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J. Dairy Sci. 88:1264-1276
© American Dairy Science Association, 2005.

Performance of Lactating Dairy Cows Managed on Pasture-Based or in Freestall Barn-Feeding Systems*

R. S. Fontaneli1, L. E. Sollenberger2, R. C. Littell3 and C. R. Staples4

1 Embrapa, Caixa Postal 569, Passo Fundo, RS 99001-970, Brazil
2 Department of Agronomy,
3 Department of Statistics, and
4 Department of Animal Sciences, University of Florida, Gainesville 32611

Corresponding author: C. R. Staples; e-mail: staples{at}animal.ufl.edu.


   ABSTRACT
TOP
 ABSTRACT
INTRODUCTION
 MATERIALS AND METHODS
 RESULTS AND DISCUSSION
 CONCLUSIONS
 ACKNOWLEDGEMENTS
 REFERENCES
 
The objective was to compare productive and metabolic responses of lactating dairy cows managed on 2 pasture-based systems using a concentrate supplement (n = 16) with those of a freestall housing system (n = 24). In a 259-d experiment, 3 multiparous Holstein cows were assigned at calving to each of 4 replicates of 2 pasture systems. For system 1, winter pastures were a mixture of rye, ryegrass, and crimson and red clover; summer pastures were pearl millet. Pasture system 2 included a rye-ryegrass mixture during winter and bermudagrass during summer. Pregraze herbage mass averaged 2.3 and 3.6 Mg/ha for winter and summer pastures, respectively; however, during August through September, pearl millet pregraze mass was reduced to about 1 Mg/ha. Daily dry matter intake by cows on pasture averaged 24.7 kg/d in winter and 19.0 kg/d in summer, of which 55% was from pasture; that of cows in confined-housing averaged 23.6 kg/d. Cows in confinement produced 19% more milk (29.8 vs. 25.1 kg/d) than those on pasture systems. Differences in concentration of milk fat, protein, or urea N were not detected among treatment groups. Grazing cows lost more body weight than confined cows (113 vs. 58 kg) and had lower concentrations of plasma glucose in the early weeks postpartum. Despite greater milk yield by cows housed in freestalls, milk income minus feed costs including that of pasture was similar for the 3 management systems. Although these pasture systems might be a viable management system in the southeastern US, extensive loss of body weight immediately postpartum for pasture-based cows are a potential concern.

Key Words: forages • grazing • management system • milk yield

Abbreviation key: EXPD = expected digestibility, FO = fecal output, IVOMD = in vitro organic matter digestibility, OMI = organic matter intake, PUN = plasma urea nitrogen.


   INTRODUCTION
TOP
 ABSTRACT
 INTRODUCTION
MATERIALS AND METHODS
 RESULTS AND DISCUSSION
 CONCLUSIONS
 ACKNOWLEDGEMENTS
 REFERENCES
 
Milk yield based on intensively managed pasture is a rapidly growing production system in the United States and Ireland, and has been important in New Zealand for many years (Hanson et al., 1998b). The key concept is substituting the cow for expensive machinery in the harvest of forages. These authors proposed that lower production costs are the primary economic benefit of intensive grazing compared with traditional systems based on mechanized harvesting and forage conservation. During the 1980s, an increasing public perception of dairies having a negative effect on the environment (Russelle et al., 1997), rising costs of machinery and housing, and reduced profit margin (Parker et al., 1992) began to make pasture systems more attractive. Staples et al. (1994) listed several reasons for greater interest in grazing including 1) lower expenses for feed, equipment, and buildings potentially leading to greater income per cow, 2) reported improvements in animal health and reproduction (less culling), 3) growing pressure from regulatory agencies and environmental interests to reduce centralized accumulation of cattle wastes, and 4) improved quality of life for managers (less stress, more leisure time, etc.).

Grazing lactating dairy cows on pasture is not a new feeding method. This approach has been advocated, abandoned, and now is being advanced again as an alternative feeding system, particularly in the northeastern United States. In a historical review, Hanson et al. (1998a) detailed these changes. By the late 1940s, farmers began to significantly increase their application of manufactured inputs, particularly purchased fertilizers, herbicides, and hybrid corn (Zea mays L.) seed. Between the late 1940s and 1990s, farmers achieved more than a 2-fold increase in yield of row crops such as corn and soybean (Glycine max [L.] Merr.), mainly due to new cultivars and use of purchased inputs. Advances associated with feeding technology pushed management toward feeding/finishing livestock in confinement. Within this context, the pasture was viewed as a low-yield source of supplemental forage or as an exercise lot. Muller and Holden (1994) described these changes in the Pennsylvania dairy industry, where the average number of cow days on pasture decreased from 170 in the early 1950s to 64 in 1990. The grazing system that has evolved in many areas of the United States during the 1980s and 1990s maintains an emphasis on concentrate feeding and high milk yield but with most forage coming from grazed pasture. Use of pasture-based dairy systems is challenging in Florida, however, because of the widely varying nutritive value of forage throughout the year, heat stress, and the difficulty in formulating balanced rations due to problems of quantifying forage intake on pasture.

