Roy Kirkwood Michigan State University

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Non-Productive Days : Their Significance and Control

Publish Date: April 19, 2011

Productive sow days are those days when a sow or gilt is either pregnant or lactating. Therefore, a non-productive day (NPD) is any day that a sow, or a gilt once entered into the breeding herd, is neither pregnant nor nursing a litter. The number of NPD is calculated as 365 days – ([gestation days + lactation days] x litters/sow/yr). The primary significance of NPD is that they reduce the number of possible productive days and, therefore, they limit the potential number of litters per year. Assuming maximum sow inventory, limiting the number of litters produced will adversely affect the efficiency of facility utilization. The economic impact of fewer litters will depend on the value of the finished product. The number of NPD influences the ideal sow inventory since with high NPD, more sows will be needed to maintain consistent weaned pig output. If there are excessive NPD (e.g. 85 days), then there are only 280 remaining productive sow days left in the year. Further, if gestation days and lactation days are combined (e.g., 114 + 21 days = 135 days), then the maximum number of litters possible per sow is 2.07 (280 days/135 days). If there are fewer NPD (e.g. 35 days), then there will be 330 productive sow days in the year, and the potential number of litters is 2.44 (330 days/135 days). In each of these scenarios, if the number of pigs weaned equaled 10 pigs, then the effect of the 50 extra NPD between the two scenarios (85 days– 35 days) would result in 3.7 fewer pigs produced each year for each sow (24.4 – 20.7 pigs/sow/year). Put another way, each NPD is worth 0.074 pigs (3.7 pigs/50 days), or more if weaned litter sizes are larger than 10 pigs. However, the true significance of this will depend on whether pork production is profitable or not.


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