Breeding mastitis-resistant cows
Selecting for disease- resistant cows has become a reality for farmers around the globe as genetic developments continue to advance.
The first step in managing mastitis is to assess what you are doing and critically examine control measures on your farm.
The most common form of transfer of bacteria from cow to cow is in the dairy shed when cups are put on a cow, because the cups will contain bacteria from milking a previous cow that had clinical or subclinical mastitis.
Bacteria do not enter the teat straight away as it takes time to migrate from the sides of the teat down to the bottom and normally enters the teat canal between milkings.
Teat spraying has been shown to prevent this form of transfer and will reduce cell counts and clinical mastitis by 50%. Yet poor teat spraying effectiveness would be the most common problem I see when investigating mastitis problems.
In a survey of 200 mastitis problems, 35% of farmers were achieving good coverage and 35% were using the correct dilution rate, but only 12% of the farmers had both the coverage and dilution rate correct. This is despite all the communication and education on the importance of teat disinfection as being probably the most important single step in a mastitis control programme.
The next most common issue is teat end damage. Bacteria that cause mastitis have to enter the udder through the teat canal and the cow is very reliant on the integrity of the teat end.
A beef cow rarely gets mastitis because her teat end is smooth and supple from suckling by calves. A dairy cow is susceptible to mastitis and a major reason for this is teat end damage from machine milking.
Look at the teat ends of 50 cows and if more than 80% of the teats are not smooth and supple, and the teat opening undamaged, then you have a problem. There are many reasons for teat end damage. The machine settings or liner type may not be suitable for your herd or there may be over-milking causing excessive wear on the teat opening.
If there is teat damage then it would pay to have an assessment done as to possible causes, otherwise you will continue to get new clinical infections and your cell counts will continue to rise.
Another important issue is cup slip. If a cup slips, air rushes in and blasts any infection in the cluster against and into the canals of the other teats. This results in transfer of bacteria into the teat during milking and teat spraying has no effect against this form of transfer. Common causes of cup slip include poor cluster alignment, unsuitable liners and vacuum too low.
The next thing to assess is how well cows are milked out. There should be wrinkles visible on the udder and you should not be able to strip more than 500ml of milk from the udder. There are multiple causes of poor milk-out, but the most common is cow discomfort due to teat damage.
Mastitis happens for a reason. Critically examining your situation is the first step in achieving 100,000 cell count and less than 10% clinical mastitis.
• Adrian Joe is a veterinarian and mastitis consultant.
This article first appeared in Getting the Basics Right 2014 edition.
