Examining pasture-based dairy systems to optimize profitability environmental impact, animal health and milk quality

Examining pasture-based dairy systems to optimize profitability environmental impact, animal health and milk quality

Summary

This report covers progress through 2 years of a 3-year study. Optimal grazing strategies require an appropriate balance between stocking rate and per cow performance in pasture-based dairy systems. This project was established to focus on questions that limit current grazing systems such as: forage species and quality, stocking rates, nutrient supplementation strategies, and use of crossbreeding. At the Center for Environmental Farming Systems in Goldsboro NC, 2 fall-calving 40-cow herds were established each year for 3 years. Based on soil maps to ensure comparable percentages of similar soil types, paddock areas were carefully defined to allow one herd access to 40 acres (1 cow/acre) and the other herd access to 27 acres (1.5 cows/acre) of pasture. Cows in each group included Holsteins, Jerseys, and crosses of those breeds. Cows at the higher stocking rate have less pasture forage available and are provided supplemental concentrates at a higher rate than the herd at the lower stocking rate. Pasture types for the grazing paddocks were set to include 50% summer and winter annuals, 30% fescue clover mix, and 20% Bermudagrass over-seeded with annual ryegrass in winter. Paddock areas were arranged to allow multiple rotational subdivisions so that cows would have access to fresh pasture allowances after each milking. Areas for each group were designated as a winter sacrifice area for feeding supplemental forage when pastures were limiting. Shade paddock areas were also designated for summer. Preliminary information revealed that cows at the higher stocking rate with more supplemental concentrate generally yield more milk (but not always) compared to the cows with more pasture and less supplement. Respective percentages of fat and protein have not been markedly different. However, multiple years of data and careful statistical and economic analyses will be required to ascertain if there are economically significant differences in production variables. Breed differences were as expected with Holsteins > crossbreds > Jerseys. Cow fertility was similar across stocking rates but crossbred cows had higher conception rates than either Holsteins or Jerseys in the first breeding season. There is also evidence that fewer Holstein cows were cyclic by 60 days after calving compared to Jersey and crossbred cows. Data from the third year are currently being collected and will include observations of grazing behavior across breed groups. Cows at the low stocking rate appeared to have greater protection against oxidative stress based on lower lipid hydroperoxide production and higher antioxidant activities in blood. Further analyses and summarization of the antioxidant data are in progress at Va Tech. In a starch supplement trial at Clemson, cows receiving citrus pulp plus molasses or barley plus molasses produced similar amounts more milk than cows receiving corn. Thus, if barley or citrus pulp are less expensive than corn, they may be viable replacements for corn in supplementingr grazing cows. Pasture and milk samples are being collected from 8 dairy grazing farms in SC, NC, and VA. Those samples will be analyzed for fatty acids, particularly for conjugated linoleic acid (CLA), a fatty acid found in milk from cows that graze that has been shown to have potent anticarcinogenic properties. We will determine the correlations between amounts of fatty acids in forages and milk CLA content. We will be also be analyzing the fatty acid content of different forages so that we can predict milk CLA content.

Objectives/Performance Targets

1). Examine and quantify factors affecting economic and production efficiency of environmentally sound pasture-based dairy systems in the region;
2). Characterize potentially beneficial differences in the composition of milk produced under pasture-based production systems;
3). Characterize the antioxidant components of forages and their impact on cow immunocompetence and health;
4). Provide interactive educational programs for dairy producers and industry leaders to enable them to make informed production and management decisions.

Accomplishments/Milestones

Preliminary discussion of some aspects of the project were presented at part of the American Forage and Grassland Council/Mid-Atlantic Dairy Grazing Conference in Roanoke, VA in June 2004.

Data on fertility of cows of the various breed groups used in this project were reported in October, 2004 as part of a national cooperative research project: “Genetic Selection and Crossbreeding to Enhance Reproduction and Survival of Dairy Cattle.”

