Agriculture Reference
In-Depth Information
Table 14.3. Estimation of energetic efficiency of milk synthesis from precursors (Farmer
et al
., 2008b).
g/d
kJ/d
Precursors (uptake for 10 l milk/d)
1
Glucose
1,359
21,328
Lactate
26
388
Glycerol
246
9,363
Triglycerides
172
6,714
Fatty acids
8
149
Amino acids
561
10,883
Total
2,373
48,825
Products (output for 10 l milk/d)
2
Lactose
560
8,960
Fat
580
22,040
Protein
530
12,561
Total
1,670
43,561
Efficiency (%)
89.2
1
Precursors were calculated from AVD measured by Renaudeau
et al.
(2002) assuming that a blood flow equivalent to 550 l plasma was required
to produce 1 kg of milk (Trottier
et al.
1997).
2
Products were estimated from Renaudeau
et al.
(2002).
observed with increasing litter size was associated with an increase in blood flow rather
than an increase in AVD (Nielsen
et al.
, 2002b). The change in AVD associated with day
of lactation raises the question as to whether this change is related to cellular transporter
protein abundance or to amino acid competitive transport inhibition. Amino acid
uptake by all vertebrate cells is controlled by a coordinated activity of protein-carriers
located in the cellular membrane that channel amino acids intracellularly (Broër
et al.
,
2008; Palacín
et al.
, 1998; Shennan
et al.
, 2000). A review of the current knowledge on
amino acid transporter proteins and their regulation in the mammary gland including
that of the sow is beyond the scope of the current topic chapter. Briely, transcripts for
the genes encoding for amino acid transporter proteins that fall under two sodium-
dependent and two sodium-independent systems have been measured in sow mammary
tissue. Of the sodium dependent systems, B
0,+
and y
+
L, the respective transcripts of the
genes encoding for ATB
o,+
, y
+
LAT1/4F2hc and y
+
LAT2/4F2hc were reported by Pérez-
Laspiur
et al.
(2009) (ATB
o,+
) and Manjarín
et al.
(2011, 2012b) (ATB
o,+
, y
+
LAT1/4F2hc
and y
+
LAT2/4F2hc). For the sodium independent system, y
+
and b
0,+
, the respective
transcripts of their genes encoding for CAT-1, CAT-2b, and b
0,+
AT1/rBAT were also
reported by Pérez-Laspiur
et al.
(2009) (CAT-1, CAT-2b) and Manjarín
et al.
(2011,
2012b) (CAT-1, CAT-2b, and b
0,+
AT1).
Transcript abundance of several of these genes was shown to increase in response to milk
demand (Manjarín
et al.
, 2011), and to dietary amino acid availability (Pérez-Laspiur
et
al.
, 2009). In contrast, in the recent work by Manjarín
et al.
(2012b), no changes were
