DAIRY HEALTH UPDATE

Clell V. Bagley, D.V.M.
USU Extension Veterinarian


Results of Recent Mastitis Research


Ways Machine Milking Influences Mastitis

The cluster can spread pathogens between cows.

Pressure changes developing during milking may transfer milk and air between teat cups, leading to cross-contamination of bacteria from teats on the same udder.

Fluctuations in vacuum within the cluster during, or at the end of milking, may lead to rapid movement of bacteria-laden milk droplets back towards the teat. These droplets may impact the teat end with sufficient velocity to implant bacteria into or through the teat canal. This is referred to as the droplet impact mechanism.

Inadequate collapse of the liner on the teat in each pulsation cycle increases bacterial penetration of the teat duct.

Malfunctions or incorrect use of the milking machine that result in trauma to the teat end or to incomplete milking increase rates of bacterial entry to the mammary gland or reduce the chances of bacteria and toxins being removed during milking.

Source: "Current Concepts of Bovine Mastitis" p. 30.


Clinical Mastitis Can Affect Reproductive Performance

Results from a University of Tennessee study suggest that clinical mastitis during early lactation can have a profound effect on reproductive performance of dairy cows. These results were not restricted to Gram-negative mastitis pathogens as observed in previous studies, since similar responses were seen in cows with clinical mastitis due to Gram-positive and Gram-negative mastitis pathogens.

Days to first service were significantly higher in cows with clinical mastitis before first insemination (93.6 days) than in all other groups of cows (71.0 days). Services per conception were higher in cows with clinical mastitis after their first service (2.9) than in cows with clinical mastitis before first service (1.6) and in cows with no clinical mastitis or cows with clinical mastitis after confirmed pregnancy (1.7). Regardless of clinical mastitis status, cows with > 5 lactations required significantly more services per conception than all other parity groups. Days to conception in cows with clinical mastitis before first insemination (113.7 days), and in cows with clinical mastitis after first insemination (136.6 days) were higher than in control cows and cows that developed clinical mastitis after confirmed pregnancy (92.1 days). The breeding period for cows with clinical mastitis between first insemination and pregnancy was higher than in all other groups of cows.

Studies examining the mechanisms by which mastitis influences reproductive performance in dairy cattle are currently underway.

Source: NMC 1997 Annual Meeting Proceedings, p. 274.
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