Deciding between hybrids containing high neutral detergent fiber (NDF) digestibility versus high starch digestibility can be difficult, and there has not been previous research directly comparing the two.  This study provides insight for better decision making on hybrid selection by dairy producers and their nutritionists.

Several factors, including nitrogen fertilization, maturity at harvest, kernel processing and ensiling period length influence the starch-protein matrix in corn kernels and hence, starch digestibility in corn silage. Additionally, selection for silage hybrids that contain more floury-type endosperm may allow for an increase in starch digestibility. Greater starch digestibility results in increased energy availability for dairy cows, and thereby greater milk production, feed efficiency, or both. Therefore, corn silage hybrids selection for enhanced starch digestibility may improve milk production per area of crop produced, and thereby profitability of dairy farms.

At the same time, improvements in NDF digestibility through varying harvest practices are possible, but inconsistent or minimal. However, selection of silage hybrids for high NDF digestibility, brown midrib (BMR) hybrids in particular, has improved lactation performance by dairy cows. Selection of silage hybrids with highly digestible NDF can reduce the effects of rumen fill in high-producing cows, thereby allowing for increased intake and milk production.

Comparisons between corn silage hybrids containing high NDF digestibility versus high starch digestibility fed to lactating dairy cows are not available in the research literature. This comparison may provide information for better decision making on hybrid selection by dairy producers and their nutritionists.

The objective of this study was to determine the effect of feeding a TMR containing a floury-leafy corn silage hybrid (LFY) compared with a brown midrib corn silage hybrid (BMR) for intake, lactation performance, and total-tract nutrient digestibility in dairy cows.

Floury-leafy (GLF97, Glenn Seed Ltd., Blenheim, ON, Canada) and BMR (F2F485, Mycogen Seeds, Dow AgroSciences LLC, Indianapolis, IN) corn hybrids were planted in separate field plots at the University of Wisconsin–Arlington Agricultural Research Station on the same day, and grown under the same tillage, fertilizer application, weed control practices, were harvested the same day, and stored under same conditions.

Both hybrids were of good quality and of similar particle size, processing score and fermentation profile. Nutrient composition was similar between hybrids except for the lower lignin and uNDF (6.9 vs. 9.4% on average) concentrations for BMR compared with LFY. During the digestibility feeding comparison, the straw added to the ration was removed from the LFY diet to keep lignin levels similar in both diets.

Starch digestibilities, in situ, in vitro, and in vivo, were greater for LFY compared with BMR; the opposite was observed for NDF digestibility. Cows fed BMR consumed 1.7 kg/d more dry matter than LFY. Although, actual-, energy-, and solids-corrected milk yields were greater for BMR than LFY, feed conversions (kg of milk or component-corrected milk per kg of DMI) did not differ. Fat-corrected milk and milk fat yield were similar, as milk fat content was greater for cows fed LFY (4.05%) than BMR (3.83%). Cows fed BMR had lower milk urea nitrogen concentration, but greater milk protein and lactose yields compared with LFY. Body weight change and condition score were unaffected by treatment.

Apparent total-tract starch digestibility was increased by 5 percentage units in high-producing dairy cows fed LFY compared with BMR in concurrence with greater ruminal in vitro and situ starch digestibilities for LFY. Although feed conversions were not different, DMI and milk and protein yields were decreased, however, for LFY compared with a BMR. Results in the present study imply that corn silage hybrid selection programs, which focus on increasing starch digestibility by dairy cows through selection of softer kernel texture, are feasible. Furthermore, these results denote the importance of NDF digestibility in silage hybrid selection programs. Further research is warranted to evaluate LFY compared with conventional hybrids to assess economic impacts of greater starch digestibility in corn silage.

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Authors: L.F. Ferraretto, A.C. Fonseca, C.J. Sniffen, A. Formigoni, R.D. Shaver, Department of Dairy Science, University of Wisconsin