A case to be made for choline as a required nutrient for transition dairy cows

The discovery of choline dates back to 1850s when French pharmacist, Théodore Gobley discovered a group of phospholipids that he named lecithin. Seventy years later, during the discovery of insulin by Frederick Banting, his student Charles Best noticed that depancreatized dogs developed hepatic lipidosis. Subsequently in the early 1930s, Best showed that supplementing lecithin reversed and prevented hepatic lipidosis in dogs and rats. It took another 67 years for dietary choline to be acknowledged as essential in human diets. Requirements have been established for several farm animal species; however, the specific amounts of dietary choline to be fed to dairy cows have not been established. The development of rumen-protected choline (RPC) products has allowed extensive research to investigate the effects on dairy cows, in particular during the transition period. Dairy cows during transition accumulate lipid droplets into the hepatic tissue, which results in approximately 40% to 50% of them having hepatic triacylglycerol > 5% in the first 2 to 3 weeks postpartum. Cows with hepatic lipidosis have increased risk of peripartum diseases. Experimental models using feed-restricted late-pregnant cows have unequivocally shown that supplementing RPC reduces the content of triacylglycerol in the liver. The mechanisms that support reduced hepatic lipidosis by RPC in feed-restricted cows are not completely understood, but involve enhanced export of triacylglycerol as nascent lipoproteins. Other mechanisms that facilitate the disposal of fatty acids from hepatocytes have been proposed and include increased cellular autophagy and lipophagy, and reduced endoplasmic reticulum stress response and hepatocyte inflammation. The effects of RPC on hepatic lipidosis are less clear in early postpartum cows, but extensive research shows an increase in production performance with some indication of benefits to peripartum health. Interestingly, the production response to supplementing RPC during the transition period extends well beyond the period of supplementation, thus suggesting effects on mammary cell metabolism that requires further investigation.

Key Words: choline, dairy cow, required nutrient