Oxidative stress is one of the processes happening inside a pig’s gut during and after weaning. Feeding trials in both China and Germany have demonstrated that high quality proteins may limit the impact of post-weaning stress syndrome.
More than 25 years of studies and practical experience on farms have demonstrated that the use of highly digestible protein in piglet starter feed results in improved weight gain, a better feed conversion rate and less diarrhoea during the critical weaning phase. While it is well known that this performance improvement is partly due to the piglets’ immature gut, which requires easily digestible nutrients, other biological processes have been less well understood.
This is starting to change. Within the past year, scientists have found strong indications of the missing link between feed proteins and piglet performance. The answer, they believe, lies with oxidative stress and related inflammatory processes.
Findings from recent studies in China and Germany suggest that, when piglets are given starter feeds containing a high quality, easily digestible soy protein, their oxidative stress level is lower – hinting at the possibility to reduce vitamin E addition in piglet diets. The German study also reports an improved inflammatory status. And, as documented in previous studies, piglet growth is improved.
近期中国和德国的研究结果表明，给仔猪喂食含有高质量、易消化的大豆蛋白的饲料时，其氧化应激水平较低 – 这暗示了可以减少仔猪日粮维生素E添加量的可能性。这项德国研究还表明炎症状态有所改善，并且，正如先前研究中所记录的，仔猪生长性能得到了改善。
The health impact of weaning
Oxidative stress is a consequence of all kinds of dietary, social and environmental stress during the life of a high-performing animal. In piglets, it is especially noticeable during the weaning phase, when young animals tend to put on less weight and are more susceptible to disease – a phenomenon known as post-weaning stress syndrome.
氧化应激是高性能动物一生中各种饮食、社群和环境压力共同作用的结果。在仔猪中，在断奶期尤其明显，这个阶段往往体重减轻、易患病 - 这种现象称为断奶后应激综合症。
Social and environmental stress are difficult to avoid, but possibilities do exist to reduce dietary stress, which is typically caused by a poor-quality feed. Although such feed is typically high in protein, much of the protein content is impossible for the young animals to digest and may contain anti-nutritional factors (ANFs), such as soy antigens – factors that can trigger inflammation in the gut. The first symptoms of oxidative stress are decreased immunity, muscle degeneration, loss of appetite, diarrhoea, liver damage and apoptosis (cell death).
社群和环境压力难以避免，但降低饮食压力的可能性确实存在，这通常是由劣质饲料引起的。虽然这种饲料通常蛋白质含量很高，但是大部分蛋白质对于幼崽来说是不可能消化的，并且可能含有抗营养因子（ANF），例如大豆抗原 - 可以引发肠道炎症的因素。氧化应激的最初症状是免疫力下降、肌肉退化、食欲不振、腹泻、肝损伤和细胞凋亡（细胞死亡）。
An opportunity to reduce vitamin E?
When gut inflammation occurs, the piglets’ own radical defence system responds by attacking the cause of the problem. However, if oxidative stress persists, prolonged activation of the radical defence system backfires, causing further gut inflammation or cell death due to the formation of free radicals.
<Figure 1 – Trial to investigate the oxidative status of piglets fed a starter feed containing a specialty soy protein*. Oxidative stress was measured by testing gluthathion peroxidase (GPX) and superoxide dismutase activity (SOD). On day 28, the diets including enzymatically treated soybean meal (ESBM)* had higher (P<0.05) concentrations of sod and gsh-px.>
<图1 - 研究饲喂添加了特种大豆蛋白*的初乳饲料的仔猪的氧化状态的试验。通过测试谷胱甘肽过氧化物酶（GPX）和超氧化物歧化酶活性（SOD）来测量氧化应激。第28天，添加酶处理大豆粉（ESBM）*的配方具有更高（P <0.05）的sod和gsh-px浓度。>
Vitamin E, in the form of alpha tocopherol, is a known natural antioxidant in the radical defence system. This is why many starter feeds contain an extra dose of vitamin E and other additives to support piglet growth and performance during the stressful weaning period. What the Chinese and German feeding trials suggest is that, if piglets are given feed containing a source of high quality protein, the addition of antioxidant additives may be reduced.
Evaluating soy proteins in starter feed
Both studies tested a highly digestible, speciality soy protein with a low ANF content (HP 300, Hamlet Protein) against soybean meal products with a higher content of the antigen beta-conglycinin. The trial conducted at the China Agricultural University in Beijing also evaluated the performance of fishmeal.
The purpose was to investigate the oxidative status of piglets fed a starter feed containing HP 300 or another protein source. Oxidative status was measured by testing gluthathion peroxidase (GPX) and superoxide dismutase activity (SOD), which are indicators of antioxidative capacity. These enzymes are considered main components of the endogenous radical defence system. In this case, the greater the enzyme activity, the higher the antioxidative capacity – and the better the oxidative status.
目的是研究给仔猪饲喂含有HP 300或其他蛋白质来源的饲料时，仔猪的氧化状态。通过测试谷胱甘肽过氧化物酶（GPX）和超氧化物歧化酶活性（SOD）来测量氧化状态，这是抗氧化能力的指标。这些酶被认为是内源性自由基防御系统的主要成分。在这种情况下，酶活性越大，抗氧化能力越高 - 氧化状态越好。
The studies also measured the malonyldialdehyde (MDA) level, which is a strong indicator of lipid peroxidation, and advanced oxidised protein products (AOPP), which indicate protein damage. Both reflect the level of cell damage by free radicals.
Best oxidative status
Piglets fed the speciality soy protein had the best score on all counts compared to other soy proteins, indicating the best oxidative status, and performed on a similar level to fish meal. Another important finding was that the speciality soy protein gave the best growth performance and lowest incidence of diarrhoea of all the soy protein sources in the study.
<Figure 2 – Effect of protein source on haptoglobin levels in piglets. The significantly lower haptoglobin level in the specialty soy protein group indicates an improved inflammatory status.>
<图2 - 蛋白质来源对仔猪触珠蛋白水平的影响。 特种大豆蛋白组中，触珠蛋白水平显着降低，表明炎症状态改善。>
Analyses of piglet blood samples in the German study proved the close relation between oxidative stress and inflammatory processes. While oxidative status was best in piglets fed the speciality soy protein, they also showed the lowest haptoglobin values, an indicator of inflammatory status. At the same time, the level of vitamin E in the blood was higher.
This suggests that piglet immune systems are less challenged when the speciality soy protein is used in starter diets. In this way, more protein and energy are available to promote piglet growth. It is also a strong indication that the use of a high quality protein with a low ANF content may reduce the need for an extra dose of vitamin E and other feed additives with anti-oxidative properties in starter feed.
Together, these studies provide the first evidence that the choice of protein in piglet diets does have an influence on gut inflammation and oxidative status. Many studies have already documented the benefits of low-ANF soy proteins for piglet growth and performance. Further studies are now in the pipeline to confirm the indications: that the biological explanation behind these benefits is reduced oxidative stress.