Type of corn endosperm influences nutrient digestibility in lactating dairy cows

An experiment was conducted to evaluate the effect of type of corn endosperm on nutrient digestibility in lactating dairy cows. Near-isogenic variants of an Oh43 × W64A normal dent endosperm hybrid carrying floury-2 or opaque-2 alleles were grown in spatial isolation in field plots and harvested as dry shelled corn. Six ruminally cannulated, multiparous Holstein cows (67 ± 9 d in milk at trial initiation) were randomly assigned to a replicated 3 × 3 Latin square design with 14-d periods; the first 11 d of each period were for diet adaptation followed by 3 d of sampling and data collection. Treatment diets that contained dry rolled vitreous-, floury-, or opaque-endosperm corn [33% of dry matter (DM)], alfalfa silage (55% of DM) and protein-mineral-vitamin supplement (12% of DM) were fed as a total mixed ration. The percentage vitreous endosperm was zero for floury and opaque endosperm corns and 64 ± 7% for the vitreous corn. Prolamin protein content of floury and opaque endosperm corns was 30% of the content found in vitreous corn. Degree of starch access and in vitro ruminal starch digestibility measurements were 32 and 42% greater on average, respectively, for floury and opaque endosperm corns than for vitreous corn. Dry matter and starch disappearances after 8-h ruminal in situ incubations were, on average, 24 and 32 percentage units greater, respectively, for floury and opaque endosperm corns than for vitreous corn. Ruminal pH and acetate molar percentage were lower, propionate molar percentage was greater, and acetate:propionate ratio was lower for cows fed diets containing floury and opaque endosperm corns than for cows fed vitreous corn. In agreement with laboratory and in situ measurements, total-tract starch digestibility was 6.3 percentage units greater, on average, for cows fed diets containing floury and opaque endosperm corns than vitreous corn. Conversely, apparent total-tract neutral detergent fiber (NDF) digestibility was lower for cows fed diets containing floury and opaque endosperm corns compared with vitreous corn. The type of endosperm in corn fed to dairy cows can have a marked effect on digestion of starch and NDF. Feeding less vitreous corn increased starch digestion but decreased NDF digestion.     

Technical note: quantification of zeins from corn, high-moisture corn, and corn silage using a turbidimetric method: comparative efficiencies of isopropyl and tert-butyl alcohols

Zeins are corn endosperm storage proteins that encapsulate starch granules into a protein matrix, which can act as a barrier to starch accessibility and digestion. Laboratory methods to quantify zein are seldom used because they are considered arduous and time-consuming. A recently published rapid turbidimetric method (mTM) was reinvestigated by changing the solution originally used for the zein solubilization step. In particular, the aim was to explore whether, and to what extent, the use of tert-butyl alcohol (t-BuOH-mTM) in lieu of isopropyl alcohol (i-PrOH-mTM) was able to improve the quantification of zeins from dry corn, high-moisture corn, and corn silage samples. The nature of the alcohol influenced the zein extraction values, and t-BuOH-mTM gave higher zein values in corn (3.6 vs. 3.3 g/100 g of dry matter) and corn silage samples (1.2 vs. 0.9 g/100 g of dry matter) compared with i-PrOH-mTM. In contrast, similar zein extraction values were obtained for high-moisture corn (2.1 vs. 1.9 g/100 g of dry matter, respectively). Sodium dodecyl sulfate-PAGE analysis revealed no contamination by nonzein proteins with the use of tert-butyl alcohol. Overall, these findings indicated that tert-butyl alcohol has a greater ability to solubilize zein compared with isopropyl alcohol and thus the t-BuOH-mTM allowed greater extraction of zeins. Considering the growing interest of animal nutritionists in zein proteins, such results should provide useful information for routine laboratory analysis.     

