Farm Tech

In The Paddock
Seasonal sheep flock management tips July 2002

Achieving target pasture covers in time for lambing

Key points

• Careful planning is needed to get the correct pasture covers for lambing.
• Too little cover at lambing will lead to underfeeding of ewes, low milk production and poor lamb growth rates.
• Too much cover will result in an early decline in feed quality, and a drop-off in milk production and lamb growth.
• To achieve target covers, you need to have adequate pre-winter cover and to adopt a slow (60–120 day) winter rotation. Strategic nitrogen use may also have a place.
• Ideal target covers vary between regions, but in most cases pre-lambing covers of 1100–1400 kg DM/ha are appropriate. This equates to 2–3 cm pasture height.
• Ewes with twins or triplets should be offered pasture at the high end of the range.
• Ewes with singles can be offered pasture at the low end of the range. If pasture supplies are limited, feed for these ewes can be supplemented with grain.

Careful planning is needed to achieve target pasture covers at lambing.

These should range from 1100-1400 kg DM/ha (2–3 cm pasture height), depending on the region and its pasture growth characteristics.

Achieving these covers is vital.

If pasture cover drops below 1100 kg DM/ha at lambing and the increased feed requirements of the ewe mob are not synchronised with the onset of spring growth, ewe milk production and lamb growth rates will suffer.

On the other hand, pasture cover in excess of 1400 kg DM/ha can lead to an early deterioration in pasture quality. This will lead to lower milk production and lamb growth rates — problems that will worsen as lactation proceeds.

The trick is to end up at lambing with enough paddocks on the farm with covers that equal the target.

A proper feed budget will help greatly. If you're not familiar with feed budgeting, it would be wise to ask a consultant for help.

Slow down the rotation

To achieve target covers, you need to go into the winter with adequate pasture cover (1800–2000 kg DM/ha on 1 May).

Pasture then should be carefully rationed by lengthening the rotation of the main ewe mob. This will involve mob stocking, or reducing paddock sizes with electric fences. Start this when the rams are removed, or slightly earlier.

Supplements can be used to slow down the rotation and prevent over-grazing. The aim is to feed ewes at maintenance, so low quality hay or silage is satisfactory at this time.

Higher quality supplements like grains or good silage or baleage, should be saved for use by priority mobs such as triplet-bearing ewes or in-lamb hoggets during late pregnancy.

Plan early which paddocks you want the ewes to lamb on. Twin and triplet-bearing mobs should be on flatter, more sheltered paddocks, preferably north-facing.

Rotation length during winter will vary from 60–120 days depending on the rate of pasture regrowth. This will be influenced by temperature, rainfall, pasture species and post-grazing pasture residual.

In very cold weather, when grass growth is minimal, the rotation should be lengthened to allow enough time for paddocks to reach target covers by lambing.

As a simple example, let's assume we have a post-grazing pasture residue of 600 kg DM/ha, and three different regions. These have winter grass growth rates averaging: 5 kg DM/day (Southland or Otago), 10 kg DM/day (Manawatu or Waikato) or 15 kg DM/day (Northland).

The spell required to get a target of 1200 kg DM/ha would be 120, 60 and 40 days, respectively. This means each paddock in the rotation would be grazed approximately once in Southland and Otago, twice in the Manawatu and Waikato, and three times in Northland.

Pasture residual also influences rate of pasture regrowth. For example, residuals of 800–900 kg DM/ha will promote faster regrowth than residuals of less than 500–600 kg DM/ha, as illustrated in the diagram.

Remember grass grows grass — peak grass growth rates occur when covers range from 1200–2000 kg DM/ha.

Regional differences

Pasture covers should be varied a little to allow for regional differences in spring growing conditions.

In Southland, a target cover of 1400 kg DM/ha is satisfactory, because lower temperatures and adequate moisture favour the maintenance of high pasture quality.

In warmer, drier regions, a cover of 1100–1200 kg DM/ha at lambing may be sufficient. Otherwise, higher covers combined with very high pasture growth rates and the onset of the summer dry, can lead to early loss of feed quality.

Different performance levels

Ewes suckling twins and triplets have higher feed requirements than those with singles, and should be grazed on paddocks with covers of around 1400 kg DM/ha.

The feed requirements of singles will be met by pasture covers of 1200 kg DM/ha or even a little less. If feed is very short, single ewes with lambs at foot may be supplemented with grain. Research at Poukawa shows there can be considerable benefits.

More information

• In the Paddock, June 2001: Ewe feeding in early- and mid-pregnancy.
• In the Paddock, August 2001: The late pregnancy countdown.
• In the Paddock, September 2001: Ewes need priority after lambing.
• A Guide to Feed Planning, Sheep Council.
• A Guide to Improved Lambing Performance, Sheep Council.
• A Guide to Improved Lamb Growth, Sheep Council.

All these publications are available from WoolPro.

Your local farm consultant or veterinarian will also be able to help. Alternatively, contact your local WoolPro extension specialist: