When is the best time to market cull sows?

Before pork producers can answer this seemingly easy question, some additional questions must be thought through:

  • Is space available in the gestation barn or an alternative facility to feed cull sows?

  • Are the cull sows healthy, but just thin?

  • Should I sell cull sows immediately after weaning — as “wet” sows?

  • Should I allow sows to dry up and attempt to add weight in order to add value?

  • How much do cull sows weigh at present?

  • Should I attempt to add weight to sows that have failed to conceive after ample attempts to rebreed?

  • What is the expected market price if sows are sold immediately after weaning vs. feeding them for a specific period of time?

  • What are the feed costs for feeding cull sows, and is storage space available for a cheaper, alternative diet designed for them?

If the answer to the first question is “no,” then the decision is easy.

However, most producers choose to give cull sows some time for their udders to dry up. Fewer than 5% of cull sows are marketed as “wet” sows, according to the U.S. Department of Agriculture (USDA) Market News Service.

Sow herd replacement rates are averaging 50% or higher in many U.S. commercial pork operations. Typically, open sows are given ample opportunity to rebreed. Consequently, a large proportion of sows are being marketed after being found as open, and long after nursing their last litter.

Additionally, wet sows are steeply discounted, typically $5/cwt. or more, based on USDA Market News Service reports. Hence, under most U.S. production systems, economic or production factors make it ill-advised to market the majority of cull sows immediately after weaning.

Understanding The Cull Sow Market

It is important to have a good understanding of the current market prices, by different weight classes, when making decisions about when to sell cull sows.

Prices for cull sows follow monthly and yearly trends and cycles similar to market hog prices. Cull sow prices are typically reported for four separate weight classes (see Figure 1). This graph also shows the yearly cull sow market price average from 1996 through 2005.

Most pork producers don't need to be reminded of the years when the price for market hogs reached unprecedented lows. The lowest prices for cull sows occurred in 1998-1999 and 2001-2002. Additionally, the price pattern between the four different cull sow weight classes was nearly identical across the 10-year period.

In addition to fluctuations in price that occur across years, a substantial difference in price between the different sow weight classes occurs within years (Figure 2).

From 1996 to 2005, the price difference between selling lightweight sows (300-450 lb.) and the next weight class (450-500 lb.) averaged $3.13/cwt. However, there can be substantial fluctuations in this price differential. Typically, when cull sow prices and market hog prices were low, as seen in 1998-1999 and again in 2001-2002, there was little, if any, price differential and, at times, there was even a disadvantage in feeding cull sows to a heavier weight category.

If a producer wanted to add weight to cull sows, the price received for the 300- to 450-lb. weight class needed to cover both the fixed and variable costs, or it would have been a losing proposition.

But, when market hog and cull sow prices are relatively high, there can be a substantial premium for feeding sows that fall in the 300- to 450-lb. weight range up to the next weight class (450-500 lb.). Generally, there is only about a $1.50/cwt. price advantage for increasing the weight of cull sows two weight classes.

Producers should also be aware of the historical, monthly price fluctuations to identify the most opportune time to add weight and value to cull sows.

Figure 3 shows the monthly cull sow price averages from 1996 to 2005. It appears that the summer months (May through August) typically offered slightly better prices for cull sows across the four different weight classes.

After examining the monthly price differential between the four cull sow weight classes, it is apparent that the greatest monthly price differential was between the 300 to 450 and the 450 to 500-lb. weight classes (Figure 4). And, within the 12-month span, the greatest differential between these two weight classes occurred in November through February, and averaged over $4.75/cwt. across the 10-year time period evaluated.

Again, it is important to keep in mind that substantial year-to-year and month-to-month variation can exist in cull sow prices. Likewise, producers should be aware of the current prices across all weight classes when considering whether to feed cull sows to attain greater returns.

Choose Cull Sows Wisely

Identifying sows that are healthy and low mortality risks is crucial when deciding whether to feed cull sows to heavier weights.

Obviously, some healthy sows with superior performance in lactation will leave the farrowing crate quite thin. These sows may be good candidates to feed.

However, sows that are thin because they are not healthy (possible ulcer or respiratory conditions) or are lame usually are not good candidates to feed for additional weight gain. Similarly, sows with shoulder sores may not be good candidates for further feeding, depending on how severe the sore is or if it appears to be causing lameness.

The relatively unthrifty and lame sows should be sold as quickly as possible or be euthanized in a timely, humane manner. Remember, if these animals have been treated, it is critical to follow all withdrawal times, according to label and veterinary instructions.

