The effect of once daily milking concentrations and yields of
plasminogen, plasmin and other whey proteins
R.J. Knutson, D.D.S. MacKenzie, S.R. Davis, S.N. McCutcheon
Massey University, Palmerston, North, New Zealand.
Proceedings of the New Zealand Society of Animal Production. 1993,
53: 155-158
The objective of this study was to examine the effects of once daily
milking (ODM) on yields of plasminogen, plasmin and other whey proteins
and to investigate this possible role of plasmin in mammary gland involution.
Twelve multiparous Friesian cows in the ninth month of lactation were
placed on a ODM regimen for 7 days. Milk yields were determined and milk
sampled for assay on the last day of twice daily milking (TDM) (day 1 of
trial), days 3 and 7 of ODM (d4 & d8) and again 7 days after return to TDM
(d15). Data are expressed as least-square means for d1 (TDM) vs d4 (ODM)
vs d8 (ODM) vs d15 (TDM) together with pooled SE (PSE). Once daily
milking was associated with a significant (P<0.05) reduction in yields of
milk, lactose, fat and total protein. The concentration of plasminogen
increased during ODM (0.92 vs 1.52 vs 1.37 vs 0.95, PSE = 0.06 µg/ml,
P<0.01) but the yield of plasminogen was only marginally influenced by
ODM (12.6 vs 14.8 vs 13.3 vs 10.5, PSE = 0.5 mg/d, P<0.05). The
concentration of plasmin remained constant during the experiment (0.09 vs
0.10 vs 0.09 vs 0.08, PSE = 0.01 µg/ml, P>0.05) while the yield of plasmin
decreased with ODM and did not recover on return to TDM (1.2 vs 1.0 vs 0.8
vs 0.8, PSE = 0.05 mg/d, P<0.001). The yield ratio of plasmin:plasminogen
decreased during once daily milking (0.10 vs 0.07 vs 0.07 vs 0.09, PSE =
0.006, P<0.01). Once daily milking was also associated with a reduction in
yield of þ- lactoglobulin but not of a-lactalbumin. The increased
concentrations of plasminogen in milk during ODM suggest an opportunity
for the involvement of proteases in mammary gland involution but their role
is unclear given that milk plasmin yields decline during ODM.
Keywords: NZSAPAB;
Plasminogen; plasmin; a-lactalbumin; þ-lactoglobulin; once daily
milking.
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Last Updated 25-01-1997