Most research done with pasture-based systems has been short-term in nature. Longer, full-lactation comparisons of pasture and confinement systems are needed. Systems should be explored where cows freshen in fall and early winter and are assigned to high quality cool-season pasture for the first 4 mo or more of their lactation, thus matching periods of peak milk yield with cooler temperatures and higher quality forage. This experiment was conducted to compare pasture-based and confinement systems for Holstein cows milking from January to October.


   MATERIALS AND METHODS
TOP
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
RESULTS AND DISCUSSION
 CONCLUSIONS
 ACKNOWLEDGEMENTS
 REFERENCES
 
The experiment was performed at the University of Florida Dairy Research Unit (DRU) in Hague, which is located about 20 km north of Gainesville (latitude 30°N and longitude 82.5°W). Soils were fine sands of moderate fertility with an average pH of 5.7, and Mehlich I extractable P of 116 g/kg, K of 40 g/kg, Mg of 46 g/kg, and Ca of 400 g/kg.

The 3 treatments were 2 pasture systems and a traditional free-stall housing management system. Pasture system 1 was designed to use the highest quality annual forages for grazing that are available in the region. Pasture system 2 was intended to reflect less intensive management, utilizing a perennial grass for warm-season grazing and annual grasses for the cool season. Concurrently, Holstein cows were managed in sand-bedded free-stall housing at the university farm as system 3.

System 1 was based on a mixture of ‘Grazemaster’ rye (Secale cereale L.), ‘Surrey’ annual ryegrass (Lolium multiflorum Lam.), ‘Flame’ crimson clover (Trifolium incarnatum L.), and ‘Cherokee’ red clover (Trifolium pratense L.) grazed during the winter-spring season and ‘Tifleaf 2’ pearl millet (Pennisetum glaucum [L.] R.Br.) grazed during the summer-fall season. System 2 used rye-ryegrass mixtures (no clover) during winter-spring and ‘Tifton 85’ bermudagrass (Cynodon spp.) during summer-fall. The cool-season annual forages were planted on 23 October, by sod seeding one replicate over bermudagrass, and 3 replicates over ‘Florigraze’ rhizoma peanut (Arachis glabrata Benth.) pastures without use of herbicide. The seeding rates for system 1 were 68 kg/ha for rye, 11.4 kg/ha for ryegrass, 10 kg/ha for crimson clover, and 6 kg/ha for red clover. The clovers were inoculated with Rhizobium trifollii. The seeding rates for system 2 were 91 kg/ha for rye and 17 kg/ha for ryegrass. Irrigation was used as needed to ensure good stand establishment.

For the warm weather period of system 1, pearl millet was seeded on 20 May at 25 kg/ha. Before planting, the area was sprayed using 5.0 L/ha of Roundup (Monsanto Co., St. Louis, MO; Glyphosate, N-phosphonomethyl glycine in the form of its isopropylamine salt, 1%) to kill common bermudagrass (Cynodon dactylon [L.] Pers.). Selection of Tifleaf 2 was based upon 2 yr of experiments that compared a group of pearl millet and sorghum-sudangrass cultivars under frequent defoliation (Fontaneli et al., 2001). Irrigation was used as needed and grazing was begun on 16 June when pearl millet reached a height of 40 cm. For system 2, well-established stands of the summer perennial Tifton 85 bermudagrass were available for grazing when growth began in late spring. Cows transitioned from winter to summer pastures in early June and grazed summer pastures until early October.

Pasture fertilization was guided by soil tests, previous experience at this location, and need for forage. The total amount applied in each system was 280-17-99 kg/ha of N-P-K, respectively, on system 1 (rye-ryegrass-clovers/pearl millet), and 360-17-99 on system 2 (rye-ryegrass/bermudagrass). An additional application of 40 kg of N/ha was made to system 2 pastures in late spring (no clover in this system) and late summer (bermudagrass production continued longer than pearl millet). Although system 1 included clover, previous experience has shown that early-season growth of rye-rye-grass-clover mixtures is slow when no N fertilizer is applied, thus a total of 120 kg of N/ha was used from 2 wk after fall planting until clovers became productive in midspring.

