Enhancing Milk Components With Pasture-Based Systems

Dairy producers receive additional payments for increased milk components, primarily milk fat and milk protein. The increased demand for cheese has increased the value of the protein and fat in milk, and dairy producers are searching for feeding strategies to enhance the production of milk fat and protein. A common question is, "Can we feed for higher milk fat and protein content?"

Milk composition is very important to dairy producers with a pasture-based system; since milk volume is often lower, it is important to maintain milk composition. This article will focus on enhancing milk components with pasture-based systems. We must focus on protein and fat yields as well as percentages. Too often, we look at the percentages more than the component yields.

The average yearly production for all Holstein cows on testing or records programs is about 20,400 lbs of milk, 3.15% total protein (649 lbs), and 3.7% fat (759 lbs) For herds with pasture-based systems, total milk yield per cow is usually 1500 to 3000 lbs lower than with confinement systems. Thus, maintaining components is even more important. (Note: True protein instead of total protein is now used. True protein is about 0.2 percentage units less than total protein).

Enhancing Milk Fat and Milk Protein

Many factors affect milk fat and milk protein. Milk fat is altered more by nutrition than milk protein. Altering the milk protein by 0.2% is about the maximum change that we can expect through nutrition.

Table 1 compares nutrition and management factors that affect milk protein and fat percent with a pasture-based system. Some of these factors will be discussed in more detail. If the item has a +, that stands for positive; - for negative; 0 for neutral, and? for not known.

Table 1. Factors affecting milk composition with pasture-based systems.

Dietary Energy

Energy tends to be the first-limiting factor for milk yield for lactating dairy cows on pasture. High energy concentrates are supplemented to increase energy intake and milk yield of cows on pasture. Depending on the type of energy supplement feed, there are varying effects to milk composition. Increasing the energy content of the diet by feeding concentrates will usually increase milk protein percent and yield. This will decrease forage (fiber) intake and milk fat percentage. We recently reviewed ten grazing studies from around the world. Increasing concentrate supplementation decreased milk fat percent in 8 studies and increased milk protein percent in 9 studies. However, the milk fat yield was similar because of the increased milk yield with the supplementation. The general responses to supplementation from these studies are:

• Supplementing pasture with 7 to 12 lbs of concentrate per day decreased milk fat percent by 0.2 to 0.3%. However, milk yield increased by about 7 to 9 lbs/cow/day, thus, milk fat yield increased by about 0.22 lb/cow/day. Milk protein percentage increased 0.1 to 0.2%. With an increased milk yield of 7 to 9 lbs/cow/day, milk protein yield increased from 0.22 to 0.35 lbs/cow/day.
• Supplementing with 12 to 20 lbs of concentrate decreased milk fat percent by 0.3 to 0.5%. Milk yield increased by about 13 to 18 lbs/day, thus, milk fat yield was increased 0.22 lbs/cow/day. Milk protein percentage increased by nearly 0.25%. With the increased milk yield of 13 to 18 lbs/cow/day, milk protein yield increased by over 0.40 lbs/cow/day.

A recent study at Penn State illustrates the effect of concentrate supplementation on milk components (Table 2). Cows fed only high-quality grass pasture averaged 45.5 lbs of milk that contained 3.81% fat and 2.95% true protein. Concentrate supplementation (19 lbs) increased milk yield to 65.6 lbs/day. Milk fat percentage decreased from 3.81 to 3.31%. However, milk fat yield/day was 0.40 lbs/cow/day higher. Milk protein percent was increased 0.15% with supplementation, and the milk protein yield was 50% greater (1.98 vs. 1.32 lb/cow/day). These results are typical of the responses found when supplemental concentrate is fed with pasture.

Table 2. Milk yield and milk component yield of Holstein cows fed pasture or pasture plus 19.1 lb concentrate.

Concentrate (Grain) Source

Feeding starch-based grains (corn, barley), which provide readily fermentable carbohydrates to the rumen, tends to decrease milk fat percent by about 0.1 to 0.2% and increase milk protein percent by about 0.1% when compared with fiber-based ingredients (beet pulp, soy hulls, citrus pulp). In a Northern Ireland study (Sayers, 1999) with high-quality ryegrass pastures, feeding 22 lbs/cow/day of a fibrous-based concentrate vs. 22 lbs of a starch-based grain resulted in higher milk fat (3.62 vs. 2.99%) and lower milk protein (3.34% vs. 3.55%). Milk yield did not differ between treatments. These findings illustrate that when very high-quality pasture is fed, which may be low in fiber, milk fat percentage is depressed. The addition of fibrous feed ingredients to the concentrate supplement was beneficial.

Some of the higher milk protein production with concentrate supplementation may be related to higher energy intake and improved body condition. The greater the negative energy balance and body weight loss, the lower the milk protein.

A study conducted at Penn State (Table 3) fed cows grazing orchardgrass either 18 lbs of ground corn (GC) or ground corn and non-forage fiber (NFF) (12.6 lbs GC and 6.3 lbs NFF). Replacing GC with NFF increased milk fat percentage 0.10% (3.53 to 3.63%) and decreased milk protein 0.04% (3.23 to 3.19%). Based on small numerical differences in milk yield, neither milk fat nor milk protein yields were different. Milk yield and DMI were similar for cows fed both supplements.

Table 3. Feeding non-forage fiber (NFF) to lactating dairy cows on pasture.

Grain Processing

The general responses to milk components with grain processing are:

• Steam flaking of corn increases rumen availability of carbohydrates, decreases milk fat percent, and increases milk protein.
• Fine grinding of corn decreases milk fat percent and increases milk protein percent. Milk yield is often increased, thus, milk component yields may be increased.

