'Extreme' pasture growth brings unique problem for Waikato farmers

Excessive grass cover can lead to problems with milk production and animal health.
Excessive grass cover can lead to problems with milk production and animal health. Photo credit: File

Farmers around the country have faced a multitude of problems so far this year, from drought to flooding - but until now excessive grass growth hasn't been one of them. 

But that's the challenge some Waikato dairy farmers are facing at the moment, with "extreme grass cover" being reported in the region.

"Ordinarily, it's reassuring for farmers to have plenty of feed ahead to cover what can normally be challenging months for spring growth," says Ken Winter, technical support manager of GrainCorp Feeds. 

"However, with covers this high and the current warm conditions, farmers risk losing pasture quality on a grand scale, which can have negative implications for milk production and animal health."

Winter said in some paddocks there was more than 4500kg of dry matter per hectare (DM/ha).

He said the problem with extreme grass cover is that digestibility can often be less than ideal, meaning cows can't physically eat enough to meet their energy requirements.

"Trying to break-feed pasture to cows while maintaining residuals can result in pushing an ever-increasing wedge of feed ahead of your herd that is dropping in feed value, slowing pasture recovery, and lowering the energy value of the feed."

He said the true extent of the effect on stock is often not realised until later in the season, when they suffer from poor fertility and lack of lactation persistence.

"If you push milkers to graze this type of feed you will underfeed them, strip weight from them, reduce their production and fertility, and compromise cow health and your whole season."

He said there was a number of things farmers could to to mitigate the risk to their farms, including:

  • Look at how many paddocks you can immediately harvest for silage. While this pasture may not make the best silage, it's more important to get your paddock back under control and in a great growing state for your milkers. The silage is also a surplus feed you can use at a later date.
  • Milkers and Colostrum cows can take the tops off many of the high cover paddocks without doing any harm.
  • Milkers can graze down to about 2,200kgDM/ha if the pasture is not of an unreasonable quality. Fully feed the cow and put your herd back onto that paddock earlier in the next round.
  • Use dry cows and springers to graze behind your milkers.
  • Be prepared to get the mower out early this year to get your residuals right. Some farmers have already been mowing ahead of the cows in August.
  • Lock up 'light silage' paddocks early where residuals need tidying up.

Winter's advice comes as vets in the Hauraki Plains have warned the grass growth can also lead to grass staggers  - a metabolic disease caused by magnesium deficiency. If left untreated it can result in seizures and death for cows.

The disease is caused when cows eat younger grasses that are high in potassium and non-protein nitrogen, and low in magnesium.

On Monday, rural vet Dr Greg Lindsay told RNZ there had been a spike in callouts about grass staggers and urged farmers who suspected their stock were at risk to speak to their vet.