Options to mitigate the effects of heat stress in sows

28th June 2021

Increasing temperatures, increasing problems

Temperatures have risen approximately 2.12 degrees Fahrenheit (1.18 degrees Celsius) since the late 19th century [1].

Source: World Meteorological Organization [2]

This rise in global temperature is causing more extreme weather phenomenon in hot climates, as well as prolonged periods of extreme heat, not only in tropical climates, but also in temperate and Mediterranean climate zones.

The last decade has seen an increase in pig production in typically hot climates such as Asia, South America and Spain. This directly coincides with the warmest seven years on record [1]. Economic losses are incurred when farm animals are raised in places and seasons where temperatures exceed the animal's natural zone of thermal comfort (ZTC). Due to climate change these zones are becoming more widespread as well as lasting for prolonged periods.

Source: EFSA [3]

Pigs are much more sensitive to hot weather than other livestock animals, genetic selection for increasingly leaner genotypes means modern pigs have increased thermal sensitivity, so produce more body heat making them much more prone to suffering from heat stress.

The upper critical temperature in sows is thought to vary between 18 and 22 degrees Celsius. A study has shown that a threshold of 25℃is sufficient to provoke heat stress [3]. Whilst another recorded that nursery sows begin to show signs of heat stress starting at 22℃ [4].

A meta-analysis of publications in the period 1970-2009 revealed the effect of heat stress on feed intake to be more pronounced in recent years [5]. The need for a nutritional strategy to combat the ever-increasing phenomenon of heat stress during lactation is urgently needed.

What is the impact of heat stress on sows?

It is important that pig producers know how to spot the signs of heat stress in their animals, as every factor of heat stress attributes to poor sow welfare. As sows start to overheat, they will begin to hyperventilate, heavily panting as their respiration rate increases. Other obvious signs of heat stress in pigs include spreading out to try to get more floor contact to cool down, as well as splashing of water or fighting for drinkers at the start of a heatwave. Diarrhoea can be a sign of prolonged heat stress, as excessive water absorption causes changes in electrolytes and the acid-base balance. As a sow's temperature rises her feed intake will drop in an attempt to decrease metabolic heat production. Prolonged farrowing is also common in sows under heat stress.

Relationship between sow feed intake and room temperature

Source: Quiniou et al, 2000 [6]

Heat stress can also have a severe impact on sow progeny. In the first five days post insemination heat stress has been shown to significantly reduce the number of viable embryos present at day 27. Prenatal stress from high ambient temperatures may increase the risk of intrauterine growth retardation. Piglets born from heat stressed sows have been shown to demonstrate the epigenetic effect of developing higher levels of back fat in the grower phase [7].

Modern hyper prolific sows can enter a severe catabolic state and undergo increased oxidative damage in late gestation and lactation. In conditions of high oxidative stress there will be reduced reproductive performance in terms of lactating capability, piglet weaning weights and subsequential weaning to service interval.

It's of incredible importance that every step is taken to avoid heat stress occurring in the first place, and there are a number of nutrition and management factors that should be considered. One such strategy is to introduce a novel dietary component to try and counter the effects of heat stress. One such product is LactoCool.


LactoCool is a Devenish technology with a unique combination of ingredients that has been shown to reduce the impact of heat stress on sows and their progeny.

Helping to upregulate the expression of antioxidant proteins, LactoCool helps to protect against the oxidative damage induced during periods of heat stress. It also contains chelated minerals to provide additional antioxidants as well as specific yeasts which have been shown to maintain appetite under heat stress conditions.

LactoCool improves the direct absorption of 1,25 dihydroxy Vitamin D into the blood plasma which helps to spare liver and kidney effort, reducing the cellular energy required for these processes. It also contains elements that aid with vasodilation and calcium and potassium homeostasis which can help mitigate the effects of lower feed intake. LactoCool also helps to increase osmotic concentrations in the cells, hence less energy is used to maintain the water volume in cells.

Research conducted by the Italian veterinary research practice, SuiVet in conjunction with the University of Parma investigated the effects of including LactoCool in the diets of lactating sows in Italian summer conditions. The control group was fed the standard farm mixed farrowing ration. The treatment group was fed the same ration with the addition of 3kg/ton of LactoCool, which lead to a significant increase (<0.001) in the piglet daily live weight gain and trending towards reducing preweaning mortality [8].

Cost of feeding LactoCool over the lactation period (21 days)


Extra weight of piglets weaned per sow

5.34 kg



*Value as of August 2019 based on Italian (CUN) market figures

Besides adding a novel feed ingredient, such as LactoCool, to the diet, there are a number of other nutrition and management factors that need to be considered in mitigating the effects of heat stress in sows.


Feed intake will likely be reduced in hot weather, so the diet should be concentrated to contain adequate energy and nutrients to compensate for lower intake levels. A higher level of fat in the diet will concentrate the energy source, vitamins and minerals must be scaled up accordingly. Fat is one of the more easily digestible dietary components and generates less metabolic heat during digestion compared to starches and protein.

Lowering the crude protein level of a diet can help reduce the amount of metabolic heat the pigs produce as protein uses more energy to digest and absorb than other dietary components.

It is advisable to use less fibre in summer diet formulations and it is important to consider the source of fibre. Fibre is notoriously difficult to digest and to do so generates heat. Fermentable fibres should be replaced with non-soluble sources as the fermentation process by microorganism in the large intestine generates further metabolic heat.


Water Supply

The pre-summer period is a good time to sanitize all the drinking lines and prevent any build-up of bio film which will actively multiply in hot conditions. At the same time, flow rates on all farrowing crate drinkers should be checked to ensure equal delivery rate at the first and last drinker in the line.

Cooling Panels

It is good practice to clean and change the evaporative cooling panels. They tend to lose efficiency over time due to build-up of calcium deposits from "hard" water, dust, pollen and dirt. Recent work in the USA has shown more effective sow cooling to be provided by cooler panels placed underfloor, directly below the forward part of the farrowing crates [7].


If possible, try and adjust feeding times to the cooler hours of the day as this may improve feed intake. Switching to smaller, more frequent meals throughout the day may encourage feed intake. Wetting the feed with water may also encourage the animals to eat and try to use pelleted feed instead of mash.

The best strategies to combat heat stress combine various techniques that reduce animal stress, improve animal performance, and boost the financial result for the farmers. Making some of these changes now can have a positive impact on reproductive and financial performance on farm. Can you afford not to act?

For more information on LactoCool and the other ways to combat heat stress, speak to your Devenish Representative or get in touch with us at info@devenish.com or call +44(0)28 90 755566

References - available upon request

Back to Press Releases