Kansas State University (KSU) researchers are using ultrasound backfat readings and estimating weights to reduce feed costs and take the guesswork out of feeding pregnant sows.

To accurately feed today's lean sows, you can no longer simply “eyeball” them to formulate the proper feed settings.

“Modern sows are younger and leaner at the time of mating, have poorer appetites, are more fertile and produce more milk than sows five or 10 years ago,” says KSU graduate student Malachy Young.

Implementing a feeding program, that was developed by KSU and fits the needs of lean gestating sows, can add $6 or more per sow in feed savings. The program can save herds thousands of dollars annually by eliminating overfeeding, he adds.

Sow Feeding Derailed

KSU Extension Swine Specialist Mike Tokach says their farm-to-farm studies suggest visual appraisals of sow condition have gotten many pork producers off track. They overfeed gestating sows, which leads to low feed intake by lactating sows, he reports.

Table 1. Sow Feeding Level from Day of Scanning to Day 101, lb./day **
Girth (in.) Estimated weight, lb. Backfat at breeding, mm*
9-11 12-14 15-17 >18
43 - 46.5 250 - 325 5.1 4.5 4.0 3.5
46.6 - 50 325 - 400 5.6 5.1 4.5 4.0
50.1 - 53 400 - 475 6.0 5.5 5.0 4.5
53.1 - 56 475 - 550 6.6 6.0 5.5 5.0
56.1 - 66 550 - 650 7.0 6.5 6.0 5.5
*1 mm. equals .04 in.
**For the last 14 days prior to farrowing, all sows should receive an additional 2 lb. of feed/day. The feeding levels are for a diet containing 1,450 kcal/lb.
Notes: All sows bred in the previous week should be scanned and backfat scores written on their sow cards. The backfat should be used to adjust their feed box using the above chart.
At seven weeks postbreeding, the group should be assessed for condition. Thin sows should be marked and scanned for backfat to determine if they are gaining an acceptable level of backfat. Ten to 15% of sows will be below target gain.
If backfat is not above the level listed below, feed level should be increased by 1 lb. feed/day.


Initial backfat (mm) Increase feed if backfat is less than (mm)
9 12
10 12
11 13
12 14
13 14
14 15


To get producers back on course, Young and Tokach are using ultrasound at breeding to measure a sow's backfat depth to the muscle behind her last rib. That reading can be used to set the pregnant sow's feeding level.

Along with ultrasound, the KSU team is taking girth measurements to estimate sow weight.

By estimating both weight and backfat at breeding, producers can refer to Table 1, which provides specific guidelines for feeding pregnant sows.

Gauging Girth

There are different views on taking girth measurements, responds Tokach. Some producers believe they have to do a few at the start to train themselves as to how large the sows are, while others believe they should measure sows continually to really be accurate.

“We try to get people to use the girth belt initially, to at least give themselves a framework on how big these sows are,” observes Tokach. “They don't have to do every animal, but to just do it periodically to make sure they don't think sows are much smaller than they actually are.”

Similarly, using an ultrasound device to measure backfat takes some dedication (see sidebar on page 38). “With some sows, it is hard to pick up that third layer of backfat,” says Tokach. “A lot of people miss it because they don't have good enough contact and they will only get the first two layers.”

Four Program Elements

There are four keys to the KSU sow feeding program, stresses Tokach.

  1. Know how to scan sows. The Renco ultrasound scanner used in the tests is a nice machine that works well — once you are trained, he says. The Renco is the most popular because it is the least costly and provides an easy digital readout that requires no interpretation. There are a number of other ultrasound machines on the market that work well but are considerably more costly. All machines require training for accurate use, he adds.

  2. Agree to do girth weight testing. “People usually underestimate the weight of their sows, so they have to do some girthing in this program to attune themselves to how heavy their sows are,” he says.

  3. Know the energy level of your sow diets.

  4. Find out what your feed boxes are dropping. The sidebar tells how to test feed drop boxes and compare settings with the actual amount dropped (Table 2).



“One of the key goals of this program is to be able to set the feed boxes at breeding and then not make any more adjustments in feeding until the sows go into the farrowing house,” observes Tokach. “The whole idea here is to put your time and effort in up front to get it right; then you don't have to continually revisit getting the feeders right.”

Results To Date

Besides the feed savings, graduate student Young suggests that using ultrasound to measure backfat will increase the percentage of sows with ideal body condition at the end of their pregnancy.

Reproductive performance is expected to be enhanced by reducing the number of fat sows in a herd, but that remains to be proven.

The feeding protocol could also help reduce the high turnover of sows. But long-term trials to determine the impact on sow longevity haven't yet been done, adds Tokach.

Eight-Step Guide to Proper Sow Feeding

Following is a list of procedures from Mike Tokach, Extension swine specialist at Kansas State University (KSU), for determining feed allowances in gestating sows.

  1. Find the last rib of the sow.

  2. At the last rib (Figure 1), find the edge of the loin (2.5 to 5 in. off the midline, depending on sow size).

  3. Liberally apply oil to ensure good ultrasound transducer contact. Move the transducer around to try to minimize scanning through hair. Hold the transducer on the sow until the red light appears on the Lean-Meater (Renco). Presence of the red light does NOT mean that this is the final backfat. It simply means that you have made good contact.

  4. Slowly adjust the angle of the transducer to make sure you are picking up the third layer of backfat. For example, if you get readings of 13, 13, 14, 13, 18, 13 and 13 mm as you move the transducer, this sow likely has 18 mm (.72 in.) of backfat (Figure 2). This one high reading was where you picked up the third layer of backfat. The probe will not overestimate backfat.

  5. If you are concerned about the accuracy of your initial readings, it is always a good idea to double-check fat depth on the sow's other side as well.

  6. Record the backfat and girth measurements. Then set the feed drop box to the corresponding amount as explained in step 8, below.

  7. Directions for measuring the accuracy of the feed drops are included in the “KSU Gestation Feeding Spreadsheet,” available by e-mailing Mike Tokach at mtokach@ksu.edu.

    To check accuracy:

    • Set feed boxes on different rows to each feeder setting (setting of 3 to 10 lb. for once-per-day feeding and 1.5 to 5 lb. for twice-per-day feeding).

    • Place bags under feed drops to collect all feed dropped.

    • Weigh the bags on a scale accurate to within 0.05 lb.

    • Average the values from each feeder setting to determine a value to place in the chart. Do at least five drops at each setting.

  8. Plot the data into the KSU spreadsheet to determine proper feed settings.

    “The spreadsheet automatically adjusts the feeding charts (from p. 36) so that if the feeding boxes are off by a certain amount, producers can print out a chart that will show the levels that the feed boxes should be set at to get the desired amount of feed into each sow,” explains Tokach.

    The feeding chart should be customized, using the KSU Gestation Feeding Spreadsheet, to include:

    • The energy level of the gestation diet (example: 1,450 kcal. of ME/lb.);

    • Date after breeding that sows are scanned;

    • Date that feeding will be increased in late gestation;

    • Feeding level in late gestation (example: Day 100 to 114 of gestation);

    • Temperature of the gestation barn (important if under 68° F.); and

    • Accuracy of the feed drops.



Table 2. Sow Gestation Feeding Comparisons*

Feeder setting, lb. Actual amount dropped, lb.
3 3.05
4 3.8
5 5.15
6 6.2
7 7.3
8 8.75
9 9.8
10 10.3
*These figures provide an example of the typical variance between feeder settings and actual amount of feed dropped.