Why the green, green grass of home is simply the best

New Zealand's grazing system was once considered "the eighth wonder of the world".

In the 1970s and 80s, a team at Ruakura led by Dr Arnold Bryant undertook grazing experiments that were to revolutionise the way pasture was managed through winter and spring.

The system matched herd demand through assigning the correct calving date and stocking rate with a store of pasture (ie cover at calving) and crop and an assumed winter growth rate.

Discipline in following recommended winter-spring rotation lengths meant that pasture growth and quality were maximised. Cows were well fed and on a 'rising plane of nutrition' going into mating, and any feed deficits, due to colder or wetter than normal winter conditions, were small and short lived.

Considering the need to minimise spending this year, it is important to revisit this work and understand its applicability for farming today.

Four pillars of grazing

Bryant and his co-workers identified four important factors to optimise winter-spring grazing management. The first two were strategic:

1. Calving date
2. Stocking rate

And two were operational:

3. Autumn pasture management and the ideal cover at calving
4. Area allocated/day during winter and the development of the spring rotation planner

Strategic management decisions around stocking rate and calving date have already been decided for this season, but they should be reconsidered in spring to determine if they are optimum for future years.

At this point, though, we can still optimise farm management through winter and spring and minimise our reliance on purchased feeds by focusing on pasture management.

Autumn pasture management

In 1984 Arnold Bryant reported that the objectives for autumn pasture management are to:
• Provide sufficient high quality feed for early lactating cows
• Ensure cows are at target body condition at calving.

These dual aims should be achieved with minimum pasture damage.

Adapting the recommendations of Bryant and co-workers, the optimum pasture cover at calving is 2300-2400kg DM/ha.

To establish optimum pasture cover in July-August,

a). rotation length needs to be extended from 40 days in April to 90 days a month before calving, where herds were wintered on-farm, or
b). the majority of cows have to be removed from the farm for 60-75 days, if off-wintering.

In the Ruakura research, a rotation of 80-120 days between April/May and July resulted in 10-15 per cent more milk before Christmas when compared with a rotation length of less than 50 days.

This is because growth rate during winter increased with average pasture cover: for every 100kg/DM increase in pasture cover, growth rate increased 7kg/DM/day, providing the daily requirements of a dry cow or more than half the requirements of a milking cow during the first month in milk.

The increase in pasture cover at calving was a result of lengthening the rotation in the autumn and this was achieved by allocating a set amount of area/day for grazing using the autumn planner.

The allocated area has to feed all stock on the farm, so the farmer needs to adjust the number of cows milking and dry to ensure:

a). dry cows are adequately fed to gain body condition and
b). milking cows receive enough feed for maintenance and milk production.

As the area allocated/day declines each day, the number of lactating cows must decline also. The autumn planner assumes that growth rate equals herd demand during the month before calving.

In warmer regions, the rotation length does not need to increase as early, while in colder regions cows must be removed from the milking platform to allow the farm to recover.

Spring pasture management

In 1986, Bryant and L'Huillier reported on an experiment which compared a low pasture cover at calving with an ideal scenario and investigated two management strategies:

a). maintain a slow rotation and allocate the available pasture each day, or
b). increase the area allocated to ensure that milking cows were well fed.

When the rotation was sped up, average farm cover declined and did not return to optimum until December.

In other words, a short-term advantage in per cow feeding resulted in a large feed deficit for four months. In fact, for a 100ha farm, the difference in pasture availability was 178 tonnes DM or tonnes 500kg/DM/cow (at three cows a hectare). At $200 tonnes DM, that is equivalent to more than $35,000 a year.

This experiment led to the development of the spring rotation planner (SRP), which took the 'guess work' out of pasture allocation during spring.

The SRP is ingenious in its simplicity. Like the autumn planner, the SRP assigns a specific area/day, and this area increases each day. At the outset, area allocated/day is small because all cows are dry.

As the number of cows calved increases, so too does the area allocated. However, dry matter intake of milking cows is still low (approximately 13-15kg DM for a 500kg cow).

The SRP accounts for the increase in cow dry matter intake by rapidly increasing the area allocated/day from 30 days post-calving.

An important aspect of the SRP is that it can be used throughout New Zealand, irrespective of stocking rate, breeding worth of the herd, breed of cow, or amount of purchased feed used.

A line between rotation length at calving and desired rotation length at balance date dictates how much of the farm should be grazed each day.

Detractors of the SRP refer to it in terms like 'controlled starvation'. This is nonsense! The SRP is a way to optimise pasture management. It does not determine whether you feed supplement or not.

That is a decision each farmer must make based on feed availability at that time and looming feed deficits.

However, by sticking to the SRP, you will minimise the size of the feed deficit and the amount of feed that will have to be purchased.

Conclusions

Although there is no recipe for farming, successful farm businesses have a strategic plan that limit their exposure to external forces. Biologically, this means a stocking rate and calving date that suits the pasture growth profile, while, from a business perspective, it means limiting risk to changes in variable expenses (such as purchased feed).

Vital components of this plan are the autumn planner and the spring rotation planner which both ensure that pasture growth and utilisation is optimised, and limit external risk.

IN A NUTSHELL:

You can manage cows through winter and spring without purchased feeds through:

• Correct stocking rate
• Achieving target pasture cover and crop yields
• Achieving target cow body condition scores at the start of calving
• Using the spring rotation planner which dictates area of the farm allocated per day.

- Kevin Macdonald is a senior scientist and John Roche a principal scientist for DairyNZ