• Nick Lyttle

Four Important Reasons For Pre-mating Pasture Analysis

Calving is mostly over and now is the time to focus on supporting your cows for the next two major events in your calendar – peak milk production (sets the bar for the lactation production capability over the season) and mating (sets the bar for herd development).

Effective feeding is critical.

And that means helping your cows extract as much value from every kilogram of dry matter consumed. So if you’re seeing grain in the dung or loads of supplement left in the paddock or feeding pad, frustration undoubtedly builds.

To optimise returns form feed offered, three factors must be considered:


  1. How much can your cows eat?

  2. How much of what they eat can they digest?

  3. What are the highest demands for what they digest?

o Tissue repair? Uterine involution and mastitis resolution.

o Growth? First calvers’ body and udders.

o Milk? All cows.

o Survival? What’s the weather like? Shelter? Distance to walk? Anxiety and stress?

And to optimise your profit, you must consider the cost of each different type of dry matter you offer from pasture to all the various supplements. But that is a topic for another article.

1. How Tasty Is Your Pasture?

Your first round is winter grown and its composition is strongly influenced by autumn fertiliser and any early spring applications of urea or sulphate of ammonia.

Common spring pasture excesses are sulphur and potassium, both of which are bad news because of their multiple impact. Not only can they depress dry matter intake (DMI) but they’re also silent killers of production in other ways. Potassium excess is the single largest factor driving up metabolic risk (both clinical and the more insidious sub-clinical). A 10 % lift in pasture potassium nearly doubles dietary magnesium requirement. And sulphur, even in the absence of high molybdenum levels, has a profound effect to reduce effectiveness of copper and selenium, both vital at this time of year.

Most dairy farmers will be supplementing with magnesium, some with limeflour and a few with salt in order to support spring deficiencies. But how much is right for your cows? And when can you stop or reduce these levels? Or do you need even more than you’re giving?

And what levels of crude protein are present in your pasture? Should you apply urea if you’ve already got a feed surplus, knowing you’ll only maintain excessive crude protein levels or lift them even higher?

Taking a pasture test will answer these questions and more.

2. When More Doesn’t Mean Better

Early season pasture growth is a key to getting your lactation curve rocketing up and to peak high. Right?


And one of the best ways to get it there is using a nitrogen/sulphur based fertiliser such as sulphate of ammonia (SOA) or calcium ammonium nitrate. Right?

But how do you choose which product to use?

Habit, cost, soil temperature or something else?

Is removal of excess sulphur and hence removal of appetite suppression a contributor to the lift in production on the production curve on the left? Possibly, but it’s too early to say. No data has been analysed yet to evaluate total comparative dry matter yield season to date.

The decision not to use SOA in 2012 was made easier by knowing that pasture sulphur levels were already above desirable and soil temperature was also above 7 degrees. So a double positive might have resulted – lower fertiliser cost and higher production.

Check our next newsletter for an update on this.

3. Rapid Change Requires Rapid Adaptation

The change from grazing winter saved, slow grown grasses to lush spring pastures is significant and quick. Weather dictates available feed volume and access to pastures which means dietary variance is also high. And when you add various supplements to the mix, the cows ability to get the most from what she eats is tested. And she fails. This is the period of negative energy balance, where demand exceeds supply.

It fails because peak intake is not generally accepted to be reached until 10-12 weeks post-calving. And common factors that minimise palatability and appetite in many pastures we analyse are missed. Namely excessive potassium and sulphur. These not only slow the intake gain curve and hence production but have another side effect to antagonise important trace elements such as copper and selenium.

4. The Green Geyser is Costing You Money

If your cows are producing green jets and not making cow pats, you’re losing dietary efficiency. Excluding infectious problems, there are a couple of contributing factors.

Firstly, excessive magnesium supplementation, particularly with magnesium sulphate, will cause an osmotic diarrhoea. This results from water being drawn into the intestinal tract as unabsorbed supplemented salt passes through. This increases the flow rate and gives less time for nutrients to be absorbed.

When metabolics occur the immediate response is to increase mag supplementation. It’s understandable because metabolics are not fun. If the risk is high, the supplementation will need to be high and it gets to a point where you simply can’t get the cows to eat or drink any more magnesium. The key is to understand where the pressure is coming from. Excessive, potassium is widely understood but excessive phosphorus is not, and the interaction with low pasture calcium can be a potent metabolic risk.

Knowing your sources of risk will expose your best course of action and true magnesium requirement.

High pasture crude protein levels are compounded by the high digestibility of this protein source – often between 70 and 80 %.


Managing excessive crude protein levels in your spring pasture will benefit your cows and your pocket by minimising the following consequences:


  • Reduced gut transit time

  • Sloppy dung

  • Lower milk production

  • Lower milk fat percentage

  • Loss of body condition

  • Increased excretion of nitrogen (adding to environmental pressure).

Further consequences of some of these factors result in delayed or deeper negative energy balance and hence weak, silent or delayed oestrus.

Analysing your spring pasture (and your supplements) will guide you to make positive dietary change and considered fertiliser decisions.

Reducing Metabolics

Reducing Metabolics

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