Introduction

It is now accepted that heat stress is one of the main factors that is causing huge losses in swine production and profits in hot climate regions throughout the world. Heat stress occurs when a physiological strain is placed on the body due to overexertion and overexposure to any combination of excessive environmental factors such as temperature, humidity, radiation and wind-producing conditions that are higher than the animal’s thermo-neutral zone. Heat stress causes discomfort and negatively affects feed intake, growth and productivity. Economic losses due to heat stress are usually caused by lowered performance, decrease in reproductive function and increase in deaths.

Heat Stress in Commercial Pigs

Pigs are more sensitive to high ambient temperatures than other species of livestock because they do not have sweat glands and do not pant very well. If presented with the option, their natural tendency is to seek out water to wet their skin by wallowing. The evaporation of water from their skin lowers body temperature. Modern pigs bred for commercial purposes are fast-growing and lean, generating more heat than their counterparts in the wild. This, in combination with confined housing and high stocking densities, makes it difficult for pigs to thermo-regulate and eliminate excessive body heat. Heat-stressed pigs have low performance, poor production results and impaired reproductive function. Above certain critical temperatures, pigs start adapting their mechanisms of balancing heat loss and heat production. High enough temperatures can even cause death.

How to Reduce Heat Stress in Pigs

In conventional pig pens, there are a number of factors that can influence animal comfort, such as air temperature, air movement, air speed, radiant temperature, flooring and use of bedding, as well as stocking density. Before an expected warm period, it is advisable to closely examine the conditions that may lead to increased pen temperatures, so that the necessary precautions may be taken to eliminate or minimise them.

As temperatures rise, a pig breathes more rapidly to increase the evaporation rate of moisture from its lungs, thereby obtaining a greater cooling effect. When the relative humidity of the pen is high, the cooling advantage from breathing is markedly reduced due to the lowered rate of evaporation. It is important to ensure sufficient ventilation to reduce the amount of moisture built up in the pen, thus effectively eliminating heat generated by the animals.

The availability of cooling systems such as floor cooling, water bath or sprinklers, all have beneficial effects on the performance and welfare of pigs under high temperature conditions. Spraying or drip cooling can be used to relieve or reduce heat stress in housed animals. Drip cooling is more suitable for restrained animals such as sows in farrowing pens. However, there is still more that can be done to help pigs cope with heat stress.

How Orego-Stim® May Help in Times of Heat Stress

Orego-Stim is a natural, phytogenic feed additive. Besides its antimicrobial and anti-diarrhoeal properties, Orego-Stim has appetising effects to help increase feed intake of pigs during heat stress periods while simultaneously boosting the immune system to help them cope with the physiological stress of high environmental temperatures.

Heat stress: scenario 1

A trial was recently conducted in a select farm of 5,000 sows in Huesca in the Aragon region of northeastern Spain to verify the ability of Orego-Stim to control heat stress in reproductive sows during a period of hot weather.

There were no significant differences between Orego-Stim-treated sows and control sows during the first four weeks of treatment. However, from the fifth week onwards, there was improved fertility in the Orego-Stim-treated sows and it remained better than the control sows until the 37th week when Orego-Stim was finally removed.

By the end of the trial, the average weekly fertility in the Orego-Stim group was 82 per cent compared to 79 per cent in the control group, an improvement of three per cent. Sows that received Orego-Stim in their diets had three per cent more piglets born alive than sows that did not receive the supplement. The weaning-to-oestrus interval improved by three per cent and the weaning-to-service interval improved by four per cent compared to the control sows. Piglets from sows whose diets were supplemented with Orego-Stim; were two per cent heavier at weaning than piglets from control sows.

Figure 1. Effect of Orego-Stim on the fertility of sows during heat stress

Heat stress scenario 2

A separate study was designed to investigate the effect of Orego-Stim on sows and their piglets’ performance and as a growth-enhancing and alternative antibacterial in sows and their piglets’ feed. The trial was conducted by Professor Dr Jowaman Khajarern from the Department of Animal Science of Khon Kaen University in Thailand in a well-managed commercial farm during a heat-stress period. Orego-Stim was supplemented in the gestation feed at day 84 of the gestation period, which is about a month before farrowing, and continued throughout the entire lactation period until farrowing. Orego-Stim was also subsequently added into the creep feed of the piglets.

The reproductive performance of sows and the growth performance and health of their litters were compared between 12 sows on Orego-Stim and 12 in the control group. Orego-Stim-fed sows produced a significantly higher number of piglets born alive, average birth weight and total number of piglets at weaning when compared with the control group.

Results from this study proved that the appetising effects of Orego-Stim stimulated a higher feed intake in lactating sows during periods of heat stress. The increase in feed intake translated to a significant increase in milk yield and milk quality which can be measured by an increase in pre-weaning weight gain, greater total weight of piglets weaned per litter and a higher average bodyweight of piglets attained at weaning.

The inclusion of Orego-Stim in the creep feed also mimicked the responses of the lactating feed, as an alternative to antibiotic growth promoters, flavours and appetite enhancers. It also assisted in digestion for better nutrient absorption. Piglets fed with Orego-Stim showed significantly higher feed intake and daily weight gain, better uniformity of bodyweight at weaning and also a higher but non-significant survival rate of piglets at weaning when compared to the control piglets. See Figure 2 for complete results of the trial.

Figure 2. Effect of Orego-Stim on the performance of sows and piglets during heat stress
Parameter	Negative control	Orego-Stim
Number of sows	12	12
Total number of piglets born	125	126
Average number of piglets born per litter	10.42	10.50
Total number of piglets born alive	119	121
Average number of piglets born alive per litter	9.92	10.08
Total birth weight per litter (kg)	15.18b	16.28a
Average birth weight of piglets (kg)	1.55	1.67
Total number of piglets at weaning	114	117
Average number of piglets weaned per litter	9.50	9.75
Survival rate of piglets at weaning (%)	96.12	97.03
Total weight of piglets weaned per litter (kg)	64.62b	70.59a
Average body weight of piglets at weaning (kg)	6.84b	7.26a
Uniformity of body weight of piglets at weaning	87.73b	89.65a
Total feed intake of piglets per litter (kg)	1.54b	1.74a
Average feed intake per piglets (g)	161b	178a
Average daily gain of piglets (g)	252b	268a
Average feed intake of sow during lactation (kg/d)	5.86b	6.33a
Average milk yield (litres/day)	9.53b	10.44a
a, b Means in the same row bearing different superscripts differ (P<0.05)

Figure 3. Observed comparison of mammary glands of control sow (left) and Orego-Stim sow (right)
Figure 4. Piglets from the Orego-Stim sow – heavier, healthier and more uniform