In the first article, the authors reported on infection results. In the eight herds, cows were divided into two treatment groups: the positive-control group where all cows with clinical mastitis were treated with antibiotic and the culture-based treatment group where the herdsman would culture milk from mild and moderate cases of clinical mastitis and treat (same treatment) only those cows that had gram-positive (staphylococci or streptococci) growth.
It is important to note that in the study, treatment was delayed until cultures were complete only for cows with milk to moderate clinical mastitis. Treatment should not be held from cows with severe (fever, off-feed, depressed) mastitis while waiting for culture. Many of these types of mastitis can result from life-threatening coliforms, and while culture is still useful for management decisions, antibiotic and supportive therapy should be given immediately.
Among the eight herds recruited for this study, personnel from four farms already did on-farm milk culturing and four were trained to do it for the course of the study. They used bi-plates that distinguished between gram-positive and gram-negative bacteria.
The researchers report on comparisons of how cows did in response to each of these treatment groups. The first thing they note is that only half the number of cows in the culture group were treated (initially or later) compared the positive control group, in which all cows showing clinical mastitis were treated. Therefore, on-farm culturing cut antibiotic use and treatment costs in half.
But how did those cows do that were not treated? Four different measures were used to answer that question:
- Days to clinical cure – The time (days) until milk appeared normal again; that is, the absence of clinical signs of mastitis. No significant difference.
- Bacteriological cure risk – The frequency that there was no subsequent bacterial growth when checked at 14 days and 21 days after mastitis was initially discovered. No significant difference.
- New intramammary infection (IMI) risk – The presence of a new bacterial species growing at days 14 or 21 that was not originally cultured. No significant difference.
- Treatment failure risk – An overall measure of treatment success that combined measures including bacteria cultured at 14 or 21 days – whether the original or new species, if a second flare of clinical mastitis required treatment after initial, or if the animal was culled or died by 21 days. Any of these was called treatment failure. No significant difference.
In addition, they looked at how long the milk from mastitic cows was kept out of the tank and found that the withholding time for the culture-based group was reduced by one day compared to the other group.
Based on these results, the authors concluded that on-farm cultures on these farms reduced antibiotic use significantly and days of nonsaleable milk with no loss in mastitis control on the farms. On-farm culturing resulted in win-win decisions.
Indeed, that is the same result seen by the producers in northeast Michigan.
Source: Phil Durst, Michigan State University Extension