Sow Non-Productive Days and Their Opportunity Costs


By Blaine Tully DVM

Opportunity costs can be defined as the opportunities forgone in the choice of one expenditure over others. We have the opportunity to work with farms ranging from 80 sows to 7,000 sows at our veterinary practice in Manitoba, Canada. No matter the farm size, shape or product, hog farms in 2013 cannot afford to leave dollars on the table at the end of the day.

With uncomfortably high production costs, and slim to negative margins, it is imperative to pay attention to Non Productive Days (NPD) in the sow farm. NPDs quickly build extra cost into all pigs produced, in addition to creating opportunity cost by missing the mark on pigs sold. The cost of NPD is a parameter that we are looking more closely at, benchmarking over time and between farms to continue to improve and look for production efficiencies.

Let’s look a little closer at the NPD in a sow farm. Defined as any day in the production cycle of a sow that she is not pregnant or lactating. All farms, no matter the ranking in a database, will have some NPD. WSI (wean-service-interval) automatically creates NPD as sows do not breed back the day after weaning. There will be repeat sows on every farm, leading to farrowing rates of less than 100% (obviously), and therefore creating additional NPD.

The 4 main categories of NPD include (Koketsu 2005)

  1. Unmated weaning-to-culling interval
  2. Weaning-to-first-service interval
  3. Sow first service-to-neg pregnancy interval (including repeat sows)
  4. Sow first service-to-culling

We need to be careful when benchmarking NPD within one farm over time, or between different farms to ensure we use similar metrics. PigCHAMP will report NPD including the gilt pool, and excluding the gilt pool. If we are only comparing NPD within a farm, I like to include the gilt pool. Although there has been much emphasis on the benefits of optimizing gilt age/weight at first mating on lifetime female productivity, we need to remember there is a cost to house and feed the gilt. For example, if we target gilts to be bred at 210 days, but have gilts not bred until 240 days, we require up to $24/gilt in extra feed costs for the additional 30 days. (Riek 2010) Many strategies work to reduce the potential for additional NPD in the gilt pool, avoiding breeding gilts too much beyond the target age/weight. These can include both management tools like good boar exposure, and hormonal manipulation using PG 600® and Regumate® (Merck Animal Health, Kirkland, QC, Canada). By removing the gilt pool, we can easily benchmark farms with each other.

We need to be careful when benchmarking NPD within one farm over time, or between different farms to ensure we use similar metrics.

Let’s look at why NPD are important to consider. If you have a non-productive sow (remember, not pregnant or lactating) she still requires feed, water, housing, heat, care, etc. In the 12 years I have worked in the swine industry in Canada, the old adage of $2/day for cost of NPD has not changed…but several things have changed in 12 years. For instance, cost of production has risen year over year (feed, energy, nutrient management, insurance, staffing cost, etc).

The cost of NPD based on cost of production calculation

So based on actual cost of NPD (dollars spent) we should be using a value 40% higher than the old adage of 2 bucks a day! Let’s change perspective and look at the opportunity cost of having an empty sow parked in a gestation space, rather than a pregnant sow.

For each day a sow is not productive, there is 1 less day in a year that she can be productive (obviously) so, in other words, the number of litters she is capable of having this year is reduced. In fact, if you do the math, her litters/year are reduced by 0.0074 litters for each NPD. This becomes the opportunity lost for that sow. What is the significance? That depends on what revenue you could make from the sale of her litter, and the productivity of the farm.

calculation opportunity cost of having an empty sow

As you can see, the opportunity cost (or loss) for a NPD will change, as the productivity of the sow changes and the revenue/pig changes. The higher producing herds will have more to lose when sows are non-productive.

calculation revenue/pig sold

(Opportunity cost based on productivity and revenue/iso-wean pig)

Based on the above formula and chart, a sow herd producing (and selling) 11.5 pigs/litter must really focus on getting sows pregnant in September and October, heading into good iso-wean returns in December/January. As much as $5.11 per day could be left behind if sows are not productive.

In the 12 years I have worked in the swine industry in Canada, the old adage of $2/day for cost of NPD has not changed…but several things have changed in 12 years.

