MANAGEMENT OF LOW MILK FAT SYNDROME IN A DAIRY HERD

Pashu Sandesh, 24th June 2018

Dr M Areshkumar

Introduction:

Fat and milk protein are the most valuable milk components. Several factors can contribute to change the proportion and total amount of fat and protein in the milk. The most common include genetic makeup, environment, health, and nutrition. The fat content in milk can be altered positively or negatively by dietary changes. Diets formulated to maximize milk production utilize a high proportion of concentrates and/or a high content of specific fatty acids. Sometimes, these energy-rich diets can exert negative effects on milk fat, causing low milk fat syndrome, widely known as milk fat depression (MFD). Several theories have been put forth to explain the cause of LMF and to suggest how to avoid the problem. The objectives of this publication are to review some of the dietary factors that induce LMF and explain how to troubleshoot this problem.

Fat:

Lipids or Fats are greasy materials occurring widely in nature. They are generally insoluble in water but soluble in fat solvents. They include substances like,

1)      Naturally occurring fats, e.g., butter and oils.

2)      Substances which are chemically related to fats but differ in certain common properties, like lecithin, a waxy substance, soluble in fat solvents, and also mixing well with water, to form a colloidal solution.

3)      Substances which are related to fats, because of certain common properties like solubility and biological origin, but differ from fat in appearance and chemical nature, e.g., Cholesterol.

4)      Oils which are liquid at room temperature.

Milk fat:

Milk contains approximately 3.4% total fat. Milk fat has the most complex fatty acid composition of the edible fats. Over 400 inpidual fatty acids have been identified in milk fat. However, approximately 15 to 20 fatty acids make up 90% of the milk fat. The major fatty acids in milk fat are straight chain fatty acids that are saturated and have 4 to 18 carbons (4:0, 6:0, 8:0, 10:0, 12:0, 14:0, 16:0, 18:0), monounsaturated fatty acids (16:1, 18:1), and polyunsaturated fatty acids (18:2, 18:3). Some of the fatty acids are found in very small amounts but contribute to the unique and desirable flavor of milk fat and butter. For example, the C14:0 and C16:0 ß-hydroxy fatty acids spontaneously form lactones upon heating which enhance the flavor of butter.

Fat appears in milk through two major routes:

1) Fat consumed by the cow or stored in the adipose tissue is absorbed into the bloodstream. The mammary gland then moves these fats from the blood directly into milk. About half of the 16-carbon fatty acids and all longer-chain fatty acids in milk come from the diet or fat reserves.

2) The mammary gland can synthesize short- and medium chain fatty acids by pulling compounds from the blood that were produced in the rumen during fermentation of feed by resident microorganisms.

Alteration in fat content:

Milk fat may be depressed in cows as a result of insufficient dietary energy intake, especially during early lactation. Cows in good flesh during the early lactation have higher milk fat percent than cows that enter lactation in thin condition. Most high-producing cows lose weight during this interval; therefore, energy intake should be maintained as high as possible without causing the cows to go off feed. When the loss in body fat is too rapid, ketosis can occur.

 

Low Milk Fat Syndrome Theories:

Low Milk fat syndrome is generally observed when dairy cows are fed diets containing a high proportion of concentrates (particularly readily fermented sources of starch), a low proportion of forages or forages that are finely chopped, and a moderate to high proportion of unsaturated fatty acids.

The first theory suggested that microorganisms in the rumen do not produce enough acetic and butyric acids so that the mammary gland synthesizes less fat to put into the milk. This theory was largely based on the knowledge that feeding high grain/low forage diets produces a less proportionate amount of acetic acid and a greater proportionate amount of propionic acid. Further research disproved this theory.

A second theory suggested that the greater proportionate amount of propionate produced when cows are fed high grain diets resulted in a greater amount of glucose produced by the liver. This, in turn, increases the hormone insulin in blood, which partitions nutrients away from the mammary gland in favor of muscle and fat tissues. This theory was rejected after studies demonstrated that cows given insulin did not suffer from LMFs.

A more current theory is that the combination of high grain and high unsaturated fatty acids in the diet causes the microorganisms in the rumen to produce more Trans fatty acids. Some of these Trans fats have suppressive effects on fat synthesis in the mammary gland. This theory was confirmed after scientists induced LMFs by infusing these Trans fats directly into the abomasum of dairy cows.

Low forage, high concentrate diets cause the rumen fluid to be more acidic, which alters the microbial population because some bacteria are sensitive to acidic conditions. The shift in rumen micro flora favors accumulation of Trans fatty acids that can depress milk fat synthesis after absorption into the blood.

 

Avoiding Milk Fat Depression:

Within a given herd, environment and nutrition are likely to explain most of the variation in bulk tank milk fat content from day to day. In hot climates, the summer months typically result in depression in milk fat concentration. Although the exact mechanisms are not entirely clear, it is thought that reductions in milk fat during hot months are the result of changes in eating patterns of dairy cows and reduced buffering capacity of saliva because of panting. It is also possible that increased body temperature during heat stress might have a direct effect on fat synthesis by the mammary gland. Therefore, proper cooling of cows is critical for producing milk in hot environments. This requires shade, forced ventilation, and evaporative cooling.

Because the two basic conditions for LMFs are the consumption of polyunsaturated fatty acids and an acidic ruminal environment, measures to minimize milk fat depression should focus on identifying the nutritional components (diet formulation or dietary management) that favor those two conditions.

