The extra effort to pre-sort market hogs to reduce transport losses to the plant may not be justified if transport losses are traditionally low.

An Iowa State University (ISU) study compared the effects of pre-sorting on the stress responses at loading and unloading and transport losses between December and March.

Researchers found that pigs pre-sorted prior to the loading had reduced open mouth breathing and skin discoloration compared to pigs that were not pre-sorted on the farm.

But after a one-hour trip to the packing plant, no differences were observed in open mouth breathing, skin discoloration or muscle tremors (Table 1). In addition, there were no differences between total non-ambulatory (0.28 vs. 0.26%) or total transport losses (0.27 vs. 0.33%) between the non-pre-sorted treatment (LNPS) and the pre-sorted treatment (LPS).

Therefore, using the management tool of pre-sorting market weight pigs in winter in the Midwest provided no improvements in stress responses and transport losses during the marketing process when transport losses on a farm are below national (dead on arrival, 0.22%) and field trial (non-ambulatory, 0.42%) averages.

The study was conducted on three commercial grow-finish sites. Each site had two rooms with both treatment groups represented in each room. The LPS treatment had 292 pigs/pen, 7.2. sq. ft./pig. Internal swing gates were used to manually pre-sort market weight pigs from pen mates about 18 hours prior to marketing. The LNPS treatment also had 292 pigs/pen, but pigs were not pre-sorted from pen mates prior to marketing.

Thirty-three loads of market weight hogs were shipped, approximately 180 pigs/truck, weighing an average of 265 lb. Pigs were loaded in small groups using sort boards and electric prods if necessary, and loaded onto  straight-floor, double-deck, aluminum trailers,  at 4.4 sq.ft./pig. Pigs were transported one hour to the packing plant.

During loading and unloading, the number of pigs displaying open mouth breathing, skin discoloration and muscle tremors were recorded. At the plant, dead and non-ambulatory pigs were recorded during unloading. Total losses were defined as the sum of dead and non-ambulatory pigs.

In effect, it did not prove cost-effective to pre-sort pigs during the winter months in Iowa considering the additional commitments of labor and time when transport losses are below national averages.

Researchers: Leah Gesing and Anna K. Johnson, Iowa State University; Michael Faga, Corky Feuerbach, Howard Hill, all of Iowa Select Farms; Ryan Bailey of JBS-Swift & Company; and Matt Ritter, Elanco Animal Health. For more information, contact Gesing at (563) 568-9651 or lgesing@iastate.edu.