One should consider the cost of repeat sows. When a breeding technician finds a regular-repeat sow (open sow in the 21 day heat check group) that nonpregnant sow will cost the farm 21 NPD; $58.80 (based on COP of $2.80/day) or $93.24 (based on opportunity cost of $4.44/day). A sow that manages to evade a breeding technician, and re-enters a farrowing crate not in pig will cost the farm 115 NPD; $322 or an opportunity loss of $510.60. There are really no excuses for NIPs in the farrowing crate!

Knowing is half the battle. Now that we have put a cost to NPD, one needs to understand where in their herd there is opportunity to reduce NPD. A detailed records analysis is required to identify key areas for improvement. Remember, there are 4 areas to address NPD:


If a farm plans to cull a sow, without breeding her, the NPD will accumulate until she is on the truck. A sow culled in PigCHAMP still has a cost, until she walks off the cull truck! Detailed analysis of the Return-Estrous-report is important.

If a sow fails to show signs of heat after weaning, one should review:

  • Lactation management (feeding, fostering, etc)
  • Post-weaning feeding program (is there opportunity to increase feed intake in the weaned sow?)
  • Breeding technician management (training, fatigue, task prioritization, etc)
  • Appropriate boar exposure and heat detection immediately following weaning.
  • Is there a place for P.G.600®(Merck Animal Health, Kirkland, QC, Canada) to induce estrous in the weaned sow?


Similar to above, close analysis of the Return to Estrous report will help determine if there is opportunity to reduce NPD in the post-weaning period. All of the above factors with respect to Unmated-weaning-culling interval apply to Wean-to-first-service interval. A few more considerations include:

  • What is the average WSI and the variation? Are there NPD being accrued with management strategies like HNS (heat-no-service, skip-a-heat programs, etc). Remember, a skipped heat costs $58.80. Is there opportunity to extend WSI in thin sows, but not skip an entire heat cycle using Regumate®? (Consult your veterinarian before considering this extra-label Regumate® use.)
  • Running the in-active Sow report weekly, to ensure there are no sows sneaking through the system without a pre-determined plan.


  • When is the first pregnancy diagnosis performed on the farm? This includes an aggressive heat check in sows bred 18-23 days ago in addition to Real-time Ultrasound scanning.
  • Is there a second pregnancy diagnosis performed? Could those sows have been found non-pregnant earlier?
  • How well is the visual inspection of gestating sows performed beyond 70 days of pregnancy?
  • How many attempts are made at getting sows pregnant? i.e. do repeat estrus sows get serviced again? What is the conception rate on those repeat sows?


  • When is the culling decision made?
  • Is the culling decision made for the right reason? If a pregnant sow is culled for lameness, could there have been earlier medical intervention to prevent the culling?
  • Are optional culls mated in order to reach breeding target before culling decisions are made?

These are a few considerations when trouble shooting the reasons for NPD on swine farms. One should work closely with the herd veterinarian to analyze performance records to identify what dollars are left on your table.

Let’s look at 2 examples of recapturing NPD.

examples of recapturing NPD

*Opportunity cost calculated at $4.44/day
** Opportunity cost calculated over entire sow inventory

Although productivity is similar between farms (both weaning approximately 24 psy), Farm B has an opportunity cost $181,833 higher than Farm A. In other words, Farm B left $181,833 on the table at the end of the year. At a glance, the production parameters that really stand out are the WSI and % of sows bred by 7 days. Both farms have room for improvement, but Farm B really needs to look more closely at which sows are not breeding back within 7 days of weaning, and why.

Farm B has an opportunity cost $181,833 higher than Farm A. In other words, Farm B left $181,833 on the table at the end of the year.

Regardless of how the cost of NPD are calculated, put a figure down on paper for your NPD, drill down into your production records and reduce your NPD. Survival in modern day hog production requires vigilant attention to inefficiencies, reduction in opportunity costs and continual improvement.


  1. Koketsu et al. Six component intervals of nonproductive days by breeding-female pigs on commercial farms. J Anim Sci. 2005 Jun;83(6):1406-12.
  2. Riek, T. Cost of Gilt Replacements. Western Hog Journal, Spring 2010.

DR. BLAINE TULLY Dr. Blaine Tully is a partner at Swine Health Professionals Ltd., in Manitoba, Canada. As a swine practitioner for more than 12 years. Dr. Tully has been involved in providing health and production services to various hog producers in Manitoba including small family farms, large iso-wean facilities, AI centres, genetic suppliers and many farrow-to-finish farms. Dr. Tully also provides veterinary technical consultation for Merck Animal Health in Western Canada.