Thursday, 31 May 2018 08:55

Do we need to cut cow numbers?

Written by  Peter Burke
John Roche. John Roche.

Is cutting cow numbers the silver bullet that would solve the issue of nitrogen leaching into soils?

Comments on the environment by Environment Minister David Parker have prompted some uninformed journalists to suggest that reducing cow numbers is the only viable alternative. But DairyNZ principal scientist Dr John Roche says reducing cow numbers is by no means the answer. Peter Burke investigated.

John Roche says it’s important to know that farmers care deeply about managing nitrogen on their land to limit environmental impacts, and that New Zealand doesn’t need to reduce cow numbers to reduce the nitrogen footprint on farms.

He says solutions have been, and continue to be, developed by scientists and will vary between regions and even between catchments within each region. 

Roche says the causes of nitrogen leaching vary from region to region and occur at different times of the year. But in some regions farmers may need adapt their farming system, meaning farming in a slightly different way but not necessarily reducing cow numbers.

“But it may see farmers reducing the amount of feed brought onto the farm, such as PKE, and adjusting the stocking rate accordingly; alternatively, it may mean putting infrastructure in place that allows farmers to take cows off the land at sensitive times of the year. The latter option, however, is expensive and may not be financially wise.”

Roche says there are differences between the North and South Island that need to be understood when looking at the whole issue of nitrogen leaching. In the North Island a lot of pasture is grown during spring, when plant uptake of water equals or exceeds the rainfall. This means there is little downward movement of water and, therefore, dissolved nitrogen through the soil. At the same time during those key months we have rapid growth of pasture which means that any nitrogen deposited by the cow is taken up by the grass which is recycled through the cow to feed her. 

“The challenge comes primarily towards the end of the year, when grass growth slows and therefore is not able to utilise as much nitrogen as earlier in the year. In addition, rainfall tends to exceed evapotranspiration. So we get downward movement of water and dissolved nutrients, one of which can be nitrate,” he says.

One solution would be to have high stocking rates during those peak grass growing times to utilise all the pasture grown and as autumn arrives aim to reduce the milking cow stocking rate to allow more grass to grow and build pasture cover to feed cows in the winter. 

Roche says the aim is reduce milking cow stocking rates at times of the year which he calls ‘drainage months’, but not necessarily stocking rate at peak. An alternative approach has been to use stand-off pads during these sensitive months. On these pads, the cow’s urine is collected and applied evenly to the pasture subsequently. However, this can be an expensive option, unaffordable at this point for many farmers.

“Both these strategies have been shown to significantly reduce nitrogen leaching without reducing the number of cows on the farm, but they have different capital investment requirements,” he says.

South Island issues

John Roche says that in the South Island the main challenge is in wintering systems. Traditionally stock have been wintered on high yielding crops. 

Dealing with the wintering system has been the subject of much research by DairyNZ and collaborators for at least ten years and some interesting solutions have been found. For example, include alternative forage crops in the pasture, in particular plantain.

“This is an amazing plant for a number of reasons. It has less nitrogen itself, which is obviously a positive. 

Also it causes the cow to drink more water, which means her urine becomes more diluted and so the urine patch is less concentrated. 

“In addition to these two advantages, plantain also has a deeper root system which means it utilises nitrogen in the soil that is below the traditional grass-white clover sward, so less nitrogen is escaping the root zone. 

But wait, there’s more. It also contains compounds we don’t completely understand, but which modify the nitrogen in the animal and the soil. It’s an exciting discovery and one we hope will, in the right catchments, provide great environmental benefits.”

How good are our cows?

John Roche is a stout defender of the NZ cow, saying that she is often taken for granted.

“The cow is a very interesting animal. In human terms, she sprints a marathon. An incredibly high performing athlete in our production system, she lives and produces for a far longer time than cows in the traditional housed systems overseas. She has fresh air and a new view every day, as well as being provided with most nutritious food on the planet every day of her life. In my bovine reincarnation I know where I’d like to be.”

Roche says it’s true that we feed our cows less than cows housed in barns and fed a mixed ration. But that must be balanced against the views of the consumers of our dairy products, who value our pasture-based systems and the fact that our cows are grazing in the open which is natural for them. He is also adamant that NZ cows are not underfed.

The fairest comparison to NZ cows are Irish cows, says Roche. He should know; he comes from a dairy farm in County Kerry, one of Ireland’s major dairy producing regions. But the comparison comes with a few caveats. 

“What you need to understand is that if both countries were in the same hemisphere the southern tip of Ireland would be almost 700km south of Invercargill. While the gulf stream warms the region and the climate, in terms of temperature, it is very similar to the Southland region; there is an enormous difference in evapotranspiration, particularly in winter, because of the latitude difference, Therefore, Irish soils remain water-logged to a degree that NZ soils do not. This is despite the fact that it feels around the same temperature and same rainfalls.”

He notes that the productivity of Irish cows is very similar to those in NZ because the Irish have sought out NZ genetics through LIC to lift the overall quality of their herd.


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