Agriculture Reference
In-Depth Information
description of ways to measure sow colostrum and milk yield, please refer to Chapter 8 on
colostrum and milk production (Quesnel
et al.
, 2015). Milk typically is collected from a
subset of functional glands or from all functional glands and a composite sample used for
analysis. Concentrations of milk fat, protein and lactose do not vary significantly between
front and rear mammary glands on the sow (Reynolds and Rook, 1977).
Milk composition can be affected by oxytocin administration, where intravenous
administration of 20 IU oxytocin results in lower concentrations of total solids (dry
matter), fat, lactose and energy compared with manual stimulation or 10 IU of oxytocin
intravenous injection (Hartog
et al.
, 1987). Intravenous administration of oxytocin
can result in lower milk fat concentrations compared with intramuscular oxytocin
administration, but the route of administration does not affect milk protein concentration
(Garst
et al.
, 1999). The composition of milk varies with the fraction that is removed
during milk ejection, with the hind milk (portion removed in response to oxytocin
injection after piglets completed suckling) having higher concentrations of total solids,
fat, and energy, but not of protein and lactose, compared with the fore milk fraction
(Atwood and Hartmann, 1992).
9.2.2
Analysis of major milk components
Many methods for determining the gross composition of milk are derived from the
Official Methods of Analysis published by the Association of Official Analytical Chemists.
A brief overview of methods used for milk component analysis is provided here. Total
solids, or dry matter, is often determined gravimetrically after drying the milk sample,
although freeze drying has also been used. Ash content is determined by incineration of
the sample in a muffle oven at 550 °C. Fat percentage often has been determined using the
Babcock method or Gerber method, both of which use sulfuric acid to hydrolyze organic
components other than the lipid. The Babcock method has been noted as giving slightly
lower fat values compared with a solvent extraction method (i.e. Mojonnier method;
Fahmy, 1972). Other methods employ a solvent extraction approach such as using a Soxhlet
apparatus or the Roese-Gottlieb or Mojonnier method which employs an extraction with
ether or petroleum ether, followed by drying and weighing the extract. Methods for
determining total milk protein have included the Kjeldahl method, or some modification
of the Lowry protein assay (copper-binding assay), or modification of the Bradford protein
assay (dye-binding assay), although more recent reports have used automated instruments
that directly determine the N content. Lactose has been determined by reducing-sugar
assays, by enzymatic hydrolysis, or by difference subtracting other components from the
total solids value. Enzymatic analysis of lactose in milk samples is carried out by hydrolysis
of lactose to D-glucose and D-galactose by β-galactosidase, followed by oxidation of
D-galactose by nicotinamide-adenine dinucleotide and then measuring the absorbance
of the reduced NADH. Total milk energy content typically is determined either directly
by combustion using an adiabatic bomb calorimeter, or by calculation from percentages
of milk fat, total protein, and lactose (Klaver
et al.
, 1981). More recent reports have used
methods that employ Fourier Transform Infared analysis (Krogh
et al.
, 2012).
