When baseball began, the game had a few self-explanatory statistics. Players struck out, walked or got hits.

Back when many pork producers pasture-farrowed one litter per year, merely counting the pigs weaned may have provided enough production data. The number of pigs per litter aided management decisions such as choosing which sows to cull.

As baseball evolved and got more competitive, managers developed more comprehensive statistics to measure a hitter’s success at the plate. Batting average is one. But it isn’t all-encompassing. For instance, batting average doesn’t take into account the number of times a batter reaches base via walks or hit-by-pitches. And it doesn’t consider the type of hit ― doubles, triples and home runs are more valuable than singles.

Similarly, with the increasing size and specialization of hog operations, managers developed more comprehensive statistics to measure performance. Pigs per sow per year is one. But it doesn’t consistently take into account when the female enters the breeding herd. Is it when a gilt does not go on the truck as a market hog, or when she gets bred, or when she first farrows?

Comparing pigs per sow on your farm this year to pigs per sow on your farm last year can help identify a trend. Rising is good. Falling is not so good.

Comparing the pigs per sow per year on your farm to other farms may or may not tell you how your performance compares to performance on those other farms. For a valid comparison, the farms need to use the same criteria for when a female enters the breeding herd.

More sophisticated statistics equal management data

Although standard statistics remain quite valuable, advanced formulas and figures now play a pivotal role in decision-making in baseball. Batting Average on Balls in Play (BABIP) measures a player’s batting average exclusively on balls hit into the field of play. It removes outcomes not affected by the opposing defense — namely, home runs and strikeouts. BABIP is a statistic that helps determine which players are “lucky” or “unlucky.” The formula is: (Hits – Home runs) divided by (At bats – Strikeouts – Home runs + Sacrifice flies).

Many advanced baseball statistics have long been tied to sabermetrics or the search for objective knowledge about baseball. Sabermetrics is the analysis of baseball statistics and other evaluations that have already been recorded. These types of advanced metrics are also valuable for interpreting USDA Hogs and Pigs reports where implied productivity figures, or biological realities, such as litters per breeding animal per year and breeding herd utilization, can transcend prescribed changes in inventories.

More pigs from fewer sows

Pigs per sow per year is one of the most common measures of overall sow farm efficiency. Pigs per sow per year is litters per sow per year multiplied by pigs weaned per litter.

The average number of annual pigs per breeding herd animal (including sows, gilts and boars as is reported in USDA’s Hogs and Pigs report) was 21.8 in 2022, up from 18.2 in 2007. This metric has doubled since 1980. Producers have upped the pig crop while cutting the breeding herd as a percent of the total hog and pig inventory.

The majority of the improvement in pigs per breeding herd animal per year has come from larger litters. On average, litter rates grew 1.3% annually from 2007 to 2022. Litters per breeding animal per year have plateaued since 2007 and show no signs of rising. This measure has actually trended lower recently.

Recent breeding herd performance mixed

The March-May 2023 pig crop, at 32.891 million head, was up 0.8% from 2022. Sows farrowing during this period totaled 2.896 million head, down 2.4% from 2022. The average number of pigs saved per litter was 11.36 for the March-May period, compared to 11.00 last year. This is the largest litter rate ever, for any quarter, and the 3.3% annual rise is the largest since 2019. The March-May 2023 litters per breeding animal annualized = (Sows farrowing March-May 2023 divided by breeding herd on March 1, 2023) multiplied by 4 = 1.90. This is down 2.4% from a year ago and the lowest annualized litters per breeding animal for the March-May quarter since 2002.

Litters per sow per year has a mathematical limit. A gestation period of 114 days, 21 days of lactation and a seven-day wean-to-rebreed interval puts each reproductive cycle at 142 days. That means if everything goes on schedule, a sow can produce 2.57 litters per year. Multiplying by a realistic pigs-weaned-per-litter target will give a lofty, but possibly achievable, pigs per sow per year goal.

The mathematically possible 2.57 litters per sow per year is well above the 1.9 annualized litters per breeding animal in March-May 2023. As the terminology suggests, a big part of the explanation is that USDA does not collect a sows-only number. Using USDA’s breeding herd inventory of sows, gilts and boars caps this measure at a lower level. But, the number plateauing, at best, over the last 15 years suggests room to improve breeding herd performance still exists.

Understand how data are gathered, tabulated

A challenging part of using litters per sow per year is that not all record-keeping systems calculate the measure the same way. Furthermore, records can be creatively managed in order to inflate litters per sow per year. One way is to wait until after a replacement gilt is mated, or even farrowed, to enter the animal into the record system, which inflates calculated litters per sow per year.

Litters per mated female per year is a preferred measure.

According to the 2019 MetaFarms Production Index Analysis report, litters per mated female per year averaged 2.34 in 2017, 2.30 in 2018, and 2.31 in 2019. In 2019, the bottom 10% for this metric was 2.09 while the top 10% was 2.45. Herds with less than 1,000 sows averaged 2.22 litters per mated female per year in 2019 while herds with 3,000 to 4,000 sows, 4,000 to 5,000 sows, and more than 5,000 sows all averaged 2.35 litters per mated female per year.

Proposition 12 potential complications

While many factors impact breeding herd performance, information collected from multiple sources indicates lower productivity in Proposition 12-compliant housing compared to conventional group housing and stall housing. For example, the farrowing rate has been cited as likely to decrease.

Some producers are adjusting housing. It is too early to determine how much the change in litters per breeding animal per year in USDA’s Hogs and Pigs report data is due to changes in sow housing and/or due to something else. Still, litters per mated female per year may be at or near its upper bound, given recent performance and ongoing adjustments in the industry.

Litters per mated female per year is affected by farrowing rate, wean-to-first service interval, multiple matings, repeat services, gestation length, farrow-to-farrow interval, weaning age and mated female non-productive days. Tracking those measures can identify areas for improvement. Doing so may position managers to make improvements that can get litters per mated female per year back on an upward track.

Breeding herd too large, or sows farrowing too low

The ratio of sows farrowing from March to May 2023 to the March 1, 2023, breeding herd was 47.51%. This compares to 48.66% a year ago and is the smallest for the quarter since 2002. Farrowing intentions in USDA’s June Hogs and Pigs report point to a June to August 2023 breeding herd utilization of 47.87%, which would be nearly 2 percentage points lower than in 2022 and the smallest for the quarter since, again, 2002.

The declines in the breeding herd utilization rate could be aberrations ― or more sows could, in fact, be farrowed than previously estimated. Of course, this assumes no revisions to the breeding herd inventory.

USDA rarely revises breeding herd estimates. However, in June, USDA revised the March 2023 breeding herd inventory 31,000 head lower. But March-to-May breeding herd utilization was still the lowest in more than two decades.

Of what value is knowing the size of breeding herd if it does not align with the number of sows farrowed? It is not a coincidence that breeding herd utilization is abnormally high in quarters for which USDA revised the sows farrowing number upward significantly from its originally estimated level while the breeding herd stayed the same.

Schulz is an Extension ag economist with Iowa State University.