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This article will center on lipid nutrition in dairy cows, sharing information on dietary lipid sources, lipid metabolism in the cow’s rumen, and the application of lipids in dairy production.
Lipid sources and importance of dairy cow diets
Whole cottonseed is widely used in dairy farms. Pasture plants contain a high percentage of linolenic acid, and grains and oilseeds contain mainly linoleic and oleic acids. These are important sources of fat required by dairy cows.
Most studies have shown that the addition of fat to the diet (especially fats and oils rich in polyunsaturated fatty acids) inhibits intestinal methane emissions to varying degrees. Unsaturated fatty acids reduce methane production by utilizing hydrogen for hydrogenation reactions and the production of propionic acid.
Lipid metabolism in the rumen of dairy cows
Lipid metabolism in the rumen consists mainly of lipid hydrolysis and biohydrogenation. (See the inside of this book for details)
Hydrolysis of lipids in the rumen
The first step in lipid metabolism is the hydrolysis of ester bonds in triglycerides, phospholipids and glycolipids, i.e., lipid hydrolysis in the rumen. Lipid hydrolysis leads to the release of free fatty acids from esters, which in turn allows hydrogenation to occur. Ruminal bacteria can hydrolyze up to 85% of lipids.
Hydrogenation of lipids in the rumen
The first step in biohydrogenation is an isomerization reaction. The rate of biohydrogenation of linoleic and linolenic acids usually accelerates with increasing unsaturation.
Lipid absorption in the small intestine
Bioabsorption
Lipids entering the small intestine, as influenced by rumen metabolism, consist mainly of soft and stearic acids. Absorption of lipids in the small intestine occurs primarily in the jejunum, and the formation of particles is essential for the efficient absorption of fatty acids.
Fatty acids in ruminant feeds are almost completely hydrolyzed in the rumen, and before they reach the jejunum, bile and pancreatic juice secreted by the organism can form particles. After particle formation, they are absorbed by jejunal epithelial cells, and the absorbed fatty acids are re-esterified to triglycerides, which are then packed into celiac particles.
Dynamic absorption
It was found that there may be small differences in the absorption of different C18:1 isomers. Compared to monogastric animals, lipid species had a smaller effect on ruminants.
Lipid synthesis and inhibition in the mammary gland
Lipids determine many of the physical properties, production characteristics, and sensory qualities of cow’s milk and dairy products.
Influence of milk fat composition
Diets can significantly affect rumen bacterial populations and metabolic processes of rumen microorganisms. Dietary nutrient composition has a significant effect on milk fat content and fatty acid composition.
Bovine milk low-fat syndrome is a common phenomenon of fat changes in bovine milk, or milk fat depression (MFD). MFD occurs when feeding a specific feed significantly reduces milk fat content and alters fatty acid composition.
Fatty acid sources and milk fat synthesis
Fatty acids in cow’s milk are derived from absorption in the blood circulation and from de novo synthesis in the mammary epithelial cells. Medium- and short-chain fatty acids come almost exclusively from de novo synthesis, long-chain fatty acids with more than 16 carbon atoms come mainly from blood circulation, and C16 fatty acids come from both of these sources. About half of the molar ratio of fatty acids in cow’s milk comes from de novo synthesis (see chart in this book).
During pregnancy in dairy cows, there is a lesser degree of increased mammary fatty acid synthesis and a concomitant increase in the activity of key enzymes of fatty acid synthesis.
Relationship between dairy cow diets and milk fat
The content and composition of milk fat in ruminant milk composition is highly variable and is a major factor affecting the nutritional value of milk. Milk fat is most susceptible to dietary influences and usually manifests itself as reduced milk fat. There are two broad categories of diets that contribute to MFD: those that provide large amounts of easily digestible sugars and low fiber content, and those that contain high levels of PUFA.
Theories of MFD induction include the acetate-propionate yield theory, the glucose-insulin regulation theory, the trans-fatty acid theory, and the biohydrogenation theory (see the inside of this book for details).
Lipids in dairy production
Nutritional Strategies for Lipid Feeding
The addition of fat at 16% of metabolic energy intake has been estimated by modeling metabolic pathways to maximize the efficiency of energy use by dairy cows.
Industry experts have developed a formula for calculating the safe amount of UFA that can be added to lactation diets (see the inside cover of this book for details), taking into account total UFA and neutral detergent fiber content added to the diet.
Fat nutrition and reproduction
Altering the intake of omega-6 and omega-3 fatty acids regulates the balance of series 2 and 3 prostaglandins. Taken together, several studies have shown that feeding fat enriched with specific UFAs consistently during the postpartum period, starting at the dry milk stage, improves postpartum health problems, milk production, embryo development, and subsequent pregnancy rates in dairy cows.
Quantification of Fatty Acid Composition in Milk and the Effect of Milk Fat Addition on Milk Protein
In 1952, James and Martin published the first article on the analysis of gas-liquid chromatographic procedures, which revolutionized fatty acid analysis and is now an important tool in milk fat research.
In modern feeding patterns, the addition of fat to the diet balances the dietary amino acids and provides the mammary gland with sufficient amino acids to maintain milk protein production.
