DairyNZ's grass-fed policy could be adding to our nitrate woes
The grass-fed dairy system advocated by DairyNZ is the cause of New Zealand's nitrate pollution problem and this could be alleviated if dairy cows were fed a more balanced diet, claims South Canterbury arable farmer Jeremy Talbot.
Talbot said the pasture-based system caused cows to excrete excessive amounts of nitrates, but a diet that included low protein silage and cereals would remedy this.
"Modern grasses are nitrogen (N) rich and at certain times of the year, like during the spring flush, are very high in proteins. This affects the urine nitrogen of the cow which is excreted and makes its way into the waterways."
A cow can't digest more than 15 per cent protein if it's diet is all grass, Talbot said. At 22 per cent protein, cows were excreting 300 grams of nitrates a day. With modern irrigation, fertiliser and dairy wash on modern pastures, the protein levels were commonly more than 30 per cent.
"The most environmentally friendly dairy systems in Canterbury are the likes of Willie Leferink ... with their [operations] where they are controlling the cow's diet. The effluent coming out of their sheds is much lower in nitrates."
Dr Lucy Waldron of LWT Animal Nutrition, Fielding said dairy farming systems in New Zealand are typically focused on fast growing species such as sugar-rich ryegrasses and nitrogen rich clover combinations.
"DairyNZ says nothing about the levels of protein in the grass affecting urine nitrogen," she said. "An all-grass system with very low imputs will result in the cows proteins at certain times of the year being incredibly high.
"We all know in the scientific world that what you feed your dairy cow has a major effect on what comes out of the dairy cow. Science shows us that the excretion from urine is directly related to the amount of protein the cow is consuming. When grass is growing quickly the protein levels can be as high as 30 per cent. Once the protein levels in the cows feed exceed 15 per cent, the nitrate excretion is extremely high and this ends up in on the pasture and ultimately the waterways."
Talbot said research by Dr Wadron and others had showed a reduction in nitrate emissions from dung and urine of up to 80 per cent, savings in irrigation water of more than 30 per cent and improved profitability in all seasons of about 20 per cent.
DairyNZ principal scientist John Roche said anyone who has visited housed systems internationally and witnessed the reality of the environmental, social, and economic problems would be unlikely to conclude they're the most environmentally sustainable approach to dairying in New Zealand.
"Environmentally, housed systems have their own problems with water and air quality, not to mention greenhouse gas footprint – we would merely be swapping one problem for another."
Nitrate leaching was a complicated issue with many factors at play, he said. The dairy industry was spending large amounts of money on research to solve this problem.
"The solution is not as simple as feeding low nitrogen silages or grains to correct this problem. In fact, you could have the opposite effect – increasing nitrate leaching by taking this approach.
"If you use silage or grain, you are importing more nitrogen onto the farm, some of which will be excreted by the cow in urine. If you do this, you will have to increase the stocking rate and keep cows milking for longer in the autumn to maintain profitability; this increases the risk of nitrate leaching.
In an article in Welfare Pulse, Ministry of Primary Industries (MPI) animal welfare publication, Professor of Animal Science at Colorado State University, Temple Grandin said the attempt by some dairy farmers in New Zealand to copy the intensive dairy practices used in other countries was a mistake.
"In other parts of the world dairy cattle are housed inside otherwise they would be covered in snow," she said.
"Another problem is that costs would skyrocket because expensive feeds would have to be brought to New Zealand by ship. The New Zealand dairy industry could really capitalise by marketing to the high-end grass fed dairy market. Do not attempt to copy other countries that have cheap grain and more severe weather," Grandin said.
Roche said pasture was a well-balanced feed. All other feeds, from a nutritional perspective, were inferior. To replace pasture a range of feed ingredients was required, most of which must be imported, he said. New Zealand could grow many of the cereal grains. However, to do this the crops would have to be tilled, which reduced soil carbon and nitrogen, sprayed with herbicides and fungicides, and use a lot of fuel which would increase the greenhouse gas footprint.
"Socially, consumers all over the world have identified access to pasture as a key animal welfare requirement. For example, organic certification in the USA requires dairy cows to consume at least 30 per cent of their diet from grazed pasture for at least 30 per cent of the year. In Europe, a number of milk companies are paying a premium to farmers that allow their animals to graze."
- An earlier version incorrectly said Jeremy Talbot believed the best environmentally friendly dairy systems in Canterbury are barns owned by some farmers which control the diet of cows. This has been changed to operations to reflect the fact that some of the systems are not barns.