus inermis) (ALF-BR), on consecutive days. Heifers had ad libitum access to loose mineral (trace 2) birdsfoot trefoil and smooth mineralized salt, dicalcium phosbromegrass (BFT-BR), or 3) smooth bromegrass plus 224 kg/ha of N (BR). phate, selenium, and copper sulfate). Water was supplied to each paddock The grazing management systems with black plastic pipe attached to assigned were: 4-paddocks with portable waterers with free flow rotation based on time (4-p) or 12valves. The heifers were dewormed paddocks with rotation based on prior to grazing. In yr 1 and 2, they forage availability (12-p). were dewormed with Ivomec® PourSmooth bromegrass (var. Barton; Croplan Genetics, Inver Grove On (Merial, Whitehouse Station, NJ) Heights, MN) was seeded at 3.6 kg/ha and in yr 3 with Totalon® and in all pastures. In addition to the Warbex® (Schering-Plough, Union, smooth bromegrass, alfalfa (var. NJ). Webfoot; Great Lakes Hybrids, Ovid, Animals grazed pastures which MI) was seeded at 6.4 kg/ha in six were divided into 4 or 12 paddocks pastures and birdsfoot trefoil (var. depending on grazing management Norcen; Michigan State Seed, Grand system assigned. The beginning and Ledge, MI) was seeded at 3.6 kg/ha in ending dates of the grazing season another six pastures. averaged May 16 and October 6, Throughout the duration of the respectively. Stocking rate was study, BR pastures were fertilized with constant at 3.75 animals per ha for urea at the rate of 224 kg/ha N/yr. each pasture. Because paddock area The application was equally split, was decreased in the 12-p system, with one application in the spring stocking density was greater in the substituted for alfalfa in grass-legume mixed pastures; and 3) to compare animal performance, forage productivity, and forage quality when stocking density varied from a 4paddock grazing management system with rotation based on time, to a 12paddock grazing management system with rotation based on forage availability.

Materials and Methods

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12-p system relative to the 4-p system (45 vs 15 animals per ha). Cattle in the 12-p system were rotated to the next paddock when the residual forage in the paddock being grazed was visually estimated to be 12 to 20 cm in height. Cattle in the 4-p system were rotated on a 10to 11-d interval regardless of forage quantity. The grazing season was terminated when available forage was insufficient to allow a 10- to 11-d grazing period in the 4-p management system. Prior to rotation in the 12-p system, pastures were “staged”. This prevented forage from becoming excessively mature. Animals grazed the entire pasture for 10 d, and then were allowed to graze two-thirds of the pasture for 10 d, followed by grazing in one-third of the pasture for another 10 d. Heifers then began rotation through the paddocks after this 30-d staging period. Prior to cattle moving into each paddock, a forage sample was taken within that particular paddock. A 0.25 m2 quadrant was randomly placed in the paddock. All forage within the quadrant was hand clipped to a height that approximated residual forage after heifers grazed the paddock. Samples were separated by hand into grass, legume, and weed components. All samples collected over the grazing season were weighed, dried at 57°C for 24 h, and their weights summed to determine forage availability on a dry matter basis. Forage quality was estimated using near-infrared spectroscopy (Model 6250 spectrophotometer, Pacific Scientific). A subset of forage samples with unique spectral properties were selected each year as a calibration set to develop appropriate calibration equations. At least 30% of the samples were used to develop unique calibration equations each year. Neutral detergent fiber and sequential ADF were determined on the samples in the calibration set using a Goering and Van Soest method (8) as modified by Cherney et al. (6). In yr 1 and 2, both NDF and ADF were corrected for ash. In yr 3, only ADF was cor-

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rected for ash because the ash component of NDF residue was negligible in yr 1 and 2. Nitrogen was determined on the calibration set by the Hach method (9). Crude protein was calculated as N×6.25. Pasture quality was determined by the summation of the legume and grass quality components. The summation was weighted by the percentage of legume and grass present in the hand clipped sample. Weeds comprised less than 12% of the total pasture composition and was not included in the calculation of pasture quality. Data were analyzed using the GLM procedure of SAS® (27). Pasture served as the experimental unit. Forage, grazing system, year, replication, and the two- and three-way interactions of forage, grazing system, and year served as the independent variables. Animal performance, forage availability, and forage quality components were dependent variables. Pasture species composition was analyzed using the SAS® GLM procedure by year (27).

