ASAE Conference Proceeding
This is not a peer-reviewed article.
Orientation on Techniques for Reducing Heat Stress amongst Lactating Sows
A.V. van Wagenberg
Research Institute for Pig Husbandry, Rosmalen, The Netherlands, M.A.H.H. Smolders
Experimental Farm for Pig Husbandry “South- and West- Netherlands” Sterksel, The Netherlands, E.N.J. van Ouwerkerk
Livestock Production Engineering Department, IMAG Wageningen University and Research Centre, The Netherlands
In Swine Housing, Proc. First Int. Conf. (October 9-11, 2000, Des Moines, Iowa), pp. 197-204 St. Joseph, Mich.: ASAE. ,Pub. Date 2000/10/09 . ASAE Pub #701P0001
The climatic requirement of the lactating sow is considerably different from the climatic requirements of her piglets. This leads to practical problems, because it is not (yet) possible to separate the piglet’s microclimate form the climate for the sow. The temperature in the barn will in a majority of the time be higher than the upper limit of the comfort zone, which may cause heat stress for the sow. A high ambient temperature for the sow causes decrease of feed intake and thus loss of body weight and back fat and decreased milk production.
In the present study two techniques for creating a microclimate for the sow were tested. The techniques were floor cooling under the sow and an air blower at the head of the sow.
The floor cooling was situated in two pens under the front (shoulder and neck) of the sow’s body. Under the steel plasticized metal slats a cold water circuit is welded. Cool water (about 14ºC) flows into a close separated water circuit under the slats. With the air-blow technique the air was blown, creating airspeed of about 0.5 m/s around the head of the sow, also in two pens.
In a preliminary study (April - October 1999) it was concluded that the cooling systems can practically be implemented in a farrowing pen without causing an uncomfortable situation for the sow and her piglets.
During two batches (October - December 1999) sow feed intake, sow weight loss and piglet growth have been recorded for the two pens with floor cooling, the two pens with air blowers and two reference pens. The measured heat loss to the water in the floor cooling circuit was between 70 and 105 Watt per sow.
The simulation software ANIPRO (Van Ouwerkerk, 1999) was used to make calculations of the upper limit of the comfort zone for the sows housed in the experimental pens. The cooling technique increases the calculated upper limit of the thermoneutral zone with 0.5ºC for air-blowers and with 1ºC for floor cooling compared to a situation without cooling technique.KEYWORDS: Heat stress, Farrowing pen, Cooling systems, Modelling
The climatic requirement of the lactating sow is considerably different from the climatic requirements of her piglets. This leads to practical problems, because it is not (yet) possible to separate the piglet’s microclimate from the climate for the sow. The climate in the farrowing pen will therefore be a compromise between the requirements of the piglets and of the sow (Makkink et al ., 1994). The temperature in the barn will in a majority of the time be higher than the upper limit of the comfort zone, which may cause heat stress for the sow.
A high ambient temperature for the sow causes decrease of feed intake and thus loss of body weight and back fat and decreased milk production. This may cause a reduced growth of the piglets (Prunier, 1997; Mullan, 1991 and Schoenherr et al ., 1988).
A low temperature for the piglets decreases their vitality and hence increases mortality during the pre-weaning period (Raap et al. , 1988). To create a warmer microclimate for the piglets floor heating and heat-lamps are used. The present study focuses on creating a cooler microclimate for the sow.
Normally a sow looses heat through convection, conduction and radiation. By cooling the floor under the sow the heat losses by conduction will increase which allows the air temperature around the sow to be higher without causing heat stress. By raising the airspeed around the body of the sow the heat loss through convection will increase.
In this research two techniques for creating a microclimate for the farrowing sow are tested on practical implementation. The techniques are floor cooling under the sow and an air blower at the head of the sow. In a preliminary phase the developed techniques were tested and fine-tuned. During the two observation periods production results were collected to generate input data for the simulation software ANIPRO, which was used to calculate the upper limit of the thermoneutral zone of the sow during the farrowing period.
Materials and Methods
A brief description of the experimental units is given, after which the cooling techniques are described in detail.
