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This article focuses on the digestion and absorption of lipids in beef cattle, lipids and beef quality.
Lipid digestion and absorption in beef cattle
Lipid metabolism in the rumen
The major lipids in beef cattle diets are triglycerides, phospholipids and galactolipids. Lipids are converted in the rumen by rumen microbial catabolism and biohydrogenation. Bacteria play a key role in lipid catabolism, and plant lipases also play a part. After hydrolysis, UFA are converted to SFA by isomerization of cis-trans isomers followed by hydrogenation.
Triglycerides are hydrolyzed to glycerol and free fatty acids by microbial lipases, and free fatty acids are also produced by hydrolysis of glycolipids and phospholipids. Free fatty acids can be partially or completely biohydrogenated.
Post ruminal digestion and absorption of lipids
Microbial lipids and dietary lipids not hydrolyzed in the rumen are broken down in the small intestine by pancreatic lipase and co-lipase. Bile acids promote the separation of fatty acids from feed particles, and phospholipids in bile are converted to lysophospholipids by pancreatic phospholipase. These components enhance the solubilization and binding of fatty acids to colloids.
Lipid energy supply in beef cattle
Lipid digestibility
The digestibility of fatty acids in the small intestine of ruminants ranges from 55% to 92%, and the reason for the wide range of digestibility is the carbon chain length. After the carbon chain length exceeds C18, the longer the fatty acid carbon chain, the lower the digestibility. Fatty acid digestibility decreases with increasing intake, so the optimal fat feeding rate is total fat intake/body weight ratio equal to 1.0g/kg or ≤7% of dietary dry matter.
Lipid energy supply
Overall, the total energy of fat is about 9.33 Mcal/kg, but the exact energy value varies depending on the length of the carbon chain and the degree of saturation.
Essential fatty acids in beef cattle
Based on comparative tests, researchers have concluded that ruminants in the growth phase require approximately 88 mg/kg (metabolic body weight) per day of essential fatty acids, which typically include alpha-linolenic acid, linoleic acid, and arachidonic acid.
Natural feed ingredients contain essential fatty acids. Cereals and soybean oil contain mainly C18:2 ω-6 fatty acids, and pasture and flaxseed contain significant amounts of C18:3 ω-3 fatty acids. Long-chain ω-6 and ω-3 PUFA can be synthesized in animals from linoleic acid and α-linolenic acid, respectively, or supplied by the diet. Some fish oils and seaweeds contain longer carbon chain ω-3 PUFA, which can directly supply EPA and DHA to animals.
Lipid addition during beef cattle breeding
Fattening Cattle Ration Additions
Grain-fed (pen-fattened) beef cattle reduce rumen PH and decrease fat breakdown, which reduces biohydrogenation in the rumen and increases the amount of UFA in products such as carcasses and buttermilk.
Research has shown (see the inside of Animal Lipid Science book for more details) that for beef cattle, the addition of mixed vegetable oils to the diet significantly increases linoleic acid, linolenic acid, and CLA levels, and tends to increase with the level of vegetable oil added.
Racking Cattle Ration Additions
Research on the use of fats and oils in diets for frame steers with low concentrate levels found that the addition of soybean oil at a dry matter level greater than or equal to 6% to a low concentrate diet supplemented with corn lowered rumen acetic acid/propionic acid ratios and lowered the digestibility of rumen organic matter.
It has also been shown that the addition of fat reduces forage organic matter intake and dietary digestibility, and that the addition of fish oil to forage silage diets increases the flow of all cis-C18:1 fatty acids, EPA and DHA, in the duodenum and decreases the flow of C18:0 fatty acids in the duodenum.
Trans rumen protection of lipids
Biohydrogenation in the rumen of ruminants can change the properties of fatty acids in the diet, and therefore, peri-rumen protection of fats is more conducive to meeting the ruminant demand for specific UFAs, which is currently a hot issue in research on ruminant lipid metabolism.
Based on the results of 93 studies on UFA (see the inside of Animal Lipid Science book for details), the degradation of linoleic acid and α-linolenic acid in the rumen as a percentage of feed intake was essentially similar for unprotected fats, oilseed fruits, or rumen-protected fats, with less degradation of linoleic acid in the rumen for oilseed fruits and rumen-protected fats.
Lipid metabolism and meat quality in beef cattle
It was found that changes in fatty acid levels from dietary sources significantly affect the properties of fatty acids in bovine tissues. (See inside of Animal Lipid Science book for details)
Adding 15% flaxseed to a pasture or silage ration fed to cull heifers was able to increase the level of omega-3 PUFA, including C18:3, in subcutaneous adipose tissue and decrease the omega-6/omega-3 PUFA ratio (see chart in Animal Lipid Science book for details). Utilizing this method increased the alpha-linolenic acid content of ground meat produced from cull cows, but also resulted in higher costs.