Both pasture systems were replicated 4 times in a randomized block design. Pasture size for each experimental unit was 1.2 ha, with 0.8 ha of this area being grazed during winter-spring and 0.4 ha being grazed during summer-fall. A total of 40 multiparous Holstein cows calving in January and February were assigned randomly at calving to the 3 treatments during about a 30-d period; 12 cows were assigned to each of the 2 pasture systems and 16 cows were assigned to serve as controls in the free-stall facility. Based on previous winter work by Macoon et al. (1997) and summer work by Fike et al. (2003), 3 multiparous Holstein cows were assigned to each replicate within each pasture system (n = 12 per pasture system) for a base stocking rate of 3.75 cows/ha during winter-spring and 7.5 cows/ha during summer-fall. The rest period between grazings for a given paddock was 28 d in winter and 21 d in summer. Target stubble heights for bermudagrass and pearl millet were 15 and 20 cm, respectively. Cows and water troughs were moved to a fresh paddock daily after the morning milking. Portable shades were provided in the summer and moved daily as well.

A concentrate supplement was fed at a rate of 1 kg (as-fed) per 2.5 kg of milk produced during winter and 1 kg (as-fed) per 2 kg of milk produced in summer. Supplement was fed in each paddock to the 3 cows as a group after each milking. Amount fed was adjusted twice weekly. During those weeks in late spring (from 26 May to 16 June) when winter forages were diminishing and summer forages were not ready to graze, cows on pasture were fed a cottonseed hull-based ration (16 kg/d per cow, DM basis) to ensure that DMI was not limiting and to manage body condition. This approach was repeated in late summer for system 1 (pearl millet) starting 6 September on 2 pasture replicates, and starting 18 September on the other 2 replicates, to the end of the experiment (7 October). During this period, the amount fed was 14.5 kg/d per cow (DM basis). From 19 February to 19 March, cows on one replicate of both pasture systems were fed 2.7 kg/d of corn silage per cow (DM basis) because excessive soil moisture on that replicate resulted in poor rye growth and low herbage mass. In addition, 3.3 kg/d of corn silage per cow (DM basis) was fed from 28 April to 18 May to cows of one replicate of system 2 (rye-ryegrass) due to a shortage of forage in that specific field. Representative samples of supplements were collected weekly, composited monthly and analyzed using wet chemistry by Dairy One (Ithaca, NY). Ingredient and chemical composition of the concentrate supplements and TMR are described in Tables 1Go and 2Go, respectively.


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  		Table 1. Ingredient composition of experimental diets and supplements fed to cows managed in freestalls or on pasture.
 

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  		Table 2. Average chemical composition of TMR fed to cows managed in freestalls and concentrate supplement and TMR fed to cows managed on pasture.
 
Pasture Sampling
Every 3 wk throughout the experiment, pasture samples were taken before and after grazing at six 0.5-m2 sites that represented average paddock herbage mass. For winter species and bermudagrass, the plants were clipped to a 2.5-cm stubble height, whereas pearl millet was clipped to a 10-cm stubble height. Forage was sampled on 12 sampling dates, 7 during winter/spring and 5 during summer/fall. At the time of pregraze sampling, hand-plucked samples were taken to represent the portion of the canopy removed during the grazing period. Herbage was severed at the height to which the most recently completed paddock was grazed. Herbage was collected at 20 to 30 locations per paddock, composited, and used to determine CP, in vitro OM digestibility (IVOMD), and NDF. An additional hand-plucked sample was taken twice in winter from each paddock to determine botanical composition. The components were separated into rye, ryegrass, clovers, and weeds. Hand-plucked samples and forage species components were dried at 65°C and ground to pass a 1-mm screen using a Wiley mill. Samples were digested for N determinations using a modification of the aluminum block digestion procedure of Gallaher et al. (1975). Ammonia in the digestate was determined by semiautomated colorimetry (Hambleton, 1977), and CP (DM basis) was calculated as N x 6.25. In vitro organic matter digestion was performed by a modification of the 2-stage technique (Moore and Mott, 1974). Neutral detergent fiber was determined using the procedure of Golding et al. (1985). Laboratory analyses were conducted in the Forage Evaluation Support Laboratory of the University of Florida. Mineral analysis was performed on one sample composited across the sampling times by Dairy One (Ithaca, NY). The herbage nutritive value and mineral composition are shown in Table 3Go.


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  		Table 3. Herbage nutritive value and mineral composition of hand-plucked samples of forages or forage mixtures. Mineral concentration was determined on one sample composited across sampling times so no standard errors are reported.
 
Animal Measurements
Milk yield was measured at each of 2 milkings daily, and samples for milk composition at 2 consecutive morning and evening milkings weekly during the first 19 wk of the experiment and biweekly thereafter. Milk samples were analyzed for fat, protein, urea N, and SCC at the Southeastern Dairy Herd Improvement Laboratory in McDonough, GA. Cows were weighed weekly after the morning milking.

