Feed costs, the single largest cost in pork production, accounts for 65-75% of input costs.

Because the grow-finish period incurs most of these costs — 70-75% — it provides considerable opportunity to decrease input costs. But let's not forget there is also considerable scope to reduce input costs and increase production efficiency through improved feeding of gestating and lactating sows.

In this first in a two-part series on sow feeding, we'll begin by discussing some feeding strategies during gestation. Next month, we'll focus on feeding sows in lactation.

All phases of the reproductive cycle are interrelated; therefore, feeding levels in one phase can have significant effects on appetite and/or sow performance in other phases. These effects may not be seen for several parities.

It has been well documented that feeding levels that result in sow backfat levels of 0.83 in. or more at farrowing will reduce feed intake during lactation, especially early lactation. Lower feed intake during lactation increases sow weight loss and may reduce milk yield and subsequent reproductive performance.

Because the developing litter has a very high priority for nutrients, feeding level during gestation has to be very low before it will reduce litter size or birth weight. Therefore, the objective of the feeding program during gestation is to neither over- nor under-feed the sow.

The question that remains, then, is this: What can we use as a guide for feeding the pregnant sow?

Guides to Gestation Feeding

Feeding levels for gestating sows are commonly based on some subjective evaluation of body condition (level of fatness) at breeding. Sows are often “scored” for condition; however, there is convincing evidence that visual assessment of sow condition is not a reliable measure of sow backfat level.

In most tests, sows with a condition score of 3 (considered “ideal”) had P2 backfat levels ranging from 0.35 to 1.02 in. The P2 position for measuring backfat is about 2.5 in. off the midline at the 10th rib.

If we want to measure sow backfat levels, then we should use a more objective measure than condition scoring. The Lean-Meater (Renco Corp.) is relatively inexpensive and, if used properly, gives a reliable estimate of backfat thickness. It is as easy to train people to use this or other ultrasound devices as it is to train them to effectively score sows for condition, and the time required for either method is very similar.

Backfat, Weight and Parity

There is no convincing evidence that backfat thickness, per se, has any influence on sow reproductive performance. In many studies, and in most herds, there are sows that perform well with low levels of backfat.

In a recent Kansas State University (KSU) study, scientists showed that some sows with relatively low levels of P2 backfat (0.49 in.) at breeding had reproductive performance as good as sows with high levels of backfat (0.73 in.). Therefore, backfat thickness by itself is not a reliable predictor of subsequent sow reproductive performance.

Recent data suggest that protein mass and protein loss are more important than fat loss or fat mass in influencing sow productivity. If a sow mobilizes more than 12% of her protein mass during lactation, subsequent reproductive efficiency will be reduced and litter growth rate is also lowered. But, because there is a high, negative correlation (0.7) between fat mass and protein mass, we can use backfat measurement as a rough estimate of the sows' protein status. Accepted levels of P2 backfat are shown in Table 1.

Also, we know that approximately 80% of a gestating sow's energy intake goes to maintenance. Naturally, maintenance costs increase with an increase in sow weight. Therefore, we need to consider both sow weight and backfat when setting a feeding schedule for pregnant sows.

Using the available data on the energy and amino acid requirements for maintenance and weight gain, we have calculated the feeding requirements of different parity sows of different backfat levels and “guesstimates” of body weight at time of breeding (Table 2).

Sow weights are simply estimates of what different parity sows might be expected to weigh. If sows are heavier than the estimates shown, they must be fed more to meet their maintenance requirements. For example, a Parity 0 sow weighing 309-353 lb. would be fed the levels shown in that weight range.

Parity and weight are included because it is known that weight gains of young and old sows have very different compositions. A young sow's weight gain will contain more lean than that of an older sow. As the energetic cost of fat deposition is very much higher (12.5 Mcal ME/2.2 lb.) than lean (2.5 Mcal ME/2.2 lb.) the composition of the sow weight gain will greatly influence energy requirements.

Other comments regarding Table 2:

  • The diet fed should contain at least 13.5% protein, 0.55% lysine and 3 Mcal ME/2.2 lb.

  • Parity 0 sows should be fed 4.41 lb./day for the first 48 hours after breeding. Multiparous sows can be fed to scale or fed at feeding levels above scale to attain P2 backfat of 0.63 in. by Day 35 of gestation, then returned to recommended scale.

  • All sows should be fed an extra 2.2 lb./day from Day 90 to farrowing (or Day 112 of gestation). Energy and all nutrient requirements increase greatly in late gestation, so total metabolizable energy (ME) intake must increase by about 33% from Day 90 to Day 112 to prevent fat loss.

Because thin sows account for at least 20% of the herd in most farms, and because these sows are likely to require more than 6.62 lb./day to reach a target P2 backfat of 0.75 in. at farrowing, it may be advisable to feed twice per day in systems using open-trough feeding. Both feedings can be fed in the morning as soon as the second drop is ready.

Feed Saving Opportunities

Recent KSU research by Malachy Young has shown that commercial sows fed on the basis of backfat level and weight were fed 10% less (59.5 lb.) per gestation period than sows fed on the basis of condition score. There was no difference in sow performance, and savings in feed costs were about $8/sow/year.

In addition, when feeding level was based on backfat and sow weight, a higher percentage of sows had between 0.67 and 0.83 in. P2 backfat at farrowing.

The closer sows are to 0.55-0.59 in. backfat breeding, the better the feeding program will be at getting all sows to 0.71-0.75 in. backfat at farrowing.

Sows with low levels of backfat (< 0.51 in.) have low insulation levels and higher maintenance requirements, and therefore need more feed than other sows to achieve target backfat levels. These thin sows also appear to have much higher activity levels than other sows.

The Kansas State study also showed that the time sows spend standing can vary from 80 to 500 minutes/day. The energy cost for sows standing for 80 minutes would be about 0.35 Mcal ME/day, whereas, the energy required for a sow standing for 500 minutes/day would be 2.15 Mcal ME/day. Thus, for a sow getting 6 Mcal ME/day, anywhere from 6% to 36% of energy intake could be used for activity. It may not be possible to get very thin sows up to 0.71-0.75 in. backfat at farrowing.

Impacts on Lactation

Feeding strategies during gestation must not be considered in isolation from those in lactation. Excessive backfat levels at farrowing will reduce sow feed intake in lactation. Feeding in the first two parities are more critical than in subsequent parities.

An essential part of any strategy to optimize sow reproductive performance, increase efficiency of feed usage and lower culling rate, is to control weight and backfat gain during gestation, and weight and backfat loss in lactation. This is best achieved by individually feeding each sow a well-balanced diet, according to her weight and backfat level.

Table 1. Acceptable Levels of P2* Backfat

P2 backfat, in.
At first service (gilts) 0.59 - 0.63
At farrowing (all parities) 0.71 - 0.75
At weaning 0.59 - 0.63
*P2 position for measuring backfat is 2½ in. off the midline at the 10th rib.

Table 2: Feed Required Per Day to Achieve 0.75 in. Backfat at Farrowing

Backfat at P2*, at breeding, in. 0.71-0.75 0.59-0.63 0.47-0.51 0.35-0.39
Target backfat gain, in. 0 0.12 0.24 0.35
Estimates of breeding weight, by parity, lb. Feed allowance, lb.
Parity 0, 265-309 lb. 3.97 4.96 5.67
Parity 1 & 2, 309-353 lb. 4.19 5.14 6.11 7.39
Parity 3+, 353-485 lb. 4.94 5.65 6.35 7.43
Mean 4.37 5.25 6.04 7.41
*P2 position for measuring backfat is 2½ in. off the midline at the 10th rib.