Corn Silage Research from Joint Meetings Reviewed
by Bill Mahanna
In this month’s column, I am going to summarize some of the excellent corn silage research presented at the joint meetings of the American Dairy Science Assn., American Society of Animal Science and Canadian Society of Animal Science that were held recently in Kansas City, Mo.
Research on five genetically different corn silage hybrids grown in 15 environmentally diverse locations in Michigan in 2013 showed that the growing environment had a highly significant (P < 0.01) effect on yield, starch content and 24-hour neutral detergent fiber (NDF) digestibility (Bolinger et al., 2014a).
Total accumulated growing degree days were related (P < 0.05) negatively to sugar but positively to starch content. Precipitation for the entire growing season ranged from 14.0 to 25.5 in. and was negatively related (P < 0.02) to crude protein (likely due to nitrogen leaching) and NDF digestibility. Locations that received fewer than 16 in. of precipitation had lower (P < 0.05) yields but greater (P < 0.05) NDF digestibility (48.3% versus 45.8% of NDF).
Attendee conversations about this poster centered around the potential for poor fiber digestibility in the 2014 corn silage crop in areas where the plants have grown extremely tall due to excess moisture during the vegetative growth stages.
The effect of drought and heat stress on eight corn hybrids grown in two locations in 2011 and 2012 was presented by Virginia Tech researchers (Ferreira et al., 2014). Whole-plant dry matter yields did not differ between hybrids but varied significantly across site-years.
In 2012, one location had maximum daily temperatures above 95°F for an extended period immediately following silking, whereas the second location experienced maximum daily temperatures in the low 80°F range.
The researchers concluded that heat stress had a major adverse effect on kernel development, resulting in higher NDF levels in hybrids grown in the heat-stressed location (56.5% versus 43.0% NDF) despite both locations experiencing similar drought conditions of only 9-10 in. of growing season precipitation.
The same Michigan study (Bolinger et al., 2014a) reinforced the recommendation of many seed companies to harvest healthy corn plants at slightly higher dry matter maturities to capture more starch without significantly sacrificing NDF digestibility.
Harvest dry matter in this study had a quadratic effect on dry matter yield, milk production per acre and starch content, with each parameter peaking at 41% dry matter. The researchers concluded that the relative nutritional value of a hybrid can be biased in evaluation programs if hybrids differ in dry matter content when harvested on the same date.
It should be pointed out that this study did not follow hybrids through the ensiling and fermentation process, and if higher-dry matter silage is to be successful in practical feeding situations, strict attention must be paid to compaction density and kernel processing.
Nine genetically different hybrids were evaluated by Brown et al. (2014) at Illinois State University for the effect of yield and nutritive value. As plant dry matter increased, the yield of starch and dry matter increased, with only a slight decline of 0.09% in NDF digestibility for each 1% increase in plant dry matter. The rankings of the nine hybrids for milk per ton changed markedly, especially when plant dry matter was less than 34%.
Similar to the findings of the Michigan study, these researchers cautioned that to prevent ranking bias, hybrids in silage test plots should be harvested at multiple moisture contents.
Harvesting all silage plot entries at a single time point has also been a concern in the evaluation of dent versus flint hybrids in European registration schemes because dent hybrids typically flower later and, thus, show lower starch content when all entries are harvested on the same early date.
Researchers from Virginia Tech (Klingensmith et al., 2014) employed in situ methods to investigate how storage time of two corn hybrids bred for varying amounts of floury and vitreous starch affected their soluble starch, starch degradation rates, slowly digestible starch and resistant starch.
While differences for these measurements existed in fresh silage at harvest, there were no differences for any starch digestibility parameter between the two endosperm hybrids when measured after 54 days of storage.
Although there were no differences between hybrids of differing endosperm types, it does not change the fact that starch digestibility in corn silage does change over time in fermented storage.
