For poultry, Choline supplementation is crucial because it supports healthy liver function, cell structure, and fat metabolism. Even though the beneficial effects of Choline in poultry are well accepted, there is some difference of opinion regarding its use in poultry feed. Some add Choline to most feed formulations, while others prefer to use it more selectively. While some prefer to use Choline, others use methionine or betaine instead. And then there is this question whether herbal or natural Choline can substitute synthetic Choline.

This article is an attempt to clarify some of the facts surrounding Choline’s usage in poultry feed.

Is Choline supplementation necessary?

Any kind of supplement is not required to be added if the birds’ dietary needs are being fulfilled from feed. These are added to improve the nutritional status of the birds or to enhance the nutrient content of feeds when the needs are not being met from feed. Broilers require at least 1,200 mg/kg choline in their feeds and layers require about 1,100 mg/kg feed (Ref: Table 1).

Choline in poultry feed comes majorly from maize, soya or wheat. Out of these, soya and wheat contain more choline as compared to maize. Hence, a formulation based on maize and soya may be required to be supplemented with additional choline (e.g. broiler feed which may contain approx. 80-85% maize and soya). Levels from dietary sources need to be taken into account while working out feed inclusion rates. When it comes to natural feed sources, one needs to keep in mind the fact that fluctuations in composition do occur. Bioavailability of choline also matters e.g. rapeseed meal has a significantly higher choline content than soybean meal but the availability is less than a third to that of soyabean meal (Emmert and Baker, 1997). Therefore, to be sure that the essential requirement for choline is met, choline should be added to the feed.

A number of factors influence a birds’ requirement for choline. Besides age and feed intake, Choline supplementation will also depend on the breed of the birds. In layers, besides age, size of the eggs needs to be considered as choline is an integral part of egg yolk.

Functions of Choline:

As a component of phospholipids, Choline is generally involved in numerous key metabolic pathways and is essential for the structural maintenance of cell membranes. It is a precursor molecule for the formation of acetylcholine in the nervous system. Additionally, Choline is a part of VLDL (very-low-density lipoproteins), which is involved in transportation of triglycerides out of the liver and prevents accumulation of fat in the liver (Ziesel et al, 1983; 1999). It also inhibits the fatty acid synthesis by downregulating fatty acid synthase gene expression as well as attenuating its activity (Sherriff et al., 2016). Furthermore, Choline is referred to as a lipotropic factor due to its role in increasing fat utilization, which results in the reduction of fat deposition in the body (Farina et al., 2017).

Many studies have been carried out to understand the impact of Choline supplementation in both broilers and layers. Lipstein et al. (1977) found that chicks receiving Choline at levels of up to 520 and 480 mg/kg in their basal diets exhibited better growth responses compared to those receiving Choline at 400 and 230 mg/kg in their diets. Pesti et al. (1979; 1980) observed significant increases of 12% in body weight gain with Choline supplementation ranging from 0.04% to 0.39% in diets for chicks and pullets from day-old up to 3 weeks of age. Jiang et al. (2014) found that Choline chloride can lower cholesterol levels in broilers. Rama Rao et al. (2001) found that a diet containing Choline at 760 mg/kg significantly reduced liver fat. Gregg et, al. (2022), reported that supplemental Choline chloride positively impacted carcass characteristics of modern, large frame broilers.

Choline is vital for layers, just as it is for broilers. One important application is in the synthesis of lecithin, a phospholipid found in egg yolks. A layer hen’s need for Choline can be influenced by a variety of factors, including age, feed consumption, and levels of methionine or crude protein in the diet. It is generally acknowledged that dietary requirement declines with age, possibly linked to a rise in feed consumption (Workel, 1998). The absence of Choline, or levels below the recommendation, increases deleterious effects on meat chickens, such as reduction in growth due to fatty liver and perosis, especially in younger birds (Santiago et al., 2020). Table 1 provides the normal Choline requirements for different poultry species.

Similarities and differences between Choline, Methionine and Betaine:

Nutritional roles of methionine, choline and betaine, are very similar yet different. Choline is a vitamin that has essential metabolic functions, which neither betaine nor methionine can substitute. These essential functions are:

• As a constituent of phospholipids (Javaid et al., 2021) – It plays an important role in cell structure maintenance and cartilage matrix maturation, including prevention of perosis in broilers
• In fat metabolism in the liver (Corbin & Zeisel, 2012) – It promotes fat utilisation and outward transport, which prevents abnormal fat accumulation in hepatocytes or fatty liver
• As a precursor to the neurotransmitter acetyl Choline (Di Zhao,2001) – It helps in nerve impulse transmission (Chaudhari et al., 2017)

It is only in Choline’s non-essential metabolic role, as a source of labile methyl groups, that betaine can substitute for Choline. Methionine is also a methyl donor just like Choline and betaine. But Methionine yields one third of methyl groups compared to Choline (Mihai & Steven, 2002). Methionine is an amino acid and has other important roles to play particularly in growth and development. Betaine can replace Choline as methyl donor but cannot replace it for the other essential functions which Choline performs.

The effect of supplementary betaine in chicks fed with graded levels of choline chloride has been studied by Emmert and Baker (1997). In these studies, a choline free basal diet was used. Adding choline chloride had a positive effect on growth and feed conversion. The addition of betaine at a concentration of 500 mg/kg feed to the basal diet and to diets containing approximately 570 mg choline chloride/kg feed had no effect at all on bird performance. This illustrates that the essential requirement for choline must be met before responses to betaine can be expected.

Choline and methionine metabolism are closely related and both are involved in the conversion of homocysteine to methionine, besides having independent essential roles in nutrition. Choline can partially replace methionine in some situations, but it’s not a good alternative in all cases. Quillin et al. (1961) had suggested that 1 gram of choline can replace 2.3-2.4 grams of methionine in rations containing high levels of fat where the deficiency is only of labile methyl groups. Results from the studies of Mahmoudi et al. (2018) indicate that the methionine requirements of heat-stressed broiler chickens can be reduced by 20% (1200 mg/kg) if the diet is supplemented with 280 mg/kg of Choline.

Can Herbal Sources of Choline Replace Synthetic Choline?

Choline has been a widely used supplement in livestock and poultry nutrition for decades. Traditionally it has been administered through synthetic sources but its high hygroscopicity and oxidation, vitamin losses, its corrosive nature, and trimethylamine formation in birds’ digestive tracts led the producers and scientists to look for alternative sources. Tavcar-Kalchar (2007) showed that Choline chloride increased the oxidation of vitamins in feed due to its hygroscopic nature.

Different types of herbs and herbal combinations have been tried to replace synthetic Choline. Most studies have concluded that natural or herbal sources can adequately replace synthetic Choline in poultry feed. Besides this, these formulations with herbs and other natural sources offer additional benefits like hepatoprotection, performance improvement and carcass quality improvement. These natural products, produced from select plants and blends of herbs, can mimic the function of Choline (Calderano et al., 2015). Additionally, phytoconstituents present in herbal Choline formulations modulate liver genes that are responsible for fat metabolism and lipogenesis, thus increasing muscular energy availability and fat utilization.

Khose et al., (2018) suggested that herbal Choline supplementation at 0.350 and 0.500 kg of feed can effectively substitute 1 Kg of synthetic Choline chloride (60%) of broiler feed. Khose et al. (2019) demonstrated the advantages of herbal Choline supplementation at 0.5 kg/t of feed in terms of enhanced liver protection, carcass traits, and economic viability in broiler production. Gangane et al. (2010) reported reduced fatty liver incidence in broilers through herbal Choline feeding.

Conclusion:
Based on the information presented, it can be concluded that Choline is a potent lipotropic agent that significantly influences fat metabolism by reducing fat accumulation in the liver and preventing fatty liver disorders. Choline is essential for certain metabolic processes and cannot be replaced by betaine for these functions. These essential properties strongly support the use of Choline as a commercial feed additive to address metabolic disorders and improve the health and productivity of poultry.

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