High Quality Corn Silage: A Gift That Keeps Giving

Dr. Bill Weiss, Professor and Extension Dairy Specialist, The Ohio State University

Arguably, the best single laboratory measure to evaluate ‘quality’ of corn silage is in vitro NDF digestibility (IVNDFD).  In numerous lactation studies, cows fed diets based heavily on corn silage usually ate more dry matter (DM) and produced more milk with the diet based on corn silage with a higher IVNDFD.  Many of these studies included brown midrib silage (BMR) because BMR usually has a higher IVNDFD than most conventional hybrids; however, some conventional hybrids can have very good IVNDFD (hybrid information regarding IVNDFD is usually available in seed catalogs). 

A study published in the November 2012 issue of the Journal of Dairy Science (pages 6665-6676) found that the benefits of feeding dairy cows a corn silage with high IVNDFD may continue long after the silage is replaced with a silage that has a lower IVNDFD.  In that study, prefresh cows (starting 3 weeks before calving) were fed diets with about 47% corn silage, 18% straw, 7% mixed silage, and 28% concentrate (DM basis). One group was fed a BMR corn silage and the other group was fed a conventional corn silage.  The 30-hour IVNDFD of the silages were 73.8 and 56.8% (this is a very large difference based on previous experiments which means responses may be less if the difference between the hybrids were more typical (approximately 7 to 10 percentage units)). After calving, cows were kept on the same hybrid treatments but diets changed to about 40% corn silage, 15% mixed silage, 1% straw, and 44% concentrate.  Those diets were fed until 3 weeks after calving.  At that time, all cows were fed a common diet based on conventional corn silage (no BMR).  Intake and milk production was measured until 15 weeks of lactation.

As expected, cows fed the highly digestible corn silage had greater intake during the prefresh period and first 3 weeks of calving (the period when cows were fed different corn silages).  Milk yields were about 7 lb/day greater for the first 3 weeks of lactation for cows fed the highly digestible silage.  The results for the next 12 weeks of lactation were intriguing.  Feed intake remained higher for cows that had previously been fed highly digestible corn silage until about the 6th week of lactation and then intakes were similar for the rest of the experiment.  In other words, the highly digestible corn silage had a 3 week carryover effect on intake.  Cows that were previously fed the highly digestible corn silage maintained high milk yields for the rest of the experiment; a 12 week carryover effect.

The reasons for the carryover effect cannot be determined from this experiment.  Cows fed highly digestible silage were in more positive calculated energy balance during the prefresh period than cows fed the conventional hybrid, which may have increased body energy stores that could have been used to support milk production (hybrid did not affect calculated energy balance after calving).  Another possible reason is that the higher intake postpartum allowed cows to have higher peak lactation, and the higher peaks were the reason for the long term responses.  Another thing that cannot be determined from this experiment was whether the highly digestible silage had to be fed during both the prefresh and post-fresh period to obtain the long term response.  Determining that will require another experiment. 

The bottom line to this research is that the milk yield benefits of feeding highly digestible corn silage to transition dairy cows may continue for at least 2 or 3 months after the silage is removed from the diet.