Blood samples were collected weekly before milking during the first 11 wk postpartum and biweekly thereafter via coccygeal venipuncture with evacuated sodium heparin tubes (Vacutainer, Becton Dickinson, Franklin Lakes, NJ). Upon collection, tubes were immediately placed in an ice water bath. Within 2 h, samples were centrifuged for 15 min at 1916 x g, plasma was separated and stored at –25°C until thawed for later analyses. Blood plasma was analyzed for NEFA using the NEFA C kit (WAKO Chemicals USA, Inc., Richmond, VA). A Technicon Autoanalyzer (Technicon Instruments Corp., Chauncey, NY) was used to measure plasma glucose [a modification of Gouchman and Schmitz (1972) as described in Bran and Luebbe Industrial Method # 339-19)] and plasma urea nitrogen (PUN) [a modification of Marsh et al. (1965) as described in Bran and Luebbe Industrial Method # 339-01].

Voluntary forage intake by cows on pasture was measured once during winter (average of 81 DIM) and once during summer (average of 178 DIM) using a pulse dose technique (Pond et al., 1987, 1989a,b) with chromium-mordanted fiber as an inert marker to determine fecal output (FO). Forage of quality similar to that consumed was collected across all pastures within a treatment and composited. Forages were dried at 65°C and ground to pass a 2-mm screen using a Wiley mill. Fiber from the forage was mordanted using the methodology of Udén et al. (1980). The ground forage (~700 g) was wetted with water (1 L of H2O per 100 g of forage) plus 50 mL of liquid laundry detergent. After boiling for 2 h, the forage was washed repeatedly with tap water to remove all soap, rinsed with acetone, dried at 105°C, and weighed. The dried forage was placed in a metal container, and sodium dichromate, dissolved in 4 volumes (approximately 4 L) of water, was added to the forage. Addition of Cr (as sodium dichromate) equaled 7% of the fiber DM. This slurry was sealed with aluminum foil and heated in a forced-air drying oven at 105°C for 24 h. The liquid was then poured off and the fiber was gently rinsed with tap water to remove excess and unbound Cr. Ascorbic acid (Aldrich, Milwaukee, WI) at half the weight of dry fiber was mixed with water, added to the fiber, and allowed to stand for 1 to 1.5 h. The fiber was rinsed thoroughly with tap water and dried at 105°C. The mordanted fiber was weighed [2.5 ± 0.01 g (as-is)] into 28-g gelatin capsules (Jorgenson Laboratories, Loveland, CO).

The cows were orally pulse-dosed with 12 gelatin capsules containing Cr-mordanted fiber (30 g, as-fed) from their respective forage assignments. Capsules were administered with a multiple-dose balling gun (Nasco, Fort Atkinson, WI) at about 1800 h, after the evening milking. Samples of feces were collected at approximately 0, 12, 15, 18, 21, 24, 27, 36, 42, 48, 60, 72, and 84 h postdosing. Most samples were collected in holding pens at the milking parlor. Samples were collected on pasture for h 15, 18, 21, 27, and 42. Fecal samples were refrigerated immediately after collection. All fecal samples were dried at 65°C for at least 48 h, and ground through a 1-mm screen using a Wiley mill. Samples (2 g, as-is) were dried at 105°C and ashed at 550°C for determination of DM and OM (AOAC, 1990). Samples were analyzed for Cr by atomic absorption spectrophotometry (Perkin Elmer model 500, Norwalk, CT) according to the procedure of Williams et al. (1962).

Each cow’s chromium excretion curve was analyzed using PROC NLIN following the method described by Pond et al. (1987). To calculate the intake of herbage, the following assumptions were made: intake of supplement was the same for all cows within a paddock, digestibility of supplement was equivalent to its calculated total digestible nutrients values based on the NRC (1989), and digestibility of forage was affected by amount of supplement intake. The measure of forage IVOMD for each paddock was used in equations to calculate forage intake by cows grazing that paddock. Fecal output (kg/d) should equal total intake (kg/d) multiplied by the indigestible fraction of a feed. However, FO observed based on the mordanted fiber method was not equal to the FO predicted based on forage and supplement digestibilities because total dietary DM in vivo digestibility may be higher or lower than expected depending upon the effects of supplements upon forage digestibility (Moore and Sollenberger, 1997; Dixon and Stockdale, 1999). Thus, forage OM intake (OMI) was calculated using an iterative SAS (SAS Inst., Inc., Cary, NC) program developed by John E. Moore (personal communication, 1998). In this program, total OMI is computed from estimates of FO (called observed FO) obtained from the marker appearance curve, and total diet digestibility [called expected digestibility (EXPD)] to balance for the estimated proportion of forage and concentrate supplement OM consumed and their respective digestibilities. Estimated forage OMI is the difference between total OMI and known supplement OMI. The equation to calculate EXPD is:


This EXPD was further adjusted to help account for associative effects (Moore et al., 1992; Dixon and Stockdale, 1999) that may result from mixed forage-concentrate diets. This new calculation of total diet digestibility, called adjusted digestibility, was obtained using an equation developed from a wide range of published data of mixed diet digestibilities showing deviation from the expected (based on calculations from the weighted intake and digestibilities of the forage and concentrate supplement components) when mixed diets are fed (Moore et al., 1999). The equation is:


Using this adjusted digestibility value (ADJ), a prediction of FO was computed:


Given that supplement OMI is fixed, the iterative SAS program then adjusted estimates of forage intake until the difference between observed FO and predicted FO is less than 0.01 kg of OM/d. Forage OMI estimates were converted to DMI estimates by dividing the OMI by OM concentration of the forage.

