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.
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.
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).
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.
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.
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
