Stress in piglets: a multi-factorial problem

 

 

 

 

Stress is a complex state and management systems – particularly stockmanship and environment – should minimise its effect in pig performance. Changes or an unsuitable situation will cause the body to react in order to maintain its balance and equilibrium, and this defines stress. The physiological event may be a change in blood hormone levels, immunity depression and behavioural changes. Stress is closely linked with welfare and where an animal is subjected to chronic or acute stress it is also very likely to be experiencing poor welfare.

 

It is very difficult to measure and categorise stress. It is also difficult to monitor the exact impact of stress on performance; however we do have some understanding of this.

 

In the newly weaned pig, stress is induced in the process of being separated from the sow, relocation and mixing with unknown piglets, introduction of a novel environment (temperature changes, different flooring types, air quality for example) and a radical change in diet.

 

Therefore, weaning leads to intense taxation of adaptive processes at the behavioural level as well as in terms of neuroendrocine and other physiological levels. The earlier weaning takes place the more impact these stressors have although detailed biological data are still scarce.

 

There is good evidence that a young piglet if exposed to a high level of chronic stress has an associated rise in blood cortisol levels. This can result in reduced feed intake and growth immediately post weaning which has an impact throughout life.

 

It is clear that stress is a multi-factorial problem and when some or all the factors are combined it can result in the piglet reducing its normal dry matter feed intake. The digestive tract will be compromised on the basis of this sudden loss of nutrient intake and the capacity for digestion and absorption of nutrients is reduced.

 

Providing a diet that is suitable for the piglet’s immature digestive tract, as well as careful management, are therefore key to reducing the effects of stress on performance.

 

Digestibility of ingredients has long been known to be imperative and more recently novel ingredients that support the functionality of the digestive tract – such as functional fibres, organic acids and essential oils are also easing the transition at weaning.

 

Stress is also generally thought to suppress the immune system and may lead to an increase in the occurrence of disease in the presence of a pathogen. As with the digestive tract, there are novel ingredients that can support the functionality of the immune system such as nucleotides.

 

In addition, natural antioxidants can also help support immune function. When an animal is stressed the natural process of cell turnover and replication is increased. This has many damaging influences in the body including the ‘release’ of free-radicals that are the products of the breakdown of cell fragments within body tissues. Free radicals are ions, molecules or atoms with unpaired electrons which makes them unstable and highly chemically reactive (oxidative). They are used very effectively in immune defence mechanisms – such as the intracellular killing of bacteria by macrophages. In contrast, these free radicals can also be extremely damaging to the body. Many forms of cancer have been linked with the interaction of free radicals and DNA, with the damaged DNA giving rise to mutations which potentially leads to malignancy. Any biological system cannot function without free radicals and yet they are also the cause of cellular demise. In order to cope with these conflicting functions and effects the body has complex antioxidant systems in place which interact with free radicals rendering them safe.

 

The balance between the processes of oxidation and the prevention of oxidation (antioxidation) is therefore critical in controlling cell integrity and health. If the balance shifts to a high level of oxidation with little inhibition then damaged immunity and poor growth will be the ultimate result for the growing pig and especially so for the post-weaned piglet.

 

Traditionally, vitamin E would be considered as playing a key role in antioxidant pathways. It has typically been supplied in the form of synthetic alpha tocopherol acetate. However, more recently trace elements and many plant based ingredients have been found to have antioxidant properties. Some of the naturally occurring plant derived polyphenols and flavonoids are very powerful complementary antioxidants.

 

There are more than 4,000 distinct species of polyphenoilic antioxidants coming from a wide range of plants – legumes, apples, blackberries, plums, raspberries, cabbage, broccoli, onion and parsley are just a small example of the polyphenoilic rich plants. These compounds can be extracted and utilised in animals feeds. A combination of natural antioxidants alongside vitamin E has been found to give improved health and growth benefits compared with the traditional supply of vitamin E alone. Flavonoids are plant secondary metabolites and actively recycle endogenous levels of vitamin E. Again these can be extracted and used in feed, reducing the requirement for vitamin E supplement in the diet. Figure 1 illustrates the results of a bio assay in broilers where the effects of including a natural antioxidant blend were tested on oxidative resistance (FRAP – Ferric Reducing Antioxidant Power) in body tissue.Replacing three quarters of the vitamin E with a specific blend of antioxidants resulted in the same level of antioxidant protection as 100 mg/kg of vitamin E alone. In the same trial TEAC (Trolox Equivalent Antioxidant Capacity) in the blood was also measured and illustrated similar benefits from the use of the natural antioxidant blend.

 

 

Therefore, natural antioxidant products have a role to play in helping the pig to cope with stress and the linked suppression of the immune system. Natural antioxidants offer cost effective benefits too due to the partial replacement of vitamin E in livestock rations. Total replacement of vitamin E is not recommended however, as vitamin E has other antioxidative functions in the body. Stress management is a major area of discussion in both human and livestock terms. For a young piglet at weaning there are lots of stressors: loss of maternal comfort, new pen mates, new environment, new diet presentation and new water source. It is imperative to minimise the impact of these stressors as far as possible to avoid the post weaning growth check and set piglets on the right track for optimal lifetime performance. Nutrition plays an important role in reducing the impact of stress on performance when it is coupled with good management techniques.