Feed Costs and Milk Income
Feed costs and income from milk were calculated for the 2 forage systems and the confined housing system. Calculation of feed costs included establishment (soil preparation and seed) and maintenance (fertilization, herbicide, and insecticide use) of pastures, costs of feed-stuffs, costs of TMR for barn cows, concentrate supplement for grazing cows, cottonseed hull-based supplement for grazing cows, total ration costs for 3 systems, costs of herbage and amount and extent of use of concentrate supplements fed per cow.

Statistical Analysis
The experimental design was a randomized complete block with 4 replications. Data were analyzed using SAS procedures for repeated measures (Littell et al., 1996, 1998; SAS Institute, 1989).

The standard model for repeated measures experiment of animal and plant response variables was


where yij = the response at time j on treatment i, µ = the overall mean, {alpha}i = fixed effect of treatment i, ßj = fixed effect of time j, ({alpha}ß)ij = fixed interaction effect of treatment i with time j, and eij = random error at time j on treatment i.

Contrasts of barn vs. pasture system 1 and barn vs. pasture system 2 were made. Interactions between treatment and sampling period (time) were determined using contrast statements in PROC MIXED. Differences were considered significant at P < 0.05. Pasture systems were tested at each evaluation date for plant response variables (herbage mass, IVOMD, CP, NDF, and intake) and all systems were tested every week for animal response variables (milk yield, milk composition, BW, and plasma NEFA, glucose, and urea N concentrations). Economic variables were analyzed using ANOVA models for a completely randomized design in PROC MIXED (SAS Institute, 1989). An F-protected least significant difference test was used to compare all treatment effects.


   RESULTS AND DISCUSSION
TOP
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
 RESULTS AND DISCUSSION
CONCLUSIONS
 ACKNOWLEDGEMENTS
 REFERENCES
 
Botanical Composition
During winter, the average contribution of ryegrass was 47% in pastures with clovers (system 1) and 59% in pastures without legumes (system 2). The ryegrass contribution increased and rye decreased as the season progressed. Crimson and red clovers made their greatest contribution late in the cool season, being 20 to 25% of total DM in April/May (>500 kg of DM/ha).

Herbage Mass
Pregraze and postgraze herbage mass in winter/spring averaged 2350 ± 330 and 910 ± 190 kg of DM/ha, respectively. Pregraze and postgraze herbage mass in summer averaged 3580 ± 830 and 2400 ± 630 kg DM/ha. Herbage mass did not differ between pasture systems during winter and through 23 July in summer (Figure 1Go). This situation changed during late summer when growth rate of pearl millet decreased. From 12 August throughout September, herbage mass of Tifton 85 bermudagrass (system 2) was greater than that of pearl millet.



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  		Figure 1. Pregraze forage mass of pastures grazed by lactating dairy cows managed on 2 pasture systems [rye-ryegrass-clovers in winter and pearl millet in summer (•) or rye-ryegrass in winter and bermudagrass in summer ({square})] over the first 37 wk of lactation. Test of {square} vs. • was significant (P < 0.05) on August 12, September 4, and September 25.

 
Nutritive Value
Forage IVOMD was not different between pasture systems grazed in the winter (74.9 vs. 75.3% for rye-ryegrass-clovers and rye-ryegrass, respectively). However, winter samples collected in April and May had lower IVOMD than those collected in January through March (Table 3Go). This may have been due to more rye-grass and less rye contributing to the herbage mass with time based upon the botanical composition data. In addition, stem elongation by rye would have resulted in a greater proportion of stem in the forage biomass. Differences in IVOMD values between pearl millet and bermudagrass were not detected (68.1 vs. 65.2% for pearl millet and bermudagrass, respectively) (Table 3Go). Throughout the summer, IVOMD on both systems ranged from >60 to just <75%.

Forage CP concentrations were not different between pasture systems 1 and 2 during winter at any of the 7 sampling times (24.8 vs. 24.7%), however, CP concentration was lower in April and May compared with the cooler months (22.1 vs. 26.8%; Table 3Go). Although mean CP concentration was not different between pearl millet and bermudagrass in summer (22.3 vs. 19.0%; Table 3Go), pearl millet CP was greater than that of bermudagrass (4 to 6 percentage units) in 2 samples collected in August and September. Mean NDF concentration was not different between pasture systems 1 and 2 during the winter season (46.6 vs. 48.1%). However, summer forages did differ, with pearl millet having lower mean NDF concentration compared with bermudagrass (58.6 vs. 72.6%). This pattern was evident at all sampling times. This lower NDF concentration did not result in greater IVOMD values for pearl millet.