Results and Discussion The grazing season was 155, 139, and 134 d for yr 1, 2, and 3, respectively. In all 3 yr, cattle grazing the 4p system were rotated approximately every 10 d, and forage availability dictated rotation of the 12-p system every 4 to 5 d. This resulted in an average rest period of 31 d and 50 d for 4-p and 12-p pastures, respectively. Table 1 displays the average temperature and precipitation totals for April through September at Lake City, MI for yr 1, 2, and 3 along with the 30-yr averages (1961–1990). Temperature, for all 3 yr, and precipitation in yr 2 and yr 3 were near historical averages. In yr 1, 23 cm more precipitation than normal were recorded and may have allowed for the longer grazing season. The forage × grazing system interaction was not significant (P>0.05) for forage availability, ADG, and gain per hectare; thus only main effects are presented in Table 2.

Barker et al.

TABLE 1. Average temperature and total precipitation for April through September at Lake City Agricultural Experiment Station, Lake City, MI. Average temperature Year

High

1994 (yr 1) 1995 (yr 2) 1996 (yr 3) 1961–1990, avg.

21.1 21.2 19.9 21.3

Low

Total precipitation

7.2 8.1 7.2 7.4

(cm) 69.50 48.82 56.67 46.69

(°C)

Forage availability was enhanced in the 4-p system over the 12-p system (P<0.05), and there were at least 720 kg/ha more available forage in ALFBR and BR pastures than in BFT-BR pastures per grazing season (P<0.05). Animal gain did not reflect the difference in forage availability; thus, forage availability did not limit animal performance. In this study, animal production per hectare mimicked individual animal gain because stocking rate was constant among treatments. Bertelsen et al. (1) reported that when stocking rate was similar, ADG of heifers did not differ between 6-paddock and 11-paddock rotational systems. In a Michigan study, Schlegel et al. (28) reported

that increased livestock density in a 13-paddock compared to a 4-paddock system did not result in enhanced animal performance. The addition of alfalfa or birdsfoot trefoil into the grass pastures increased average daily weight gain when compared to BR (12 and 17% increase, respectively; P<0.05). The BFT-BR supported this increased gain with 9% less available forage (P<0.05). Several researchers have reported lower carrying capacity when animals grazed pure stands of birdsfoot trefoil (15 21, 22) or birdsfoot trefoil-grass pastures (14) relative to pure alfalfa and alfalfagrass pastures. In contrast, Hoveland et al. (13) reported that birdsfoot

TABLE 2. Forage availability, daily weight gain, and gain per acre of heifers grazing alfalfa-smooth bromegrass (ALF-BR), birdsfoot trefoil-smooth bromegrass (BFT-BR), or smooth bromegrass plus nitrogen (BR) in a 4paddock (4-p) or 12-paddock (12-p) management system over three grazing seasons. Treatment Forage Item

ALF-BR BFT-BR BR

System SEM

Number of pastures 6 6 6 Forage available, tons/ha 9.86 a 9.14b 10.04a 0.16 Animal gain, kg/d 0.93a 0.97a 0.83b 0.01 Total gain, tons/ha 497.8 a 516.4a 443.3b 8.0 a,b Forage x,ySystem

4-p

12-p

9 9 9.95x 9.41y 0.90x 0.93x 479.8x 491.1x

means in the same row with different superscripts differ (P<0.05). means in the same row with different superscripts differ (P<0.05).

