Milk is composed of many components, including protein, lactose, fat, etc. Milk fat is an important component in dairy farming, playing a major role in milk's economic value and nutritional quality. Milk fat is composed of fatty acids, with milk having over 400 fatty acids. The common groups or milk fatty acid profile include denovo synthesized fatty acids, which are synthesized in the mammary gland from precursors such as acetate derived from the degradation of fiber in the rumen. Another group is preformed fatty acids, which are often found in body reserves. The varying proportions of these milk fatty acids determine the overall fat content of milk. Nowadays, the focus on dairy farming has shifted from milk quantity only to a combination of milk quantity and milk composition, especially milk fat, which has the highest value in the multiple-component milk pricing system. However, dairy producers face the challenge of milk fat depression (MFD), a condition that impacts the profitability of the dairy farm. Here is an overview of the importance of milk fat and the risk factors associated with its depression.
Importance of Milk Fat
Milk fat is important because of the economic value of directly influencing the price dairy farmers receive for their milk.
Higher fat content in milk often translates to higher payments and increased revenue for the dairy farm because milk fat has a higher price than other milk components. Milk fat is also essential for producing various dairy products, including butter, cheese, and cream, all of which have high market value. Beyond the economic value, milk fat also plays a role in the nutritional value of milk and milk products (Waldron et al., 2020). Milk fat provides the essential fatty acids, which are vital for human health. Furthermore, milk fat is also a source of fat-soluble vitamins (A, D, E, and K), which are crucial for various important bodily functions. When it comes to milk processing, milk fat also contributes to the enhancement of the flavor and texture of dairy products. For instance, milk fat contributes to the mouthful creamy texture of ice cream as well as contributes to the flavor, texture, and aroma of cheese (Waldron et al., 2020). When compared with other milk components, for instance, milk protein, milk fat is the most variable component and can range from 3.3% to 5% depending on management and other factors (Jensen et al., 1991). Some of the factors that affect milk fat range from breed type or genetics, nutrition management, stage of lactation, season of the year, and individual animal variation.
Milk Fat Depression (MFD) Risk Factors
MFD is a condition characterized mainly by a significant decrease in milk fat content without a corresponding drop in milk yield or in the yield of other milk components. Several factors can contribute to this condition, which can have a huge negative impact on the dairy farm's revenue.
Dietary Factors
Dietary management remains the cornerstone of a profitable dairy farm, and balanced nutrition management is crucial to ensure consistent milk and milk component production. One of the major risk factors for milk fat depression in lactating dairy cows is feeding a large proportion of readily fermentable carbohydrates (Dewanckele et al., 2020). Excessive quantities of rapidly fermentable carbohydrates, such as those found in grains, such as barley, can disrupt rumen fermentation, leading to MFD. The challenge with these carbohydrates is that they have high fermentation rates in the rumen, causing a buildup of volatile fatty acids, and this, in turn, overwhelms the capacity of their absorption by the rumen wall and causes a decrease in rumen pH. Cereal or grain processing methods and level of processing have received a lot of attention and research focus over the years. Several research has alluded that finely and severely processed grains, such as finely ground barley, lead to an increased risk of milk fat depression (M.A. López‐Soto1, 2010).
However, based on emerging research, recent studies argue that although severity and method of processing play a key role, the real culprit may be dietary starch inclusion levels in the dairy diets; hence, at low dietary starch inclusion levels, the method and severity of grain processing has minimal effects on rumen function. A low rumen pH leads to a cascade of events that have a negative effect on milk fat synthesis, for example, lowering the proportion of acetate to propionate ratio, and acetate plays a significant role in the synthesis of milk fat in the mammary gland. On the other hand, prolonged exposure to low rumen pH negatively impacts the function of rumen microbes and reduces fiber digestion by the microbes, leading to reduced acetate. Furthermore, low pH also results in the disruption of essential processes such as biohydrogenation of unsaturated fatty acids, leading to altered proportions of milk fatty acid profile, hence the reduction of milk fat (Dewanckele et al., 2020).
High Intake of Unsaturated Fatty Acids
One of the strategies used to increase milk fat is the supplementation of dairy diets with supplementary fats, such as palm fat. However, it's crucial to avoid over-supplementation and remain below 5-6% total fat supplement in cows' diets. Diets rich in unsaturated fatty acids, particularly polyunsaturated fatty acids (PUFAs), can interfere with rumen biohydrogenation, resulting in the production of fatty acid intermediates that inhibit milk fat synthesis in the mammary gland, resulting in reduced milk fat and increased risk of milk fat depression (Rico & Harvatine, 2013). Rumen biohydrogenation is when the rumen microbes convert the unsaturated fatty acids into saturated fatty acids as a protective mechanism to prevent their toxicity. Disrupted biohydrogenation can have a spiral negative effect ranging from producing intermediates that end up blocking milk fat synthesis in the mammary gland to even reduced rumen function, especially fiber digestion, due to negative effects on fibrolytic rumen microbes. This further worsens in situations where there is low rumen pH.
Low Dietary Fiber
The provision of fiber is essential for rumen function and promotes chewing. It is also important for acetate production, a volatile fatty acid that is a precursor for milk fat in the mammary gland. Furthermore, the fiber component promotes chewing behavior commonly known as rumination, essential for stabilizing rumen pH. Diets with insufficient fiber alter or lower rumen pH, causing a reduction in acetate production and increasing the risk of MFD (Hackmann & Vahmani, 2023).
