The energy, protein, lysine and other nutrient requirements of a lactating sow depend on her weight, milk yield, and to a much lesser extent, the environmental conditions under which she is housed.

Unfortunately, we rarely know the sow's weight or her milk yield. So, we feed her to appetite, using automatic dry or wet/dry feeders to make fresh feed available at all times.

If feeding lactating sows is really this simple, why do we still have an ongoing discussion about the best way to feed them? And, why does survey data still show very large differences in average feed intake levels, ranging from 8 to 20 lb./day?

Some of the feed intake differences amongst farms can be explained by differences in genotype, herd size, lactation length, litter size and parity distribution. However, much of the differences are still due to feeding management.

Quality of farrowing unit management is the most likely cause of the large variation in lactation feed intake. Caring, knowledgeable, skilled stockpersons who are given enough time to treat each animal as an individual will probably increase feed intake more than any other single factor.

The Critical First Week

The differences in lactation feed intake among farms is most obvious in the first week of lactation. The basic reason: Many farms adopt a feeding program that gradually increases sow feed allowance over the first 5 to 10 days of lactation. In many cases, this approach will reduce sow feed intake during the first week of lactation by 15% or more compared to a more aggressive system of feeding.

Consequently, most lactating sows are in an energy and amino acid deficit for the first week of lactation. Normally, this will not reduce milk production, but it will result in significant sow weight loss (both protein and fat).

It has been shown that if sows lose 10-12% of their protein mass during lactation, they will have longer wean-to-estrus intervals, poorer farrowing rates and lower subsequent litter sizes (Table 1).

Although a short-term nutrition deficiency may not affect milk yield, there is evidence showing that it can cause acute and chronic changes in the reproductive hormone system. And, even though the changes in body composition are not apparent, these negative effects can reduce ovulation rate and embryo survival. Similarly, under-nutrition during any week of lactation can reduce subsequent litter size.

Why Regulate Sow Feed Intake?

Restricted feeding in early lactation is commonly practiced by those who believe that over-feeding sows in early lactation may cause udder congestion and hypogalactia, piglet scours and sow constipation, and may lead to sows “going-off” feed in mid- to late-lactation.

Survey data reveals that 5-30% of lactating sows show a marked dip in feed intake for 2-3 days in the second week of lactation. These dips in feed consumption were associated with longer wean-to-estrus intervals, reduced farrowing rate and smaller subsequent litter size.

A review of farm records using a gradual feeding system shows that litter weaning weights are lower, and wean-to-estrus intervals longer and more variable, than those of farms that encourage a rapid increase in early lactation feed intake. Therefore, a major objective of the farrowing barn staff must be to maximize sow feed intake without upsetting the sow.

Composition of the lactating sow diet is also important, but is secondary to feed intake.

Familiarity with some of the major factors affecting sow feed intake in lactation is essential to achieving high feed intake levels. Barn temperature, condition of sow at farrowing and feeding system are among the most important.

Barn Temperature

Whenever possible, the farrowing room temperature should be kept between 66° and 72° F. High barn temperature will decrease feed intake of all lactating sows, but first-parity sows are the most sensitive. As a rule of thumb, average daily feed intake will decrease by 0.2 lb./°F when temperatures rise above 66° F.

Use of properly managed drip coolers will increase sow feed intake by 20-25% during hot weather. Wetting sow feed at feeding will also increase feed intake by about 2 lb./sow/day, but is a very time-consuming chore.

If feed is available to them, lactating sows will consume 20-25% of their daily intake in late evening and during the night. Therefore, it is particularly important to have feed available to sows during the cooler period of the day during hot weather.

Sow Condition at Farrowing

Most studies have shown that sow backfat level at farrowing only reduces daily feed intake if backfat levels exceed 0.83 in. In one study, daily feed intake decreased by about 0.3 lb./0.04 in. backfat above 0.75 in.

Feeding System

The energy, amino acid and other nutrient requirements of lactating sows are primarily dependent on their milk yield and its composition, and sow weight and parity. Obviously, the larger the sow and the more milk she produces, the more energy and nutrients she will require.

First-parity sows and, to a lesser extent, second-parity sows are still growing, so they are still depositing protein. But milk production has a priority over growth. A young sow will sacrifice growth, and will even mobilize body reserves of fat and protein, to maintain milk production. But this sacrifice is made to a certain point; After a 10-12% loss of protein mass, then milk production will be decreased.

Milk yield is determined by genotype, but it is also greatly influenced by the number and vitality of pigs in a litter.

The objective of the feeding program must be to maximize milk yield and limit loss of the sow's protein mass. In a recent study at Kansas State University, there was no difference in performance of sows that lost virtually no backfat and those that lost up to 0.31 in. of backfat (or between 0.25 and to 30 lb. of fat), during lactation when loss of protein mass was minimal.

Guide to Feeding Lactating Sows

What do we need to know to develop a feeding program for lactating sows?

First, we need some estimate of sow feed intake. This can be calculated from feed deliveries over a period of one to three months. If feed wastage is not excessive, then feed disappearance should approximate feed intake. Feed disappearance (assume a three-month period of feed deliveries) can be calculated as:

lb. feed/sow/3 months = Total lactation feed delivered/No. of lactations in the 3-month period

Correct for gestation sow days in the farrowing barn and divide by the number of days per lactation.

