Overstocking Barns: How Much Are You Losing?
By Dr. Mike Brumm, Brumm Swine Consultancy, Inc.
Stocking density, in 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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