Dietary Unsaturated Fatty Acids

Polyunsaturated fatty acids are commonly present in dairy cattle diets. Vegetable oils present in grain byproducts and oilseeds as well as fish oil from fishmeal are common sources of unsaturated fatty acids implicated with LMF. The contribution of high-fat byproducts can be more problematic given the variability in composition of some of them. Increased use of distiller’s grains from either corn or sorghum, which have between 8% and 14% crude fat, has been the culprit causing LMF on many farms. In order to minimize the risk of LMF, the amount of polyunsaturated fatty acids present in the diet should be controlled. In many cases, the total dietary fat in lactating cow rations should be less than 6% of the dry matter, and less than 3% is suggested to be unsaturated fatty acids.

Balancing Dietary Carbohydrates

Excessive amounts of fermentable carbohydrates, particularly starch, can depress rumen pH and favor LMF. Most lactating cow diets contain approximately 35%–40% non-fiber carbohydrates of which 70%–75% is from starch, with the remainder provided by sugars and soluble fiber. Excessive starch feeding (i.e., diets with > 28% starch) predisposes cows to MFD. This is particularly important when the starch source is rapidly fermentable in the rumen, such as that from extensively processed grains (steamflaking or finely ground) or grains harvested with high moisture (high-moisture corn).

On the other hand, diets that provide sufficient fiber, particularly from forages with long particle size that stimulate cud chewing and saliva production, maintain a more stable rumen environment and favor milk fat synthesis. Typical dairy cattle diets contain 40%–55% forage, and the dietary fiber (neutral detergent fiber) from forage sources should make up at least 20% of the dietary dry matter, in most cases. When high-fiber byproducts are used in the diet to replace forage fiber, it is prudent to increase the total amount of dietary fiber at the same time that dietary starch is reduced. This is because the fiber in byproducts does not have the same ability to stimulate cud chewing and salivation as forage fiber.

Buffer and Alkalinizing Agents

Sodium bicarbonate and sesquicarbonate are rumen buffers commonly used in diets of dairy cattle to improve milk fat synthesis. Sodium bicarbonate is typically fed at 0.7%–1% of the diet dry matter to neutralize the organic acids produced in the rumen. This makes the rumen fluid less acidic, thereby minimizing the risk of LMF. Concurrent with buffers, feeding of alkalinizing agents such as magnesium oxide to increase dietary magnesium content to 0.35%–0.40% of the diet dry matter also tends to favor milk fat synthesis.

Ionophores

Diets for lactating dairy cows in many countries can be supplemented with ionophores to improve feed efficiency and minimize the risk of ketosis. In the United States, the Ionophores monensin is typically fed to lactating cows at 5.5–11 mg per lb of feed (12–24 ppm) on a dry basis. Because Ionophores kill some of the populations of rumen microorganisms, it shifts the rumen microflora favoring populations that produce more trans fatty acids. When Ionophores are combined with diets high in starch and in unsaturated fatty acids, the risk for LMFs substantially increases. Therefore, it is prudent to evaluate ionophore feeding practices when dietary circumstances favor greater use of starch and fat sources.

Feeding Management:

Although diet composition is key in preventing LMFs, feeding management and diet presentation to cows cannot be neglected. Preventing slug feeding by minimizing competition in the feed bunk is critical, which allows less dominant cows to consume feed that has not been sorted through by more dominant cows. As space in the bunk is reduced, cows increase their eating rate to compensate for less time available for eating. Also, proper presentation of diet minimizes sorting against longer particles. Although mixing of diets should preserve long particles, particularly forages, the length of long particles should not be excessive. Excessive long forage particles (usually longer than the muzzle of the cow) favor sorting against them. Use of wet ingredients, such as silages and wet byproducts (as well as feeding of molasses), tends to favor agglomeration of feed particles and prevent sorting.

Supplemental Dietary Fat:

Milk fat percent should be maintained or perhaps increased if it was originally depressed because of high grain feeding. The milk fat response to supplemental fat can be highly variable, depending on the amount of supplement, physical form of the fat, and the fatty acid composition of the supplement. Supplemental fat generally does result in a slight decrease in milk protein percent. The magnitude of this depressed milk protein percent varies, but is usually up to about 0.3 % units. Fatty acid composition of milk fat is altered by supplementation of the diets with fat. Changes in milk fat fatty acid composition reflect the fatty acids supplemented to the diet. Generally there is an increase in the proportion of long chain fatty acids (saturated or unsaturated depending on the dietary source) and a decreased proportion of short and medium chain fatty acids. Most fat supplements contain long chain fatty acids.

Several other nutrient changes need to be considered when supplementing diets with fat. Adequate fiber needs to be available in the diet to stimulate ruminal fermentation. Calcium complexes with the fatty acids to form soaps, resulting in lowered availability of Ca for absorption. Calcium level in the diet should be adjusted when fats are added. And, the decrease in proportion of grain in the diet that occurs when adding fats results in lowered available energy to the rumen microorganisms, and therefore less microbial protein synthesized and made available to the cow. A good source of dietary protein that is of low rumen degradability will make up for this deficit.

The type of fat used in the diet can substantially affect the result. Seed oils extracted from plants (such as cottonseed oil, sunflower seed oil, soybean oil and cod-liver oil) have a negative effect on ruminal fermentation. An "inert" fat source will not alter ruminal fermentation. Acceptable supplemental fats include oil seeds (such as whole cottonseeds, whole soybeans, and whole sunflower seeds), tallow, hydrolyzed animal-vegetable blends, calcium salts of fatty acids, and prilled fats

 

Dr M Areshkumar, M.V.Sc, M.Sc., PGDORT,

 

 

 

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