Grazing paddocks when soils are wet results in pugged pastures and soil damage.
On-off grazing is a practice that can reduce damage to soil and pasture when grazing wet paddocks.
In on-off grazing, cows are allowed to graze their next daily allocation for a short period (usually two to four hours) and are then moved off the pasture to a stand-off area to reduce damage from pugging.
If cows are not removed after this period, they tend to keep searching for clean pasture or seek shelter from rain and wind.
They usually consume very little extra pasture, but pugging damage increases substantially.
Requirements for on-off grazing
Research and farmer experience have shown that on-off grazing appears to have a negligible detrimental effect on daily milk production.
But for this strategy to be successful, your pastures and cattle must meet the following conditions:
● Pasture cover must be enough to maintain or extend the first (and possibly second) rotation to avoid a feed shortage.
● Pastures being grazed must have good length and density to allow high and rapid intakes. Pastures should have a height of about 10cm to 15cm (2200kg to 2500kg dry matter/ha), or be in the two to three green leaf stage.
● Cows should be healthy, have no lameness and low in mastitis incidence.
● Ensure there is enough magnesium in the diet. If it is limited, supplement the diet with magnesium.
● Cows must be in good condition.
Adjusting the grazing time
Research in south-west Victoria showed cattle can consume about 6kg to 10kg DM per cow in two to four hours of grazing as long as pasture cover is high.
Extending the grazing period beyond this period resulted in severe pasture damage due to pugging.
After two hours of grazing, the cattle had eaten about 70 per cent of the pasture they would eat over the full grazing period.
After four hours grazing, 77 per cent to 88 per cent of the pasture was eaten. (The lower intake of 77 per cent was because of the lower initial pasture cover — 2120kg versus 3100kg DM/ha. On shorter pasture, cows must take a greater number of bites per kilogram DM intake and walk further to achieve similar intakes.)
The extra pasture intakes of 1.5kg to 2.1kg DM per cow doesn't warrant leaving cows on pastures after about four hours.
If the paddocks are extremely wet and serious pugging damage is likely, then removing cows after two hours will be justified.
Some soil types are also more prone to pugging damage after varying periods of grazing at the same moisture content.
Effects on pasture regrowth
Data from New Zealand research that compares 24-hour block grazing with on-off grazing suggests that regrowth rates for on-off grazing increased by 18 per cent to 52 per cent in early spring.
Past research in south-west Victoria found major improvements in pasture growth and utilisation when grazing wet pastures when using the on-off grazing technique in the late winter to spring period.
Relative to an unpugged to dry soil, all-day grazing (seven to eight hours) suffered a 30 per cent reduction in pasture yield and 23 per cent reduction in utilisation.
In comparison, the two and four hour on-off grazing treatments only suffered a three per cent and nine per cent reduction in yield and eight per cent and three per cent reduction in utilisation.
The on-off grazing treatments also resulted in considerably less pugging damage to the pasture than the seven to eight hour grazing.
Perennial rye-grass tiller densities by the end of spring had fallen to 1800 tillers per square metre for the seven to eight hour grazing and 3250 and 2800 tillers per square metre for the two and four hour on-off grazings.
- Agriculture Victoria