Dry cows at pasture

Time at pasture increases a cow’s exposure to mastitis-causing bacteria. Find out how to manage the risk and prevent infection.

Time at pasture is a considerable risk period for clinical mastitis and increased somatic cell counts for many dairy herds. Risk is often attributed to exposure to different disease-causing bacteria, as well as variable environmental conditions.

• Keep dry cows in the same lying area (pasture, paddock, field) for a maximum of 2 weeks and leave at least 4 weeks before using it again
• Maintain adequate pasture drainage to avoid surface flooding or severe poaching
• Move dry cows to a different field if severe poaching of the land and/or gateways occurs
• Manage poaching around gateways/feeders (for example, using bark)
• Maintain housing conditions as in winter if dry cows have access to housed lying areas during the grazing months

Flies can transmit bacteria that are involved in the summer mastitis complex (‘August bag’), which is most prevalent during the grazing months.

• Ensure good fly control by frequently reapplying pour-on product (monthly, depending on product type) for all dairy cows throughout the summer period
• Avoid high-risk areas associated with summer mastitis (for example, fields near to trees and damp, sheltered areas)
• Isolate dry cows with summer mastitis to stop the spread of infection

• Never exceed a stocking density of 100 cows/acre/day in a 2-week period
• One acre is 50 x 100 yards and 1 hectare is 2.5 acres
• The calculation should always be based on the group with the highest stocking density for the longest time

Calculation:

Cow acre days = (number of dry cows in group per number of acres grazed by that group) x days

Useful questions to ask yourself are:

• What is the largest field grazed by dry cows and how long did the largest group spend there?
• What is the smallest field grazed by dry cows and how long did the largest group spend there?

An increased bulk milk somatic cell count (SCC) is recorded in May and June for a spring-calving herd.

Analysis of the cell count data highlights that 30% of cows have an SCC of >200,000 cells/ml at the first milk recording after calving (dry period new infections).

Using the Mastitis control plan, the farmer explains that the outwintered dry group of 120 cows is moved daily around areas of the paddock that are pre-arranged with bales, having access to 0.2 ha each day.

This works out to be a stocking rate of 240 cow acre days (120 in 0.5 acre for 1 day) – a ‘target’ stocking density at pasture is 100 cow acre days, so ideally we would try and double the size of the bale area, at least in the early dry period when susceptibility to new infection is so high.

Calculation:

1 hectare = 2.5 acres

Therefore, 0.2 hectare = 0.5 acres. Stocking rate is cows/acre/day (120/0.5/1 = 240)