Offering fresh pasture breaks - is there a benefit to milk production?

Date: 24 Dec 2004 Author: Brad Granzin

Research conducted at Wollongbar Agricultural Institute examined whether offering fresh pasture to cows at various times throughout the day would increase pasture intake and milk production.

Experiment 1 - Kikuyu pastures

There were two reasons for undertaking this experiment:

  • Could pasture intake be increased by offering fresh pasture which hasn’t been fouled?
    Cows offered pasture once or twice daily usually graze intensively for 2 to 3 hours and then are reluctant to graze fouled areas. British research has shown that fouling of paddocks can result in 10% to 45% of pasture offered being rejected.
  • Could pasture intake be increased by offering fresh pasture at night during summer?
    High temperatures experienced during summer can reduce daytime grazing and increase night-time grazing. Given this, it may be beneficial to offer fresh pasture during the night at this time of the year.

Experiment 1 details

During January to February 2000, two groups each of 12 cows were selected.

One group received:

  • 3/4 of their daily pasture allowance after pm milking;
  • 1/4 after am milking.

See Figure 1 (2 breaks/24 h).

The other group received:

  • approximately 2/5 of their daily pasture allowance after pm milking
  • 1/6 at 7 pm
  • 1/6 at midnight
  • 1/4 after am milking.

See Figure 1 (4 breaks/24 h). The 7 pm and midnight pasture breaks were offered using an automatic electric gate release system.

Cows were supplemented with 6 kg/cow.day of a barley and maize based concentrate.

Figure 1. Proportions of daily pasture allowance offered during Experiment 1 (kikuyu pastures)

Experiment 1 results

Despite our positive expectations, there were no effects on either pasture intake or milk production (see Table 1).

Table 1. Daily milk production and pasture intake, Experiment 1
Pasture type: Kikuyu
Breaks per day 24
Milk yield (L) 21.1 20.7
Fat (%) 3.57 3.43
Protein (%) 2.96 2.91
Pasture intake (kg) 11.0 10.7

Experiment 2 - Ryegrass / prairie grass pastures

There were two reasons for undertaking this experiment:

  • As proposed in Experiment 1, could pasture intake be increased by offering fresh pasture which hasn’t been fouled?
  • Making use of high sugar levels in pasture during spring.
    During spring, sugar concentrations in temperate pastures such as ryegrass gradually increase throughout daylight hours and are at their highest in late afternoon. Work in southern NSW has shown a benefit to milk production when a daily pasture allowance is offered after pm milking instead of after am milking. We wanted to see if a similar benefit occurred in northern NSW.

Experiment 2 details

In September to October 2000, 32 cows in early lactation, grazing ryegrass and prairie grass pastures, were allocated to four groups. These groups were offered their daily pasture allowance as either 1, 2, 3 or 4 allocations, in the proportions shown in Figure 2, during daylight hours. Cows were also supplemented with 6 kg/cow.day of a barley-based concentrate.

Figure 2. Proportions of daily pasture allowance offered during Experiment 2 (ryegrass /prairie grass pastures)

Experiment 2 results

As in Experiment 1, there were no effects on either pasture intake or milk production (see Table 2). Milk composition did vary, but this was not statistically significant.

Table 2. Daily milk production and pasture intake, Experiment 2
Pasture type: Ryegrass/prairie grass
Breaks per day 1234
Milk yield (L) 24.5 24.0 23.6 24.7
Fat (%) 3.95 3.78 3.94 3.78
Protein (%) 3.10 3.08 3.06 3.05
Pasture intake (kg) 10.7 10.3 10.2 10.5

Why wasn’t milk production increased?

An explanation for the unexpected results may be that other factors were limiting pasture intake:

  • The daily pasture allowances offered in these experiments were generous, but not wasteful. Cows were given the opportunity to eat more pasture.
  • In the kikuyu experiment (Experiment 1), it would appear that rumen fill may have physically limited intake.
  • Alternatively, in the ryegrass / prairie grass experiment (Experiment 2), it would appear that cows were able to access enough unfouled ryegrass to satisfy their hunger.
  • In Experiment 2, the sugar levels in ryegrass and prairie grass pastures at dusk during spring were not as high as had been observed previously. This was despite the days being almost cloudless for the duration of the experiment.
  • In Experiment 2, milk production might have increased if the ‘one break’ treatment had been offered after the pm milking instead of after the am milking.

Practical outcomes

At the high pasture allowances offered, giving multiple pasture breaks within a day provided little practical benefit. In this situation, it may be preferable to allow cows free access to a paddock larger than 24 ha, instead of placing and removing electric fences during the day.

Further research is required to examine whether offering pasture breaks at lower pasture allowances would affect milk production.

Further reading

Granzin, BC  2003, 'The effect of frequency of pasture allocation on the milk production, pasture intake and behaviour of grazing cows in a subtropical environment', Tropical Grasslands, vol. 37:84–93.