That’s one of the key findings after four years of Pastoral 21 trial work at Lincoln University’s Research Dairy Farm (LURDF) and a year of the system running at a commercial scale on the university’s demonstration dairy farm, LUDF.
DairyNZ principal scientist Dr David Chapman has led the research at LURDF along with Lincoln’s professor of dairy production Dr Grant Edwards.
The research team compared a low stocking rate efficient (LSE) farmlet using an average of 153kg nitrogen (N)/ha/year and importing less than 200kg drymatter (DM)/cow of supplement running 3.5 cows/ha, with a much higher stocked, more intensive farmlet.
The higher stocking rate efficient (HSE) farmlet had a stocking rate of five cows per ha, used an average of 296kg N/ha/year and bought in 1.1 tonnes DM/cow of supplement.
LSE also included diverse pastures including chicory, plantain, lucerne, clover and ryegrass, on a third of total farm area, with the remaining two-thirds split between tetraploid ryegrass only and diploid ryegrass only.
Cows in both farmlets had high Breeding Worth values.
Maintaining pasture quality was essential if the farmlet scale results were to be replicated at a commercial level and hitting target residuals was imperative, Edwards said.
Pasture cover and growth rate monitoring were intense throughout the trial and a feed wedge, generated with the information and overlaid with a demand line, were used to show where any impending deficits or surpluses were lurking.
Proactive management decisions were made depending on the time of the season. For instance, deficits in late summer could be managed by early culling and lengthening the round before the feed supply-demand balance tipped into the negative.
Tactical amounts of nitrogen fertiliser and supplement were used to make this move but withdrawn as soon as things came back into balance.
There was always a lot of discussion and consideration of the consequences of any action when a looming surplus or deficit became apparent.
Early identification of surpluses to be conserved as silage was critical for managing pasture surpluses during spring and summer.
Round lengths on the LSE never got below 23-24 days and on occasion the mower was used either in front or following the cows if a residual target hadn’t been repaired in the previous round.
Chapman said on average half to two-thirds of the farmlet area was mown for silage or to restore a residual.
Grazed pasture was 96.5% of the LSE cows’ total intake while for the HSE cows it was 78%. The LSE cows ate 4.34t DM/cow/year of pasture while the HSE cows ate 3.4t DM/cow.
Cows on both farmlets consumed similar total amounts of feed per cow with HSE cows eating less pasture and more supplement.
Despite similar apparent intakes an interesting finding from the project was LSE cows produced more milk per cow, at an average of 509kg MS/cow over the four lactations, compared with 468kg MS/cow on the HSE farmlet.
Edwards said they hadn’t teased out why that was but the scientists noted as the trial progressed clover content on the LSE increased.
Chapman said the results had shown high per cow production from high Breeding Worth cows was possible on what was almost an all-grass diet.
“There’s no need to put them in a shed and feed them a complicated ration,” he said.
Key points
LSE:
- Reduced nitrogen leaching
- Used low levels of supplement and nitrogen
- Maintained profit
- Increased per cow production.
But must:
- Have low nitrogen fertiliser inputs
- Have low supplement inputs
- Pay close attention to grazing management
- Proactively manage feed supply and demand.
