Strategies to Increase Starch and NDF Digestibility in Whole-Plant Corn Silage and High-Moisture Cor

Corn is the predominant feed energy source in the dairy industry and can be fed as forage or concentrate. Thus, increasing starch and NDF digestibility of whole-plant corn silage (WPCS) and starch digestibility in high-moisture corn (HMC) may improve lactation performance by dairy cows. For this Thesis, eight studies were conducted: a meta-analysis, two feeding trials with lactating dairy cows, four mini-silo trials, and an analysis of commercial feed testing laboratory data.;A meta-analysis was performed to determine the effects of WPCS hybrid type on intake, digestibility, rumen fermentation, and lactation performance by dairy cows. Positive effects of hybrids of greater NDF digestibility on intake and milk yield were observed for lactating dairy cows, but the reduced total tract starch digestibility for these hybrids merits further study. Except for negative effects of high-oil hybrids on milk components, differences were minimal among corn silage hybrids differing in kernel type. Feeding genetically-modified WPCS did not affect lactation performance by dairy cows.;The first feeding trial was designed to determine the effect of feeding a total mixed ration (TMR) containing corn shredlage ( SHRD) or conventional-processed corn silage (KPCS) on lactation performance by dairy cows. Cows fed SHRD had greater total tract starch digestibility and tended to consume more DM and produce more fat- and energy-corrected milk than cows fed KPCS.;Our objective in the second feeding trial was to determine the effect of feeding a TMR containing a floury-leafy corn silage hybrid (LFY) compared to a brown midrib corn silage hybrid (BMR) for intake, lactation performance and total tract nutrient digestibility in dairy cows. Apparent total-tract starch digestibility was increased by 5 percentage units in high- producing dairy cows fed LFY compared to BMR in concurrence with greater ruminal in vitro and situ starch digestibilities for LFY. Although feed conversions were not different, dry matter intake and milk and protein yields were decreased, however, for LFY compared to a BMR.;The objective of the first mini-silo trial was to evaluate the effect of ensiling time and hybrid type on fermentation profile, N fractions and ruminal in vitro starch (ivSD; 7 h) and NDF (ivNDFD; 30 h) digestibility in WPCS. Fermentation profile, ammonia-N, soluble-CP and ivSD were influenced to a greater extent by ensiling time than by hybrid type. However, data reported in the present study suggest that N fraction response to time of fermentation varies with hybrid type which may be related to variation in starch digestibility.;A second mini-silo trial was performed to evaluate the effects of ensiling time and microbial inoculation on N fractions and starch digestibility of either well-processed corn shredlage or late-maturity corn silage. Ammonia-N concentration and starch digestibility were greater after 120 d of fermentation in both. Inoculation with lactate-producing bacteria, however, did not increase starch digestibility.;The third mini-silo trial evaluated the effects of ensiling time and exogenous protease addition on fermentation profile, N fractions and ivSD in WPCS of various hybrids, maturities and chop lengths. Extended time in storage increased ammonia-N, soluble CP and ivSD in WPCS of various hybrids, maturities and chop lengths. However, extended ensiling time did not alter the negative effects of kernel vitreousness and maturity at harvest on ivSD. Exogenous protease addition did not attenuate the negative effects of vitreousness on ivSD. In addition, despite the positive effects of exogenous protease addition on ivSD observed for late maturity WPCS, it did not overcome the negative effects of maturity on ivSD. An experiment using commercial laboratory data was performed to: 1) determine relationships between HMC DM, ammonia-N and soluble CP concentrations, pH, and ivSD, and 2) evaluate the effect of ensiling on pH, ammonia-N, soluble-CP and ivSD measurements in HMC. Ruminal in vitro starch digestibility was greater when HMC was harvested at lower DM content, ensiled for an extended period or was lower in pH. In addition, ammonia-N, soluble CP, pH and DM content were good indicators of in vitro starch digestibility for HMC.;The fourth mini-silo study evaluated the impact on fermentation profile, N fractions and ivSD of the following: 1) rehydration and ensiling of dry ground corn; 2) exogenous protease addition to rehydrated un-ensiled and ensiled corn; 3) exogenous protease addition or inoculation in rehydrated ensiled corn; and 4) exogenous protease addition or inoculation in HMC. Starch digestibility was increased by exogenous protease addition and ensiling. Microbial inoculation decreased pH and increased organic acid concentrations in rehydrated corn and HMC but did not affect ivSD. (Abstract shortened by UMI.).