A study was conducted at Penn State, replacing cracked corn with steam-flaked corn for lactating cows grazing orchardgrass. There was no statistical difference in milk composition for cows fed cracked or steam-flaked corn. The numerical values are shown in Table 4 and may indicate some of the expected trends of milk composition when feeding steam-flaked corn.

Only a few studies have been conducted feeding steam-flaked corn to lactating dairy cows on pasture. Most studies have not indicated major differences in milk yield. However, studies to date have been done with low-producing dairy cows.

Table 4. Grain processing effects on milk composition

Forage Supplementation

Corn Silage

Corn silage is high in fermentable carbohydrates and low in protein and thought to be complementary to pasture diets. Results are mixed, but a study at Penn State feeding corn silage and high levels of concentrate showed no difference in milk yield, milk fat, or milk protein.

Hay Supplementation

The fiber content of the diet is thought to be a key factor in high milk fat content and maybe even more important when the high quality, highly digestible fiber of pasture is combined with concentrate, usually fed in two large slugs a day. However, supplementing pasture with hay seems to have little effect on milk yield, milk fat, or milk protein. This means that lower milk fat content usually seen on pasture may be due to more than just fiber content of the diet.

Partial TMR

Many dairy producers in the U.S. supplement pastures by feeding a partial total mixed ration (TMR), which complements the nutritional profile of pasture. A recent 21-week study at Penn State compared pasture plus 18 lb of concentrate with pasture (cows grazed half days) plus a partial TMR (Table 5). Cows supplemented with the partial TMR produced 8 lb more milk/day, and the milk was 0.22% higher in milk fat percent and 0.13% higher in true milk protein. The partial TMR appeared to provide added fiber and energy, which had a positive influence on rumen fermentation and milk yield and components.

Table 5. Pasture plus concentrate vs. pasture plus a partial TMR for Holstein cows.

Milk Fat Depression

Milk fat is typically lower for cows fed high-quality pasture as compared to cows receiving stored forages. Pasture, in combination with high-energy concentrates, can cause severe milk fat depression (usually indicated by a milk fat:protein inversion). There are many theories explaining milk fat depression. One theory states that milk fat depression is caused by the direct effects of a fatty acid produced in the rumen under specific conditions on the mammary gland. The theory states that under feeding conditions that cause a low pH in the rumen and high levels of unsaturated fat, a fatty acid is produced (trans-10, cis-12, CLA) that directly reduces milk fat. Pasture provides high levels of unsaturated fat, and if high levels of concentrate are fed, milk fat depression may result. In a study conducted at Penn State (unpublished) with lactating cows grazing high-quality alfalfa and fed 17 lbs of concentrate, milk fat, and protein averaged 2.64% and 2.83%, respectively.

Fat Supplementation

Providing supplemental fat to lactating dairy cows on pasture may increase energy intake, improve energy efficiency, reduce the risk of acidosis, and alter the fatty acid composition of milk. In a recent review, we found that feeding supplemental fat can increase milk yield; however, there is a large range of effects. Milk fat composition changes are dependent on the type of fat. Saturated fat sources tend to increase milk fat composition (0.15%), while feeding unsaturated fatty acids decreases milk fat composition (0.20%). Feeding supplemental fat in confinement generally reduces milk protein concentration. Under grazing conditions, milk protein tends to be lower, but not to the same extent found in confinement studies.

Milk Fatty Acids - CLA

Over the past several years, reducing dietary fat intake has been a focus of human health issues. One method to reduce fat intake is to minimize fat consumption in dairy products. Consumers have the choice of many low-fat dairy products, including milk, cheeses, and ice cream, and can also switch from butter to margarine. However, research indicates that conjugated linoleic acid (CLA), a type of fatty acid in dairy products, can benefit human health. Current research has revealed a positive role of CLA in the fight against cancer, and CLA is the only fatty acid shown to inhibit carcinogenesis. The inclusion of CLA in the human diet generates anti-carcinogenic effects by inhibiting some types of cancer, including skin, prostate, and mammary cancers in animals.

The dairy cow's unique digestive system has billions of microorganisms in the rumen to break down feed for utilization by the cow. With this process, it is possible for a common dietary fatty acid, linoleic acid, to be changed to CLA through the action of microorganisms in the rumen. This fatty acid is incorporated into the milk fat of cows and, ultimately the dairy products for human consumption. CLA is especially high in milk and suggests an enormous marketing opportunity, particularly if levels of CLA can be increased in dairy products.

Factors affecting CLA levels in milk are shown in Table 6. Researchers are evaluating several nutritional factors that can increase CLA content in milk. Most of these efforts are in the nutrition area. Feeding fresh pasture increases the level of CLA in milk. Research at Penn State in cooperation with Cornell (Kelly et al., 1998) found a two-fold increase in CLA in milk when cows were fed pasture as the sole forage compared to a TMR. Wisconsin and Virginia researchers reported a similar finding.

Supplementation of diets with various dietary fat sources increases CLA in milk. CLA content of milk with pasture-fed cows was further increased by supplementation of mechanically extracted soybean meal compared to solvent-extracted soybean meal. Other factors can increase CLA in milk and are shown in Table 6.

Table 6. Factors affecting CLA concentrations in milk fat.

1.CLA increases may be due to both addition of lipid substrate and modified rumen environment.

2.CLA increases may be due to a modified rumen environment.
3.CLA increases may be due to addition of a lipid substrate.

Conjugated linoleic acid provides new opportunities in cancer prevention, and milk fat is the richest natural dietary source of CLA. However, questions remain unanswered as to how best to deliver CLA in the human diet. Pasture-based forage systems and direct supplementation of various fat sources show promise for increasing the content in dairy products. In addition, CLA may improve the public's perception of dairy products.