The three weeks preceding parturition and the three weeks following it are known as the transition period, and this phase represents one of the most challenging windows in the productive life of a dairy cow (Grummer, 1995; Drackley, 1999). During this window, cows experience significant metabolic and physiological adaptations to support fetal growth, parturition, and the onset of lactation, which increases their susceptibility to metabolic and infectious disorders. At the end of the dry period, rapid fetal growth increases internal pressure on digestive organs. This, combined with major hormonal changes during the prepartum period, including increased blood concentrations of estrogen and corticosteroids and decreased progesterone levels (Chew et al., 1979), leads to a reduction in dry matter intake (DMI) of up to 30% (Hayirli et al., 2002). At calving, requirements for lactation increase rapidly, whereas feed intake does not immediately meet this demand, resulting in a negative energy balance.
Under conditions of reduced DMI, low blood glucose leads to catabolic pathways to maintain energy supply. Cows utilize reserved glycogen, which is rapidly mobilized from hepatic stores to maintain blood glucose concentrations. In the liver, glycogen is broken down through glycogenolysis, releasing glucose into the bloodstream. When glycogen reserves are limited, and cows also utilize amino acids, which are catabolized and used as substrates for gluconeogenesis in the liver.
The main energy reserve mobilized is adipose tissue. In adipocytes, energy is stored as triglycerides (TG), and the breakdown of TG results in the release of glycerol and non-esterified fatty acids (NEFA). In the liver, glycerol can be converted into glucose, contributing to the energy supply of glucose-dependent tissues. NEFA serves as an important energy source for peripheral tissues. During gestation, glucose is primarily directed toward the fetus, whereas during lactation it is required for lactose synthesis in the mammary gland. In the liver, NEFA may undergo three metabolic fates: complete oxidation, incomplete oxidation, or re-esterification (Loor et al., 2013; McArt et al., 2013). Complete oxidation produces ATP, whereas incomplete oxidation generates ketone bodies that are released into the bloodstream and used as alternative energy substrates by other tissues. Re-esterification results in the resynthesis of TG within hepatic tissue. To avoid hepatic lipid accumulation, TG must be incorporated into very-low-density lipoproteins (VLDL) and transported to other tissues. Cows experiencing severe negative energy balance and intense lipid mobilization show elevated plasma concentrations of NEFA and ketone bodies, which increases the risk of metabolic disorders such as hepatic steatosis and ketosis and may compromise health and productive performance (Loor et al., 2013).
Therefore, strategies that maximize dry matter intake during the transition period are essential. Management practices such as appropriate grouping of animals and adjustment of diets according to each stage of the lactation are important to meet energy, protein, and mineral requirements. In addition, providing adequate comfort and effective heat abatement is a critical aspect of management, as stress can impair immune function and reduce appetite.
Nutritional strategies aimed at minimizing excessive lipid mobilization and ketosis can contribute to reducing economic losses and promoting optimal lactation performance. Choline is an essential nutrient that composes the phosphatidylcholine molecule, which is required for the formation of lipoproteins such as VLDL (Lombardi et al., 1968). The ruminant liver has a limited capacity to secrete VLDL compared with other species (Emery et al., 1992), which increases the risk of hepatic lipidosis during early lactation (Bobe et al., 2004). Choline is primarily absorbed in the small intestine and can be metabolized into several forms, including phosphatidylcholine, an important component of cell membranes, and acetylcholine, a key neurotransmitter. In ruminants, however, most dietary choline is degraded in the rumen, making supplementation in rumen-protected form necessary to ensure intestinal absorption (Sharma and Erdman, 1988).
Supplementation with rumen-protected choline (RPC) has been associated with improvements in liver function and lipid metabolism in transition dairy cows. Choline supports the export of hepatic triglycerides through the synthesis of VLDL, reducing lipid accumulation in the liver. In addition, evidence suggests that choline may stimulate autophagy and lipophagy pathways involved in the degradation of intracellular lipid droplets, further contributing to the prevention of hepatic lipidosis. Choline supplementation has also been associated with reductions in endoplasmic reticulum stress and hepatic inflammation, both of which are commonly observed during the transition period when metabolic load is high. Together, these mechanisms support liver health and improve metabolic adaptation during early lactation (Zenobi et al., 2018; Arshad et al., 2023a,b,c; Arshad and Santos, 2024).
Ghaffari et al. (2025) conducted a systematic review and dose-response meta-analysis evaluating the effects of RPC supplementation on lactation performance in dairy cows. The analysis included 30 studies from 19 articles and one dissertation published between 2000 and 2024. These studies evaluated different levels of choline chloride supplementation during the transition period and assessed variables such as dry matter intake, milk yield, milk composition, body weight, and body condition score. The results demonstrated a significant nonlinear dose-response relationship between choline supplementation and production variables. The optimal dose for increasing dry matter intake and milk yield was approximately 13 to 14 g per day of choline chloride, resulting in increases of about 0.48 kg per day in dry matter intake and 1.29 kg per day in milk yield compared with control cows. In addition, 3.5% fat-corrected milk increased progressively at higher supplementation levels, particularly between 15 and 21 g per day, reaching an estimated increase of about 2.19 kg per day. Milk fat and milk protein yields also increased with supplementation, although milk fat, protein, and lactose percentages were not significantly affected. Likewise, no significant effects were observed on body condition score or prepartum body weight, although overall body weight increased at moderate supplementation levels. Overall, these findings suggest that RPC supplementation during the transition period improves nutrient utilization and metabolic efficiency in dairy cows, resulting in increased milk production without major changes in milk composition.
Supplementation with RPC during the transition period may increase the export of triglycerides from the liver through greater synthesis and secretion of VLDL, helping to reduce lipid accumulation in hepatic tissue. Improved export of triglycerides may also be associated with reduced mobilization of adipose tissue and lower plasma concentrations of NEFA and β-hydroxybutyrate. Several studies have reported positive responses to RPC supplementation, however, the magnitude of these responses may vary depending on nutritional, physiological, and management conditions. The metabolic changes that occur during the transition period involve complex physiological processes that interact with many factors present in dairy production systems. Therefore, additional research is needed to further clarify the mechanisms through which RPC may support metabolic adaptation and to better define the conditions under which its supplementation may provide the greatest benefits for transition dairy cows.
References
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