In addition to sow health, it is important to consider the likelihood that sows are capable of adding weight efficiently.

Little information exists regarding the average daily gain and feed efficiency of the modern lean genetic sows. As a result, the National Pork Board funded a project to estimate the cull sow performance from modern genetic lines and provide producers with a tool to better evaluate sow body condition.

Twenty-nine modern, lean-type sows were purchased from a large production system and housed on a separate site. Seventeen of the smaller sows were housed in crates, while 12 larger sows were housed in pens.

During an initial adjustment period (24-36 hours), the health status of each sow was evaluated by an Iowa State University swine veterinarian, and treated as needed. Of note, the greatest problem the sows exhibited upon arrival was lameness, followed by respiratory disease, digestive disorders and shoulder sores.

All sows were fed a commercial, 14% gestation ration. Sows received fresh feed approximately every 12 hours. Any feed that was not consumed was removed and weighed to calculate feed disappearance. This figure was used to estimate the amount of feed offered for the next 12-hour period.

Fresh, clean water was available by standard, automatic water bowls in crates and pens.

Initial body condition scores (BCS) were assigned to each sow using last-rib backfat measurements as outlined by Tri-State Nutrition Guide. Backfat measurements were obtained using real-time (B-mode) ultrasound equipment, operated by a National Swine Improvement Federation-certified ultrasound technician. Backfat, loin muscle area and depth were evaluated at the 10th rib using the same machine.

In addition to the real-time ultrasound measurements for fat and muscle, a commonly used A-mode ultrasound machine, the Lean-Meater from Renco, Inc., was also used to estimate fat depth.

The BCS distribution appears in Table 1. Seventeen of 29 sows had an initial BCS of 1, while eight and four sows had an initial BCS of 2 or 3, respectively. Sows were photographed at the beginning of the study and when they attained the next BCS. Body condition scoring was undertaken at approximately two-week intervals.

Using the real-time ultrasound as the standard, the A-mode ultrasound machine tended to overestimate sows having a BCS of 1 and 2 (by 1.7 mm) and underestimate BCS of 4 and 5 (by 2.4 mm and 3.4 mm of backfat), respectively.

Sows with a BCS of 3 had similar values, regardless of whether A-mode or B-mode ultrasound machines were utilized to estimate fat depth. For heavier-conditioned sows or sows with more fat cover, A-mode machines frequently have difficulty detecting the third fat layer.

It is important to become familiar with the equipment used to estimate BCS and apply it consistently. In this manner, any under- or over-prediction bias that occurs when assigning BCS will be minimized.

At each BCS increase, average daily gain (ADG), feed efficiency (FE), average daily feed intake, days for BCS increase (DAYS) and weight gain (WT) were calculated.

Sows were removed from the trial after meeting one of two criteria — successfully reaching a BCS of 5 or failure to gain weight over two, 14-day intervals. Sows removed from the trial were transported to the Iowa State University Veterinary Diagnostic Lab for necropsy evaluation to determine any similarities between sows that completed the trial compared to those that did not.

Sow performance by initial BCS is listed in Table 2. The results showed that sow performance declined with each additional BCS increase, regardless of the beginning BCS. In other words, the most rapid and efficient weight gain is attained when adding one additional BCS.

For example, sows that began the trial at a BCS 1 had an ADG of 4.3 lb./day and FE (Feed:Gain) of 2.3 when taking them to BCS 2. The performance of these same sows dropped to 2.5 lb./day ADG and 4.1 FE when adding the second BCS.

This trend held for sows that had a BCS of 2 at the beginning of the trial. The performance of these sows was 3.4 lb./day ADG and 3.9 FE. When adding the second BCS, the same sows' performance dropped to 2.9 lb./day ADG and 4.7 FE.

It is likely that the sows have some compensatory gain that is more efficiently added in the first BCS step.

If producers decide to feed cull sows, it is imperative that they carefully monitor performance relative to market price. In most cases, producers can only justify adding additional weight to sows that are thin (BCS 1 and 2 or in the 300 to 450-lb. weight category). This is when the fastest and most efficient weight gain occurs, and where the greatest increase in market price occurs — taking sows from the 300-450-lb. to the 450-500-lb. weight class.

Payback Potential

Table 3 illustrates breakeven sow market price under three different operational costs/day and three different feed costs (both expressed on a per-sow basis). These values are calculated for sows with different BCS starting points, and are based upon the corresponding ADG and FE shown in Table 2.

