The effect of health status of the udder on plasminogen activator activity of milk somatic cells in ovine milk

• The main form of PA of milk cells in ovine milk is u-PA.
• PA activity increases in milk with more than 300,000 SCC/ml.
• The increased PA activity possibly contributes to the increased conversion of PG to PL in milk with high SCC.

This study was conducted to examine the effect of health status of the udder on plasminogen activator (PA) activity of milk somatic cells in ovine milk. Milk samples were obtained from 4 breeds [Boutsiko, Chios, Karagouniko and a synthetic breed (50% Boutsiko, 25% Arta, and 25% Chios)]. A total of 192 milk samples were collected bi-weekly throughout the lactation period. Milk somatic cells were isolated and milk cell-associated PA activity per cell was determined. Milk samples were divided in three somatic cell count (SCC) groups: group 1 with high SCC (>1,000,000 cells/ml), group 2 with an intermediate level of SCC (from 300,000 to 1,000,000 cells/ml) and group 3 with a low SCC (<300,000 cells/ml). Results indicated that PA activity per cell was approximately 4-fold higher in the intermediate group, when compared to the low SCC group. An increase of the milk SCC from <300,000 to >1,000,000 cells/ml resulted in a 10-fold increase of PA activity per cell. The predominant form of PA in milk somatic cells is urokinase-PA. No relationship was found between breed, stage of lactation and milk cell-associated PA activity. Further research is needed to examine the possibility that increased PA activity per cell in the high SCC group may explain the higher plasmin levels, which are observed in ovine milk obtained from mastitic glands.