Bile Acids Minimize Ketosis in Transition Dairy Cows

Bile acids and functions

Bile acids are synthesized from cholesterol in the liver and afterwards to be stored in the gallbladder before secreted in the small intestine (Fig. 1). Bile acids contribute to lipids digestion by breaking down large fat globules, a process known as emulsification. Emulsification provides pancreatic lipase with more surface area on which to act, which finally increases digestion efficiency. Additionally, bile acids regulate their synthesis and triglyceride homeostasis (in addition to other functions). Farnesoid X receptor (FXR) is a nuclear receptor, it is activated by bile acids. After activation of FXR, it can regulate the synthesis of bile acids, transport, and many other aspects of lipid and glucose metabolism; hence, it can support managing the metabolic disease.

Figure 1.?Bile acids biosynthesis.

Role of bile acids in fat digestion in ruminants

Currently, high-milking cows need to provide an adequate amount of fat in their diet, which in some cases can be up to 7% of dry matter (DM), to help them meet the high nutrients needed to cover high milk production. Bile acid and lipase are necessary for lipid digestion. Fatty acid emulsification and micelle formation inside the small intestine are mandatory for the efficient digestion and absorption of lipids. Emulsifying fat can increase the surface area of fats and later maximize the digestion efficiency by pancreatic lipase. An overview of fat digestion and absorption in ruminants is presented (Figure 2).?

1)????Hydrolysis mainly occurs in the rumen by microorganisms that separate triglycerides into fatty acids and glycerol.

2)????Biohydrogenation: unsaturated free fatty acids are converted by microorganisms to saturated fatty acids.

3)????In the small intestine, with the addition of bile acids and lipase, free fatty acids form micelles.

4)????Absorption: lipids absorption happens via the small intestine wall. Free fatty acids and glycerol inside the small intestine wall are converted back to triglycerides and packaged into chylomicrons and lipoproteins.

5)????Chylomicrons and lipoproteins then transport the absorbed triglycerides to the lymphatic system for delivery to the body tissues for use as an energy source, e.g., milk fat or body fat store.

Figure 2.?Mechanism of fat digestion & absorption in ruminants.

Bile acids boost liver health and minimize the occurrence of ketosis???????????

Bile acids possess several biological functions that contribute to maximising liver's health. Here, we could ask a question, how do bile acids alleviate ketosis? Hereafter, maximize milk yield. In general, liver's non-esterified fatty acid (NEFA) is going to follow one of two ways, esterification or oxidation (Figure 3).

1.?Esterification: The main esterification product is triglycerides. Triglycerides can be exported as very-low-density lipoprotein (VLDL) or stored as fat in the liver. In ruminants, triglycerides are exported at a slow rate. Therefore, under elevated hepatic NEFA uptake (eg, low glucose and low insulin concentrations), fatty acid esterification and triglyceride accumulation commonly occur, causing fatty liver disease. In the existence of adequate concentrations of bile acids, bile acids stimulate hepatocytes in the liver to synthesise VLDL, thereby reducing the accumulation of fat in the liver, and diminishing the occurrence rate of fatty liver.

2.?Oxidation: complete oxidation of NEFA leads to producing energy; however, incomplete oxidation of NEFA creates ketones bodies, such as β-hydroxybutyrate and acetoacetate. Ketone bodies are water-soluble molecules containing the ketone groups produced from NEFA by the liver.?

The study conducted by Lachance's group on transition dairy cows that were supplemented with bile acids revealed a lower ketosis incidence. To clarify this point, we assumed that bile acids improve hepatic oxidation by enhancing the bioavailability of L-carnitine (by enhancing transporting long-chain fatty acids from the cytosol to the mitochondrial for oxidation). L-carnitine is a chemical that is formed in different organs, such as the brain, liver, and kidneys. L-carnitine helps the body transport fat for oxidation; it is also essential for heart and brain functions, muscle movement and activity, and many other processes. Therefore, NEFA can be efficiently oxidized to produce energy (instead of making ketone bodies), which solves the problem of ketosis and the beyond secondary disorders linked with ketosis. This may assist in explaining the function of bile acids in reducing ketosis in perinatal dairy cows.?

Ketosis (ketogenesis) happens when glucose and insulin concentrations are low, which then the ketone body becomes the body and brain's primary source of energy. There are many reasons for ketosis; the main reason is increased mobilization of fatty acids from adipose tissue (mostly around calving). Ketosis is a common perinatal disorder during a sudden increase in NEFA concentrations.??Ketosis usually occurs when the requirements of energy and metabolizable protein for milk synthesis are higher than the energy and metabolizable protein intake provided by the diet, as well as other secondary factors. Dairy cows can eat more dry matter when their' liver is healthy to support milk production and other biological functions.

Figure 3.?Lipid metabolism and the role of bile acid in dairy cows.

Application of RUNEON in?transition cows

Succinctly, a study has been carried out to assess the effectiveness of providing bile acid on the appearance rate of ketosis of transition dairy cows (besides other parameters of health and production) at one of the leading dairy farms in China. A total of 430 prepartum Holstein dairy cows were used in the current study and divided into two treatments; (1) control cows and (2) bile acids cows. Blood samples were collected periodically one time every week from the tail during the experiment (a total of 8 weeks, 4 weeks pre-calving and 4 weeks post-calving), milk yield was recorded, and Alpro Dairy Herd Management Software generated data (Other results will be published later). Bile acids were adjusted to 0.15% of dry matter (DM, corresponding to?≈?30 g/head/day). Bile acids were mixed with the total mixed ration (TMR) one time/per day during the trial; according to the manufacturer, the product contains 30% bile acids(RUNEON, Shandong Longchang Animal Health Products Co., Ltd, China).

Figure 4.?Bile acid supply and the ratio of subclinical ketosis of transition dairy cows. * The mean values differed significantly between treatments (p?< 0.05).

There was a 15.1% reduction of subclinical ketosis for cows that consumed bile acids compared to control cows.

Summary & Conclusion

Based on the results obtained from the current study, dietary supplementing with bile acids at a rate of 0.15 of DM (corresponding to about 30 g/h/d) fed to Holstein dairy cows through the transition can minimize the incidence rate of subclinical ketosis, and consequently, help in improving the health of perinatal dairy cows.

Author

Samy A. Elsaadawy, PhD.

Ruminant Technical Manager at LachanceGroup, Jinan, Shandong, China?

[email protected]

www.sdlachance.net