FEEDING STRATEGIES FOR SOWS

Eric van Heugten
Department of Animal Science
North Carolina State University
Raleigh, NC 27695

Introduction

Proper nutritional management of sows is important to maximize the number of pigs per sow per year and for sow longevity. Current research and feeding recommendations for gestating and lactating sows will be discussed.

Gestating Sows

A simple layout of metabolism in sows is shown below. Nutrient requirements of sows can be calculated from the metabolic processes taking place during gestation.


For example, energy needed for maintenance of sows is dependent on sow body weight and can be calculated from the following equation: ME (kcal) = 106 * (body weight)0.75. Energy for uterine growth (fetuses, fluids and membranes and empty uterus) and maternal growth (mammary gland and sow body weight gain) can be estimated based on some assumptions on parity, litter size, weight at birth and sow body weight. Most of the energy requirements of sows will be due to maintenance as shown in Table 1. The proportions will change as gestation progresses because growth of the products of conception will increase, particularly during the later stage of gestation (Figure 1). Typically, requirement estimates are made for the overall gestation phase and attempts are made to provide proper levels of nutrition through changes in feed allowance. Estimates for the nutritional needs of sows are shown in Table 2. These estimates were based on the assumption that a sow will strive to reach a certain body protein mass and that a slow development of this protein mass is desired to maximize N utilization. Assuming a standard corn-soybean meal ration containing 3260 kcal of ME/kg of feed and 0.60% total lysine one can calculate the amounts of feed needed to meet these requirement estimates. When considering energy, 4.4 to 4.6 lbs. of feed is required to meet the average energy requirement for gestating sows. To meet the energy requirement of a sow at mating, 3.9 lbs. of feed is needed, whereas 5.3 lbs. is required for a sow at the end of gestation. When we do the calculation based on lysine, the average lysine requirement during gestation can be met with 3.6 to 4.0 lbs. of feed. The requirement at mating can be met with just 1.6 lbs. of feed, however to meet the requirement at the end of gestation 5.9 lbs. of feed is needed. To meet the requirement for both nutrients, it appears that 4 to 6 lbs. of feed would cover the range. Of course, this would only hold true if sows are not excessively thin at mating and are managed properly, under thermoneutral conditions.

Table 1. Example of a calculation to estimate energy requirements of gestating sows


Source: Noblet and Etienne, 1987

Figure 1. Development of fetuses, fluids, membranes, and the empty uterus during gestation (from: Walker and Young,1991).

Table 2. Estimated nutrient requirements for gestating sows

ME Requirement, kcal/d
Total Lysine Requirement, g/d
Parity
Weight at Mating, lb
Weight gain, lb
Day 0
Day 115
Overall
Day 0
Day 115
Overall
1
260
120
5260
7650
6455
5.8
16.0
10.9
2
300
120
5500
7890
6695
5.4
16.0
10.7
3
335
110
5740
7890
6815
4.4
15.3
9.9
4
360
100
5740
7890
6815
4.4
15.3
9.9
5
380
100
5740
7890
6815
4.4
15.3
9.9

Adapted from Everts, 1994

The amount of feed supplied during specific phases of gestation can positively or negatively affect sow performance. There are a number of specific phases to consider, each of which will be briefly described below.

Weaning to breeding

The rate of ovulation, particularly in first litter sows, appears to be influenced by feed intake following weaning. King and Williams (1994) showed that first parity sows fed 9 lbs. per day between weaning and breeding had greater ovulation rates and litter sizes (10.0 vs. 8.8) than control sows fed 3.5 lbs. per day. Additionally, some studies suggest that feeding ad libitum after weaning shortens the rebreeding interval (Aherne and Kirkwood, 1985; King and Williams, 1984). However, results are not completely clear because other studies have shown no effect and the response to high levels of feeding may be related in part to body weight at weaning. Allowing sows to consume feed ad libitum between weaning and breeding may be a prudent practice, however, to help sows recover from weight loss during lactation and take advantage of a possible increase in ovulation rate and shorter wean to breed interval.

Early Gestation

High levels of feed intake during the first 3 weeks of gestation may have a negative impact on embryo survival. For example, Dyck et al. (1980) reported a reduction in embryo survival from 82.8% to 71.9% for sows fed 3.3 lbs. versus sows fed 6.6 lbs. The critical time period appears to be 24 to 48 hours after mating, when implantation of embryos in the uterus takes place. Limiting feed intake to 4 to 4.5 lbs. per day during the first 21 days post-breeding may be a safe practice.

Early to Mid Gestation

This period encompasses day 21 to day 75 of gestation. It is the most appropriate time period to get sows back into the correct body condition. A body condition score of 3 is desirable (Figure 2). Everts (1994) suggested a moderate net body weight gain of sows of approximately 75 lbs. for first parity sows, 65 lbs. for 2nd parity sows, 55 lbs. for 3rd parity sows and 45 lbs. for older sows. Boyd and Touchette (1997) estimated the amounts of feed needed to replenish body reserves based on body condition scores (Table 3). In addition to replenishing body reserves, level of nutrition from day 21 to 50 may be important to maximize the number of muscle fibers in piglets. Primary muscle fibers develop between day 21 and 50 of gestation and the number can be affected by nutrition. In studies where feed intake of sows was severely restricted during gestation, growth of piglets after birth was reduced (Pond et al. 1985, 1987). The extent to which this occurs under more practical circumstances is not clear at this point.

