Mammary blood flow and nutrient uptake - The Gestating and Lactating Sow - page 315

10

Amino acids
Fatty acids
Triglycerides
Lactate
Glucose

8

6

4

2

0

1 2 3a 3b

Figure 14.2. Partition of energy uptake by the mammary gland in different studies (Farmer et al ., 2008b). 1 =
Linzell et al . (1969b); 2 = Renaudeau et al . (2003); 3 = Dourmad et al . (2000). 3a = post-prandial; 3b = fasted.

intermediate between that of fed and fasted sows (Renaudeau et al. , 2003), with free fatty
acids contributing 15% of total mammary energy uptake.

The energetic efficiency of milk synthesis from plasma precursors can be calculated
(Table 14.3) using mammary AVD measured by Renaudeau et al. (2003) and assuming a
plasma flow of 550 l/l of milk. For a daily milk production of 10 kg, the amount of energy
present in precursors and products was 48.8 and 43.6 MJ/d, respectively, corresponding
to an energy efficiency of 0.89. This value is greater than the usual estimate of ME
efficiency for milk production (0.72) derived from energy metabolism studies but is
very close to that reported for the efficiency of energy use from body reserves (0.88;
Noblet and Etienne, 1987). This discrepancy between the estimates of efficiency obtained
from energy metabolism studies, on one hand, and mammary balance studies, on the
other hand, could be partially related to other metabolic processes associated with milk
production but occurring outside the mammary gland. It may however also originate
from an under-estimation of either the uptake of nutrient or blood flow. Indeed, using
a biochemical model describing the stoichiometry of nutrient transformation in the
mammary gland, Van Milgen et al. (2003) showed that with the data from Renaudeau et
al. (2003) blood flow or AVD had to be increased by about 10% to ensure correspondence
between observed and stoichiometric balances.

14.3.5 Uptake of amino acids

In contrast to other nutrients, the AVD and net uptake of amino acids by the sow
mammary gland has been extensively measured in response to the diet (Guan et al. ,
2002, 2004a,b; Manjarín et al. , 2012b), to stage of lactation, and to milk demand (Guan
et al. , 2004a,b; Nielsen et al. , 2002b). Guan et al. (2004a,b) showed that net mammary
uptake of amino acids increases with advancing lactation from approximately 6 d up
to peak milk (i.e. d 14 to 18) demand and decreases thereafter. This increase in uptake
was associated to an increase in AVD. In contrast, the increase in net amino acid uptake