The experiment was carried out in one farrowing room of the Experimental Farm for Pig Husbandry “South- and West- Netherlands” at Sterksel in October and November 1999. Both cooling techniques were installed in two pens in a compartment with 12 sows. In figure 1 a cross section of the experimental room is shown.
The room was equipped with a control path with a solid floor and with two rows of six farrowing pens of 1.65 x 2.45 m on each side. The farrowing pens were fully slatted with plastic coated metal slats with a solid floor area for the piglets of 0.6 m 2 . At the front of every row of sows a narrow control path was built. The floor of this path was made of metal slats and the path was used as an air inlet from under the floor.
In the compartment manure trays were installed. A manure tray is a shallow plastic tray installed below the slats which reduces the ammonia emission based on the principle of reducing the emitting surface using a sloped floor and frequent manure removal from the compartment. The height of the air channel under the manure tray was 0.4 m. The clean space between the concrete floor of the compartment and the underside of the manure trays was used as an air-inlet channel.
Figure 1. Cross section of the experimental farrowing compartment with air inlet system
Detailed description of the cooling techniques
The floor under the front (shoulder and neck) of the sow’s body was cooled ( ˜ 0.1 m 2 ). Under the steel plastic coated slats a cold water circuit was welded. Cool water (about 14ºC) flowed into a closed separated water circuit under the slats. The temperature of the water in this circuit could be adjusted and was automatically controlled. The location of the cooling elements was designed so that the udder was only marginally affected hardly cooled. Cooling the udder would cause a higher risk for mastitis (udder inflammation). A detailed pen layout is drawn in figure 2.
Figure 2. Detailed pen layout with cooling element in the floor under the sow (plan from above)
The air blowers have been tested in two pens. In both the pens the air blower was orientated in a different way, but both were based on the same principle and had the same estimated cooling effect on the sow (see figure 3). The two different air-blowers were developed to measure the effect of the air-blower on the airspeed in the heated piglet zone.
The air was blown at the sow’s head creating airspeed of about 0.5 m/s around the head of the sow. The air was taken from the inlet channels in front of the pens, so the air temperature was equal to the room temperature.
Figure 3. Details of air blowers in the sow pens (plan from above)
Weight of the litter
The daily weight gain of the litter was derived from the birth weight and the weight at weaning according to the method of Everts et al. (1995).
Milk production of the sow
For determining the milk production of the sow the method from Everts et al . (1995) was used. In this method the milk production is estimated from the weight gain of the litter. It is corrected for the weight gain of the piglets caused by the feed intake of the piglets (van der Peet - Schwering, pers. inf.). The output of the model of Everts et al . (1995) is based on weekly means. A polynomial fit (second order) was used for calculating the milk production per day for each sow.
The simulation software ANIPRO
To calculate the influence of the cooling technique on the upper limit of the thermoneutral zone the software ANIPRO was used. ANIPRO is a simulation model what can solve an energy balance over an imaginary sow. Input variables are feed intake, sow body weight, milk production and environmental conditions (Van Ouwerkerk, 1999).
Observations and measurements
Starting up phase
Lying behaviour of the sows and her piglets on the cooling system was recorded (May 1999 - October 1999) to investigate whether the systems could practically be implemented and whether there was any effect on the comfort of the animals. The observations were carried out 8 times per period, randomly during the day.
The results of the preliminary phase were used to adapt the systems and determine the water temperature in the floor and the air speed near the heads of the sows.
The main experiment was started in October 1999. The results presented in this paper have been collected during two periods (October 1999 - December 1999). The observations and measurements that were done are: feed intake sow (daily), body weight sow, (before farrowing and at weaning), body weight litter (at birth and at weaning), feed intake piglets (from birth till weaning), number of piglets (daily), heat uptake water in floor (daily).
Starting up of system
Adjustments and adaptations to the cooling system were necessary to make a practical experiment possible without causing an uncomfortable environment for the sow and her piglets. The set point of the water temperature for floor cooling was determined at 14ºC. A lower water temperature resulted for one sow in a red udder, a higher water temperature would reduce the cooling effect. For the air-blowers the fan-speed was adjusted to 0.5 m/s around the head of the sow so that a high airspeed would not affect the piglet zone negatively. The sows in the pens with air-blowers were in 75% of the time lying with their heads in the zone with the high airspeed. In 25% of the time the sow was lying in the back of the pen. The piglets in the pen with air-blowers were sometimes lying in front of the air-pipe what gave a lower airspeed around the sow’s head. The lying behaviour of the sow and her piglets in the pen with floor cooling was not different from the lying behaviour in the reference pen.
