EFFECT OF STRESS IN PIGS.

What a farmer needs to know!

Stress in animals increases with an increasing need for commercial production. Though subsistence farmers do not consider it as a major concern, commercial farmers report mega economic losses due to stress-related factors.

Economic growth and improving standards of living have increased demand for livestock products which calls for intensive production. This comes with confining animals to maximize space as well as making management easier. Animal confinement comes along with different stress factors starting with the environment, nutrition and infection. Abrupt changes of stress factors such as diet, weaning, temperature and infection have a negative impact on livestock health and production. Since animals live in a controlled environment, such stressors are inevitable.

At birth, the porcine immune system is immature and, consequently, there is no protection against the entry of the pathogen. Therefore, hygiene and maintenance of a proper vaccination schedule is key during this time. Additionally, avoiding exposure of the piglets to infection-related stress factors during this period will improve the growth rate and survivability of the piglets.

From seven (7) weeks of life, the gut epithelial cells communicate with intestinal innate immune system, forming a functional barrier to antigens from diet and pathogens. Pathogenic and viral infections e.g. Enterotoxigenic E. Coli and Porcine Epidemic Diarrhoea virus may loosen the intestinal epithelial barrier which affects the animal health and performance.

Common Stress factors in swine:

Heat stress (HS).

Global warming has resulted in climate change which has led to high ambient temperatures globally thus making HS a critical factor in the swine industry. This has led to an economic loss of over 300 million USD per year in the US and billions of dollars on a global scale.

HS increases permeability of porcine gut epithelial cells, oxidative stress and inflammatory responses in the gut. Increased permeability increases the chances of pathogen entry into the animal’s body to cause infection.

Animals have a temperature range called the thermoneutral zone (TNZ) within which they can maintain body temperature and control heat loss. Temperature below TNZ increases feed intake in pigs which expends more energy to remain warm. Since more energy is used in temperature regulation, less energy is available for growth and other physiological activities. This impends growth and development. Additionally, pigs reduce blood flow to the skin, burrow into beddings or huddle together to reduce heat loss. Continued exposure to cold will lead to shivering (skeletal contraction) and eventually death.

Unlike other mammals, pigs lack sweat glands. Therefore, lowering temperature becomes more stressful than raising it back to normal. Hot weather affects the pig’s performance more significantly than cold weather. Therefore, a farmer should ensure a proper ventilation mechanism during summer and hot days.

Additional heat source for piglets in the creep area.

In lactating sows, ambient temperatures above the evaporative critical temperature (ECT) lead to a reduction in food intake, milk yield, and reproductive performance. The fall in food intake is closely associated with a rise in deep body temperature. It is suggested that the direct effect of high temperatures on milk yield may result from a redirection of blood flow to the skin and away from other tissues, including the mammary gland.

Nutritional stress (NS).

Most pig industries monitor growth performance and take it as the most critical factor in production

making nutritional stress the greatest concern for them. NS may be due to nutrient deficient or starvation. Nutrient deficient is always linked to poor feed rations, poor feedstuffs or presence of antinutritional factors that suppress nutrient availability.

It is important to note that some management practices like restricted feeding during gestation confer beneficial effects to the sows.

Generally, feed deprivation and fasting lead to the following:

• It generally has a negative impact on the porcine gut health in terms of immunology and physiology.
• It increases cortisol levels in blood leading to gluconeogenesis in the liver whereby protein reserves are metabolized for energy during stress.
• Fasting may lower glycine availability leading to reduced cell proliferation and protein synthesis.
• There is increased apoptosis in porcine gut epithelial cells whereby cells attach and kill themselves.

In a nutshell, nutritional deficiency or intake of contaminated feed induces the change of intestinal

pro-inflammatory cytokines and modulates barrier function in pigs.

Infectious stress:

The most frequent diseases in swine industry are enteric and respiratory infections which are majorly caused by Escherichia coli, porcine epidemic diarrhoea virus (PEDV), porcine delta coronavirus (PDCoV) and transmissible gastroenteritis coronavirus (TGEV).

Enteric pathogens are pathogens hosted in the intestines and are mainly transmitted through:

•   Drinking water.
•   Feeds and
•   Faeces.

Enteric infection suppresses feed intake and feed conversion efficiency thus lowering productivity because:

•  They disrupt the homeostasis of the epithelial barrier.
•  Pathogens like E.coli induce intestinal damage through osmotic stress which cause diarrhoea.

 In conclusion, a farmer should have good risk analytical skills to easily identify any changes in the animal's environment that may predispose it to stress.