Multiparous Border Leicester x Romney ewes were weaned early (day 35 of lactation), milked to empty the mammary gland and again milked 18 h later (day 0 of experiment) to establish baseline milk yields and concentrations in milk of the proteolytic enzyme plasmin and its zymogen plasminogen. They were then divided into 3 groups to be milked 3 (n=5), 8 (n=6) or 15 (n=5) days after the day 0 milking to determine changes in concentrations and yields of plasmin and plasminogen in mammary gland secretions during involution. Yields (mean±SE) on days 0 (groups 1 + 2 + 3), 3 (group 1), 8 (group 2) and 15 (group 3) were: secretion (g), 785±31.2 v. 598±94.8 v. 478±86.8 v. 51±66.6; plasminogen (mg), 7.8±2.2 v. 78.7±11.1 v. 22.4±4.6 v. 3.9±2.1; and plasmin (ug), 11.5±2.38 v. 148.5±8.00 v. 51.6±7.92 v. 4.9±2.32. Corresponding concentrations in the secretions were (ug/ml): plasminogen, 0.01±0.002 v. 0.15±0.027 v. 0.046±0.005 v. 0.061±0.007; and plasmin, 0.015±0.006 v. 0.275±0.027 v. 0.118±0.011 v. 0.083±0.009. There was a linear decline in the volume of secretions from day 0 to day 15. In contrast there was a transient increase (15 fold) in plasminogen and plasmin yields by 3 days after milking. These data suggest that any role of plasmin in mammary gland involution is likely to be limited to the first week after early weaning.
Proceedings of the New Zealand Society of Animal Production, Volume 54, , 107-110, 1994
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