Example:
1,250 sow unit, 16-day lactation, 3-month period.

Calculate “crate cycle” days:

7 days/week × (No. farrowing rooms ÷ weaning frequency/week)

Crate cycle = 7 × (6 ÷ 2) = 21 days

Calculate gestating sows' days in farrowing barn:

Crate cycle 21 days
Washing 1
Moving 1
Lactation 16
Total 18


Gestation days = 21 - 18 = 3

Calculate feed fed to gestating sows:

3 days at 5.5 lb/day = 16.5 lb.

Calculate feed intake per lactation:

Feed delivered 94.8 tons
No. litters weaned 756 (63/wk)
Feed use/litter 94.8 T ÷ 756 = 0.125 T or 250 lb./litter


Feed intake/day, lb.: (250 - 16.5) ÷ 16 = 14.5 lb.

But what should the sows be eating and what should the composition of that feed be?

For this calculation, we need to know average litter weight gain. We can guess birth weight at 3.1 to 3.3 lb., but we need an estimate of weaning weight and number of pigs weaned/litter. With this data, we can make a lot of useful calculations:

We'll assume the 1,250-sow herd used as our example had the following performance levels:

No. weaned/litter: 10

16-day lactation
Avg. birth weight 3.1 lb.
Avg. weaning weight 12.5 lb.
Avg. piglet gain 9.4 lb.
Total litter gain 94.6 lb.
Litter gain/day 5.9 lb. (94.6 ÷16)


Energy requirements for the litter: 3.1 Mcal DE/lb. litter gain:

3.1 × 5.9 = 18.3 Mcal DE/day

This can be supplied by 12 lb. of a diet containing 1.53 Mcal DE/lb. (DE = digestible energy). Average intake on this farm was 14.5 lb., so sow weight loss should not be a problem. Also, note that 12 lb. feed/day for a litter of 10 pigs, allows 1.2 lb. feed/pig in the litter. This is close to the old recommendation of 1 lb./pig.

Energy requirement for the sow (Mcal DE/day): 110 kcal DE/kg (2.2 lb.) metabolic weight Metabolic weight calculated as 13 + 0.2 wt.

Assume 200 kg (440 lb.) sow, energy required for maintenance is:

13 + (0.2 × 200) = 52.6 × 110 = 5786 kcal/day or 5.79 Mcal DE/day.

If the diet contains 1.53 Mcal DE/lb. (corn-soy, and this is close to optimum) then the sow needs 3.78 lb. of feed/day for maintenance. This is pretty close to the age-old recommendation of 4 lb. for the sow.

So bringing science to a practical feeding program, we might suggest the following:

Day of farrowing 3-5 lb.
Day 1 & 2 of lactation 5-7 lb.


Complete all crossfostering by Day 2. Set target feeding level to gradually reach an intake level of 4 lb. for the sow and 1 lb./pig in the litter by Day 8 of lactation.

For a litter of 10 pigs, that is 14 lb. feed/day by Day 8. Hold this level from Day 8 to Day 12 to help avoid dips in feed intake by some sows. Then, from Day 13 to weaning, increase feed intake to the sow's appetite level.

It has been suggested that this increase in feed intake may “flush” the sow and may decrease wean-to-estrus interval and increase subsequent litter size. Such a feeding system will ensure a minimum sow weight loss and optimize litter weaning weight.

Many herds can manage ad lib feeding systems either by hand-feeding or automatic full-feeding systems without experiencing drops in sow feed intake in mid-lactation, and achieve high sow feed intakes. For such systems, there is no need to change the system.

As to the energy and nutrient levels in the diet, there is little reason to go above 1.53 Mcal DE/lb. diet. The estimate of 12 g. lysine and 0.4 lb. protein/lb. of litter gain still looks good. Add 2 g. lysine and 0.4 lb. protein/day for maintenance.

Using data for the example herd, we have:

Daily protein need = 0.4 × 5.9 lb. litter gain + 0.4 lb. protein for the sow = 2.76 lb./day

% protein in diets = 2.76 × 100 = 19%/14.5 lb. feed/day

Daily lysine need = 12 g lysine × 5.9 lb. + 2 g. = 72.8 g./day or 0.16 lb.

% Lysine required 0.16/1435 × 100 = 1.10 %

Sow Feeding Wrap Up

Estimates of the energy and nutrient requirements of lactating sows are generally pretty good. Most problems occur when we fail to apply these estimates, especially when we aim for high lactation feed intake.

The old advice of 4 lb. for the sow and 1 lb. for each pig in the litter is still a good guide to the minimum levels lactating sows should be fed. Formulation of the diet is also important, and using current data together with measures of litter weight gain can help develop very adequate, farm-specific diets for lactating sows. Whether or not such estimates should be based on the values for average sows, or the top 25% of sows, is a debatable question.

Table 1: The Effects of Protein Loss in Lactation on Sow Reproductive Performance
Lactation protein loss, % 6.9 9.4 15.1
No. follicles 4-6mm in diameter* 25.1 23.6 9.7
*Follicles of 4-6 mm are the ones most likely to produce viable ova at time of estrus.
Clowes et al 1999