Agriculture Reference
In-Depth Information
recommended feed intake is reached. Recently, Thingnes
et al.
(2012) showed that stepwise
increases may also be important in later lactation. These authors slowly increased feed
allowance of sows until day 9, after which sows either remained on this step-up schedule
or were given
ad libitum
access to feed. Twice as many sows on the
ad libitum
access
subsequently had drops in feed intake (defined as a decrease in feed intake of more than
3 kg for at least 3 days) during the remainder of the 35 day lactation (50% vs. 25%), and
sows with drops in feed intake had a lower overall feed intake and greater weight loss
during lactation. However, advices on optimal feed intake patterns to use during lactation
may be genotype dependent, related to differences in voluntary feed intake of sows and in
factors that affect this intake. On problem farms, it is advised to optimize feed intake by
continuous evaluation of higher feed allowances without drops in feed intake.
Dietary protein and fat levels during lactation
Dietary protein levels may affect post-weaning performance. Yang
et al.
(2000b) compared
five dietary lysine concentrations during lactation, from 0.6% total lysine (low) to 1.6%
total lysine (high). Although the increase in dietary lysine concentrations resulted in a
linear increase in lysine and protein intake in primiparous sows, it also resulted in a linear
reduction in feed intake and, as a consequence, a linear reduction in subsequent litter size.
Therefore, high protein levels limit feed intake and thereby negatively affect subsequent
reproductive performance. On the other hand, low dietary protein may increase body
protein losses (Mejia-Guadarrama
et al.
, 2002) and thereby negatively affect reproductive
performance, such as impaired follicle development and oocyte maturation (Yang
et al.
,
2000a), and lower ovulation rate (Mejia-Guadarrama
et al.
, 2002). It was concluded that
lysine (protein) requirement for subsequent reproduction is not greater than that needed
for optimal milk production (Yang
et al.
, 2000b) and daily dietary lysine requirements
for lactating sows can therefore be followed without adverse effects on subsequent
reproduction (see NRC, 2012). Another approach to influence mobilisation of body
stores is to increase dietary fat content. Although high fat diets often result in a reduction
in feed intake, Drochner (1989) showed that in older parity sows total metabolisable
energy (ME) intake was still increased by an average of 12% (3 to 32%) compared with
diets with lower fat levels. Using dietary fat as an energy source increases milk fat content
and, in some cases, total milk output (Drochner, 1989). Van den Brand
et al.
(2000b)
found that a diet rich in fat (13.5% vs. 3.4%) resulted in an increased milk fat content
(+1.5%) and a significantly greater body fat loss (+3.8 kg) in primiparous sows over a 21
day lactation. The milk fat driving effect of fat-rich diets may therefore not prevent body
condition losses. On the other hand, fat-rich diets may result in a higher energy intake
in hot climates since heat production of sows is lower when dietary fat is used for milk
production. High-energy diets may therefore be beneficial for reproductive performance,
especially if they increase energy intake to a greater extent than the extra energy required
for milk production with such diets. Recently, Smits
et al.
(2012) found a linear increase
in daily digestible energy intake (from 61 to 72 MJ DE/day) using diets with increased
levels of both energy (5 levels, from 13.0 to 15.3 MJ DE/kg) and protein (5 levels, from
218 g/kg to 259 g/kg). Although lactational feed intake was similar for the 5 diets, a
linear decrease in weaning-to-oestrus interval was found (from 8.1 to 5.7 days) and the
proportion of weaned sows that farrowed a second litter tended to increase (from 49 to
