Climate may have a direct and indirect influence on the onset of mastitis. Exposure to intense cold, draughts, excessive humidity or heat predisposes cattle to mastitis. A particular type of ma~titis often called summer mastitis is caused by biting insects that contaminate the udder with the bacteria. Climate may also have an indirect influence. For example, muddy conditions outdoors caused by abundant rainfall will increase the number of microorganisms and thus increase risks of infection.
The mere fact of keeping cows indoors increases the incidence of mastitis. When cows are inside, the risk of udder injury increases. There are also microorganisms whose populations are less concentrated outdoors. It would appear that mastitis is less common with loose housing systems than with tied housing systems. Draughts excessive humidity and frequent changes in temperature in a barn are factors that lead to increased incidence of mastitis.
Whether with loose or tied housing systems, bedding plays an important role in the incidence of mastitis. This is easy to understand when considering the mastitisinfected milk that reaches the ground, the humidity that favours the development of microbes on bedding and that cows often spend 14 hours out of 24 in contact with their bedding. Inadequate bedding in loose-housed herds, particularly large herds, may lead to serious situations in the case of contagious mastitis.
In the stressed environment, the immune system of the animal is less efficient, therefore resistance to microbial infestations is less. Therefore, the more stress there is, the greater the chance of mastitis.
The following are some sources of stress: o Excessive density of animals. The proximity of cows encourage microbial exchanges and tense relations between animals;
- The excessive density of animals. The proximity of cows encourage microbial exchanges and tense relations between animals;
- Irregular management, unpredictable behaviour on the part of the farmer;
Hereditary factors may influence susceptibility to mastitis. The different dairy cattle breeds are not equally susceptible to mastitis. High yielding cows are more likely to be affected. Selective breeding that focuses solely on milk production is undoubtedly an important factor in higher rates of mastitis. According to different sources, hereditary factors account for 12% to 20% of susceptibility to mastitis in a single breed. Genetically, there is a correlation between the percentage of milk fat and the incidence of clinical mastitis.
Two practices that increase the risks of mastitis are rapid changes in diet and excess or imbalance in the different components of rations. Excessive nitrogen or protein in feed is often mentioned as one of the factors causing mastitis. It is recommended that reduced quantities of concentrates be given to a cow with mastitis. A high energy content in rations increased the incidence of mastitis in first lactation cows whereas it had the opposite effect on the other cows.
Silage and hay
Poor quality silage has a very negative effect on the immune system. The overheated proteins and sugars may kill the white blood cells protecting the udder. Cows fed with hay and grain have greater resistance in every way to several pathogens than cows fed with silage. In some cases, Pseudomonas and Proteus are the only microorganisms that survive the high temperatures produced in silage. Although rare, silage contaminated this way may then be a source of mastitis caused by these types of organisms. Mouldy hay and mycotoxins also harm white blood cells and therefore weaken the immune system.
Selenium and vitamin E
Maintaining an adequate level of selenium in the system helps to prevent mastitis, reduce the severity of infection and causes it to last for a shorter period of time. Selenium serves to reinforce the immune system response by increasing the release of leucocytes and increasing the efficiency of phagocytes. Selenium and vitamin E work together in the system. Thus, a vitamin E supplement of 1000 IU/day alone reduces the somatic cell count but not the incidence of mastitis.
The role of selenium is considered to be most significant in the case of subclinical mastitis. Vitamin A deficient rations reduce immunity. Integrated human factors with herd management influence the causation of mastitis. The geographical position of the farm, treatment of dry cows, replacement cows produced on the farm, positive attitude towards milking, family enterprise result in the low somatic count. Tied housing, obsolete milking equipment, short withdrawal period after antibiotic treatment are responsible for the high bacterial count. Average herd, treatment of dry cows, tendency to seek out information, elimination of cows that are too susceptible are ideal for high milk yield.
- Central Coastal Agricultural Research Institute, Ela, Old Goa, Goa