Researchers from the Netherlands (Doorenbos and van Laar, 2014) presented in situ data on the effect of ensiling time and harvest dry matter on the effective rumen degradability of starch.
Doorenbos and van Laar found that starch degradability increased from 70.8% at harvest and stabilized at 86.3% at eight months of ensiled storage. Higher-dry matter silages (40% dry matter) showed lower initial harvest starch degradability (61.3%), which also increased over time to stabilize at 78% at eight months of storage.
Their conclusion was that the starch ruminal degradability of corn silage is significantly affected by the combined effects of ensiling time and whole-plant dry matter at harvest.
A study reported by Ferraretto et al. (2014a) supported the fact that ruminal in vitro starch increased over time in fermented storage among four leafy and four brown mid-rib (BMR) hybrids and that ammonia-nitrogen and soluble protein were both good proxy indicators of in vitro starch digestibility.
An interesting study from Brazilian researchers (Arcari et al., 2014) involved the harvest of fully mature (post-black layer), medium-vitreous (67%) corn grain that was then ground to 2 mm, rehydrated to 67% dry matter and ensiled for 330 days. The effective dry matter degradability of this rehydrated, ensiled grain — adjusted for a rumen passage rate of 8% per hour — increased (P < 0.001) from 57.6% to 84.9% after 330 days of ensiled storage.
Bolinger et al. (2014b) investigated whether increasing kernel vitreousness and prolamin content — known to reduce in vivo digestion in fully mature kernels — also occurred in kernels harvested at corn silage maturity (pre-black layer). Across five hybrids harvested at 15 different locations, prolamin content was not closely related to seven-hour in vitro starch availability (r = -0.06, P = 0.63).
The range in starch digestibility among the hybrids tested was less than half the range among growing locations (2.9 versus 6.3 percentage points), causing the researchers to question the accuracy of predicting starch availability from hybrid genetics alone. It appears that the best way to evaluate starch availability due to genetics, harvest maturity and growing environment is to conduct an in vitro analysis prior to feeding new-crop corn silage and then adjust ruminal availability accordingly over time in fermented storage.
It should be kept in mind that these studies are reporting only ruminal starch disappearance, which can certainly affect the tendency for subclinical ruminal acidosis in dairy cows. However, they do not account for the subsequent intestinal digestion and that perhaps the best way to evaluate total tract starch disappearance, due to kernel maturity, ensiling time and particle size differences, is monitoring fecal starch levels.
Two research groups reported on the performance of cows fed a leafy-floury endosperm (LF) hybrid versus a BMR hybrid and found similar results. Morrison et al. (2014) from the Miner Institute reported that the BMR-fed cows had higher intake and yield of solids-corrected milk (P < 0.001). Starch digestibility was similar for the LF and BMR diets, although chewing time and rumination were greater for the LF hybrid.
Wisconsin researchers (Ferraretto et al., 2014b) did find greater in vivo starch digestibility (P < 0.05) with the LF hybrid. However, similar to the Miner Institute trial, dry matter intake (P < 0.01) and yield of solids-corrected milk (P < 0.10) were greater for the cows fed the BMR silage.
Chop Length, Processing
Wisconsin researchers (Ferraretto et al., 2014c) presented data on a study designed to compare milk production and rumination in diets containing BMR corn silage harvested as either typical silage (19 mm chop length processed using a conventional roller mill with a 2 mm gap and 40% differential) or Shredlage silage (26 mm chop length processed using a shredlage roller mill with a 2 mm gap and 32% differential).
The forage component of the lactation diets consisted of 45% corn silage (KP), 35% corn silage and 10% chopped alfalfa hay (KPH) or 45% shredlage corn silage (SHRD).
There was greater and less-variable kernel processing with SHRD compared to KP. There was a treatment-by-week interaction for milk yield, but the SHRD treatment averaged 3.3 lb. more milk during weeks 3, 7, 8, 9, 12 and 14 of the lactation study. Surprisingly, there was similar rumination activity among treatments, although the researchers did cite some problems with the rumination monitors.
