Assessment of Value Added Milk from Pasture-based Dairies

Assessment of Value Added Milk from Pasture-based Dairies

Summary

Growing evidence suggests that conjugated linoleic acid (CLA) is a potent anticarcinogenic compound. Milk fat is the richest natural dietary source of CLA. Results from our research suggest that milk from pasture-based dairies is high in CLA. The CLA contents in milk were higher in summer months than in winter months. The consumer acceptability characteristics (flavor, taste, texture, color, and overall quality) of CLA-enriched milk and cheese produced from cows grazing on pasture was the same as milk and cheese from cows fed conserved forages and grains. The higher CLA in milk from grass-fed cows means higher nutritive and therapeutic value.

Objectives/Performance Targets

OBJECTIVE 1:
To assess the year-round supply and value of CLA-enriched dairy products produced on pasture-based dairies.

OBJECTIVE 2:
To characterize physical, chemical, and sensory properties of CLA-enriched dairy products

OBJECTIVE 3:
To assess the market values of CLA-enriched milk, cheese, and butter.

Accomplishments/Milestones

Objective completed:
Results are summarized below:
A 2-year experiment was conducted to study the status of milk fat c-9, t-11 conjugated linoleic acid in four commercial dairies of Utah and Idaho. Farms A and C grazed the cows on pasture and supplemented with 7.0 kg/cow per day of a grain mix during summer and fed conserved forage and their respective grain mix during winter. Farm B fed a total mixed diet all year, with 10% of diet dry matter as fresh cut pasture during summer. Farm D had one-third of its cows gazed and supplemented with a total mixed diet while the rest were fed a total mixed diet during summer with all cows fed a total mixed diet during winter. Farms A, B, C, and D had on an average 90, 400, 150, and 500 milking cows with Holstein or its crosses as the major breed in all the farms. Farms A and C produced milk with 60% or more milk fat c-9, t-11 CLA and TVA contents on year round basis compared with farm B. Similarly, farm D produced 30% or more c-9, t-11 CLA and TVA in milk compared with farm D. Individual cows varied from 0.16 to 2.22% in milk fat c-9, t-11 CLA contents and 89% of the cows had c-9, t-11 CLA contents between 0.3 and 1.0% of milk fat. Individual cow variation was larger in farms A and C compared with farms B and D. Variation was larger in summer than in winter. The bulk tank milk c-9, t-11 CLA content varied from 0.27 to 1.35% of milk fat. Milk supply was highest from November through January while the supplies of c-9, t-11 CLA and TVA were highest from June through September. Milk fat c-9, t-11 CLA and TVA contents and their supply were lowest from January through March, which should be the months for targeting the improvement on the content and supply of milk fat c-9, t-11 CLA and TVA.

Objective 2 completed:

Summary:
Two experiments were conducted to determine physical, chemical and sensory properties of CLA- enriched milk and cheese.

Experimental approach
Experiment 1
Fifteen dairy cows were assigned to three treatments and fed either a mixed diet containing 51% conserved forage and 49% grain diet (TMR), grazed on pasture (PS) or received 3.2 kg/day of grain supplement while grazing on the pasture (PES). Grain supplement in PES treatment contained 75% full-fat extruded soybeans, 10% sugar beet pulp, 10% ground corn, and 5% molasses. Experimental duration was 7 wk. The diets were designed to produce low CLA milk in TMR and high CLA milk in PS and PES treatments. Cows in PES treatment were given full-fat extruded soybeans with the intent of further enhancing the CLA content of milk from cows grazing on pasture only. Milk from two consecutive a.m. and p.m. milkings was collected from individual cows during week 5 through 7 of the experiment and mixed for each treatment. Milk was pasteurized, homogenized, vacuum packed, and refrigerated at 4°C for 3 days before being used for physical and sensory evaluation by an open and trained panel of judges. Average CLA contents in milk were 5.2b, 16.2a, and 16.9a mg/g of fat for TMR, PS, and PES treatments, respectively.

Experiment 2
Eighteen dairy cows were assigned to three treatments and fed either a mixed diet containing 51% conserved forage and 49% grain diet (TMR), grazed on pasture (PS) or received 2.5 kg/day of full-fat extruded soybeans while grazing on pasture (PES). Cow feeding, duration of the experiment and milk collection procedures were the same as described in experiment 1. Milk collected during week 5 and 7 was used to manufacture cheddar cheese. To make 4 replicates of cheese/treatment, cows were further randomly blocked into 2 groups per treatment and milk collected twice during week 5 through 7 was used for cheese manufacturing. Cheese blocks weighing an average of 30 kg were vacuum packaged and refrigerated at 4ºC. Cheese had 4.7b, 15.7a, and 14.6a mg of CLA/g of fat for TMR, PS or PES diet, respectively.
An open panel of consumers (n=75) evaluated CLA- enriched milk (mouth-fill, color, flavor, and overall quality) and cheese (color, flavor, texture, and overall quality) from experiment 1 and 2, respectively, on a hedonic scale of 1-9. A trained panel evaluated the milk (n=8) and cheese (n=7) for evenness of color, flavor, and overall quality in a scale of 1-10.

Results:
• Feeding full-fat extruded soybeans to cows grazing on pasture failed to further enhance the CLA content of milk from cows grazing on pasture alone.
• Evaluation by open and trained panel of judges suggested that the CLA-enriched milk and cheese produced from cows grazing on pasture had no different color, flavor, texture and overall quality than low CLA milk and cheese from cows fed conserved forages and grains.
• Results from open and trained panel of judges also suggested that milk from cows fed full-fat extruded soybeans (PES) had similar flavor, color, and overall quality as milk from cows fed conserved forage and grain (TMR) or grazed on pasture (PS).
• However, cheese made from cows fed full-fat extruded soybeans while on pasture had perceived oxidized flavor compared with cheese made from cows grazed on pasture only (PS) or fed conserved forage and grains.

Conclusion:
The consumer acceptability characteristics of CLA- enriched milk and cheese produced from cows grazing on pasture was the same as milk and cheese from cows fed conserved forages and grains.

The objective is in progress.

Impacts and Contributions/Outcomes

1. The content and yield of CLA in milk from pasture based daries in Utah and Idaho were high in summer when green grass was available compared with winter months.

2. Dairy producers need to adopt feeding practices for dairy cows that will enhance the CLA content of milk in winter months.

3. The consumer acceptability characteristics (flavor, color, taste, texture, and overall quality) of CLA-enriched milk and cheese produced from cows grazing on pasture was the same as milk and cheese from cows fed conserved forages and grains.

Publication:
R. C. Khanal, T. R. Dhiman, C. Brennand, R. L. Boman, and D. J. McMahon. 2002. Consumer acceptability characteristics of conjugated linoleic acid (CLA) enriched milk and cheese. J. Dairy Sci. 85 (Suppl. 1):142, Abstract.