M. Aslam et al., 2-DIMENSIONAL ELECTROPHORETIC ANALYSIS OF PROTEINS OF BOVINE MAMMARY-GLAND SECRETIONS COLLECTED DURING THE DRY PERIOD, Journal of dairy science, 77(6), 1994, pp. 1529-1536
Proteins in mammary gland secretions, collected from Holstein cows dur
ing the dry period, were analyzed by preparative isoelectric focusing,
followed by SDS-PAGE. Protein profiles changed throughout the dry per
iod. intact casein bands were present throughout the dry period, but i
n reduced proportions from d 7 after dry-off through d 7 prepartum. Br
eakdown fragments of casein were particularly apparent in secretions f
rom d 7 to 21 of the dry. period. A fragment of beta-CN (approximately
13 kDa) was identified in secretions collected on d-1 prior to dry-of
f through d 21 of the dry period. Beta-Lactoglobulin generally focused
in a limited number of fractions, but, in the sample at d 21 prepartu
m, beta-LG focused over a broad pH range. Lactoferrin was found in all
fractions after isoelectric focusing, but specific degradation produc
ts of lactoferrin were apparent only at certain times during the dry p
eriod. This method is a valuable approach for separation of proteins f
rom the complex mixtures found in mammary secretions during the dry pe
riod. A number of peptides identified by this method may be generated
from breakdown of milk proteins in the mammary gland during the dry pe
riod and could have a role in the involuting gland.