Economic Impact of PRRS: The Difference Between All-In/All-Out versus Continuous Flow Nursery Management

Delegates to the recent Centralia Swine Research Update heard that an outbreak of porcine reproductive and respiratory syndrome (PRRS) can have a considerable economic impact on mortality and growth in the nursery and that these are greater for a continuous flow nursery than one that operates an all-in/all-out system.
calendar icon 27 March 2015
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Centralia Canada


Porcine reproductive and respiratory syndrome (PRRS) is the most economically significant swine disease in Canada and yet there are few studies documenting the cost of outbreaks of the disease, according to R. Zorzolan of Agribrands Purina Canada Inc.

In a paper co-authored by R. Friendship and Z. Poljak of the University of Guelph, they report that there is one American study (Neumann et al., 2005) that is frequently quoted that suggests PRRS results in more that $500 million in losses per year in the US. The study also attributes over 80 per cent of the economic losses to the post-weaning period (nursery and grower production).

The objective of this study was to examine production records from Ontario nurseries before and after a PRRS outbreak to calculate the effect of PRRS on post-weaning performance.

The authors also used the information from this study to examine the possible cost-benefit of performing a nursery depopulation once the PRRS immunity status of the sow herd stabilised at about six months post-outbreak.

Materials and Methods

Six large production systems with accurate production records and a clearly defined PRRS outbreak were chosen for the study. Nursery production records related to the six months before a PRRS outbreak and for the year following the PRRS outbreak were used in the study.

Approximately 750,000 pigs were included in the study; however, data were analysed on the basis of the performance of weekly batches. The impact of the disease was examined for the first six months and the second six months after the outbreak, as well as by type of pig flow. Some of the nurseries operated as continuous flow (CF), which typically involved emptying individual rooms and cleaning between batches, and some nurseries operated as all-in/all-out by site (AIAO). All nurseries were off-site from the sow units.

In order to conduct the cost-benefit analysis, the authors assumed a pig that died in the nursery was a loss of C$40, that the price for feeder pigs as C$2.50 per kg and that reduced growth rate was calculated as the cost of selling lighter weight pigs. Feed cost was assumed to be C$450 per tonne.

They calculated the cost of the increased losses in nursery performance for a hypothetical 1,000-sow operation producing 25 pigs per sow per year, comparing AIAO with CF nursery scenarios in the second six-month period after a PRRS outbreak.

Results and Discussion

Mortality increased in the first six-month period following a PRRS outbreak and growth was reduced for CF and AIAO nurseries (see Table 1).

In the second six-month period after the outbreak, for the AIAO nurseries performance returned to normal but for the CF nurseries, mortality and growth were even worse than in the first six-month period after the outbreak. Feed efficiency was not affected in either pig flow.

Table 1. Nursery performance parameters before and after an outbreak of PRRS, based on six large production systems in Ontario
All-in/All-out by siteContinuous flow by site
Time6 months
6 months
7-12 months
6 months
6 months
7-12 months
Mortality (%) 2.39 3.38 1.95 2.01 5.97 10.49
Average daily gain (g/d) 436 3.99 443 430 394 360
FCR 1.64 1.60 1.61 1.66 1.69 1.67

The most likely explanation for the difference between the pig flows is that in the AIAO nurseries, after six months following the outbreak the sow herd has stabilised and piglets are entering the nursery free of PRRS virus and remaining free of disease. However, in the CF nurseries, the piglets are also entering the nursery free of PRRS virus but there are rooms of pigs in the nursery that have PRRS-positive pigs that infect the incoming pigs and the disease continues to cycle in the nursery. These data suggest that the common strategy for controlling PRRS by depopulating the nursery once the sow herd is stable is warranted.

The cost-benefit analysis comparing 12,500 pigs entering AIAO nurseries versus CF in the second six-month period following a PRRS outbreak is as follows:

  • Mortality (a difference of 8.5 per cent) = 1,062 pigs × $40 per pig = $42,480
  • Slower growth (360g vs. 430g/d) results in pigs being 3.5kg lighter after 50 days in the nursery and therefore would cost 3.5kg × 12,500 pigs × $2.50 per kg = $109,357
  • The feed efficiency remains essentially unchanged so there are some savings (3.5-kg lighter pigs × 1.6 feed conversion rate × $0.45/kg feed cost × 12,500 pigs = -$31,500

Therefore in the six-month period after a PRRS outbreak a 1,000-sow herd would possibly lose about C$120,000 by operating a CF nursery compared to performing a nursery depopulation or operating AIAO.


Although a great deal of attention is paid to the losses in the breeding herd that occur during a PRRS outbreak, there is a considerable economic loss experienced in the nursery from both mortality and slow growth.

The findings of this study demonstrate a great difference in performance in the second half of the year following a PRRS outbreak between nurseries that operate as all-in/all-out by site and those that empty and clean rooms of a continuous flow nursery.

These data support the strategy of performing a nursery depopulation once the sow herd becomes stable and negative piglets are being weaned.


Neumann E., Kliebenstein J., Johnnson C., Mabry J., Bush E., Seitzinger A., Green A. and Zimmerman J. 2005. Assessment of the economic impact of porcine reproductive and respiratory syndrome on swine production in the United States. J. Amer. Vet. Med. Assoc. 227: 385-392.


Zorzolan R., R. Friendship and Z. Poljak. 2015. Economic impact of PRRS: the difference between all-in/all-out versus continuous flow nursery management. Proceedings of 34th Annual Centralia Swine Research Update. 28 January 2015. I-25-I26.

Further Reading

You can view the full report by clicking here.
Find out more information on PRRS by clicking here.

March 2015

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