RESEARCH RESULTS

Longitudinal comparison of milk fatty acid composition and conjugated linoleic acid levels among three different management systems

Investigator: Linda Tikofsky, DVM, Quality Milk Production Services, Cornell University, Ithaca, NY
Project location: Central New York State

Project links: Complete project report (8 pp) submitted by Linda Tikofsky.

OFRF funding for this project was awarded in Spring 2004.

Summary
Milk is a generous source of valuable nutrients and consumers are becoming more aware of the link between diet and health. Omega-fatty acids and conjugated linoleic acid (CLA) have been shown to have beneficial impacts on human health. Many seek out organic meat and milk products and expect that these products will have greater health benefits than conventionally produced products. Since access to pasture is a requirement of organic production, one would expect organic dairy products to have enhanced levels of the ‘functional food’, conjugated linoleic acid. 

Linda Tikofsky/Cornell University
Cornell University dairy cow herd, July 2006.

The objective of this study was to determine if there was a difference in vitamin A, vitamin E. conjugated linoleic acid and other fatty acids among milk from certified organic, conventional grazing, and conventional non-grazing herds in a region of New York state. 

Eight certified organic (O), five conventional grazing (G) and four conventional non-grazing (NG) herds located in Central New York state were invited to participate in the study. All farms were visited monthly on two consecutive days each month from November 2005 to October 2006.  At each farm visit, a bulk milk sample was collected into a 236 ml sterile container after five minutes of agitation and was placed on ice in a cooler for transport back to the laboratory.  At the laboratory, a 30 ml aliquot of milk was removed from each sample and submitted for somatic cell counting. All  remaining milk samples were stored at -80 degrees C until submitted for analysis. Milk production and diet information was collected at each farm visit. One organic herd and one grazing herd dried all cows off from January until March; data for these herds is limited to eight months.

Production data, diet information (including pound of dry matter from pasture) and number of animals milking were collected from each farm at each visit.

198 samples were shipped on ice by overnight express to the Nutrition Section of the  Diagnostic Center for Population and Animal Health at Michigan State University (Lansing, MI).

Fatty acid and vitamin A and E content of the milk samples were analyzed.

Key findings

• Because of the high level of dry matter intake provided by pasture in organic cow diets, we expected to see significant elevations of beneficial fatty acids, vitamin A and vitamin E in organic milk during the grazing season and decreasing levels as percentage dry matter intake from pasture decreased in diets. However, this was not our finding. 
• All herds experienced an increase in vitamin A and vitamin E levels in milk during the spring and summer months which decreased during the winter housing season.
• Although not significant in most cases, there was a tendency for organic milk to be higher in poly-unsaturated fatty acids (PUFA) and in two of the omega-3 fatty acids [α-linolenic and eicosapentoic (e.p.a)] during the grazing season.
• There were no differences in the percentage content of the two CLA isomers among the three groups.
  
• We did note increased ­trans-vaccenic acid (TVA;C18:1, trans-11) in milk from organic herds in June and July.  TVA is a precursor to cis-9, trans-11 CLA and has been shown to be protective against mammary cancer in rats.
  

Small sample size likely had an impact of the results of our study since we were constrained by finances and the number of farms that could be visited in a 48-hour period monthly.  Our study included only 17 farms in total.

A multitude of factors influence the fatty acid and vitamin content of bovine milk, including farm management, season, geography, diet and breed.  Many of these aspects are not easily quantifiable.  This study did not elucidate statistically significant differences in milk from three management styles.  However, milk from cows with a high percentage of dry matter intake coming from lush pasture did tend to have higher levels of some nutrients beneficial to human health.  A larger study, limited to the grazing season and including more frequent sampling, would be necessary to confirm the trends seen here. 

A final report describing the results of this project was submitted in August 2009.