By Guest Blogger: Dr. Charles J. Sniffen
There has been a lot of discussion and controversy about conventional vs. BMR hybrids. The producers like the to see the increase in DMI they get when feeding BMR hybrids but they do not like the yield drag nor do they like the uncertainty of the poor standability they see with BMR hybrids.
Background on vitreousness and floury
A vitreous hybrid is one where the starch has poor fermentability in the rumen and poor digestibility in the small intestine. We can offset this to some degree by grinding the corn very fine or by steam flaking it. With corn silage we can process or make Shredlage which reduces the kernel particle size. We have only in recent years begun to understand the impact of hybrids that are very vitreous. We know now that highly vitreous corn has a high proportion of the starch incased in prolamin proteins which are very hard to digest in the rumen and also in the small intestine. These proteins are very poor quality proteins. Finely grinding the corn creates more surface area and partially fractures the prolamin proteins giving more access by the rumen bacteria and the amylases produced by the cow. A key to understanding this is one can be reasonably assured if a corn silage (with starch over 30 %DM) or a grain is high in protein it will be high in prolamin proteins.
In contrast floury hybrids are very low in prolamin proteins and the starch is highly available in the rumen and highly available in the small intestine. This is good for both ruminants and for monogastrics. We should add, from a milling standpoint floury hybrids need significantly less energy to grind a ton of corn.
Floury hybrids are a problem, however, for exporting and for most feedmills in that the kernel integrity is not good so there is a lot of broken kernels and hard to handle. Additionally there is the additional problem of grading which governs the price paid for a bushel of corn. The standard bushel weight is 56 lbs. per bushel or greater. Less than this then the price received for a bushel is decreased; which is the case for floury corn which also has less prolamin proteins.
Dynamics of gut fill and intake
The issue of gut fill has been a part of ration formulation for a long, long time. Dave Mertens many years ago introduced the concept of feeding cows based on the idea of NDF intake as a %BW; this was a significant step forward. This then became modified as forage NDF intake as a %BW and then modified again with the introduction of fermentable NDF as a %BW. This last concept was with Mertens and Allen collaborating. Fast forward to today, Drs. Larry Jones and Joanne Siciliano-Jones have introduced the concept of uNDF30 which is the fiber not digested after a 30hr Invitro fermentation. The concept is that the fiber that digests in the first 30 hours will disappear very quickly and not have an impediment on intake. The fiber not disappearing in the first 30 hours will have an impact on intake and the suggestion is that 5 to 6 lbs. is the maximum that should be fed. The latest suggestion is that uNDF240 is a good predictor of gut fill. This is the fiber unavailable after 240 hr Invitro fermentation and is now part of the CNCPS model. The recommendation is 0.35 to 0.4 %BW. Both of these approaches need to be verified with further research and field observations.
BMR corn silage will have a lower uNDF30 and uNDF240 which will allow a greater intake than conventional corn silages. This will translate into higher % forage in the ration with a BMR. It will be lower with conventional forage. In reality if we feed to the gut fill limit for both conventional and BMR forages then in comparison there should be no difference in DM intake between the two forage types. There would be more BMR being fed than conventional but the downside would be that the fermentability of the starch would be lower than a floury conventional hybrid.
Definition of feed efficiency
Thinking in terms of corn silage only, the producer almost usually sees an intake response when feeding BMR hybrids; actually in the early days of feeding BMR hybrids there was an issue of not feeding enough effective fiber or peNDF with a BMR because the effectiveness of the fiber was lower than with a conventional hybrid which caused nutrition issues. Another issue with the BMR is often producers ran out of inventory more rapidly due to the increase in intake. The thing that most producers observed is that even though the intake increased with BMR the milk did not increase because of the high vitreousness with BMR hybrids; more corn and protein needs to be fed to offset the decreased microbial protein supply and decreased energy from the fermentable starch. This difference decreases after the silage has been in the silo for several months. With a floury hybrid that also has good fiber digestibility intake response increases however due to the floury nature of the starch the milk is flow is maintained or increased.
Differences in feed efficiency between MC & BMR hybrids
Feed efficiency is either the lbs. milk per lb. DM (the fast calculation) or more correctly lbs. FCM milk per lb. DM consumed. This measurement is looked at routinely today.
MC hybrids with good fiber and starch digestibility will routinely result in higher feed efficiency, especially with corn silage fed in the fall when compared to a BMR ration due to the lower starch fermentability. Additionally the income over purchased feed cost will be greater. In the spring of the year, the differences will be smaller because the vitreous starch in the BMR will have a higher fermentability. One would add that this is dependent on the DM at ensiling. If the DM is over 35% and closer to 40% the % acid in the silage will be lower and the breakdown of the prolamins will be reduced.
Summary & conclusions
The use of a MC hybrid with high fiber and starch digestibility makes more sense when one takes into account higher yields/acre, better agronomic performance year over year, and better dairy performance in terms of productivity with more consistent health throughout the year. Added to this is the improved efficiency that is coupled with lower feed costs and greater income over purchased feed costs.