10 May 1996

More precise management

is vital

Efificient grass use depends on improved precision in grass management.

Sue Rider reports

DAIRY producers keen to add precision to growing grass must improve feed budgeting skills.

This involves assessing yields of grass on paddocks at regular intervals, said Dr Gearoid Stakelum of the Moorepark Research Institute, speaking at the Irish Grassland Associations dairying conference in Limerick.

In this way it was possible to monitor grass supply and how this supply was changing over time. "Is it increasing or decreasing, what level of intake is being achieved and how much is growing are important questions," said Dr Stakelum.

Cover monitoring

Monitoring grass cover would also show how severely a paddock was grazed, and over a number of rotations, reflect how much grass was being grown on individual paddocks.

"Walking the farm on a regular basis, say once a week, and assessing all paddocks for grass cover will show if grass is reducing," he said. For example you would see when intake was greater than grass growth, or when grass was increasing, that is if intake was less than growth. "They are, in reality, forecasts of impending surpluses or deficits," he said.

Assessing post-grazing yield in a paddock, would give a good idea as to the level of grazing severity. The task was made easier when grazing was based on temporary sub-divisions of existing paddocks. "This is a very practical way to assess pasture yield," he said.

"When an existing paddock is assessed for yield, and an area allocated for a single grazing if the pre-grazing yield is underestimated, the feed will be over-lenient," he said. If, on the other hand, pre-grazing yield is overestimated, the paddock will be grazed too severely." Using this method it was possible to assess grazing yields and feeding levels (see Table 1).

Farm cover of grass was the average yield of grass on all the paddocks being grazed. It was an average of the paddocks about to be grazed and those just grazed as well as those in the middle of the grazing rotation.

Farm walk intelligence

Table 2 shows what type of information could be gleaned from a farm walk where all the paddocks are assessed for yield. Cows have grazed paddock one and are going into paddock two. All paddocks are grazed down to 1600kg dry matter a hectare (in practice this will vary). Farm cover is 2443kg DM/ha (the average of the 10 paddocks). Pre-grazing yield is 3760 and post-grazing yield 1600kg DM/ha.

Highest growth rates since the last grazing in the paddocks are on paddocks with the most grass. These paddocks are now in an active stage of recovery. Paddocks grazed recently (8-10) have low growth rates. By combining the data from each farm cover estimation what is happening on the farm over timecan be seen.


Table 1: How to calculate intake based on yield assessments

1. Pre-grazing yield = 3500kg DM/ha (to ground level)

2. Post-grazing yields = 2000kg DM/ha (to ground level)

3. Paddock size = 0.809ha (2 acres)

4. Time in paddock = 2 days (four grazings)

5. Herd size = 40 cows

Then intake a cow a day can be calculated as(1-2) x 3

4 x 5

eg3500-2000 x 0.809 = 15.2kg DM

2 x 40


Table 2: Grass cover data accumulated from a farm walk

Paddock No12345678910

Yield

(kg DM/ha)1600376033903000268024002160196018001680

Rest interval(days)018161412108642

Growth rate since lastdefoliation0120112100908070605040

To get the most out of rotational grazing, subdivide fields tinto square or rectangular blocks.