Tuesday, September 16, 2014

The Circle of Life

One advantage of experience, or some would say old age, is the perspective it provides.  When I was a baby in the world of agronomy, the accepted rule of thumb regarding hybrid selection for corn silage was the best grain corn hybrid was also the best silage hybrid.  Maximizing grain yields and the subsequent energy in that grain seemed logical to me, even though my only direct experience came from feeding corn silage to beef cattle.  
Dairy customers complained about this recommendation, citing whole kernels present in the manure and having to sweep loony sized cob pieces out of the feed bunk.  These were valid criticisms.  I have vivid memories from 20 years ago of a respected dairyman taking me to the woodshed about Pioneer's lack of commitment to corn silage breeding. Francis Glenn with his development of leafy corn silage genetics turned the silage market upside down and gave dairy customers what they wanted.  Specifically, high feed intakes, clean feed bunks and fully digested kernels.  The cold world of economics was not as kind to the leafy silage producer because leafy hybrids provided no flexibility, took more silage acres to feed his/her herd and required more storage to make it from one season to the next.  
Self propelled harvesters with kernel processors, plus the adoption of TMR feed mixers, eliminated the problems associated with grain corn hybrids being used as silage hybrids.  Mature corn kernels and cob chunks were smashed into tiny pieces that could not be separated by fussy four legged dairy cows.  Silage acres have swung back to conventional dual purpose type hybrids.  Tim Emerson  a respected independent dairy nutritionist, told me a year ago that if he had his way, the perfect silage hybrid would simply be a great big cob on a short stick.  After 30 years of evaluating corn hybrids for silage I was back to where I started.  
Despite this back to the future type experience, there is a lot we have learned about corn silage in the last 30 years.  One important point is the role of environment with respect to fibre digestibility.  With the exception of brown mid-rib hybrids, only 3% of the variation in fibre digestibility can be attributed to genetics.  97% of the variation is due to weather.  We know that warm, hot years like 2012 increase fibre digestibility.  Cool slow growing seasons like 2014 depress fibre digestibility.  It will be normal for corn silage this winter to not have the punch that it otherwise might have.  
The next chart appears complicated, but the message is simple.  Waiting to harvest corn silage until whole plant moisture is in the 60-65% range increases starch levels and maintains fibre digestibility
A standard rule of thumb for silage timing has been to target the period of 45 days after silking to begin harvest. Another measure is 1/3 – 1/2 milk line descent from top of kernel.  While these recommendations get us into the corn silage window, they tend to target 70% whole plant moisture.  If harvest does not happen until 55-60 days after silking or 2/3 milk line, what are the effects?
Silage producers that use modern genetics with good late season plant health, fungicides and kernel processors can allow corn silage to mature into the 60% moisture range without sacrificing silage quality. The starch deposition rate into the kernel will more than compensate for the small decrease in fibre digestibility.  The net benefit is greater energy density. 
Stress tolerant hybrids and fungicides extend plant health later in the season.  Kernel processors allow the starch to be available to rumen and intestinal breakdown. 
The caveat to making this all happen is the processor must be set correctly.  That is where the train will leave the rails.  An easy way to make sure the processor is set properly is to look for whole or half kernels.  In a two handed fistful of silage there should be no more than 2-3 whole or half kernels. The grain needs to be pulverized.  Poor kernel processing does not allow the energy captured in the grain to be expressed in the milk tank.
While we are at it we need to make sure the bunk is packed properly.  This may be hard to believe, but you can over pack a bunker.  The following are two images of a bunker that Martina Pfister, one of Pioneer's dairy specialists, and I were at this summer.
This is the face of the bunk, which in this case is very well managed and neat.  The next shot is using an infrared camera which presents a different story.
Purple colours indicate cool silage, while yellow colours indicate hot spots.  The wavy yellow lines near the top are the residue of too much wheel traffic on top of the pile.  A great packing job can be undone by spending too much time overdoing it once the bunk is full.  The constant back and forth will have the opposite effect of what is intended. The physical structure of the plant's cells is destroyed by the pressure of the tire treads. The cell contents leak out and instead of packing tighter, they actually will dry out and air moves in.  It takes a real artisan to properly pack a bunk.  One who knows where the right touch is required and when enough is enough.