Forage and Total Intake
Average DMI by cows in free-stall confinement was 23.6 kg/d. Once in winter and once in summer, DMI was determined using chromium marker techniques. Neither forage nor total intake was different between pasture systems in either season (Table 4Go) but cows consumed more forage (13.4 vs. 10.6 kg/d) and more DM (24.7 vs. 19.0 kg/d) in winter than summer. This was likely due to a greater nutritive value of winter compared with summer forages (Table 3Go) and to a greater energy need of cows producing more milk in winter. Herbage DM consumed was 55% of total DMI in winter and summer. These total DMI are similar to those reported by other authors. Muller et al. (1995) reported daily DM consumption of 22.2 kg/d by grazing cows of which 65% came from grass-alfalfa (Medicago sativa L.) pasture. Holden et al. (1994) reported pasture intake ranging from 11.6 to 15.6 kg of DM/d by cows grazing a mixture of perennial cool-season grasses between April and September, with forage intake lowest in summer. The total DMI varied only between 19.9 and 22.4 kg/d.


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  		Table 4. Dry matter intake by lactating dairy cows managed on 2 pasture systems.
 
The DMI (herbage disappearance) calculated using the sward difference method appeared similar to that measured using the chromium marker method in winter (13.1 and 14.7 vs. 13.3 and 13.5 kg/d) but not in summer (7.5 and 8.0 vs. 10.9 and 10.3 kg/d) (Table 4Go). Macoon et al. (2003) also reported greater intake estimates of pasture DM using the marker method compared with the sward method.

When using the sward difference method to estimate forage intake, cows grazing winter pastures without clovers consumed more DM on February 24 and March 17 than those on pastures containing clovers (Figure 2Go). Differences may have been due in part to numerically greater herbage mass (Figure 1Go) and greater proportion of ryegrass in system 2 than in system 1 (54 vs. 46%). During the summer period, cows grazing pearl millet consumed more herbage DM in July evaluations (Figure 2Go) but less in late September. This drop off in late September was probably due to very low pearl millet herbage mass at that time (Figure 1Go).



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  		Figure 2. Intake of pasture forage (measured by the sward difference method) by lactating dairy cows (kg/d) managed on 2 pasture systems [rye-ryegrass-clovers in winter and pearl millet in summer (•) or rye-ryegrass in winter and bermudagrass in summer ({square})] over the first 37 wk of lactation. Test of {square} vs. •was significant (P < 0.05) on February 24, March 17, July 1, July 22, and September 25.

 
Milk Yield and BW
Cows in free-stall housing produced 19% more milk (29.8 vs. 25.1 kg/d) over the duration of the study than cows managed on pasture systems. This advantage of barn-housed cows was detected at nearly every week of the study when only cows on pasture system 2 were considered (Figure 3Go). Cows managed in pasture system 1 produced less milk only after wk 13 postpartum compared with cows in free-stalls. During a 4-wk experimental period, Kolver and Muller (1998) reported that cows consuming an all-pasture diet produced 33% less milk than cows fed a TMR (29.6 vs. 44.1 kg/d), and had a milk protein concentration that was 0.19 percentage units lower. Fike et al. (1997) reported large decreases (10 to 15 kg/d) in milk yield for cows moved from a confined housing system to bermudagrass or rhizoma peanut (Arachis glabrata Benth.) pastures in Florida in midsummer. Based upon DMI (Table 4Go) and energy density and digestibility of the dietary components (Tables 2Go and 3Go), intake of energy may not have differed between housed and pastured cows. However, 48-h IVOMD values for grazed forages do not account for the fast rate of passage of digesta from the rumen during grazing and therefore may overestimate the digestible energy derived from the pasture forage. In addition, energy expenditures must have been greater for pastured cows due to their grazing activity and their round trips from pastures to the milking parlor twice daily, thus leaving less dietary energy for productive purposes. In addition, pastured cows did not have the benefit of fans and sprinklers, as did the cows housed in cooled free stalls.



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  		Figure 3. Milk yield by lactating dairy cows managed on 2 pasture systems [rye-ryegrass-clovers in winter and pearl millet in summer (•) or rye-ryegrass in winter and bermudagrass in summer ({square})] and in free-stall housing ({triangleup}) over the first 37 wk of lactation. Test of {triangleup} vs. •was significant (P < 0.05) at wk 13 through 37. Test of {triangleup} vs. {square} was significant (P < 0.05) at all weeks except wk 6 and 7. The pooled SE was 1.0 kg/d.

