Dairy farmers often comment that pushing cows for production leads to more mastitis from stress. While it's probably true that as production climbs some herds do begin to have more environmental mastitis, it's a possibility that mastitis increases because of changes in the herd's diet.
The changes in the diet lead to production of more wet manure as well as more milk. Increased wet manure volume exposes teat ends to more mastitis-causing bacteria. This situation persists if you don't change housing and management practices.
The level of exposure of the teat ends to bacteria in manure partly depends on bedding hygiene and environmental conditions such as humidity and temperature. While we understand this, defining actual values for adequate cleanliness and dryness has been difficult in research and farm investigations. New research from the United Kingdom gives us some theories to test under Ontario conditions. It shows too that the winter season may not give much relief to mastitis problems on some farms feeding for higher production.
The study's overall goal was to measure features of bedding, housing and cow cleanliness suspected to relate environmental mastitis risk. Mastitis-casing bacteria need three items for optimum growth-food, moisture and warmth. Researchers wanted to identify factors they could easily measure that affected the availability of food and moisture to bacteria, and let bacteria multiply in bedding.
Four dairy farms were studied intensely. The research focused on the housing of the early-lactation and dry cows for the six-month winter period, October to March, in each of two years. These herds predominantly used loose housing with straw bedding. While most Ontario herds don't use this style of housing, many do use straw bedding. The lessons learned about straw, cow hygiene, bedding practices and environmental influences on mastitis bacteria are worth noting. We can also apply many of the principles of assessing bedding hygiene to other bedding types, such as shavings.
Researchers visited each farm weekly. During visits, they tested the moisture content of big straw bales to be used for bedding. They measured actual bedding for its relative humidity, pH, bacteria count and the types of bacteria present. The amount and quality of the straw used for bedding was noted.
Also recorded were temperatures at the top of the bedding, deeper in the bedding and of the air at two sites outside and four inside the barn. Cows were scored for cleanliness, and manure consistency was noted, The manure was rated from very dry, a score of one, to very loose and diarrhoeic, a score of five. The herdsperson recorded cases of clinical mastitis cases.
The researchers compared measurements made on the farm to benchmarks they had set. These bench- marks defined the conditions the researchers felt would be needed to limit bacterial multiplication in the bedding, and bacterial contamination of cows' bodies and teats. These benchmarks came from previous research and knowledge of the conditions needed to grow E. coli and the environmental streptococci optimally in lab studies. Here are those bench- marks:
* straw prior to use, to have a moisture level of less than 15 per cent;
* coliform count ( the family that includes E. coli, Klebsiella sp. and others) less than one million CFUs
(colony forming units) per gram of bedding;
* bedding to have minimal time at a temperature friendly to bacterial growth (between 15 and 45
* relative humidity on the surface of the bedding to be less than 75 per cent;
* bedding pH to exceed 9.5 on weekly measurements (high pH, or more alkaline, conditions restrict
bacterial growth and survival).
Moisture measurements taken immediately after bedding replacement revealed surface straw was above the 15 per cent relative humidity benchmark about 75 per cent of the time. The relative humidity of the air inside the barn frequently exceeded 75 per cent even though the study was done in winter. This further reduced the ability of the bedding surface to dry.
Both E. coli and environmental streptococci bacteria survived well in the top layer of bedding. The number of organisms never fell below the bench- mark of one million CFU per gram. The bedding of early-lactation cows had about twice the number of E. coli and environmental streptococci bacteria than the bedding of dry cows.
The fermentation of bedding in the pack provided a comfortable, warm environment for the cows to lie on. But the same heating also produced an ideal environment for bacterial growth. After the entire pack was replaced, the new pack took about one week to reach the temperatures that again favoured bacterial growth-between 15 and 45 degrees C. Rarely did the bedding temperature drop below 15 degrees, even though it was winter.
The pH of the bedding rarely exceeded 9.5. A small experiment on one farm added lime in an attempt to raise the pH. The bedding exceeded 9.5 for only one day after 30 kilograms of lime were added.
On three of the four farms, the cow cleanliness scores showed early lactation cows to be unacceptably dirty while the dry cows were clean. The researchers found a significant relationship between the manure consistency scores and the cleanliness of the flanks, udders and legs of the cows. Looser manure was associated with poorer cow cleanliness.
These four herds consistently maintained average bulk tank somatic cell counts below 250,000 cells per millilitre, yet recorded 10 to 39 clinical cases of mastitis per 100 cows during the six-month time period. The average BactoScan count ranged from 10 to 24. Manure was proven to be a significant source of mastitis bacteria. Of 78 mastitis cases, 30 were caused by E. coli and 14 by environmental streptococci.
Overall, the researchers found the bedding was too wet and stayed at a temperature and pH that allowed bacterial numbers to become too high. Adding lime or completely cleaning out the pack and rebedding failed to reduce bacterial numbers. Early-lactation cows could not be kept clean and were at particular risk of mastitis. Although herd SCCs were acceptable, too much environmental mastitis occurred.
The researchers considered the factors that influenced some of the poor performances they identified on the four farms. Their opinion was that the type of ration fed influenced the manure consistency scores, and the relative humidity of the air and bed- ding. Higher producing cows fed wetter rations with higher energy density and lower fibre produced greater amounts of moisture as urine and manure. Researchers estimated these cows added at least 30 litres of urine daily to their environment and about the same amount of water via loose manure.
This added moisture contributed to the high relative humidity values for bedding and air. Inadequate ventilation kept air temperatures too high and compounded humidity problems.
Loose manure sticks to the hair and skin of the cows. Loose manure splashing onto feet and legs and onto the backs of stalls from alleyways increases the exposure of the teat ends to mastitis-causing bacteria. Herds with higher production and looser manure expose the teat ends of the cows to more bacteria. In this study, the highest producing herd had the greatest rate of clinical mastitis in both of the two six-month periods studied.
Diet and nutrient changes widely adopted in Ontario herds result in the production of increased volumes of wet manure. That, in turn, leads to the exposure of the teat ends to more mastitis-causing bacteria. Facilities that have historically met the needs of cows may not continue to do so as production per cow or production per facility increases. When the system fails, environmental mastitis takes advantage of opportunities. Failure to change housing, ventilation and management practices to match the needs of higher producing herds and cows allow this situation to persist.
The results of studying these four farms are noteworthy as a basis for investigating environmental mastitis on Ontario farms. Reaching the desired benchmarks should be associated with lower rates of environmental mastitis. Next, we need to validate these benchmarks. Then we can look for practical ways that all herds can use to achieve these values.
By Ann Godkin - DVM/OMAFRA
Published at OMAFRA website (Government of Ontario Ministry of Agriculture, Food and Rural Affairs)
Ann Godkin is a veterinary scientist with OMAFRA. The full study can be found at: Observational study of temperature, moisture, pH and bacteria in straw bedding and fecal consistency, cleanliness and mastitis in cows in four dairy herds. Ward WR, JR Hughes, WB Faull, PJ Cripps, JP Sutherland and.JE Sutherst. Veterinary Record (2002) 151, 199- 206.
This article appeared in the November 2002 Ruminations in the Ontario Milk Producer magazine.