The improved milk response in this BMR study supports the trend for more milk production that was also observed in non-BMR hybrids fed as shredlage in a 2012 Wisconsin study (Ferraretto and Shaver, 2012).
The Bottom Line
Corn silage genetics greatly influence total dry matter yield and starch content. However, the growing environment can trump genetics, particularly concerning fiber digestibility.
Nutritionists and producers have become accustomed to utilizing analytical methods to assess fiber digestibility in new-crop corn silage. Research has clearly shown that tremendous variation also exists in starch digestibility, but unlike NDF digestibility, it continues to increase for the first six to eight months of storage.
For corn silage to provide optimum starch levels and digestibility, attention should focus on harvest maturity and methods to improve and monitor kernel processing as harvest progresses.
Laboratory methods are now readily available to target the starting point for new-crop ruminal starch disappearance, along with inexpensive proxy measurements such as soluble crude protein to detect how it is changing over time in storage.
Ferraretto, L.F., and R.D. Shaver. 2012. Results of UW-Madison corn shredlage feeding trial. Proceedings of the Four-State Dairy Nutrition & Management Conference. Dubuque, Iowa. June 13-14.
The following abstracts were presented at the 2014 joint annual meeting of the American Dairy Science Assn., American Society of Animal Science and Canadian Society of Animal Science:
Arcari, M., C. Martins, J. Goncalves, D. Sousa, T. Tomazi, L. Silva and M. Santos. 2014. Effect of rehydration and silage storage period Reprint Feedstuffs, August 11, 2014 3 of corn with medium vitreous endosperm on chemical composition and dry matter in situ degradability. Abstract 1699.
Bolinger, D., L. Nuzback and F.N. Owens. 2014a. Impact of hybrid and growing location on yield and composition of corn plants harvested for silage. Abstract 1075.
Bolinger, D., L. Nuzback and F.N. Owens. 2014b. Relationship of in vitro starch digestion to corn kernel measurement from farms in Michigan. Abstract 1696.
Brown, L., L. Nuzback, B. Redenius, P. Walker and F.N. Owens. 2014. Impact of corn plant maturation and planting density on nutrient composition and potential milk yield. Abstract 1076.
Doorenbos, J., and H. van Laar. 2014. Ruminal starch degradation of maize silage affected by ensiling time and dry matter content. Abstract 1695.
Ferraretto, L.F., A. Fonseca, C. Sniffen, A. Formigoni and R.D. Shaver. 2014b. Effect of corn silage hybrids differing in starch and NDF digestibility on lactation performance and total tract nutrient digestibility by dairy cows. Abstract 304.
Ferraretto, L.F., R.D. Shaver, S. Massie, R. Singo, D. Taysom and J. Brouillette. 2014a. Effect of ensiling time on fermentation profile and starch digestibility in whole plant corn silage from two different hybrid types. Abstract 1087.
Ferraretto, L.F., L. Vanderwerfd and R.D. Shaver. 2014c. Case study: Fermentation profile, physical form and starch digestibility of whole-plant silage harvested with novel processing. Abstract 1039.
Ferreira, G., H. Behl, E. Hokanson, W. Thomason and C. Teutsch. 2014. The interaction of drought stress and heat stress as determinant of dry matter yield and nutritional composition of corn whole-plant for silage. Abstract 305.
Klingensmith, E., L. Harthan and M. Hangan. 2014. The effect of starch digestibility of two corn silage varieties on lactation performance in dairy cows. Abstract 607.
Morrison, S.Y., K. Cotanch, C. Ballard, H. Dann, E. Young, R. Grant and C. Key. 2014. Lactational response of Holstein cows to brown midrib or leafy-floury corn silage. Abstract 1070.
Originally published in the August 2014 Feedstuffs issue. Reproduced with permission.