Producers should carefully compare the breakeven prices in Table 2 with the historical prices discussed earlier in the article. These values, along with the current cull sow market prices, will be useful for producers determining whether or not to feed cull sows.

Operational costs/day, excluding feed costs, greatly influences the profitability of feeding cull sows. Market prices needed for profitability rapidly increase as fixed costs rise beyond $0.50/head/day.

The situation is similar with feed costs. If the price of feed increases to more than $0.07/lb. ($140/ton), it will be extremely difficult to make feeding cull sows to heavier weights profitable. The only likely exception to this case involves cull sows that lost excessive body condition due to outstanding performance throughout lactation, have no health problems and are in the lowest weight class (300-450 lb.).

A cautionary note: once the first condition score has been added to cull sows, market prices need to increase a minimum of $13.26/cwt. (using $0.05 feed cost and $0.25 operational costs) before profit thresholds can be reached again, and that price situation is not likely to occur.

Closing Thoughts

It is very important to determine if health is the likely reason a sow is thin. Sows that have obvious health issues are not good candidates to feed to heavier weights. Frequently, it is difficult to add weight to unhealthy sows, and they are at a greater risk of dying.

After carefully evaluating sow health, you will need a great deal of information to determine whether or not to feed cull sows to heavier weights. Current market price and the relationship between different cull sow weight class prices will help estimate the potential for additional revenue if cull sows are fed to heavier weights.

Additionally, you should evaluate historical monthly and yearly price fluctuations relative to current prices to aid in your decision. You will have to determine whether existing, relatively low-cost facilities are available for feeding cull sows. High operational costs (due to labor allocation and/or facilities) will likely make feeding cull sows unprofitable.

It is also important to control feed costs when adding weight to cull sows. It may even be necessary to develop a specialized, low-cost, cull-sow diet in order to add weight economically and efficiently.

Realistically, profit can be captured only when feeding healthy sows, with the lowest price feed available, and with cheap, underutilized or depreciated facilities.

Table 1. Distribution of Sows by Beginning and Ending Body Condition Score (BCS)
Number of Animals within each ending BCS
Original BCS 1 2 3 4 5 Total
1 1 1 3 3 8
2 1 2 1 3 10 17
3 4 4
Total 2 3 1 6 17 29
Table 2. Cumulative Performance of Cull Sows by Beginning Body Condition Score (BCS)
Cumulative Additional BCS
Trait Beginning BCS Adding the first BCS Adding the second BCS Adding the third BCS Adding the fourth BCS
Feed efficiency, lb. 1 2.28 4.11 4.15 5.63
2 3.93 4.70 5.16
3 3.53 5.41
Average daily gain, lb./day 1 4.30 2.52 2.72 2.04
2 3.38 2.90 2.72
3 2.74 2.05
Feed intake, lb. /day 1 9.60 10.12 11.12 11.51
2 11.83 12.58 13.80
3 10.73 11.02
Weight gain/BCS increase, lb. 1 81.00 120.41 187.72 195.00
2 70.90 115.43 155.12
3 65.26 98.30
Feed/BCS increase, lb. 1 21.73 50.77 72.49 95.50
2 23.52 43.61 55.50
3 36.85 66.88
Table 3. Breakeven Cull Sow Price/cwt. by Beginning Body Condition Score (BCS), Assuming Three Different Operational Costs/Day and Three Different Feed Prices
Feed Price, $/lb. ($/ton)
Operational Costs, $/day1 $ 0.05/lb. ($100/ton) Addition of the first, second and third BCS $ 0.07/lb. ($140/ton) Addition of the first, second and third BCS $ 0.09/lb. ($180/ton) Addition of the first, second and third BCS
Beginning BCS 1 2 3 1 2 3 1 2 3
$ 0.25 1 17.21 30.47 29.94 21.77 38.69 38.24 26.33 46.91 46.54
2 27.05 32.12 34.99 34.91 41.52 45.31 42.77 50.92 55.63
3 26.77 39.25 33.83 50.07 40.89 60.89
$ 0.50 1 23.03 40.39 39.13 27.59 48.61 47.43 32.15 56.83 55.73
2 34.44 40.74 44.18 42.30 50.14 54.50 50.16 59.54 64.82
3 35.90 51.44 42.96 62.26 50.02 73.08
$ 0.75 1 28.84 50.31 48.32 33.40 58.53 56.62 37.96 66.75 64.92
2 41.84 49.36 53.37 49.70 58.76 63.69 57.56 68.16 74.01
3 45.02 63.64 52.08 74.46 59.14 85.28
1Operational costs include all expenses, excluding feed costs.