Interpretive Summary: Meta-regression analysis to predict the influence of branched-chain and large neutral amino acids on growth performance of pigs.
By: Dr. Thomas Powell
The optimization of diets to provide adequate amounts of essential amino acids at minimum cost is at the core of swine nutrition management. Common practice is to fortify a low crude protein diet with specific amino acids, typically lysine (Lys), threonine (Thr), methionine (Met), tryptophan (Trp) and valine (Val). This allows for use of low cost feedstuffs for the majority of the ration and still meet the nutritional requirements of growing pigs.
While straightforward in concept, there are caveats. One characteristic of common swine diets is that though the diet may be optimized to provide the minimum required level of amino acids, there are some amino acids present in very high levels. Specifically, leucine (Leu) is typically in excess in corn-based diets (including corn by-products such as distillers grains). The branched-chain amino acids (BCAA) Leu, Isoleucine (Ile) and Val are similar in structure and share the same brain transporters as the other large neutral amino acids. Research has shown that the ratios of specific amino acids can affect the metabolism of other amino acids and can alter neurotransmitter feedback mechanisms in the animal that regulate feed intake.
Researchers at Kansas State University recently published an analysis in the Journal of Animal Science that mined the data from 44 feeding trials published in 25 papers from 1996 to 2018. They developed prediction equations to quantify the effects of dietary BCAA and their interactions with other amino acids on the growth of nursery and growing-finishing pigs.
Optimum equations were reached for average daily gain and grain-to-feed ratio. Average daily feed intake was not predictable directly from the data set so estimates were calculated from the predicted average daily gain and grain-to-feed ratio values.
The core finding after analysis of the equations is that increasing the Leu:Lys ratio has a negative effect on predicted performance. Based on prior research findings, it is hypothesized that during metabolism of the BCAA, stimulation of enzymatic activity by one of the BCAA will increase the catabolism of all BCAA. This antagonistic metabolic response is detrimental when the excess of one BCAA occurs while the others are marginally meeting or below the requirement.
According to the equation models, the addition of Val, Ile and Trp has the potential to mitigate the negative effects of high dietary Leu. The paper includes an extensive description of the metabolic pathways and feedback mechanisms that are affected by levels of and interactions between BCAA and other long chain amino neutral amino acids.
Field trials are the next necessary step in validating the predicted growth performance generated by these equation models. If the models are confirmed, these equations will be a valuable tool enabling nutritionists to compensate for the negative effects of high Leu:Lys in common diet formulations. This would further increase growth performance at the lowest possible cost.
To view the full article, visit the Journal of Animal Science.