SEM

0.13 0.01 6.3

Intensive Grazing of Bromegrass With or Without Legume

TABLE 3. Forage quality of pastures seeded to alfalfa-smooth bromegrass (ALF-BR), birdsfoot trefoil-smooth bromegrass (BFT-BR), or smooth bromegrass plus nitrogen (BR) in a 4-paddock (4-p) or 12-paddock (12-p) grazing management system over three grazing seasons. Forage Item

ALF-BR

Number of pastures Pasture CP, % 4 paddock 12 paddock Pasture ADF, % 4 paddock 12 paddock Pasture NDF, % 4 paddock 12 paddock Legume CP, % 4 paddock 12 paddock Legume ADF, % 4 paddock 12 paddock Legume NDF, % 4 paddock 12 paddock Grass CP, % 4 paddock 12 paddock Grass ADF, % 4 paddock 12 paddock Grass NDF, % 4 paddock 12 paddock a,b,c,dMeans

6

BFT-BR

BR

6

SEM

6

17.9b 18.1b

17.3ab 17.8b

17.7ab 17.0a

0.3

31.5bcd 30.8ab

31.3bc 30.4a

31.8cd 32.0d

0.2

53.1b 52.0ab

53.1b 51.2a

59.0c 59.7c

0.5

23.1a 22.8a

22.9a 23.3a

– –

0.2

27.2b 27.3b

26.8ab 26.4a

– –

0.3

37.7 b 37.5b

35.7a 35.2a

– –

0.3

14.8a 15.2a

14.5a 14.4a

17.7b 17.0b

0.3

33.9c 33.0b

33.4bc 32.9b

31.8a 32.0a

0.2

62.0bc 61.0b

61.7bc 61.3bc

59.0a 59.7a

0.3

within the same quality item with different superscripts differ (P<0.05).

trefoil-orchardgrass mixed pasture produced as much forage as a fertilized orchardgrass stand in a 3-yr study. Although BFT-BR and ALF-BR pastures supported similar animal ADG when heifers grazed grasslegume mixed pastures in this study (P<0.05), there is evidence that animals grazing birdsfoot trefoil may have enhanced performance over those grazing alfalfa. Marten et al. (21) reported 21% greater daily gain and 11% greater gain per hectare for heifers grazing pure birdsfoot trefoil pastures relative to pure alfalfa

pastures. In an earlier study, ADG of lambs and production of lamb per hectare were increased when onethird of a rotationally grazed grassalfalfa mixed pasture was replaced with pure birdsfoot trefoil (20). Replacement heifer development represents a large portion of the total cost of milk production (10); thus increased growth rates during the development period may lower the total cost of production. Gardner et al. (7) reported accelerated growth rates of Holstein heifers (0.89 vs 0.78 kg/d) resulted in reduced age at breeding and age at first calving with

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no detrimental effect on milk production. Radcliff et al. (25) also reported that increased growth rate during the growing period (1.19 vs 0.77 kg/d) reduced the age of puberty of Holstein heifers without affecting mammary development and lowered costs incurred during that period. The average body weight gain in the present study was 0.91 kg/d. This rate of growth would be considered accelerated and would allow for achieving target breeding weights for calving at £24 mo of age. Table 3 shows the percentage of CP, NDF, and ADF for the pasture and the legume and grass component within each sward. There was an interaction of forage × system for quality measurements (P<0.05). Although pasture CP was different (P<0.05) due to forage treatment, it ranged from 17 to 18%. Extrapolating from NRC recommendations (24), large-breed heifers at an average weight of 300 kg and gaining 1 kg/d would require approximately 944 g/d of CP. Assuming their daily dry matter intake was at least 7 kg/d, 1190 g of CP would have been provided daily in the diet, therefore exceeding protein intake recommendations. The BR pastures had higher NDF than the legume-grass mixtures (P<0.05), which may have contributed to lower heifer gains. The greater NDF of the BR pastures may have lowered digestibility of the diet and likely depressed dry matter intake. Van Soest (31) reported that forage intake decreased rapidly when NDF was greater than 50% of the dry matter. Urea fertilization may have reduced palatability in the grass pastures and also lead to depressed intake (26). In the BFT-BR pastures, the 12-p system resulted in lower NDF and ADF values than the 4-p system (P<0.05). However, there was no difference in animal performance due to grazing system (P<0.05). This lack of a difference may be explained by reports that increasing livestock density will not improve nutrient intake when stocking rate is constant. McKown et al. (23) reported an increase in livestock density in a 42-

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Barker et al.

