The transition period is the most challenging time for a dairy cow. Right after calving cows start producing colostrum first and then milk in large amounts, depending on their genetic make-up. At this point in time however, they are in recovery mode from calving, and a combination of general discomfort/pain and hormonal changes results in a significant reduction of feed intake.
This mismatch between nutrient requirements for production and nutrient uptake through feed intake, results in imbalances, with the supply of energy being the more striking. One example of hormonal changes is the decreased production of insulin that leads to decreased glucose utilization by insulin-sensitive organs, which is essential for milk production. Concomitantly, body fat reserves are mobilized to supply additional energy which increases the non-esterified fatty acids (NEFAs) blood concentration.
The abundance of circulating NEFAs leads to increased availability of the product from their degradation, acetyl-CoA, which may exceed the capacity of its incorporation into the carboxylic acid cycle. As a result, end-products normally utilized in ketogenesis will build-up, such as acetone, acetoacetic acid, and beta-hydroxybutyric acid (BHBA).
L-carnitine helps to handle excessive non-esterified fatty acids
The increased circulation of NEFAs leads to triacyl glyceride synthesis later deposited in the liver. To handle the excessive NEFA availability L-carnitine is needed which is essential to transfer fatty acids into the mitochondria for their oxidation. L-carnitine is synthesized endogenously, and it is essential in the initial steps of the ß-oxidation of free fatty acids. When in short supply, all the events described above can happen leading to frequent metabolic problems in transition cows such as fatty liver and/or ketosis.