Pigs are often fed low-protein diets to reduce nitrogen excretion and improve environmental sustainability.
However, this can have negative effects on their welfare, such as increased tail biting and liver damage.
A new study from Wageningen University & Research has found that supplementing low-protein diets with essential amino acids can prevent these problems and improve pig health.
The role of amino acids in pig nutrition
(Photo : BERTRAND GUAY/AFP via Getty Images)
Amino acids are the building blocks of proteins, which are essential for the growth, health, and welfare of pigs.
Pigs cannot synthesize some amino acids, such as lysine, methionine, and threonine, and need to obtain them from their diet. These are called indispensable amino acids (IAA).
Low-protein diets can limit the intake of IAA, which can affect pig performance and behavior. Previous studies have shown that pigs fed low-protein diets tend to be more active and show more foraging and damaging behaviors, such as tail biting, than pigs fed normal-protein diets.
Tail biting can cause stress, pain, infection, and reduced growth in the affected pigs, as well as carcass condemnation and economic losses for the farmers.
One of the possible reasons for the increased tail biting in pigs fed low-protein diets is the reduced production of odd-chain fatty acids (OCFA) and short-chain fatty acids (SCFA) in the liver.
These fatty acids are derived from the metabolism of amino acids by the peroxisomes and mitochondria, the organelles that regulate energy and lipid production in the cells.
OCFA and SCFA have been shown to have anti-inflammatory and neuroprotective effects, and to correlate inversely with the risk of obesity, insulin resistance, and non-alcoholic fatty liver disease (NAFLD).
Another possible reason is the altered gut microbiota composition and activity in pigs fed low-protein diets.
The gut microbiota is the community of microorganisms that live in the digestive tract and influence various aspects of pig health and behavior.
The gut microbiota can also produce OCFA and SCFA from the fermentation of dietary fiber and protein.
However, low-protein diets can reduce the diversity and abundance of beneficial bacteria and increase the production of harmful substances, such as ammonia and indole, that can damage the intestinal barrier and cause inflammation.
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The benefits of amino acid supplementation in low-protein diets
The researchers from Wageningen University & Research conducted an experiment to test the effect of supplementing low-protein diets with IAA or providing extra environmental enrichment on tail biting and liver health in pigs.
They used 48 groups of 12 undocked pigs that received either a normal-protein diet (NP), a low-protein diet (LP), a low-protein diet with supplemented IAA (LP+), or a low-protein diet with extra environmental enrichment (LP-E+) during the starter, grower, and finisher phases.
They measured the feed intake, growth, behavior, and body damage of the pigs, as well as the liver weight, histology, and gene expression at slaughter.
The results showed that pigs fed LP and LP-E+ had lower feed intake, growth, and feed efficiency than pigs fed NP and LP+.
Pigs fed LP also showed more tail biting than pigs fed NP, LP+, and LP-E+ during the starter phase and the finisher phase (tendency).
The tail damage was more severe in pigs fed LP than in pigs fed NP and LP+, with pigs fed LP-E+ in between.
The liver weight was lower in pigs fed LP and LP-E+ than in pigs fed NP and LP+. The liver histology and gene expression revealed signs of inflammation, oxidative stress, and fibrosis in pigs fed LP and LP-E+, indicating NAFLD.
The researchers concluded that IAA supplementation was more effective than extra environmental enrichment in counteracting the negative effects of a low-protein diet on tail biting and liver health in pigs.
They suggested that IAA supplementation could restore the production of OCFA and SCFA in the liver and the gut, and modulate the gut microbiota composition and activity, thereby reducing the inflammation and oxidative stress in the liver and the attraction to blood in the tail.
Implications and limitations of the study
The study provides valuable insights into the role of amino acids in pig nutrition and welfare, and the potential of using IAA supplementation as a strategy to improve the sustainability and profitability of pig production.
However, the study also has some limitations that need to be considered.
First, the study used a relatively small number of pigs and groups, which may limit the statistical power and the generalizability of the results.
Second, the study did not measure the concentrations of OCFA and SCFA in the liver and the gut, or the gut microbiota composition and activity, which would have provided more direct evidence for the mechanisms underlying the effects of IAA supplementation.
Third, the study did not compare the effects of different levels and patterns of IAA supplementation, which could have optimized the formulation and efficiency of low-protein diets .
Therefore, further research is needed to confirm and expand the findings of the study, and to explore the optimal ways of using amino acid supplementation in low-protein diets for pigs.
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