Sow allocation to the treatments was balanced for parity and body weight. The weight of the sow after birth was determined from the sow’s bodyweight before birth minus the weight of the litter at birth and minus the afterbirth (assumed to be 5 kg) (van der Peet - Schwering, pers. inf.). In table 1 the average production results in two experimental periods are presented.
Table 1. Average results during the suckling period in the experimental and reference pens (October - December 1999)
number of sows
average sow feed intake [kg/day]
sow body weight loss [kg/day]
litter growth [kg/day]
litter feed intake [kg/period]
loss in backfat thickness [mm]
The heat loss of the sow to the cooling system was between 70 and 110 Watt (see figure 4). Heat uptake in floor cooling circuit is compensated for heat uptake in the system caused by friction of streaming water in the circuit and convection in an empty pen.
Figure 4. Measured heat loss to water in the floor in pen with floor cooling
Weight of the litter
The results for one period (November - December 1999) in the six experimental pens are shown in figure 5.
Figure 5. Calculated body weight of the litter during farrowing period
Milk production of the sow
In figure 6 the calculated milk production during one period (November - December 1999) is shown for the six sows in the experiment.
Figure 6. Calculated milk production of the sows (kg/day) during farrowing period
From figure 5 and figure 6 it can be concluded that there are differences in production between the pens. For the air-blowers pen 2 and the reference pen show the most comparable results, for the floor cooling this is pen 2 and the reference pen. For the sows in those pens the upper limit of the thermoneutral zone was calculated.
The upper limit of the thermoneutral zone
The calculated difference in upper limit of the thermoneutral zone for the sows are shown in figure 7.
Figure 7. Calculated difference in upper limit of the thermoneutral zone (cooling - reference)
The peaks in figure 7 are caused by a reduced feed intake during one day. In the example (figure 7) the average difference between the upper limit of the thermoneutral zone for the sow on floor cooling compared to the sow in the reference pen is 1.4 o C. This implies that the room temperature can be 1.4ºC higher for sows in pens with floor cooling. For air blower this difference is -0.2ºC. The difference in upper limit were, besides by the cooling technique, predominantly affected by differences in the production of the sows (figure 5 and 6).
With comparable input data, the difference between the calculated upper limits of the thermoneutral zone is caused by the cooling technique that is used. The calculated upper limit of the thermoneutral zone increases with 0.5ºC for air-blowers and with 1ºC for floor cooling compared to the situation without cooling.
The main experiment was set up to collect input data for the ANIPRO simulation software. The collected data during the experiment were suitable as input variables in the software ANIPRO, which calculates upper limits of the thermoneutral zone. The calculated upper limit of the thermoneutral zone was always lower than the room temperature. Theoretically this will result in a reduced feed intake, however this was not observed during the research. This indicates that the ANIPRO calculations might overestimate the amount of heat stress the sow really experiences. However, the calculated difference in upper limit of the thermonuetral zone between a locally cooled sow and a reference sow give good insight in the cooling effect of the cool technique.
Too few sows were in the experiment to compare production results, the production of the locally cooled sows in the experiment wasn’t higher than the reference sows. A large scale experiment should be set up to determine the influence of local cooling on the production of the sows. For this more pens have to be equipped with local cooling and the sows have to be selected carefully.
In the pilot phase of the project it was concluded that floor cooling as a cooling system to create a micro climate for the sow can be applied in farrowing pens without causing an uncomfortable environment for the sow and her piglets.
The experimental set up was not suitable to determine influence on productivity of cooling systems on the sows. From the ANIPRO calculations it can be concluded that the upper limit of the thermoneutral zone of the sows in the pen with floor cooling was about 1ºC lower than of the sow in the reference pen, for air blower this was about 0.5ºC.
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