 
No differences among treatments were detected in concentration of milk fat (3.69, 3.60, and 3.70%), milk protein (2.90, 2.96, and 2.95%), or milk urea N (16.5, 17.1, and 15.6 mg/100 mL) for cows managed in freestalls, pasture system 1, or pasture system 2, respectively. However, mean SCC was greater in milk from cows managed in free-stalls compared with those on pastures (654,000 vs. 223,000 and 364,000).

Grazing cows lost approximately 113 kg in the first 8 wk postpartum compared with 58 kg for confined cows (Figure 4Go). This greater loss of BW was accompanied by lower milk yield compared with barn-confined cows. These dual responses must have been driven by a greater negative energy status of grazing animals possibly due to lowered energy intake and greater energy expenditures as described earlier. With the growth of new forage in the summer (approximately wk 11 to 21 postpartum), cows on pastures gained BW so that BW of cows in barns or on pastures did not differ during this period. Toward the end of the summer growing season, pearl millet stands became somewhat depleted and cows lost BW and therefore were lighter than cows in free-stalls (Figure 4Go). Cows grazing bermudagrass did not differ in BW from cows managed in free-stalls.



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  		Figure 4. Body weight of lactating dairy cows managed on 2 pasture systems [rye-ryegrass-clovers in winter and pearl millet in summer (•) or rye-ryegrass in winter and bermudagrass in summer ({square})] and in free-stall housing ({triangleup}) over the first 37 wk of lactation. Test of {triangleup} vs. • was significant (P < 0.05) at wk 4 through 13 and 27 through 35. Test of {triangleup} vs. {square}was significant (P < 0.05) at wk 5 through 10. The pooled SE was 15.6 kg.

 
Plasma Metabolites
Plasma NEFA concentrations gradually decreased from calving until wk 15 postpartum, at which time concentrations remained unchanged. Plasma NEFA concentrations were greater during the first 4 wk postpartum for cows grazing pasture system 1 compared with those in free-stalls (Figure 5Go). This may have been because the 2 groups of cows did not differ in milk yield but BW loss was greater for this group of grazing cows.



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  		Figure 5. Concentration of NEFA in plasma of lactating dairy cows managed on 2 pasture systems [rye-ryegrass-clovers in winter and pearl millet in summer (•) or rye-ryegrass in winter and bermudagrass in summer ({square})] and in free-stall housing ({triangleup}) over the first 37 wk of lactation. Test of {triangleup} vs. • was significant (P < 0.05) at wk 1 through 4. Test of {triangleup} vs. {square} was not significant (P ≥ 0.05) at any week. The pooled SE was 19.5 mEq/L.

 
In a reciprocal fashion to NEFA, concentrations of plasma glucose gradually increased in the first 10 wk postpartum (Figure 6Go). This pattern followed increases in forage intake (Figure 2Go). Cows managed in free-stalls had greater concentrations in the first 5 wk and 2 wk postpartum compared with cows grazing pastures with and without clover, respectively. In addition, grazing cows had lower concentrations of plasma glucose during a 12-wk summer period that coincided with BW loss compared with barn-housed cows (Figure 4Go).



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  		Figure 6. Concentrations of glucose in plasma of lactating dairy cows managed on 2 pasture systems [rye-ryegrass-clovers/pearl millet (•) or rye-ryegrass/bermudagrass ({square})] and in free-stall housing ({triangleup}) over the first 37 wk of lactation. Test of {triangleup} vs. • was significant (P < 0.05) at wk 1 through 5 and 25 through 35. Test of {triangleup} vs. {square}; was significant (P < 0.05) at wk 1, 2, and 23 through 33. The pooled SE was 1.0 mg/100 mL.

 
Concentrations of PUN increased with week postpartum, probably reflecting DMI patterns (Figure 7Go). Because the CP concentration of the pasture forages and supplements were greater than that of the TMR fed in the barn (Table 3Go), concentrations of PUN in pastured cows rose faster in the first 10 wk postpartum. However, PUN values from grazing cows decreased during the summer season because summer forages were lower in CP concentration than winter forages (Table 3Go) and because DMI was lower in summer than winter (Table 4Go). Grazing cows had lower PUN values than barn-fed cows probably because of lower DMI. The PUN values were ≥12 mg/100 mL for almost the entire trial, indicating that dietary CP intake was seldom, if ever, limiting milk yield.



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  		Figure 7. Concentrations of plasma urea nitrogen (PUN) of lactating dairy cows managed on 2 pasture systems [rye-ryegrass-clovers/pearl millet (•) or rye-ryegrass/bermudagrass ({square})] and in free-stall housing ({triangleup}) over the first 37 wk of lactation. Test of {triangleup} vs.• was significant (P < 0.05) at wk 21 through 33. Test of {triangleup} vs. {square} was significant (P < 0.05) at wk 1, 2, 21 through 31, and 37. The pooled SE was 0.6 mg/100 mL.

