Choline has long been considered an essential nutrient and has an identified requirement in most species, including humans. Though most can synthesize choline endogenously, it cannot be produced in sufficient quantity to satisfy the body’s requirements and must be supplemented in the diet.
Choline is crucial for normal function of all cells. It is the precursor to the neurotransmitter acetylcholine which controls virtually all major systems and muscle movements within the body ranging from cardiac function to the central nervous system. Choline also serves as a source for methyl groups for the formation of methionine and is important in DNA methylation. Deficiency symptoms include suppressed growth rates, renal dysfunction, and development of fatty liver.
In human nutrition, studies have shown that higher prenatal choline intake was suggestive of improved infant cognitive function (Caudill, M.A., et al. FASEB J., 2018) and reduced instance of neural tube defects (Sahw, G.M., et al. Epidemiology, 2009) showing the in utero impact choline can have.
The most common form of choline in biological systems is phosphatidylcholine (PC). Of particular importance is PC as a constituent of very low-density lipoproteins (VLDL), which are synthesized in the liver and transport fat from the liver to muscle, adipose, and mammary tissue. Several experimental models have shown that PC deficiency limits VLDL export and leads to development of fatty liver. This vital role of choline in hepatic metabolism explains why fatty liver is the classic deficiency symptom when diets do not deliver adequate choline for intestinal absorption.
At the time of the 2001 Dairy NRC publication, choline was not recognized as an essential nutrient for lactating dairy cows or transition cows due to the lack of “extensive feeding experiments.” Since that time however, a recent meta-analysis published in 2020 (Arshad et al.) revealed 48 publications (spanning more than three decades) related to transition dairy cows in which diets were supplemented with rumen protected choline.
With the growing body of scientific and empirical data it is abundantly apparent that choline is in fact an essential nutrient for transition dairy cows and their calves.
Choline is Vital for Transition
Several studies have shown 50 to 60% of transition cows experience moderate to severe fatty liver (Bobe et al., 2004). Because fatty liver is a classic deficiency symptom for choline, it is reasonable to question if transition cows are deficient in choline. At calving there are hormonal changes that trigger an intense period of lipid mobilization from adipose tissue and as a result, blood nonesterified fatty acid (NEFA) concentrations typically increase 5- to 10-fold (Grummer, 1993). NEFA remain elevated, albeit to a lesser extent, during early lactation when cows experience negative energy balance. Due to increased NEFA concentration and increased blood flow during this period, daily fatty acid uptake by the liver increases 13-fold at calving (Reynolds et al., 2003). The most desirable fate of fatty acids entering the liver would be complete oxidation to provide energy to the liver or reesterification and export as triglyceride from the liver as part of a VLDL. Though the liver becomes more metabolically active in terms of oxidation during the transition period, the increases are not sufficient to cope with the increased load of fatty acid being presented. This leads to fatty liver and increased ketones in the blood (ketosis) which can negatively impact feed intake and further exacerbate negative energy balance, leading to even more NEFA mobilization.
It is apparent that choline deficiency is the limiting factor for VLDL export from the liver. It has been shown in many species, using a wide variety of experimental approaches, the rate of VLDL export is highly related to the rate of phosphatidylcholine synthesis (Cole et al., 2012). Hence when animals are deficient in choline they are prone to develop fatty liver. In fact, during the first week of lactation when the cow is undergoing negative energy balance, choline metabolites in the plasma are at their lowest (Artegoitia et al., 2014; Imhasly et al., 2015).
Ruminal destruction of dietary choline is high in dairy cows and very little is available to the small intestine for absorption (Atkins et al., 1988; Sharma and Erdman, 1989). Therefore, ruminants are highly dependent on supplemental forms of rumen protected choline. Several published research experiments have provided evidence of fatty liver alleviation when supplying cows with rumen protected choline (Cooke et al., 2007; Zom et al., 2011 and Zenobi et al., 2018). Additionally, Dutch researchers (Goselink et al., 2012) demonstrated greater gene expression for proteins involved with lipoprotein synthesis and assembly in liver of transition cows supplemented with rumen-protected choline.
Choline is Essential for Cow Health and Productivity
The effects of supplying intestinally available choline go beyond improvements in just liver health. A review of university trials has consistently shown a milk production improvement for cows receiving choline during the transition phase. University of Florida data demonstrates the lasting impact choline delivers. In the study, cows fed ReaShure during the transition period had higher peaks and produced an additional 2,10 kg of milk per day during the 40-week trial period. That resulted in 640,50 kg more milk per cow over a 305-day lactation, on average.
Reduced incidences of metabolic disorders, such as clinical ketosis and mastitis, have been observed when feeding rumen-protected choline during the transition period (Lima et al., 2011). A recent meta-analysis of 21 experiments in which rumen-protected choline was fed to multiparous transition cows revealed increases in pre- and postpartum DMI, and improved yields of milk, ECM, protein and fat when compared to unsupplemented controls (Arshad et al., 2020).
Choline Impacts Calf Health and Growth
While health and milk production benefits alone solidify choline as a valuable nutrient for transition cows, new research shows additional benefits for calves when dams receive rumen protected choline during the transition period. Calves exposed to choline in utero or fed colostrum from cows fed choline are healthier, eat more dry matter and grow faster than calves not exposed to choline. These beneficial effects highlight choline’s role as a source for labile methyl groups, playing an important role in DNA methylation and nutrigenomics during the critical periods of gestation. (Table 3 from ReaShure-XC EMEA brochure)
Choline is Required
Research demonstrates choline’s essentiality for growth, development and good health for animals and humans. Choline is a biochemical building block and precursor to numerous compounds involved in supporting life. For dairy cattle, choline serves many roles and is essential for health and productivity. Decades of research shows that supplementing with rumen-protected choline can increase milk production, reduce the incidence of transition metabolic disorders and improve growth and survivability of calves born to cows supplemented with choline. All of these improvements are economically important to dairy producers and solidifies the fact that choline is not an optional nutrient for dairy cows, but that it is required.