January 8-9, 2002

COOPERATIVE AGENCIES AND PRINCIPAL LEADERS: 

State Agricultural Experiment Stations 

University of California E.J. DePeters
University of Illinois J. Drackley
University of Maryland B. Teter 
University of Minnesota L. Metzger 
The Ohio State University D. Palmquist 
South Dakota State University D. Schingoethe
Utah State University T. Dhiman
University of Kentucky S. Franklin
University of Nevada, Reno H. Hussein
University of Arizona L. Baumgard
Iowa State University D. Beitz
North Carolina State University V. Fellner

Administrative 

Administrative Advisor R. Pardini 
USDA-CREES Representative H. Tyrrell 

Collaborators 

California Dairy Research Foundation J. O'Donnell 
Land O'Lakes C. Luhman, P. Porter
Queen’s University, Belfast A. Fearon 

When completed, the minutes will be posted at: www.advs.usu.edu/advs/Dhiman/milkfat.html

STATEMENT OF THE PROBLEM:

The committee members will address cooperatively modifying milk fat composition to enhance manufacturing qualities and to address consumer concerns. To accomplish this efforts will be coordinated to:

1. characterize metabolic regulation of milk fat synthesis and identify those factors, including genetic, that influence functional and nutritional attributes of milk fat; 

2. document changes in milk fat composition induced by manipulating the diet and environment of the cow;

3. and characterize the quality of modified milk fat for manufacturing, sensory, and nutritional properties.

JUSTIFICATION:

Dairy products are an important source of vital nutrients in the human diet. Nevertheless, many health-conscious consumers perceive dairy products to contain excessive amounts of total fat, saturated fat, and cholesterol. Butter and other high-fat dairy products are excluded from diets designed to decrease blood cholesterol and prevent or treat coronary heart disease (Ney, 1991). Dairy products provide only 15% of the total fat in the diet, but 25% of the total saturated fat (O'Donnell, 1993).

This proposed project addresses four goals/objectives outlined by FAIR '95 (1993) which address enhancing the quality of dairy products for human consumption. They are:

Goal 1.  Identify and qualify societal concerns about food products from animals and production systems to enhance communication between consumers and the food industry.

Objective 1. Identify societal concerns that affect the marketplace through food choices.

Goal 2. Meet consumer needs to domestic and international markets for competitive and high quality food products from animals.

Objective 2. Enhance the quality of food products from animals.

Goal 3. Develop integrated food animal management systems and animal health systems that support efficient, competitive, and sustainable production of safe and wholesome food consistent with animal and environmental well-being.

WORK COMPLETED IN 2001

A. Cornell University:

PRINCIPAL INVESTIGATOR: Dale E. Bauman, Department of Animal Science

COLLABORATORS: Dave Barbano, Department of Food Science, Cornell University; Mikko Griinari, University of Helsinki

COOPERATORS: In addition to students and staff in our own group, several studies involved collaborations with other scientists. Additional collaborators during this period were: S. Banni (University Cagliari, Italy), W.R. Butler (Animal Science, Cornell), Y. Chilliard (INRA, France), P.Y.Chouinard (University Laval), J. Drackley (University of Illinois), C. Ip and M. Ip (Roswell Park Cancer Institute, Buffalo), K.L. Houseknecht (Pfizer Inc.), C. Luhman (Land OLakes), T.R. Mackle (Dairy Board, New Zealand), T.R. Overton (Cornell University), B.S. Phillips (ARS/USDA), J.R. Zierath (Karslinska Institute, Sweden).

REGIONAL OBJECTIVES:

1.To identify and characterize important regulatory steps in fatty acid synthesis and desaturation and their positional distribution on glycerol in milk fat.

2.To quantify modification of milk fat composition by manipulating the diet of the cow.

3.To characterize the effects of modified milk fats on physical, chemical, manufacturing and sensory properties of dairy products.

ACCOMPLISHMENTS AND IMPACTS:

Objectives 1 and 2

The uniqueness of ruminant-derived foods as a source of CLA relates to rumen biohydrogenation. CLA is an intermediate in the rumen biohydrogenation of linoleic acid and it had been assumed this was the sole source of the CLA found in milk fat. However, this seemed unlikely based on the kinetics of rumen biohydrogenation and observations that dietary polyunsaturated fatty acids other than linoleic also increased the CLA content of milk fat. We suggested an alternative source could be endogenous synthesis involving the enzyme D9desaturase. The substrate for this reaction would be trans-11 C18:1, another intermediate formed in rumen biohydrogenation. In a series of studies, we manipulated the supply of trans-11 C18:1and altered the activity of D9desaturase under different experimental conditions. Overall, our results indicate that endogenous synthesis is the major source accounting for over two-thirds of the CLA in milk fat (Table 1). Thus, considering rumen production of trans-11 C18:1is critical in attempts to increase the CLA content of milk fat.

Previous studies investigating dietary influences on CLA production have demonstrated a wide range in CLA content of milk fat among individual cows on a given diet. These observations combined with the data on the contribution of endogenous synthesis to milk fat CLA discussed above, led us to investigate the sources of variation in CLA production in dairy cows. Briefly, our study consisted of three groups of animals (n = 10 per group); one maintained on a standard TMR, one maintained on a diet that included extruded full-fat soybeans as a slow-release source of linoleic acid designed to elevate milk fat CLA, and a third group that was switched between these diets at 3 wk intervals over the course of the 12 wk study. The diets gave the expected difference in CLA content of milk fat and similar to previous studies we observed a 2- to 3fold range in CLA concentration in milk fat among individuals on each of the diets. A key observation was the impressive consistency in hierarchy of CLA content among cows over the 12 wk period. As illustrated by the graphic representation for the treatment group that switched between diets, the rank order was maintained over time and across dietary shifts (Figure 1). Also evident in this treatment group was a range in the magnitude of response to dietary shifts among cows; some cows had a minimal response to diet shifts while others increased the content of CLA in milk fat by more than double.