Spring 2024 has been extremely challenging for grazing but the use of on-off grazing can be a key tool to minimise poaching damage while simultaneously increasing grass intake in the short term.

In a normal day, a dairy cow grazes for approximately nine to 11 hours, ruminates for between seven and nine hours; and spends the remainder of her time walking, idling or being milked.

The first main grazing bout occurs early in the morning where some cows can graze for up to three hours continuously, typically after morning milking. The second longest grazing bout occurs later in the evening after milking.

The aim behind the concept of on-off grazing is to take advantage of the cow’s own natural instinctive ability to graze, to ensure a high intake level is achieved when given access to grass.

When cows are given full-time access to grass, they only graze for 41% of their time.

The remainder of the time is spent ruminating, standing, walking, etc. During periods of heavy rainfall or on heavier soil types, such activities increase the poaching risks.

Cows given restricted access to grass (two three-hour periods) graze for 96% of their time at pasture. Restricting access time increases the mean duration of grazing bouts while the total number of grazing bouts is reduced.

Effects of on-off

A number of experiments investigating the effects of on-off grazing on dairy cow production have been undertaken at Teagasc Moorepark.

In February/March, an experiment was carried out with early lactation spring-calving cows (as part of this experiment cows grazed for 30 continuous days).

All cows were offered a daily grass allowance of 15kg DM/cow/day and 3kg DM/cow/day of concentrate.

The treatments included full-time access to grass, two 4.5-hour grazing periods, two three-hour grazing periods and additional silage was fed in one treatment also.

There was no difference in milk yield between the treatments which shows that the cows adapted their grazing behaviour to the on-off grazing regime.

Even with an additional 3kg DM of silage the milk solids yield of cows on this treatment was not greater than any of the other treatments.

Cows offered two three-hour or two 4.5-hours’ access to pasture achieved 95% of the intake of cows given full-time access to pasture.

Given the high levels of intake that can be achieved and the fact that there is no reduction in milk production, it appears that three hours after each milking is sufficient for spring-calving cows in early lactation.