Figure 1 - Thermoneutral zone of growing pigs on fully slatted floor.
24 25 26 27
23
18 19 20 21 22
17 20 40
60 Body weight, kg
80 100 Source: Adapted from Holmes and Close (1977), Van den Hel and Verstegen (1974), and Renaudeau et al. (2011) 120 Comfort Hot
Cold
Figure 2 - Post-prandial heat production depends on meal size (then on the number of meals for a given feed allowance).
0.3 2 meals/d 4 meals/d 7 meals/d 0.2 0.1 0 0 Source: IFIP-INRAE 2 4 6 8 10 12 14 Time of the day 16 18 20 22 24
0 5 10 15 20 25 30 35
long term effects, with impaired performance even when the heat waves are over. In contrast, dividing feed intake into numerous small meals before the arrival of the heat wave can prevent rocketing post-prandial heat production with a potentially reduced intensity of heat stress and long- term consequences (Figure 2). Dividing feed intake over the day should be associated with changes in the time of feed delivery, mainly towards the “less warm” periods of the day (Figure 2). Under a heat wave, it is not always possible to refer to the coldest period of the day as the decrease in ambient temperature that may occur during the night is rather limited, in contrast to what is observed under milder summer days. Under mild hot conditions, for example when temperature rises up to 29°C during the afternoon and decreases to around 20°C during the night, it is possible for the sow to consume the same amount of feed under a constant temperature of 25°C. But when temperature remains above 25°C, it is no longer the case and the higher it is, the more important it is to decrease the feed intake. Therefore, changing the delivery time of the feed is an option to decrease the intensity of heat stress during the warmest periods of the day.
Figure 3 - Heat production is reduced with smaller meals. 0.3 2.05 kg/d/pig 2.50 kg/d/pig 0.2 0.1 0 0 Source: IFIP-INRAE 2 4 6 8 10 12 14 Time of the day 16 18 20 22 24
Contact the authors
nathalie.quiniou@ifip.asso.fr and
david.renaudeau@
inrae.fr for more information.
22 ▶ HEAT STRESS | MAY 2021
0 5 10 15 20 25 30 35
Water intake should be priority Even though this article focuses mainly on nutritional strategies for coping with acute heat stress, the first attention has to be paid on water supply. Providing clean and cool drinking water at all times can really helps animals that are kept under hot conditions. The animals have access to water ad libitum, all day long even when no feed is delivered. As pigs can stop eating in hot conditions, the administration of functional additives via the drinking water supply would have benefits to help the animal cope with heat stress. In the past, in farms equipped with liquid feeding system but without a drinking bowl in the farrowing pens, farmers were advised to deliver water separately from the feed instead of diluting the liquid feed. Nowadays, if drinking bowls or nipples are installed to fit in with legislation, that solves the problem.
Weather warnings Finally, based on weather forecasts, it is possible to anticipate and mitigate extremely hot periods. When a heat wave is forecast, this gives ample time to modify the parameters of the feed delivery; reducing the amount of feed delivered per animal and at modified times (Figure 3). The aim is to reduce the thermoregulatory effort for pigs, so that they can recover rapidly after acute heat stress. Such a strategy could also help prevent mortality rates, which increases with heat waves.
Short-term thermic of feed, kJ/h
Short-term thermic effet of the feed, kJ/h
Ambient temperature, °C
Ambient temperature, °C
Ambient temperature, °C
Lower critical temperature
Upper critical temperature
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