Agriculture Reference
In-Depth Information
energy secreted in milk
Additional heat loss, MJ/d =
- energy secreted in milk
(1)
k
where energy secreted in milk is in MJ/d and k is the efficiency of converting metabolizable
energy to energy secreted in milk. The k has been reported to be 0.78 in a study where sow
milk production was assessed by the deuterated water (DO) dilution technique (Theil
et
al.
, 2004). After parturition, the amount of energy secreted increases from approximately
26 MJ on d 2 to 45 MJ on d 10 and, concomitantly, the additional heat production
increases from 7.3 to 12.7 MJ/d. The increment in heat production due to milk synthesis
from d 2 to d 10 corresponds to the amount of energy present in approximately 0.5 kg of
feed. This increase in additional heat is only associated with the extra heat due to milk
synthesis and does not include extra costs associated with diet-induced thermogenesis
which, expectedly, will increase the amount of feed required.
7.2.12
Physiological adaptations and role of the liver during transition
The energy and protein balances and the intermediary metabolism of sows change
considerably during the transition period (Hansen
et al.
, 2012a; Mosnier
et al.
, 2010;
heil
et al.
, 2002, 2004, 2013). Around parturition, the sows change from an anabolic to
a catabolic metabolism and concomitantly the protein balance is lowered considerably
(Theil
et al.
, 2002, 2004). Moreover, hepatic metabolism also changes and, for instance,
portal blood flow is 2-fold and arterial plasma flow 3-fold greater during lactation than
in late gestation (Flummer
et al.
, unpublished data). The liver weight only accounts
for 2 to 4% of the sow live weight, but the hepatic oxygen consumption accounts for
40% of the cardiac output during lactation (Kristensen and Wu, 2012). Interestingly,
as metabolic activity increases dramatically in the liver during the transition period,
indicated by the pronounced increase in hepatic supply of arterial and portal blood, the
total heat production of sows changes only moderately from an average of 31 MJ/d 10 d
before parturition (Theil
et al.
, 2002) to 37 MJ/d 10 d after parturition (Theil
et al.
, 2004).
Milk synthesis requires substantial amounts of energy and nutrients as well as increased
metabolic activity in the mammary glands. The 3-fold increase in hepatic arterial blood
supply suggests that the liver carries out part of the metabolic burden associated with
milk production. Another role of the liver is to maintain glucose homeostasis and at
peak lactation the liver uses glycogen depots to buffer the plasma glucose from 4 h after
feeding until the next meal (Flummer
et al.
, unpublished). In addition, the liver extracts
propionate very efficiently (>95%) when compared with the amount absorbed from the
gastrointestinal tract. The liver converts propionate to lactate, which can be used as an
energy source in either muscle or mammary tissues (Flummer
et al.
, unpublished data).
A low dietary n-6:n-3 ratio is beneficial both for the inflammatory profile of sows during
transition and for the feed intake shortly after parturition (Papadopolous
et al.
, 2009).
These last authors further claimed that the dietary n-6:n-3 ratio was associated with a
better metabolic adaptation to the altered physiology of the sows around parturition. The
metabolic adaptation may involve alterations in hepatic metabolism, as it is known that
the dietary n-6:n-3 ratio affects the hepatic gene expression of weaned pigs (Theil and
Lauridsen, 2007). The nutrients supplied via the feed during the transition period are,
of course, important for the intermediary metabolism of sows. In a recent study, sows
