The research behind on-off grazing

On-off grazing is an excellent way of minimising soil damage, particularly if you’ve been affected by water logged conditions or a lack of grass covers recently. But how does it impact on animal productivity? DairyCo’s R&D manager Dr Debbie McConnell takes a look at the research behind on-off grazing strategies and their impact on animal production.

The risk of soil damage during grazing is greatest when soil moisture contents are high, typically at the shoulders of the season. Grazing in early springtime, while a good way of reducing costs and reducing pressures on forage sources, can result in soil damage if it is not appropriately managed.

In cases of moderate damage in early spring, researchers in New Zealand have noted reductions of as much as 60% of sward DM production 28 days after the event and annual reductions in DM production of up to 34% on dairy grazing pastures.

The risk of damage at these times of year will vary from soil to soil. Fine textured soils, with high organic matter content or a high soil water retention capacity, are all particularly susceptible to compaction. In addition, recently reseeded swards are susceptible as the root mass hasn’t developed enough to strengthen the soil.

One way of reducing treading damage to the soil in early spring is to minimise time at pastures. On-off grazing strategies have been found to reduce soil damage, reducing the impact on sward re-growth and infiltration rates at subsequent grazing.

For example, research from Ireland suggests a 20% improvement in grass re-growth with on-off grazing compared to 24 hour grazing. But what impact do these practices have on cow performance?

Researchers at Teagasc, Ireland, have investigated the performance of both autumn and spring calving cows in on-off grazing systems in early spring.

Spring calving cows

Fifty-two spring calving Holstein-Friesian dairy cows (26 days in milk at the beginning of the experiment) were split into four treatment groups:

  • Full time grazing (22hrs)
  • 2x 4.5 hour periods after each milking
  • 2x 3 hour periods after each milking
  • 2x 3 hour periods after each milking, with 4kg DM silage supplementation at night.

These groups were grazed for 30 days (25 February – 27 March) during which researchers measured milk yield, grass intakes and grazing behaviour in order to investigate the effect of on-off grazing practices on cow performance.

Researchers found that on-off grazing practices did not alter cow performance. Milk yield averaged 28.3kg across all treatments, while milk fat and protein content and body condition over the 30 day period, did not change significantly.

To maintain performance, animals on the on-off grazing treatments altered their grazing behaviour to maintain their required DM intake. They also compensated for the reduced time they had available to graze by increasing the length of their grazing bouts and grazing more aggressively. The researchers noted increases in both the DM intake per bite and the number of bites per minute (Table 1).

This was not as evident on the 2x 3 hour group and consequently pasture utilisation was lower, at 67%, on this treatment compared to the other three non-supplemented treatments (80%).

Table 1: Effect of on-off grazing strategies on grass intake and grazing behaviour in spring calving cows

(Source: Kennedy et al. 2011)

Autumn calving cows

Similar results were found with late lactation Holstein-Friesian dairy cows (202 days in milk) grazing in spring. Cows were split into four treatment groups and monitored for four weeks.

  • Full time grazing (22hrs)
  • 9 hours grazing (between AM and PM milking)
  • 2x 4.5 hour periods after each milking
  • 2x 3 hour periods after each milking.

Again, animals on the on-off treatments altered their grazing behaviour to account for the reduced time they spent grazing. On both these treatments animals grazed more aggressively, not through increasing the number of bites per minute but through increasing grass DM intake per bite. As a result, grass DM intake was not significantly different between the treatments and consequently milk performance was similar across all groups (Table 2).

Table 2: Effect of time at pasture on cow performance of autumn calving cows in spring.

(Source: Kennedy et al. 2011)

While this research suggests on-off grazing can be implemented successfully, it is important to recognise that there are a number of pre-requisites to make the most of this system:

  • Pasture cover must be sufficient 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 approximately 10-15cm (2,200-2,500kg DM/ha). Alternatively, pastures should be in the 2-3 green leaf stage
  • Cows should be healthy, in good condition, have no lameness and low in mastitis incidence.

For more information on either of the studies mentioned, visit:

Kennedy, E. , Curran, J., Mayes, B., McEvoy, M., Murphy, J.P. and O'Donovan, M. (2011). Restricting dairy cow access time to pasture in early lactation: the effects on milk production, grazing behaviour and dry matter intake. Animal 5 (11) 1805-1813 ISSN 1751-7311

Kennedy, E., McEvoy, M., Murphy, J.P. and O'Donovan, M. (2009). Effect of restricted access time to pasture on dairy cow milk production grazing behaviour, and dry matter intake. Journal of Dairy Science 92:168-176 ISSN 0022-0302

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Milkproduction.com

Milkproduction.com