The impact on the environment, welfare issues, as well as the economic implications are challenging globally the modern livestock production. Employment of new nutritional strategies to limit the impact of the livestock production on the environment, have become an important task.
Optimization in the feed formulation lowering the crude protein content, for the so-called N-reduced feeding, is one of the best possible nutritional strategies for environment consideration, where the synthetic amino acids have a significant role. The synergy between low-protein feed formulation and nutritional solutions for better bioavailability of the nutrients in the feed, could really contribute to the reduction of nitrogen excretion in the nature.
The main physiological functions of betaine (BET) or tri-methyl-glycine widely known are 1) related to its methyl donor role, converting homocysteine into methionine and 2) related to its osmolyte role, restoring and maintaining cellular integrity and functionality, protecting against dehydration.
Beside of these effects, when BET donates one methyl group to homocysteine, the remaining two methyl-groups, will form the so-called di-methyl-glycine, which will be converted into glycine. So, that means that BET also provides indirectly one glycine molecule to the animals as depicted in Figure 1.
Even though glycine is considered a non-essential amino acid (NEAA), it became an important issue in the last years due to the reduction of crude protein (CP) content in diets for monogastric animals. As already noted, a reduction of CP without negative impact on performance is possible only with a proper supplementation with amino acids; in fact, we are talking about the supplementation of the essential amino acids (EAA). When CP is reduced more than 3%, glycine and serine levels may decrease drastically, which can result in lower performance responses (Ospinas-Rojas et al. 2013). Besides protein synthesis, glycine plays also an important role in the energy metabolism (gluconeogenesis) and digestion of fat, since it is one of the amino acids present in the bile salts.
Moreover, glycine has many other functions and that is why Akinde (2014) calls it in his review paper, a multitasking amino acid involved in multiple metabolic and functional systems as highlighted in Table 1.
One of these functions is to produce uric acid to eliminate the excess of nitrogen from the body via the urine. Glycine and serine but also threonine are important amino acids in glycosylated proteins in mucins. When the glycine level is low, some essential amino acids such as threonine, which is a precursor of glycine, will have to be converted into glycine, meaning that less threonine will be available for production purposes. Considering the above mentioned, the requirement of glycine in low CP diets can be higher and according to Corzo et al. (2009), among all NEAA that have been tested, only glycine could restore performance. So therefore, birds fed diets low in CP levels (and consequently low in glycine plus serine) might respond positively with the supplementation of BET since the “glycine deficiency” might be counteracted by the glycine supply coming from BET. In that case, we talk about diets with normal levels of all essential amino acids, including methionine.
Based on this, a trial was carried out in The Netherlands, which aimed to determine the effect of BET supplementation in diets with mid-low CP and glycine levels on productive performance of broiler chickens, from day 0-21 of age.
480 one-d-old Ross 308 male broilers were allocated in 4 treatments, with 6 replicates of 20 birds (24 pens / 2.2 m2 each). Three BET products were added in the starter (day 0-7) and grower diets (day 7-21) (700 and 600 ppm of active BET respectively), containing a mid-low CP and glycine levels as presented in Table 2 and figure 2, respectively figure 3:
All diets contained normal levels of all essential amino acids. The premix of the starter diet contained 110 ppm choline and no choline was added in the premix used in the grower diet. Diets were pelleted and based on maize, wheat and soybean meal.
Results from the starter (day 0-7) and grower (day 7-21) phases as well as from day 0-21 of age are described in Table 3.
In the starter phase, no significant differences among treatments were observed for the parameters studied. A significant effect for BWG and FCR where observed from day 7-21 and 0-21 of age. Diets containing either ActiBeet L, ActiBeet VC or ActiBeet SD resulted in higher BWG and better FCR compared with the diet without BET (see Figure 4):
Considering the results, we can conclude that the use of natural betaine product as liquid or dried, in diets with:
1) mid-low CP and lower glycine plus serine levels,
2) low levels of choline and
3) with normal levels of essential amino acids, can improve performance of broilers up to day 21 of age.
The results confirm, that glycine is an important NEAA and can counteract the negative effect on performance in diets formulated with mid-low levels on CP. The dietary NEAA/EAA ratio seems to be an important factor in defining the performance of broilers in N-reduced feeding strategies. However, the results shown that betaine can contribute to increase the glycine level in diets with lowered levels on CP.
The global protein gap, the almost weekly headlines linked to livestock production and environment pollution, and consumer acceptance are the driver to re-consider the N-reduced feeding strategies.
Due to its multi-functionality, natural betaine is a proven nutritional aid to protect against heat- and osmotic-stress, it is the most efficient methyl-group donor in the homocysteine - methionine cycle and it is an important source of glycine.
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