Background:
Over the summer of 2003, DDI encountered a high occurrence of E.coli mastitis. There were several factors that DDI managers believe could have contributed to the onset of a mastitis outbreak. The summer was hot and humid, with several days above 90 degrees Farenheit. Also, some of the older stall mattresses had become lumpy, causing pooling of moisture. However, herd managers felt that these factors alone were not significant enough to cause the outbreak.
After thoroughly reviewing management strategies and finding nothing obvious that could be causing the mastitis problem, DDI managers had the veterinarian pay a visit to analyze milking procedures. Dr. Griep initially visited the farm during milking time to observe the normal milking procedures and to gather data using a milk flow meter.
There are several factors in the milking process that could contribute to mastitis--poor teat condition and sanitation, poor stimulation of milk letdown and excessive length of unit attachment. Optimally, the teats should be clean and in good condition and the milking machines should be attached for the minimum length of time necessary for milkout. Any additional time that the machines are on can cause teat end irritation and open the door for a mastitis infection. Proper stimulation during the pre-milking routine, followed by appropriate milking unit attachment will help to minimize unit-on time. Maintaining a sanitary teat-end environment both pre- and post milking is also important in minimizing the possibility of infection.
Dr. Griep evaluated all of these factors in the DDI milking routine. After the observations were made, he met with the herd managers to discuss the information gained from his time in the parlor. He had calculated average times for completing all parts of the milking process, and found them to be within accepted standards. The products and processes used for pre- and post dipping the teats were all appropriate, as well. Teat end condition is regularly evaluated in the herd for various research studies and no problems have been discovered to date, so this was not a major concern. Dr. Griep also evaluated teat end condition, and found it to be acceptable.
During the observation process, the vet noted another potential problem. He noticed that, in some cases, the cows were positioned awkwardly in the row, causing some machine attachment problems. This could have been caused by the indexing rail being slightly too high in pressure. This had been noticed by the herd manager as well, and will be addressed by adjusting the pressure of the indexing rail.
The information from the milk flow meter was displayed in both graphic and tabular form, making it easy to read. On the graphs, the x axis displayed time and the y axis displayed flow. The vet used the graphs to demonstrate the following instances:
- The normal flow/time for a cow that was adequately stimulated and milked out quickly and evenly would display a quick, continuous increase in flow (ascending phase) with a somewhat slower but steady drop (descending phase). The “taller” the peak, the greater the flow per unit of time.
- A cow that was not adequately stimulated would have a brief initial flow followed by a drop then another increase in flow (bi-modal) as the milk letdown began. This was not often the case with the cows sampled at DDI, as milk letdown was stimulated during the pre-milking routine.
- If the graph displayed a rough descending phase, it could indicate that one or more quarters milked out more quickly.
- If the graph was bi-modal following the descending phase, it could indicate a kickoff or an issue with take-off timing (depending on how often it occurred). At DDI, this happened when the machine was kicked off by a cow.
From his observations of the milking process and analysis of the flow data, Dr. Griep was able to conclude that the mastitis problem was probably not caused by the milking process. He surmised that the problem could be the result of a buildup of pathogens in an unidentified location. As the herd manager pointed out, the stalls are clean, the barn is adequately cooled and the SCC is acceptable, leaving the source of the E. coli outbreak as yet undetermined.
The source of the E. coli infection is still unclear, but the visit with the veterinarian was a useful step in eliminating some possible causes. Several days after the vet’s visit a likely problem area was indicated when herd managers analyzed days in milk and lactation number of the affected animals. In general, most of the E. coli infections were occurring in lactation 2 or higher cows that were more than 180 days in milk. Other large dairies have indicated similar problems. This coincides with the timing of the J5 vaccinations. First lactation cows are given their 2nd J5 vaccination at about 20-26 days in milk (DIM) and their 3rd J5 vaccination at about 50-56 DIM while mature animals receive their 3rd vaccination within the first month of lactation. As a result, a fourth J5 vaccination at 120 DIM has been initiated for lactation 2 and greater cows in the DDI herd.
Currently, the number of mastitis cases has decreased significantly, probably due to cooler/drier weather. Herd health will be monitored to determine whether the change in the vaccination protocol is effective. |