It's also essential to consider fiber length on the fiber provision component. Excessively chopped or very short fiber lacks the effects of promoting rumination. A chop length between 3 to 4mm is recommended because it promotes chewing and in turn, salivation. However, very long fiber takes time to degrade and stays longer in the rumen, which also reduces feed intake, which can negatively affect milk production. Cows receiving insufficient fiber are at risk of milk fat depression.
Other Factors
According to (Rico & Harvatine, 2013), another important factor that increases the risk of MFD is heat stress, especially in hot summer seasons. High environmental temperatures can reduce feed intake and alter rumen function, contributing to MFD and negatively affecting dairy productivity. Therefore, providing cooling mechanisms during hot seasons, such as shade or cooling fans, is essential. On the other hand, the dairy cow's physiological state also plays a role in the fat yield of milk. The stage of lactation can influence milk fat content; usually, at peak milk production, dairy cows have a low milk fat content due to a dilution effect. Cow genetics also influence milk fat content. Some cows have a genetic predisposition to produce milk with higher or lower fat content. For example, the Jersey cow breed generally yields milk with high-fat content when compared with Holstein. General herd management also plays a crucial role, and this includes strategies such as feeding strategies and general herd health (Schutz et al., 1990). Poor herd management can result in reduced milk fat production.
Managing MFD
There are several strategies dairy farmers can use to mitigate the risk of MFD. Milk fat depression management is important for a dairy farm's economic benefits, production of high-quality milk, and promotion of cow health and rumen function.
1 . Balanced Rations
Dairy farmers should ensure their dairy cows' rations are properly balanced for fiber and carbohydrates. Ensure a proper fiber-to-concentrate ratio that promotes rumen health (Humer et al., 2018). Furthermore, the recommended fiber length ensures sufficient fiber that promotes rumination and salivation. Another key area to carefully manage is the intake of unsaturated fatty acids and supplementation levels, never over-supplement by going beyond 5-6% total fat in the diet to ensure that the biohydrogenation process and rumen function are not compromised (Dewanckele et al., 2020). Furthermore, regular and continuous monitoring of milk fat levels is also essential so farmers can tailor strategies based on the changes in milk fat content.
2. Rumen Health Management
It is also essential that dairy farmers maintain a stable rumen pH to promote healthy rumen fermentation and the proper function of rumen microbes through the provision of adequate fiber (Hackmann & Vahmani, 2023). Another common strategy involves the use of feed additives or rumen stabilizers such as limestone in situations where a high-risk diet is being fed, for instance, ground barley (Boyles et al., 2015).
3. Environmental Control
Implementing measures or strategies to reduce heat stress, such as providing shade, ventilation, and clean water, is also essential to minimize the negative effects of heat stress on lactating cows. Over the years, research has focused on improving dairy cow comfort and welfare, and if these are well maintained, they positively affect dairy cow milk production and milk composition yield. Other management cases, such as overcrowding, should be avoided because they can lead to increased competition and reduce the risk of milk fat depression.
Conclusion
In dairy farming, understanding the importance of milk fat and the factors contributing to the risk of MFD is crucial for a dairy farm's profitability and producing high-quality milk. For dairy farmers to maintain milk and milk composition production levels, they must understand the nutritional aspect of dairy cows, including levels for supplementary dietary fat and fiber provision, as well as modification of the cow environment to minimize the effects of heat stress while maintaining cow health, comfort and welfare.
References
- Boyles, S. L., Anderson, V. L., & Koch, K. B. (2015). FEEDING BARLEY TO CATTLE.
- Dewanckele, L., Toral, P. G., Vlaeminck, B., & Fievez, V. (2020). Invited review: Role of rumen biohydrogenation intermediates and rumen microbes in diet-induced milk fat depression
- Hackmann, T. J., & Vahmani, P. (2023). Perspective: How to address the root cause of milk fat depression in dairy cattle.
- Humer, E., Petri, R. M., Aschenbach, J. R., Bradford, B. J., Penner, G. B., Tafaj, M., Südekum, K. H., & Zebeli, Q. (2018). Invited review: Practical feeding management recommendations to mitigate the risk of subacute ruminal acidosis in dairy cattle.
- Jensen, R. G., Ferris, A. M., & Lammi-Keefe, C. J. (1991). The Composition of Milk Fat.
- M.A. López‐Soto1, A. B. J. F. C. A. P. J. D. U. J. A. A. B. S. A. M. R. M. B. A. E. and R. A. Z. (2010). Influence of Processing of Barley Grain on Characteristics of Digestion, Ruminal Fermentation and Digestible Energy of Diet in Lactating Cows. www.ijas.ir
- Rico, D. E., & Harvatine, K. J. (2013). Induction of and recovery from milk fat depression occurs progressively in dairy cows switched between diets that differ in fiber and oil concentration.
- Schutz, M. M., Hansen, L. B., Steuernagel, G. R., & Kuck, A. L. (1990). Variation of Milk, Fat, Protein, and Somatic Cells for Dairy Cattle.
- Waldron, D. S., Hoffmann, W., Buchheim, W., McMahon, D. J., Goff, H. D., Crowley, S. V., Moloney, C., O’regan, J., Giuffrida, F., Torres, I. C., & Siong, P. (2020). Role of Milk Fat in Dairy Products.