Information about the project has also been shared with many visitors to the dairy unit at the Center for Environmental Farming Systems (CEFS) in 2004 and 2005. These have included a faculty group from Auburn, Alabama A&M, and Tuskegee Universities, the NC Board of Agriculture, an external review team evaluating dairy research programs in NC, two groups of NCSU veterinary students, two groups of NRCS workers studying Pastureland Ecology, 24 CEFS student interns, representatives of the NC Environmental Defense, a faculty group from University of Louisiana- Lafayette, a group of agents and livestock producers from Northeastern NC, a group of 12 agricultural workers from Turkey as part of a short course, 10 Dairy Science Club students from NCSU, CEFS external stakeholders, two groups of NC dairy producers, and many other individual visitors. The CEFS dairy project was one of four dairy articles featured on August 17, 2004 in the on-line magazine, New Farm: http://www.newfarm , published by the Rodale Institute. Project updates have been included in the CEFS quarterly electronic newsletter and Dairy Extension News, the quarterly dairy newsletter of the Department of Animal Science.

The project hosted an animal science student intern from Peru during the breeding season for cows calving in the second year of the project. Also, 2 student interns from Brazil have participated in the project. Three graduate students have had research projects associated with the work at CEFS.

Two abstracts were published in the Proceedings of the 2005 joint meeting of the American Dairy Science Association (ADSA) and the American Society of Animal Science (ASAS) and an additional abstract will be presented at the ADSA/ASAS meetings in 2006.

Gehman, A. M., J. A. Bertrand, T. C. Jenkins, and B. W. Pinkerton. 2006. Effects of starch sources on nitrogen capture in dairy cows on pasture. J. Dairy Sci. 88: (Suppl 1): 98 (Abstr.).

Saker, K. E., J.H. Fike, S.P. Washburn, and A. Meier. 2005. Immune function and oxidative stress vary by management and lactation stage for dairy cows in a pasture-based production system. J. Dairy Sci. 88 (Suppl 1): 374 (Abstr.).

Williams, C. M., S. P. Washburn, A. N. Elias, and C. S. Whisnant. 2006. Breed differences in postpartum cyclicity of pasture-based dairy cows. J. Dairy Sci. 89: (Suppl 1): Abstract in press.

The Clemson experiment to evaluate different starch sources for grazing cows has been completed and a manuscript has been submitted and accepted for publication in the Journal of Dairy Science. Briefly, the objective was to determine if feeding carbohydrate supplements with faster degradation rates than corn to dairy cows grazing ryegrass would improve nitrogen capture, milk production and components. Treatments were grain supplements based on: (1) corn, (2) barley and molasses, or (3) citrus pulp and molasses for cows grazing annual ryegrass pasture. Yield of milk, 3.5% fat-corrected milk, energy-corrected milk, and milk fat, as well as milk fat percentage, were not different among treatments. True milk protein percentage was slightly higher for the corn supplement (2.81%) as compared to the citrus pulp and molasses (2.70%), but was not different for barley and molasses (2.77%). However, true milk protein yield was similar among treatments. Milk urea N was higher for the barley and molasses supplement (11.43 mg/dL) compared to the other supplements (average: 9.95 mg/dL). There were no differences among treatments for overall BUN (average: 10.60 mg/dL). However, at 0400 h, cows receiving corn had higher BUN than cows on citrus pulp plus molasses (11.43 vs. 9.96 mg/dL), but there were no differences among treatments at other sampling times. Partial replacement of corn with citrus pulp for grazing cows should be further studied using pasture with higher CP content. Although cows receiving citrus pulp plus molasses or barley plus molasses did not produce more milk than cows receiving corn, if barley or citrus pulp are less expensive than corn, then substitution of those for corn may be a viable option for grazing cows.

Gehman, A. M., J. A. Bertrand, T. C. Jenkins, and B. W. Pinkerton. 2006. The effect of carbohydrate source on nitrogen capture in dairy cows on pasture. J. Dairy Sci. 89: In press

Impacts and Contributions/Outcomes

This SARE project is expected to be of interest to many dairy graziers throughout the United States. It has served and will continue to serve as a training site for farmers, student interns, and graduate students with interests in sustainable agricultural systems.

The Mid-Atlantic Dairy Grazing Conference will be hosted at the research site at CEFS on October 31-November 1, 2006. This event will include dairy graziers from several states as well as researchers and other professionals working with dairy grazing systems. The results shared at this event and in subsequent publications should strengthen the network of information transfer in support of dairy grazing systems.

Collaborators: