Betaine can spare dietary methionine, choline
Betaine is a feed additive with many functions, one of which can confer direct feed savings.
Betaine is commonly produced by extraction from sugar-beet molasses through chromatagraphic separation and crystallization. The end product is an off-cream powder. Recently, the surge in popularity of bio-ethanol production has allowed the extraction of betaine from vinasse, a by-product of sugar beet-derived bio-ethanol. Synthetic betaine is available as anhydrous betaine, betaine monohydrate, betaine monohydrochloride salt (contains 25 percent hydrochloride to preserve betaine from storage degradation), and betaine monophosphate salt.
One of the most crucial roles of betaine in poultry nutrition is that of a methyl donor in intermediate metabolism. Methyl molecules are important factors to many biological and chemical processes in the body and they must be derived from feed, as the animal cannot synthesize them. In this role, betaine can replace an equal function provided by the amino acid methionine and the vitamin choline, thus sparing both from this side role. Methionine (an expensive amino acid) can thus be used for growth and development, whereas choline (an expensive vitamin) supplementation can be kept at minimum required levels.
Recent evidence suggests that animals might have a requirement for preformed (that is of dietary origin) methyl groups. Whereas methionine and choline are used for protein synthesis and the formation of cell membranes and neurotransmitters, excess (dietary) betaine may be used directly as a methyl group donor. It is interesting to note that for choline to serve as a methyl donor, it needs first to be converted to betaine. Dietary betaine can act as a direct replacement for choline, saving the organism of one metabolic step, and of course sparing dietary choline itself.
In regards to methionine, the transfer of a methyl group depends on the activation of methionine to S-adenosyl methionine (SAM). This compound transfers then the methyl group to an acceptor for the synthesis of substances such as creatine, carnitine, phosphatidylcholine and epinephrine. Following the transmethylation, SAM is degraded to S-adenosyl homocysteine (SAH) and subsequently to homocysteine, which can have two distinct fates, one involving betaine.
First, homocysteine can be transformed to cystathionine and then to cysteine (an essential amino acid used for protein synthesis). Second, homocysteine can be re-methylated back to methionine, either via the betaine pathway or by means of the tetrahydrofolate (THF) pathway (involving folate and vitamin B12). The former pathway involves the transport of the preformed methyl group from betaine to homocysteine. Thus, betaine’s sparing effect on methionine.
In practical terms, research has indicated betaine can indeed spare a portion of dietary (added) methionine and choline. In fact, betaine is at least as effective as methionine in promoting growth performance in poultry fed diets marginal in methionine. Under practical conditions, it appears that the relative bioavailability of betaine compared to methionine is about 60 percent. Based on this figure, it can be said that 1 kg betaine can replace 0.6 kg of added methionine. Conversely, 1 kg methionine must be replaced by at least 1.65 kg betaine. Whether it is economical to use betaine instead of methionine, this depends on the relative prices of the two ingredients, with methionine price being widely variable within any given year.
In regards to choline, it has been estimated that on average betaine can replace about 25-50 percent of added choline in broilers, and up to 100 percent in laying hens. Here, it should be emphasized that research on this issue is rather limited, and as such, under practical conditions it is best to follow a conservative approach. It should be remembered that choline has also other roles in the organism and thus, no more than 25 percent added choline should be replaced by betaine. Similar calculations based on current prices for choline and betaine will determine potential savings.