TABLE 4. Pasture component percentages in alfalfa-smooth bromegrass (ALF-BR) or birdsfoot-smooth bromegrass (BFT-BR) pastures grazed in a 4-paddock (4-p) or 12-paddock (12-p) management system for three grazing seasons. Treatment Forage Season

ALF-BR

Yr 1 Number of pastures Legume, % Grass, % Weed, %

6 37.0a 58.7a 4.3a

System

BFT-BR

6 32.9b 62.0a 5.1a

4-p

6 33.8x 62.6y 3.7x

12-p

6 36.1x 58.1x 5.7y

SEM

1.2 1.1 0.5

Yr 2 Number of pastures Legume, % Grass, % Weed, %

6 38.3a 52.8a 8.9a

6 39.3a 50.7a 10.0b

6 38.9x 51.6x 9.5x

6 38.7x 51.8x 9.4x

1.7 1.7 0.3

Yr 3 Number of pastures Legume, % Grass, % Weed,%

6 31.8a 57.3a 10.8a

6 28.0a 61.6a 10.4a

6 28.0x 62.1x 9.8x

6 31.8x 56.8x 11.4x

1.9 2.8 1.1

a,bForage x,ySystem

establish, yet when seeded with smooth bromegrass produced similar animal gain when compared to alfalfa-smooth bromegrass pastures stocked at the same rate. Although subtle differences existed in forage availability and quality between the 4-p and 12-p grazing systems, no difference in animal gain or gain per hectare resulted. All pasture mixes and both grazing management systems allowed for sufficient heifer daily gain during the developmental period.

Acknowledgments The authors would like to thank D. Nielson and the crew at the Lake City Experiment Station for the care of the experimental animals and J. Paling for forage sample analysis. Acknowledgment is made to the Michigan Agric. Exp. Sta. and the Rood Trust Fund for support of this research.

means in the same row with different superscripts differ (P<0.05). means in the same row with different superscripts differ (P<0.05).

paddock compared to a 14-paddock rotational system did not enhance organic matter or metabolizable energy intake. The results of the present study support the conclusion that forage quality is most likely affected by stocking rate, not grazing system (11, 23). There was no difference in CP of the legume portion, but NDF of the legume portion was 5.6% lower for BFT-BR than for ALF-BR (P<0.05). Buxton and Hornstein (4) reported similar cell wall concentrations between birdsfoot trefoil and alfalfa when the forages were at similar maturity. Other studies have also reported that the in vitro dry matter digestibilities of these legumes were similar (5, 19). As expected, the grass component had greater fiber content than the legumes (P<0.05). Alfalfa was more quickly established than birdsfoot trefoil in the legume-grass mixtures (Table 4). In yr

1, ALF-BR pastures consisted of 37% legume (dry matter basis) as compared to 33% legume in BFT-BR pastures (P<0.05). The difference in percentage of legume present was primarily offset by a higher percentage of grass in BFT-BR pastures. Three years after seeding (yr 2), both ALF-BR and BFT-BR had the same percentage of legume present in their swards (P<0.05). There was no difference in persistency of the legume over the 3 yr due to grazing system (P<0.05), as indicated by similar percentages of legume present in ALF-BR and BFT-BR pastures in yr 3.

Implications Cattle grazing legume-grass mixtures may have increased ADG compared to those grazing grass pastures, due to higher forage quality (lower NDF). Birdsfoot trefoil took longer to

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