Economic conditions in the dairy industry are challenging farmers to reduce costs and thus increase profitability. Research indicates that pasture-based dairies are an economically competitive management system (White et al., 2002). Pasture-based systems have fewer incidences of mastitis, lower feed and capital costs, and are more efficient in operating and labor costs (Ford, 1996; Dartt et al., 1999). In recent years, pasture-based operations have been adopted by 10 to 20% of dairy producers in the Northeast and Midwest (Handson et al., 1998). With increasing pasture-based dairy operations, there is a demand for high quality forages that can expand the grazing season.

In addition to the economic benefits of pasture-based dairies, the potential health properties of dairy products from intensively grazed cows are promising. Nutritional studies indicate that cattle grazing fresh forage produce milk that contains higher levels of Conjugated Linoleic Acid (CLA) than compared with hay or concentrate. CLA is a naturally occurring fatty acid found in foods derived from ruminants (AbuGhazaleh et al., 2002). A particular isomer of CLA, cis-9, trans-11, is thought to be anti-carcinogenic, anti-atherosclerotic, and anti-inflammatory.

Currently, it is unknown why cattle grazing fresh grass produce milk with greater CLA content than those fed either hay or concentrate. Forage species may have an influence on this increase. Previous research suggests that red clover has the potential to increase CLA content more than grass paddocks alone (Wu et al., 1998). Yet, there is little research investigating the differences in other forage species.

Stockpiling autumn grown forage for deferred grazing is a low cost substitute to hay and can create an excellent source of feed during the winter. This practice fits well in seasonal dairies to reduce feeding costs and supply dairy quality feed. Also, the greater time spent grazing fresh grass may improve the CLA content of milk. Research conducted at the University of Missouri suggests that stockpiled annual ryegrass and cereal rye are excellent forages for late winter and early spring grazing because they retain excellent quality through the winter and have rapid autumn growth. However, there is virtually no information that documents the yield and CLA quality of milk produced by dairy cows when grazing these forages. The objective is to determine the yield and quality of milk produced by dairy cows rotationally grazed on annual ryegrass and cereal rye pastures.

This experiment is designed to compare the production and performance of two rotational grazing systems: one based on stockpiled annual ryegrass; the other based on stockpiled cereal rye. The variables of this experiment include: 1) length of grazing season, 2) yield and 3) quality of the forages; 4) supplement intake, 5) body weight, 6) milk production and 7) milk composition of the dairy cattle.

Materials and Methods

This experiment was conducted during a 12-week period from March to June at the Southwest Research and Education Center. The study used 30 dairy cows in early lactation that had been exposed to intensive grazing during previous seasons. The cattle were divided into six groups based on calving date, breed and milk production. Treatments included rotationally grazed 1) stockpiled annual ryegrass and 2) stockpiled cereal rye. Each treatment was replicated three times in six four-acre pastures that were subdivided into sixteen paddocks of equal size. Animals were rotated between paddocks on a 12-hour grazing schedule based on forage availability. Additional cows were added to paddocks as needed to maintain equal forage availability between treatments. In addition to stockpiled pasture, cows received 14 pounds of grain supplement while in the milking parlor.

On 3 September 2003, Roundup was applied to kill existing vegetation. The annual ryegrass and cereal rye were no-till seeded on 10 September at 35 and 120 lb/acre pure live seed, respectively. Pastures were fertilized with 75 lb/acre N as ammonium nitrate. Each pasture was fertilized again on 19 March with 50 lb/acre N as ammonium nitrate to stimulate spring growth.

Results and Discussion

These are preliminary results presented that represent only one year of data. In the fall 2003, ideal weather produced an abundance of fall growth, and may have produced atypical results particularly for the annual ryegrass treatment.

Forage Yield. Cereal rye began growth earlier in the spring and was able to sustain approximately 2 cows/acre/day, which was 0.65 cow/acre/day more than annual ryegrass (Figure 1) from March to May. Also, annual ryegrass growth in early spring was slower and thus a two-week rest period in early April was needed to allow it to recover. However, over the entire grazing season, annual ryegrass gave 14 days more use than cereal rye.

Forage Quality. A preliminary test on stockpile quality was preformed on 20 January 2004 (Table 1). The results concluded that both annual ryegrass and cereal rye could sustain a dairy cow in early lactation provided some grain was fed to supply additional energy. Forage quality samples from the rest of the season are still being analyzed.

Milk production and composition. There were no treatment differences in daily milk yield, (67 lb milk /cow/day) or in milk yield per acre (7920 lb/acre of milk). There were significant differences in milk fatty acid composition. CLA (Figure 4), C18:1 11t (Figure 5), and C22:4n6 (Figure 6) in milk were elevated when cows grazed annual ryegrass. In late May, milk from cows grazing annual ryegrass contained 14.2 mg CLA/g of fat, 30 % more CLA than milk from cows grazing cereal rye.

Summary

Results of this study show that both cereal rye and annual ryegrass are practical forages for late winter-early spring on pasture based dairy operation. While cereal rye was a better late winter forage, annual ryegrass persisted longer into the spring season. This study also stresses the importance of further research on forage species and fatty acid content and fall management of accumulated forages.

References

Table 1. Preliminary forage quality analysis of annual ryegrass and cereal rye from January 20 based on a DM basis

Figure 1. Comparison of stocking rates for 1000 lb. unit dairy cows in early lactation grazing annual ryegrass (ARG) and cereal rye (CR)

Figure 2. Estimated pounds DM per acre from forage harvested from annual ryegrass (ARG) and cereal rye (CR) pastures with a flail-type harvester

Figure 3. Comparison of milk production on 4% fat corrected basis for cows in early lactation grazing annual ryegrass (ARG) and cereal rye (CR).

Figure 4. Comparison of CLA content expressed in mg/g of fat for cows grazing annual ryegrass (ARG) and cereal rye (CR) It takes 3 g/d for CLA to have effective health benefits to humans.

Figure 5. Comparison of C18:1 11t content expressed in mg/g of fat for cows grazing annual ryegrass (ARG) and cereal rye (CR)

Figure 6. Comparison of fatty acid C22:6n4 content in milk content expressed in mg/g of fat for cows grazing annual ryegrass (ARG) and cereal rye (CR)