 
Feed Costs and Milk Income
Although the costs of producing milk involve a number of variables, feed cost is the largest component. This section assesses the feed cost relative to milk income of the 2 pasture systems compared with the conventional housing system. The fixed and variable costs of building and maintaining a free-stall barn and purchasing and maintaining a mixer wagon were not part of this analysis.

Pasture cost was calculated to be $298.95/ha for rye-ryegrass-clovers, $289.21/ha for rye-ryegrass, $332.80/ha for pearl millet, and $288.91/ha for bermudagrass. The cost ($9.74/ha) for the winter component of system 1 was 3% higher due to the cost of clover seed that was not totally compensated for by additional N fertilization on system 2 (rye-ryegrass-without clovers). Summer pastures of system 1 (pearl millet) had a 15% greater ($43.89/ha) cost than those of system 2 (bermudagrass). Pasture costs were $0.35 and $0.30/d per cow for pasture systems 1 and 2, respectively (Table 5Go).


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  		Table 5. Feed cost and milk income of 2 pasture systems and a confined housing system.
 
The cost of the TMR was $0.093/kg as fed, which calculated to $4.20/d per cow. Average supplement costs for grazing cows were $0.151 and $0.153/kg (as fed), or $1.94 and $1.83/d per cow for systems 1 and 2, respectively (Table 5Go). The greater cost incurred for feeding cows on system 1 was basically due to the cottonseed hull-based supplement fed during the last month of the trial due to a shortage of pearl millet forage.

Milk price was set at $31.95/kg. Greater milk income but greater feed costs of cows in free-stalls compared with those of grazing cows (P < 0.05) resulted in milk income minus feed cost values being not statistically different between the systems, ranging between $5.32 and $5.84/d per cow (Table 5Go). If costs of labor, feeding and harvesting equipment, and housing facilities were included in the analysis, profitability among the dairy management systems would likely differ. In another study, a pasture-based system was economically competitive because costs were reduced, even though milk yield of cows was lower when cows were pastured compared with being confined and fed in a barn (White et al., 2002). Cows on pasture had less clinical mastitis and lower BW and BCS than confined cows; but Holsteins generally had lower BCS, reduced reproductive rates, more mastitis, and higher culling rates than Jerseys in both the pasture and confinement systems (Washburn et al., 2002). Individual dairy producers will need to assess their own situations when making decisions regarding management systems to adopt.


   CONCLUSIONS
TOP
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
 RESULTS AND DISCUSSION
 CONCLUSIONS
ACKNOWLEDGEMENTS
 REFERENCES
 
Cows managed in free-stall housing and fed a TMR produced 19% more milk than cows grazing 2 different pasture systems and supplemented with concentrates during the first 37 wk postpartum. Concentrations of milk fat, milk protein, and milk urea N were not different. During the first few weeks postpartum, cows on pasture lost twice the BW and had lower concentrations of plasma glucose compared with cows in barns. Greater loss of BW was accompanied by increased concentrations of plasma NEFA in cows grazing rye-ryegrass-clover pastures compared with cows fed TMR during the first 4 wk postpartum. Although the planting of clovers along with rye and ryegrass in winter had some benefit in early lactation, benefit to cow performance over the 37 wk postpartum appeared negligible. Although containing more NDF and less CP, well-managed Tifton 85 bermudagrass proved to be of equal or superior value to pearl millet as a summer forage for lactating dairy cows. This was likely due to the shorter season of production and the greater cost of growing millet vs. bermudagrass, and to the relatively high amount of concentrate fed to grazing animals, which likely reduced the impact of grazing higher nutritive forage such as pearl millet. The feed cost of grazing cows was about one-half that of barn-confined cows but milk income was 20% less, resulting in similar milk income minus feed cost values.


   ACKNOWLEDGEMENTS
TOP
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
 RESULTS AND DISCUSSION
 CONCLUSIONS
 ACKNOWLEDGEMENTS
REFERENCES
 
Excellent assistance was provided by staff at the Dairy Research Unit in care of the cows, pastures, and facilities. Sid Jones and Dwight Thomas provided valuable help with field activities. Jocelyn Jennings, Richard Fethiere, and many students provided assistance with collection and analysis of biological samples.


   FOOTNOTES
 
* This research was supported by the Florida Agricultural Experiment Station and approved for publication as Journal Series No. R-10271. Back

Received for publication June 1, 2004. Accepted for publication November 9, 2004.


   REFERENCES
TOP
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
 RESULTS AND DISCUSSION
 CONCLUSIONS
 ACKNOWLEDGEMENTS
 REFERENCES
 


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