ARTICLE FEED & ADDITIVE MAGAZINE September 2023 81 Dairy cows affected by fatty liver exhibit lower plasma phosphatidylcholine concentrations. Although phosphatidylcholine can be endogenously synthesized by tissues, it is likely that the demands of choline during the transition period are greater than the supply from dietary sources and from endogenous synthesis, particularly because endogenous synthesis requires methyl groups originated by compounds such as methionine, which can be in short supply at the onset of lactation. Ruminants, unlike nonruminants, face limitations in choline availability from dietary sources because of rumen microbial degradation. Therefore, supplementing rumen-protected choline (RPC) becomes essential. Despite widespread recognition of choline as a required nutrient for most mammals, established feeding guidelines for lactating or dry dairy cows remain absent. CHOLINE PLAYS IMPORTANT ROLES ON HEPATIC LIPID METABOLISM Numerous experiments at the University of Florida studied the role of choline in hepatic lipid metabolism. The experiments used a feed-restriction model to simulate the negative nutrient balance that dairy cows typically experience in the first weeks of lactation3-6. The initial utilization of this model can be credited to Ric Grummer from Wisconsin. Grummer demonstrated that the application of RPC led to a reduction in the extent of triacylglycerol accumulation within the livers of dry cows. In subsequent experiments carried out in Florida, a total of 187 pregnant dry cows in the late stages of gestation were intentionally provided with less than 40% of the energy required for both cow maintenance and sustaining the pregnancy. This restricted feeding regimen lasted for a span of 9 days and was designed to induce fatty liver in the cows. The diets administered to the cows contained varying amounts of choline ions, ranging from 0 to 25,8 g/day, in the form of the ReaShure brand of RPC. To ensure consistency, the cows were also given rumen-protected methionine supplementation during the period of restricted feeding, thus replicating the exact metabolizable methionine intake that would occur when the cows consumed 11 kg of dry matter on a daily basis. Administering choline as part of the diet resulted in a substantial 31,7% reduction in hepatic triacylglycerol concentration, while concurrently increasing glycogen concentration by 54,2%. Importantly, these effects were directly proportional to the quantity of choline ion introduced through the diet. Notably, a noteworthy outcome emerged from one of the experiments: cows that received a supplementation of 25,8 g/day of choline ion via RPC exhibited an elevated hepatic secretion of triacylglycerol-rich lipoproteins5. This finding aligns with observations from research involving non-ruminant species and underscores the significance of choline in supporting the synthesis and subsequent export of lipids from the liver through the production of VLDL. The introduction of RPC into the diet during the period of feed restriction induced modifications in the expression of multiple genes within the hepatic tissue, specifically those associated with lipid metabolism. These alterations in gene expression patterns indicate a decrease in hepatic lipogenesis and a simultaneous improvement in the export of lipids4-6. This phenomenon sheds light on the mechanism behind the reduction in hepatic lipidosis observed in cows that were supplemented with RPC. SUPPLEMENTING RPC ENHANCES FAT DIGESTIBILITY Choline serves as a constituent of phosphatidylcholines, a subset of phospholipids that constitute crucial components of both cell membranes and lipoproteins. These phospholipids play a pivotal role in facilitating the absorption and transportation of lipids. As cows approach the period of parturition, their dry matter intake typically decreases, followed by a gradual increase after giving birth. Research conducted by Lance Baumgard at Iowa State University has demonstrated that sudden shifts in dry matter intake can disrupt the structure of the gastrointestinal tract lining, leading to alterations in the integrity of the intestinal epithelium. This, in turn, affects the absorption of nutrients7.
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