Composition of sow colostrum and milk - The Gestating and Lactating Sow - page 196

filtering the supernatant and quantifying nitrogen in the supernatant using the Kjeldahl
method (Csapo et al. , 1996; Klobasa et al. , 1987). Colostrum NPN is relatively low (64
mg N/100 g of colostrum; Csapo et al. , 1996). Content of NPN increases in milk through
lactation, with reports ranging between 68 and 158 mg N/100 g of milk (Csapo et al. , 1996;
Gurr, 1981; Klobasa et al. , 1987; Mahan et al. , 1971; Perrin, 1958; Sheffy et al. , 1952).

Wu and Knabe (1994) characterized free and protein bound amino acid concentrations
in sow colostrum (collected 6 to 10 h postpartum) and milk (up to day 29 of lactation).
Most free amino acids are found in the micromolar concentration range, in contrast
to protein-bound amino acids that are in the millimolar range. The major free amino
acids in colostrum are histidine, which subsequently decreases in concentration during
lactation, and taurine, the concentration of which increases to day 8 of lactation and then
remains constant. Most other free amino acids increase in concentration from colostrum
to day 8 of lactation. Changes in concentrations of free amino acids between days 8 and
29 vary with the individual amino acid (Wu and Knabe, 1994). Total concentration of
free non-essential amino acids is lowest in colostrum and increases through most of
lactation, whereas the total concentration of free essential amino acids remains constant
throughout lactation. Concentrations of urea increase from colostrum to day 3 of
lactation and then decline to levels similar to those of colostrum (Wu and Knabe, 1994).
Ammonia concentrations are highest in colostrum and then decline to day 8, and remain
constant through the reminder of lactation (Wu and Knabe, 1994).

Nucleotide concentrations in sow colostrum change through lactation (Mateo et al. ,
2004). For example, adenine 5'monophosphate follows a quadratic pattern with a peak
at day 7 of lactation. However, uridine 5'monophosphate is highest at parturition and
then declines through lactation (Atwood et al. , 1995; Mateo et al. , 2004). Concentrations
of the polyamines, spermine and spermidine, increase from parturition to peak between
1 and 2 weeks of lactation and then decline as lactation progresses (Moytl et al. , 1995).
Considerable individual variation is observed for concentrations of those polyamines. A
number of nitrogen-containing sugars have also been identified in sow colostrum and
milk (Tao et al. , 2010).

9.8 Energy

Gross energy of mammary secretions is estimated by combustion of the organic matter
and quantification of the carbon dioxide released. Alternatively, some studies have
estimated gross energy based on calculations using the content of organic components
of milk (Laws et al. , 2009). Detailed reports on gross energy of sow mammary secretions
during the post-parturient period and throughout lactation are less prevalent than
for other components (Table 9.2 and 9.3). Gross energy of colostrum at parturition is
approximately 6.7 kJ/g and remains elevated at least through day 3 of lactation, before
declining later in lactation. The relatively high level of gross energy estimated in colostrum
at parturition is associated in part with the high concentration of immunoglobulins in
colostrum. However, immunoglobulins tend to be more resistant to digestion than other
milk proteins and contribute a smaller proportion of absorbed amino acids compared