Figure 2. Body condition scoring chart for sows

Table 3. Estimated Amounts of Feed Needed to Replenish Body Reserves in Sows

Body Condition Score
Back Fat (P2), In.
Minimum Intake, lbs
1
0.4 - 0.5
7.7
2
0.6 - 0.7
6.0
3
0.8 - 0.9
4.2

From: Boyd and Touchette (1997). Calculated for a 400 lb sow to reclaim body reserves from 21 to 80 days of gestation.

Mid to Late Gestation

The development of the mammary gland reaches the critical stage between day 75 and 90. This is the period that secretory cell proliferation occurs, which will determine cell number and ultimately milk synthesis capacity. Excess energy intake (10.5 Mcal/d vs. 5.7 Mcal/d) reduced secretory cell numbers (Weldon et al., 1994) and could, therefore, reduce milk production. An energy intake of 10.5 Mcal/d would be equivalent to approximately 7 lbs of feed (corn-soy type diet; 3260 kcal/kg of feed). Therefore, feeding of high levels of feed should be avoided during this time-frame. Sows should be in the correct body condition at this time if they were properly fed in the early to mid gestation period.

Late Gestation

As can be seen from Figure 1, weight gain of fetuses will increase substantially during days 90 to 115 of gestation. Consequently, nutrient requirements will be increased (Table 2). According to this table, 5.3 to 5.9 lbs. of feed is required for sows at day 115 of gestation (depending if calculations are based on energy or lysine needs). However, care should be taken not to overfeed during this period either because a negative impact of overfeeding during this period has been reported to decrease feed intake and performance during lactation (Figure 3).

Figure 3. Effect of gestation feed intake on feed intake during lactation.
Source: Hardy, 1994

Lactating Sows

The lactating sow can obtain nutrients either from the feed or from body tissue reserves to support milk production as shown below.

Mobilization of sow body reserves should be avoided, but may not be possible depending on the milk production and feed intake of the sow. Noblet et al. (1989) estimated the energy requirement for lactating sows based on the maintenance requirement for energy (106 * (body weight)0.75) and the energy requirement for milk production (Table 4). Based on the assumptions indicated, the requirement for energy intake per day was 20.7 Mcal. This would be equivalent to 14 lbs. of feed/day for a corn-soybean meal diet without added fat or 12.6 lbs. of feed/day for a diet with 7% added fat. This level of feed intake may be difficult to achieve. In another example (Table 5), sow weight loss is calculated based on assumed daily gain of the litter and feed intake estimates. It is clear from these examples that feed intake is critical in preventing body weight loss during lactation. Extensive body weight loss during lactation (particularly protein) can have a negative impact on rebreeding and subsequent lactation performance. Therefore, feeding management during lactation should aim to maximize feed intake. Feeding multiple times per day may help accomplish this goal.

Table 4. Example calculation of the energy requirement of a lactating sow.

From: Noblet et al., 1989

Table 5. Theoretical example of energy needs of lactating sows

Week of Lactation
1
2
3
4
Mean
Gain, lbs/d
.35
.49
.62
.62
.52
Piglet Weight, lbs
5.5
8.8
13.2
17.6
Milk Prod, lbs
14.1
19.4
24.7
24.7
20.7
ME required, Mcal/d
16.2
21.0
25.5
25.5
22.1
Intake, lbs/d
9.7
12.1
13.2
13.0
12.1
ME/lb of feed
1670
1736
1932
1962
1826
ME intake (1550 in diet)
15.0
18.8
20.5
20.2
18.8
Deficit, Mcal
1.2
2.2
5.0
5.3
2.3
Sow Wt Loss, lbs/d
.44
.81
1.84
1.95
1.26

Adapted from Aherne, 1994. The line "ME/lb" in the table refers to the theoretical ME content required in the feed to meet the daily ME requirement of the sow. The line "ME intake (1550 in diet)" refers to the actual ME intake of sows at the given feed intake if the diet contains 1550 kcal/lb of feed.

Lysine requirements of lactating sows can be calculated from Figure 4. Based on this figure, the lysine requirements can be estimated to increase by 10.8 grams/day for every 1 lb increase in litter gain/day. For example, a litter of 10 pigs weighing 33 lbs. at birth (pig birth weight of 3.3 lbs.) and 130 lbs. at weaning at 21 days would have gained 97 lbs. in 21 days or 4.62 lbs./day. The total lysine need in grams per day =

(10.768 x 4.62) - 3.74 = 46.0. Assuming a feed consumption of 12 lbs./day from the time of farrowing to the time of weaning the lysine requirement in the diet can be calculated as follows: 46.0 (g of lysine/day) / (12 lbs. * 4.54) = 0.84%. The factor 4.54 will convert lbs. to kg and kg to percent in these calculations. This calculation can be done on farm as a guideline for the lysine requirements of sows under on-farm conditions.

Figure 4. Effect of litter weight gain on daily lysine requirements

Adapted from Pettigrew, 1993.

Take-Home Message

Proper nutritional management of gestating and lactating sows includes feeding the correct nutrient levels to meet the sow's requirement, but also correct management of feed amounts given to the sows at critical times in their development.

Literature Cited

Available upon request