Agriculture Reference
In-Depth Information
9.3
Physico-chemical properties
Specific gravity of sow colostrum at parturition starts at approximately 1.06 g/ml,
reflecting the high concentration of total protein at that time. It then declines within the
first day and stabilizes at about 1.035 g/ml throughout much of lactation, before rising
slightly in an extended lactation beyond 6 weeks (Fahmy, 1972; Krakowski
et al.
, 2002;
(Sheffy
et al.
, 1952; Whittlestone, 1952). The pH of sow colostrum is more acidic than that
of milk. Kent
et al.
(1998) reported that the pH of colostrum immediately before and after
parturition was 5.7, rising to 6.0 at day 1, and reaching 6.9 by day 9, consistent with other
reports (Coffey
et al.
, 1982; Miller
et al.
, 1971). Others have reported more basic ranges
of pH for sow milk, even with pH above 7.0 (DeRouchey
et al.
, 2003; Sheffy
et al.
, 1952;
Whittlestone, 1952). The pH of milk is related to the equilibrium of calcium between the
aqueous and casein micellar phases (Gaucheron, 2005).
There are limited reports describing other physico-chemical properties of sow colostrum
or milk. Viscosity of sow colostrum is highest at parturition and then declines,
with estimates of milk viscosity at 3.855 millipascal-seconds (Whittlestone, 1952).
Conductivity increases during the initial day of parturition, and then declines slowly
to about day 16 of lactation, where the average conductivity of sow milk is estimated at
3.248 ohm
-1
×10
3
(Whittlestone, 1952). The freezing point of cow milk is often used as a
means to determine if water has been added to the milk. For sow milk, the freezing point
is estimated at -0.563 °C (Sheffy
et al.
, 1952).
9.4
Water and total solids
Water is a critical component of mammary secretions. It provides a medium for mixing
of the other components during milk synthesis and secretion, as well as for providing
this nutrient to the young. The secretion of water as part of milk is closely linked with the
synthesis and secretion of the major milk carbohydrate in mammary secretions, namely
lactose. Total solids or dry matter content of mammary secretions are typically reported
rather than water content. Total solids or dry matter are determined gravimetrically by
evaporating the water from the secretion sample, usually at temperatures below 100 °C.
Therefore, estimates of total solids content include all organic and inorganic components
of mammary secretions.
9.4.1
Stage of lactation
Accounting for the total solids content of mammary secretions of the sow (Table 9.2),
water makes up approximately 73% of the secretion mass during and immediately after
parturition. Water content then increases to about 80% by 12 h postpartum and remains
in the 77 to 81% range throughout lactation (Table 9.3). The increase in water content
during the initial day postpartum occurs as a result of the rapidly declining concentration
of proteins, primarily immunoglobulins, which is only partially offset by the increase in
lactose content during the same period (Table 9.2).
