Sow and boar slaughter is indirect data that can provide clues on breeding herd inventory changes.
Each quarter USDA’s National Agricultural Statistics Service surveys pork producers and then estimates the kept for breeding hogs and pigs inventory, or breeding herd, as of the first day of each quarter. That is direct data. USDA also publishes direct data on market hogs and pigs, sows farrowing and farrowing intentions, pigs per litter and pig crops in each Hogs and Pigs report. Direct data provides evidence of facts. A smaller breeding herd is evidence of industry contraction. There is no need to connect any dots.
Indirect data, such as sow and boar slaughter, can provide clues on breeding herd trends. An uptick in sow and boar slaughter is suggestive evidence of industry contraction. In the case of hog and pig inventories, USDA compiles direct data once per quarter. Slaughter data are available daily, weekly and monthly. Indirect data can help fill in the gaps between direct data reporting periods.
USDA’s Hog Inventory survey does not ask producers about breeding herd culling rate and replacement rate. However, these rates, and their interplay, drive breeding herd expansions and contractions. Indirect data can anticipate direct data. It may confirm it, or it may suggest direct data is inaccurate. Inferences from indirect data need to be made using reason, experience and common sense.
The significance of different data varies depending on the specific analysis being performed and the prevailing market conditions. A market analyst’s role is to determine the optimal weighting or importance of numerous factors, including direct and indirect data, to forecast market trends, and pivots, accurately. Ultimately this helps market participants make informed decisions.
September breeding herd drop far exceeded trade expectations
USDA surprised many market participants on Sept. 25 when it published a larger than expected annual decrease in the number of sows, gilts and boars kept for breeding. The U.S. breeding herd inventory on Sept. 1, 2025 was 5.934 million head. This was down 110,000 head or 1.8% from last year, and down 15,000 head or 0.3% from June 1, 2025. This is the smallest Sept. 1 breeding herd since 2014.
Market participants and analysts use indirect data and knowledge of previous Hogs and Pigs reports to anticipate inventory numbers. On average, the seven analysts polled prior to the latest Quarterly Hogs and Pigs report expected the breeding herd to be down 0.5% compared to Sept. 1, 2024. The trade estimates ranged from down only 0.1% to down 1.2%. USDA’s estimate was below the lower bound of pre-report expectations and more than one percentage point below the average of pre-report expectations. It was surprise to say the least.
It is possible USDA will revise the Sept. 1, 2025 breeding herd in subsequent reports. In fact, USDA did revise the June 1, 2025 breeding herd down by 30,000 head or 0.5% in the September report.
Understanding USDA revision schedule and historical track record
USDA uses actual hog slaughter as it unfolds and hog check-off receipts to revise, if needed, previous inventory estimates to improve quarter to quarter relationships. Each quarter, estimates for the previous four quarters are subject to revision.
Each December, USDA reviews estimates from all quarters of the current year, all quarters of the previous year and December two years prior. Estimates are also reviewed after data from the every five-year Census of Agriculture are available. No revisions are made after that date.
From 1980 to 2024, USDA revised up the final estimate from the first estimate for the Dec. 1 breeding hogs and pigs inventory 20 times (Figure 1). They revised it down 16 times. They made no revisions nine times including the last two years in 2023 and 2024. The average difference between the first estimate by USDA and the final estimate by USDA of the Dec. 1 breeding herd over the last 45 years was a downward revision of 3,002 head or 0.03%.
Not all indirect data presents a clear and compelling inference
Sow and boar slaughter is indirect data that can provide clues on breeding herd inventory changes. September 2024 through August 2025 federally inspected sow and boar slaughter was down 206,551 head or 5.9% compared to the same period a year prior.
Yes, sow and boar slaughter was lower than the year prior, but it wasn’t as low as you may think, so the breeding herd might not be as large as you think.
The slaughter of U.S. sows and boars, after imports of Canadian sows and boars for slaughter were deducted from the total, was 148,339 head or 4.8% lower in September 2024 through August 2025 than it was in September 2023 through August 2024. Why remove imports of Canadian sows and boars for slaughter? Because the 58,212 head or 16.0% decline in imports of Canadian sows and boars for slaughter over the most recent 12-month period compared to the previous 12 months contributed to the decline in sow and boar slaughter that went beyond any decisions of U.S. hog producers to expand or contract the breeding herd.
September 2024 through August 2025 had 258 slaughter days, one less than September 2023 through August 2024. After accounting for slaughter days, slaughter of U.S. sows and boars was down 136,329 head or 4.4%. Truing up indirect data provides a better indicator of direct data.
Culling rate provides more insight than just slaughter numbers do
Year over year comparisons of U.S. sow and boar slaughter can be misleading if the size of the breeding herd is much higher, or lower, than the previous year. For example, if the industry has fewer sows and boars overall then producers will also have fewer sows and boars to cull.
Slaughter of U.S. sows and boars for September 2024 through August 2025 was 2.961 million head. The U.S. swine breeding herd inventory on Sep. 1, 2024 was 6.044 million head. This implies an annualized slaughter of U.S. sows and boars to U.S. breeding herd inventory, or culling rate, of 49.0% (Figure 2). This is similar to industry representative culling rates which gives validity to using this indirect data to help inform of industry-wide expansion or contraction decisions.
A lower culling rate is indicative of a steady or expanding breeding herd. The higher the ratio, the more likelihood of contraction. The ratio of 49.0% for the last year was higher than the five-year average of 48.5% and the ten-year average of 47.6%. This indirect data alone suggested the breeding herd was contracting. Importantly, from a forecasting standpoint, we did not have to wait for the latest Quarterly Hogs and Pigs report to know that, only confirm it with the direct data. The breeding herd did decline 110,000 head or 1.8% from Sept. 1, 2024 to Sept. 1, 2025.
Separate data on gilt retention and gilt slaughter would provide further insight
A normal culling rate occurs as producers remove unproductive sows and replace them with new gilts. Some of the attrition in the breeding herd may well have happened this way. Producers may have opted not to replace sows at the rate they culled them. Or, maybe too few gilts were available to replace sows being culled. Regardless, the replacement rate has been below the culling rate.
To estimate the swine breeding herd inventory each quarter, USDA asks producers:
USDA publishes data on the aggregate breeding herd. It does not provide individual estimates for sows, gilts and boars. For Cattle reports, USDA publishes individual estimates for beef cows, heifers for beef cow replacement and bulls. Collecting and publishing analogous direct data for hogs would improve market analysis.
If publishing gilt replacement numbers is not possible, USDA could alternatively track gilt slaughter. Market hogs are either barrows or gilts. Prices and head counts in Livestock Mandatory Reporting and slaughter volumes derived from data collected by inspectors from the Food Safety and Inspection Service are published together by USDA. No way currently exists to separate barrow and gilt data for market analysis. USDA publishes steer and heifer slaughter data separately. Heifer slaughter goes down when heifer retention increases. Increased heifer retention and reduced cow culling key beef cattle herd expansion.
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