Post-Drought Pasture & Stock Management.
by Brian Hockings, Autumn 2008
Without doubt very many farmers in NZ will, this year, be experiencing the worst drought effects for a very long time – if not for all time. Without doubt also they will be looking forward with ever increasing desperation, to that magic time when a solid and ongoing rainfall will herald the fact the drought has broken and pastures will start to move again. However the danger is that this will engender the thinking that the crisis is over – or at the very least there is now considerable light visible at the end of the tunnel. Unfortunately though, this can very easily transpire to be one of those classic cases when the light at the end of the tunnel turns out to be a bloody great train coming the other way.
There is a big paradox in the fact that the worst and most critical effects and impact of a major drought will come immediately after it has broken – rather than while it has been occurring. In practice this could well mean that the onset of drought breaking rainfall could actually be the signal to in fact increase the rate of supplementary feeding – rather than reducing or eliminating it. Despite appearing illogical there are very good reasons for this.
Animal Production Effects
Drought conditions on a farm affects animal production by reducing both the quantity and the quality of the pasture feed available. As the drought increasingly takes hold, pasture feed quality will be the first to begin to decline as plants become more stalky and leaves begin to dry up.
The impact of this shows up firstly, and relatively quickly, in milking cows, as quality feed is essential for good levels of milk production.
For dry stock the critical factor is much more likely to be feed quantity, as growing cattle, particularly older ones, can still make reasonable weight gains on lower quality feed – providing there is enough of it.
Conversely as maintenance requirements of a growing animal will likely be less than half the total required for desirable or target LWG, it follows that if young stock can still be kept at maintenance on a fairly restricted feed availability – and it will take a reasonably severe level of underfeeding for them to suffer actual condition and weight loss.
High Dry Matter
This factor is greatly enhanced by the high dry matter of the pasture. A farmer can look across a withered, drought stricken pasture and compare it in the minds eye with fresh, green, leafy, highly nutritious spring pasture and conclude there is not much feed there.
Not necessarily so. The likely best DM% for spring pasture will be 15%.
Whereas the dead stalky material in the drought paddock will, in effect be hay attached to the ground, and so have a DM of 85%. The more leafy dried material will likely be 40 – 45%DM.
Even if the drought has not reached full severity and there is still a tinge of green leaf scattered through the sward – this will still have a DM above 25%. All this means there is actually much more and concentrated feed in a drought affected paddock than would appear.
Add to this the minimal maintenance requirements resulting from the warmer temperatures and the animal’s generally lazy summer disposition and it can be seen that dry stock can survive quite well during a drought, with minimum supplements.
Now lets look at what happens when the rain finally comes.
Firstly, all the dead stalky high DM material described above gets flattened down to ground level where it the becomes unavailable to the stock – because they cant get at it and/or it is rotting away very quickly.
So feed availably drops markedly.
Where the drought has been severe, this will still be the situation for some time, (At the very least 3 weeks) – due to the fact that the plants will be completely burnt off and dead, recovery and regrowth has to come from the roots.
The Obvious Thing To Do?
However, once this recovery is well underway the farmer will be faced with the pleasing spectacle of good fresh green grass on all paddocks.
The obvious thing to do then is to get the stock onto this as soon as there is enough there – and so help conserve the remaining winter supplements – which undoubtedly have been severely depleted.
Unfortunately though this is not a good thing to do – from both the stock and pasture viewpoints.
Stockwise, the sudden massive change in diet is harmful – as is usually the case.
Over the past weeks the rumen has built up a huge population of micro-organisms, able specifically to break down, process and digest the dry stalky material which has primarily been the sole diet.
These micro-organisms will be of little use in processing the very different lush green material now being ingested, and it will take a bit of time for the appropriate ones to build up and take over – so that feeding hay over the transition period is definitely recommended.
(This is reinforced by the fact that in numerous cases where LWGs are being monitored, quite severe LW losses on post drought fresh feed, following modest gains during the drought – have been recorded – ie where no transition feeding occurred)
Bad Pasture Effects
The bad pasture effects are related to too intensive, too early grazing.
As mentioned previously regrowth will be coming from the roots. Vigorous and productive plant growth will not get going until a reasonable leaf canopy has formed and the plants are actively photosynthesising.
This will be greatly inhibited if the leaves are being virtually nipped off as soon as they are formed so that the longer recovering paddocks can be left before grazing the better.
The obvious way to slow the rotation is feeding supplement. A farmer may well be very reluctant to do this in the light of a limited reserve remaining. However the best and cheapest method of increasing the winter feed supply is to grow more grass and carry it forward and in this scenario it is quite probable that one bale of hay fed to lengthen the rotation will result in an extra 2 – 3 bale equivalents being grown,
Feed Hay AFTER the Drought Has Broken.
In summary, it has been truly said, that the most critical time to feed hay in a drought is after it has broken.
A final point on pasture recovery.
A feature of drought affected pasture is always the large amount of dead organic matter in and on the ground. In the normal course of events this would have been broken down by soil micro-organisms, and reincorporated into plant material – ie the Nitrogen Cycle.
During a drought this hasn’t happened because the dry has also shut down the micro-organisms so that all this accumulated organic matter represents a big N reserve.
It would thus be expected that with the rain the micro-organisms would recover, get to work and thus create a big pool of N reserve for the pasture plants.
It does – but not immediately. Short term, because the micro-organisms are