Today's Pigs Need More Cooling
By Dr. Mike Brumm, Brumm Swine Consultancy, Inc.
While the upper Midwest is still dealing with snow and other winter related weather issues, it is not too late to begin planning for summer heat relief in swine facilities. Because of the pigs inability to sweat and create its own evaporative cooling, management of facilities in warm weather is a major contributor to overall pig comfort and performance.
Many producers make the mistake of thinking that because today’s pigs are leaner than in previous years, the pigs need for assistance with heat removal is reduced. In fact the opposite has occurred. Figure 1 is a chart of heat production by growing pigs. Note that the data set used to produce the chart sorted the pigs according to pre-1988 and post-1988 genetics.
Figure 1. Metabolic heat production by growing pigs.
This natural break in the data set also coincides with a major change in thinking by producers and their genetic suppliers. Around this time, genetic selection for grow-finish traits began placing a major emphasis on high rates of lean gain.
If one thinks about the physiology of growth, the increase in heat production by pigs with higher rates of lean gain should be expected. In the deposition of calories as fat, there is very little heat generated by the pig as the liver has little involvement in the process, other than the creation of the tri-glyceride structure of fat.
On the other hand, when lean growth occurs, the liver is very involved in the conversion of energy, amino acids, minerals, vitamins, etc. into muscle. This conversion process results in an increased amount of heat generation. The net consequence is that growing pigs today generate more heat that must be dissipated from swine facilities than previously dealt with.
Further proof that heat relief is a major concern for growing pigs is provided in Figure 2. This graph is the drinking pattern for finishing pigs in winter and summer. In thermal neutral conditions such as finishing facilities in the winter, growing pigs show a distinctive single daily peak in both eating and drinking behavior. However, when conditions in the pig zone are above their thermal neutral temperature, the pig changes its behavior in response to the need to reduce the impact of warmer temperatures on its well being. This response in behavior is accomplished by the pig eating and drinking earlier in the day, reducing activities associated with eating and drinking during the mid-day heat and resuming eating and drinking during later evening hours.
Figure 2. Drinking patterns in finishing pigs by season of the year in a 1200-hd room. Data courtesy dicamusa.com.
Figure 3 is a plot of both drinking activity and temperature in the pig zone in a facility in northeast Nebraska in late May, 2004. The top graph is a plot of air temperature as logged by the ventilation controller probes. The bottom graph is the drinking water usage for the facility. The vertical blue lines are the amount of water use logged every 15 minutes, while the horizontal red lines are the 24 hour totals.
Figure 3. Plot of temperature, fan run time, feed auger run times and drinking water disappearance in a finisher facility. Data courtesy dicamusa.com.
Note that prior to the two days in the middle of the time line when air temperatures in the pig zone were warmer than 80 F, the water pattern as indicated by the blue line was basically the single peak pattern, indicating that the pigs were in their thermal-neutral zone for temperature. On the first day of temperatures higher than 80 F, the water pattern changed to the double peak. Even when temperatures declined to the low to mid 70’s, note that the water pattern did not return to the single peak. When air temperatures returned to 80 F or higher at the right side of the time line, the pig once again reverted to the double peak pattern.
This lack of return to the preferred single peak pattern suggests that the growing pig is more sensitive to high temperatures than many producers think. The pig is willing to adapt a non-preferred behavior (double peak pattern of drinking water usage) for several days after a heat event as a preventive measure in anticipation of another heat event.
All of this data suggests that producers need to be more aggressive in helping pigs deal with summer heat in confinement facilities.
n terms of floor area per pig, has traditionally been expressed as area per pig or pigs per pen. Under conventional management systems, pigs remain in the same pen for several weeks and space allowance is based on the maximum space required during a given period of growth. For pigs that are removed from a pen as a group, such as when pigs are moved from a nursery to a grow-finish facility or when pigs in a double-stocked wean-finish facility are sorted down, the maximum space requirement occurs on the day of pigs leaving the pen. For finishing pigs, the maximum space requirement usually occurs the day that the first pig from a pen is removed for slaughter.
Results from numerous research trials make it clear that as nursery and growing-finishing pigs are provided less space per pig, feed intake decreases with a resultant decrease in daily gain. The impact on feed conversion is less consistent.
Space allocation recommendations have tended to be weight specific. Welfare audits have typically cited 3 ft2 per pig for 50-pound pigs and 8 ft2 for pigs greater than 150 pounds as a standard. The challenge of this type of recommendation is that they are often considered as absolute values with a given weight range, rather than as a continuum of values relating to pig growth.
The space needs of the growing pig can be expressed as this continuum using an equation that incorporates an estimate of body size. The formula ‘A’ = ‘k’ x ‘BW.67’ can be used to express this relationship where A is the space per pig in ft2, BW is bodyweight in pounds and k is a constant. Body weight to the 0.67 power reflects the fact that the pig’s space requirement is defined in 2 dimensions (length x width) while the pig grows in 3 dimensions (length x width x height).
A recent summary of research studies suggests that the maximum growth rate for the entire grow-finish period will be achieved when ‘k’ has a value of 0.2145. If space greater than this is provided, there generally was no increase in daily gain or feed intake. When this ‘k’ value is used in the above equation, the space requirement is very close to the predicted average space occupation of 220-pound lying pigs in pens that were 40% slatted.
Table 1 lists the space allocation predicted to have no impact on daily gain and the space allocations predicted to reduce daily gain 5%. For fully slatted facilities, each 3% decrease in space allocation results in a predicted 1% reduction in daily gain and daily feed intake. Surveys suggest that the average stocking density of both fully and partially slatted grow-finish facilities in the US is 7.2 ft2 per pig, while the estimated density that would maximize pig performance is 8.3 ft2 per pig. This suggests that there is a 5% reduction in overall daily gain in production facilities because of space allocation decisions.
Because of the large capital investment associated with fully slatted facilities, producers have generally chosen stocking densities that result in the maximum gain per unit of space (pounds per square foot per year) rather than densities which maximize individual pig performance.
Table 1. Space allocations (based on final weight) that are estimated to maximize daily gain
Pig weight
(lb) |
Space that maximizes gain
(ft2/pig) |
Space that reduces gain 5%
(ft2/pig) |
50 |
2.9 |
2.5 |
100 |
4.6 |
3.9 |
200 |
7.3 |
6.2 |
240* |
8.3 |
7.1 |
*A typical pen average weight at time of first sale from a pen.
Dr. Mike Brumm is the owner of Brumm Swine Consultancy, Inc. of North Mankato, Minnesota. He was previously a professor at the University of Nebraska. Dr. Brumm's areas of expertise include management and housing of the growing pig, industry issues including production networks, contracts, cost of production and record systems.
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