This article appears in the May/June issue of Pig International. View all of the articles in the digital edition of this magazine.


Climate during the summer months differs between Southern and Northern China; high temperatures and excessive humidity characterize the South, whereas the North is also hot but much drier. Thus, the nutrition program of breeding sows requires different consideration.

Normal physiological response to summer heat

In China, like everywhere in the world during hot months, sows, and especially lactating sows, suffer from reduced feed intake that affects their milk yield and subsequent reproductive performance. The process of eating, digesting and metabolizing food nutrients requires the expenditure of energy. This energy is transformed into thermal energy (heat) that is released into the environment. When the external, ambient temperature is already high, this transfer of thermal energy from the animal to the environment becomes problematic, especially when humidity is also very high. As such, the animal naturally avoids all activities that involve production of extra heat, the most important of which are feed and physical activity. This is a natural response to an uncomfortable situation.

Reduced performance due to heat stress

As a result of reduced feed intake in response to heat stress, lactating sows mobilize body energy reserves (lipids) to sustain milk production. This process is highly inefficient and results in reduced milk yield, leaving the sow at a poor body condition at the end of her lactation period. Thus, not only litter weight gain and survivability are reduced, but also sow reproductive performance is reduced. Sows in bad body condition take longer to conceive their next litter, and a subsequent number of piglets born alive is always reduced.

Sows will consume enough feed only if they are able to drink enough water.

Thus, every effort to enhance feed intake without causing heat discomfort to the animal is beneficial in the short- (piglets) and long-term (sows). Of course, the most important advice is to shield sows from the adverse effects of summer heat. These include providing ample shade (in outdoor operations), insulation and ventilation (in indoor operations). Also, water dripping at shoulder level has been proven a relief under extreme heat stress.

Nutritional intervention measures

When it comes to nutrition, there are several areas where we can help sows cope with summer heat stress. Not all measures described below are applicable in all farms, and the assistance of a qualified nutritionist should be sought after to ensure the right approach is used in each case.

1. Nutrient density

It is generally assumed that some part of the normal nutrient intake can be maintained during the summer months if nutrient density increases proportionally to the expected reduction in feed intake. For example, if feed intake is expected to drop by 10 percent, then all nutrients (including vitamins, minerals and trace minerals) should be increased by 10 percent to compensate for the reduction in feed intake. For several nutrients, however, there are manufacturing limits that may restrict the application of this strategy. For example, it is not always practical to add more than 6-8 percent fat or oil in commercial diets to increase dietary energy concentration. Also, the concentration of certain additives cannot be altered due to regulations.

2. Dietary protein

Excess protein is invariably deaminated and excreted in the form of urea. This process also generates heat, and to this end, it is highly recommended to reduce dietary protein concentration with the aid of feed-grade amino acids. The extent of reduction is a matter of current diet formulation, available ingredients and cost of feed-grade amino acids as the diet must remain balanced in all amino acids. Usually a drop of 1-2 points is sufficient.

3. Fiber concentration

Fiber digestion and metabolism generates considerably more heat compared to carbohydrates and protein, with fat and lipids generating the least amount of internal heat. One of the more common measures to combat heat stress is to reduce dietary fiber. Care should be taken to avoid constipation through other means, perhaps by adding a suitable additive or by rebalancing the ratio of soluble versus insoluble fiber.


4. Fats and oils

As mentioned above, fats and lipids not only increase dietary density, but they also generate less heat during digestion and metabolism. Therefore, diets high(er) in fat and lipids are suitable for summer feeding. However, it is always imperative to also increase (proportionally) the levels of all amino acids and other nutrients, to avoid unbalancing the diets.

5. Additives

Research and practical experience has clearly demonstrated that adding certain additives may actually improve feed intake in lactating sows. Some additives work through enhancing nutrient digestibility, others by increasing palatability, yet others by controlling internal metabolic processes reducing release of heat through digestion. In other monogastric species, certain vitamins such as vitamin C and vitamin-like compounds such as betaine have been shown to reduce the impact of heat stress. This is a new area for pigs that is promising good results.

6. Pelleted diets

Pelleting increases physical density resulting in higher uptake of nutrients at a given volume of feed. Combined with increased nutrient density, these two strategies help markedly in sustaining daily nutrient intake during heat stress. Pelleting, however, increases feed cost.

7. Liquid diets

One of the major benefits of liquid feeding is that sows can achieve higher feed intakes during the summer months. Perhaps the increased intake of water enables them to control better their internal temperature compared to dry-fed sows. In addition, liquid feed may be more appetizing.

8. Feeding time

Feeding during the cooler evening hours, or even during the night, is an effective measure against severe summer heat. This might create an increase in labor, but withstanding this problem it is a very effective method in enhancing feed intake.

9. Feeding frequency

Smaller and more frequent meals prevent sows from overloading with food, creating an overload of heat released during a short period of time. The exact number of additional feedings depends on available labor, but usually going from two to three meals a day is sufficient.

10. Water intake

Sows will consume enough feed only if they are able to drink enough water. We suggest a minimum of 25 liters per day for lactating sows and up to 40 liters per day during summer months. For this, drinker design, water flow, water quality and drinker management are important areas that need to be revisited before summer heat becomes problematic.


Read more: 6 feed additives for pigs under heat stress