Agriculture Reference
In-Depth Information
supplying the posterior mammary glands (Ghoshal, 1975). The anterior mammary glands
are mainly supplied by the cranial epigastric artery originating from the internal thoracic
artery (Ghoshal, 1975; Trottier
et al.
, 1995a). Blood leaving the mammary glands uses
two distinct pathways (Turner, 1952); the anterior glands are drained cranially through
two subcutaneous abdominal veins which run parallel on each side of the mammary
system to reach the internal thoracic vein (Trottier
et al.
, 1995a). Blood that exits the
posterior glands in the inguinal region does so caudally by way of the same subcutaneous
abdominal vein thereby draining into the external pudic vein (Turner, 1952). In contrast
to other litter baring species studied to date, superficial veins arising from the mammary
parenchyma and branching from the epigastric veins are joined between the right and left
side of each pair of glands through venous anastomosis (Lignereux
et al.
, 1996).
14.2.2
Estimating mammary blood flow
Mammary venous and arterial blood samplings are required to measure blood flow
and to estimate mammary nutrient uptake. Mammary blood flow in lactating sows has
been estimated both directly and indirectly. All porcine mammary blood flow values
obtained by indirect methods (Guan
et al.
, 2002, 2004a,b; Linzell
et al.
, 1969a; Nielsen
et al.
, 2002a,b; Trottier
et al.
, 1997) are based on Fick's original principle of diffusion
(Fick, 1870). Kety and Schmidt (1945) adapted the Fick's principle to measure cerebral
blood flow using nitrous oxide as an inert marker. Linzell
et al.
(1969a) used the Kety-
Schmidt method (Kety and Schmidt, 1945) and DO as an inert marker to estimate blood
flow across one single mammary gland. This value was then used to estimate blood
flow across the entire udder (Table 14.1). In that same study, Linzell
et al.
(1969a) also
measured for the first time, the arteriovenous difference in nutrient concentrations by
sampling mammary venous and arterial blood following catheterization of the external
pudic artery and of a mammary vein draining a single functional gland (Figure 14.1).
Milk yield of the gland was measured over a 5-h period and total mammary tissue was
weighed at the end of the study to allow estimation of milk yield and blood flow per 100
g of mammary tissue. For the purpose of comparison with other studies, milk yield and
blood flow values in this chapter were estimated for an entire udder based on an udder
weight of 770 g (Table 14.1).
When applying the Fick's principle to measure blood flow in lactating sows, catheter
placement for the arterial infusion of an external inert marker and blood sampling may be
done using any arterial sites. The Fick approach, however, is more feasible for determination
of long-term changes in blood flow (i.e. daily) as opposed to changes occurring in the
short term (i.e. minutes). More recent studies (Guan
et al.
, 2002, 2004a,b; ManjarÃn
et al.
,
2012b; Nielsen
et al.
, 2002a,b; Trottier
et al.
, 1997) applied the Fick's principle to estimate
mammary blood flow using an internal marker. The advantage of an internal marker is
that there is no need for arterial infusion of an external marker. In those studies, lysine or
phenylalanine + tyrosine were used with the major premise that lysine and phenylalanine
are negligibly catabolized or utilized by the porcine mammary gland, other than their
incorporation into milk proteins (Guan
et al.
, 2002, 2004a). Such assumption may however
have led to an underestimation of mammary plasma flow. For instance, Lapierre
et al.
(2009) reported lysine to be utilized and oxidized through pathways for non-milk protein
