A meta-analysis was performed to determine the influence of cereal grain type and corn grain harvesting and processing methods, dietary starch, rumen-digestible starch, and forage NDF concentrations on intake, digestion, and lactation performance by dairy cows using a data set comprising 414 treatment means from 102 peer-reviewed journal reports from 2000 to 2011. Categories for corn processing were dry ground, cracked or rolled corn (DRY), high-moisture shelled or ear corn (ENS), and steam-flaked or -rolled corn (STM); categories for kernel mean particle size were 500 to 1,000, 1,000 to 1,500, 1,500 to 2,000, 3,000 to 3,500, and 3,500 to 4,000 µm for dry corn and <2,000 and ≥2,000 µm for ensiled corn. Dietary starch and forage NDF concentrations were used as continuous variables. Data were analyzed using PROC MIXED in SAS (SAS Institute Inc., Cary, NC), with treatment as fixed and trial as random effects. Total-tract starch digestibility was reduced and milk fat content was greater for DRY compared with ENS or STM. Total-tract digestibility of dietary starch was reduced for both DRY and ENS as particle size increased. Increased dietary starch concentrations increased milk yield and protein content, but decreased ruminal and total-tract NDF digestibilities and milk fat content. Dry matter intake, total-tract starch digestibility, and milk protein concentration decreased as forage NDF in the diet increased. Total-tract starch digestibility was positively related to ruminal (percentage of starch intake) and postruminal (percentage of duodenal flow) starch digestibilities.

The objective of this study was to determine lactation performance responses of high-producing dairy cows to a reduced-starch diet compared with a normal-starch diet and to the addition of exogenous amylase to the reduced-starch diet. Thirty-six multiparous Holstein cows (51+/-22 DIM and 643+/-49kg of body weight at trial initiation) were randomly assigned to 1 of 3 treatments in a completely randomized design: a 3-wk covariate adjustment period during which the cows were fed the normal-starch diet, followed by a 12-wk treatment period during which the cows were fed their assigned treatment diets. The normal-starch TMR did not contain exogenous amylase (NS-). The reduced-starch diets, formulated by partially replacing corn grain with soy hulls, were fed without (RS-) and with (RS+) exogenous amylase added to the TMR. Starch and NDF concentrations averaged 27.1 and 30.6%, 21.8 and 36.6%, and 20.7 and 36.6% (dry matter basis) for the NS-, RS-, and RS+ diets, respectively. Dry matter intake for cows fed the RS- diet was 2.4 and 3.2kg/d greater than for cows fed the NS- and RS+ diets, respectively. Intake of NDF ranged from 1.19 to 1.52% of body weight among the treatments, with the RS- diet being 28% greater than the NS- diet and 13% greater than the RS+ diet. Milk yield averaged 50.4kg/d and was unaffected by treatment. Fat-corrected milk yield was 2.9kg/d greater for cows fed the RS- diet than for cows fed the NS- diet. Body weight and body condition score measurements were unaffected by treatment. Fat-, solids-, and energy-corrected milk feed conversions (kilograms/kilogram of DMI) were 12 to 13% greater for cows fed the RS+ diet than for cows fed the RS- diet. Dry matter and nutrient digestibilities were lowest for cows fed the NS- diet and greatest for cows fed the RS+ diet, and were greater for cows fed the RS+ diet than for cows fed the RS- diet, with the exception of starch digestibility, which was similar. Greater conversion of feed to milk for dairy cows fed reduced-starch diets that include exogenous amylase may offer potential for improving economic performance.

Over the last 25 years, whole-plant corn silage has become an important and popular feedstuff for dairy production. Copious research has been dedicated to the development and evaluation of alternatives to enhance the nutritive value of whole-plant corn silage. These efforts have been aimed at manipulating the physical and chemical characteristics of whole-plant corn silage in an effort to maximize dairy profitability. Results from this review indicate that optimization of harvest maturity, kernel processing, theoretical length of cut, and cutting height improve or maintain the nutritive value and milk production of lactating dairy cows. Technological advancements have been developed and made available to dairy producers and corn growers desiring to enhance fiber and starch digestibility of whole-plant corn silage. Future research should be directed toward further assessment of new processors available in the market and the development of assessment methods for optimization of crop processor settings, harvest efficiency, and nutritional modeling.

Dietary starch from feed grains represent the major energy-yielding sources in diets for large animals and starch effective digestion has a great impact on animal energy intake for meeting the substantial energy requirement to improve meat or milk productions. In general, site, extent and rate of starch digestion are affected by intrinsic and external factors that can be interrelated and are thus not easily defined. As a consequence, research to obtain a deeper knowledge on how starch chemical and structural compositions may affect starch digestion potential of feed grains and therefore their nutritional value has progressed recently. The objectives of this review are: (1) to give an overview on inherent starch primary structures and interactions with other compounds within feed grains; (2) to discuss factors affecting starch digestion potential in feed grains; (3) to explore starch digestion mechanism, and linkages with animal performances, both for swine and ruminants. The criticism of methods commonly used to estimate starch digestibility from feed grains for swine and ruminants are also discussed.

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