Influence of the protein distribution of maize endosperm on ruminal starch degradability

This study was aimed at determining the influence of the protein distribution of maize endosperm on ruminal starch degradation using 14 maizes differing in endosperm texture (eight dent and six flint maizes). Ruminal starch degradability was determined by an in situ technique on ground samples with a particle size of 3 mm. The distribution of endosperm proteins was assayed by a method based on their differential solubilities in solvents. The (α,β,δ)‐zeins and the true glutelins were the predominant proteins in the endosperm. The (α,β,δ)‐zeins (66.1 and 70.1 g kg⁻¹ of recovered protein for dent and flint types respectively) and the true glutelins (21.8 and 18.4 g kg⁻¹ of recovered protein for dent and flint types respectively) were related to the vitreousness, ie the ratio of vitreous to floury endosperm. Ruminal starch degradability averaged 619 and 462 g kg⁻¹ for dent and flint maizes respectively. It was correlated negatively with the (α,β,δ)‐zeins and positively with the true glutelins. The (α,β,δ)‐zeins located in the protein bodies should limit the accessibility of starch granules to ruminal micro‐organisms and, as a consequence, the ruminal starch degradability. © 2000 Society of Chemical Industry     

Tortillas from Extruded Masa as Related to Corn Genotype and Milling Process

The effect of mill type (Knife and Hammer mill) and screen size (500 and 800μ) on properties of masa and tortillas from two types of corn (dent and floury endosperm) were evaluated. The traditional process was a control. Particle size and starch damage were highest for knife mill with screen opening 500μ. Tortillas from dent corn had better quality than those from floury corn. Cutting force, tensile strength, and rollability of tortillas from extruded masa from dent corn hammer milled with 800μ screen, and those made with floury corn knife milled with 500μ screen, compared favorably with traditional tortillas. Overall quality score correlated with starch damage, adhesiveness and peak viscosity.     

The effect of an exogenous protease on the fermentation and nutritive value of high-moisture corn

The objective of this study was to determine if treating high-moisture corn at harvest with an exogenous protease could accelerate the increase in in vitro ruminal starch degradation that is normally found with advancing times of ensiling. Ground high-moisture corn (HMC; 73% dry matter) was untreated or treated with an exogenous protease to achieve a final concentration of 2,000 mg of protease/kg of fresh corn. Corn was ensiled in laboratory-scale bags (approximately 500 g) that were evacuated of air, heat-sealed, and stored at 22 to 23°C for 70 and 140 d. Samples of freshly treated corn samples were collected to represent d 0 samples. Treatment of HMC with protease did not affect the gross populations of lactic acid bacteria or yeasts throughout the ensiling period. Treatment of HMC with protease resulted in higher concentrations of lactic acid and ethanol after 70 but not 140 d of ensiling. Concentrations of crude protein, water-soluble carbohydrates, and starch were unaffected by treatment with protease within each sampling day. After 70 or 140 d of ensiling, HMC that was treated with protease had higher concentrations of soluble protein (as a % of crude protein) and NH₃-N, and had lower concentrations of prolamin protein, compared with untreated corn. In vitro rumen degradability (7-h incubation) of starch was greater in protease-treated versus untreated corn at all sampling days but the difference was more pronounced after 70 and 140 d compared with d 0. Concentrations of soluble protein and NH₃-N were positively correlated with in vitro starch degradation. Conversely, the concentrations of prolamin protein in HMC were negatively correlated with in vitro starch degradation. Treating HMC with an exogenous protease could be a method to obtain greater potential for ruminal starch fermentation after a relatively short period of ensiling.     

Short communication: In vitro ruminal fermentability of a modified corn cultivar expressing a thermotolerant α-amylase

The fermentability of a corn cultivar that expresses a thermostable α-amylase (CA3272) was evaluated under various in vitro conditions. The CA3272 corn was developed as a replacement to microbial enzyme additions during the high-temperature processing of corn to produce ethanol. The α-amylase activity in the corn might have the potential for positive effects on ruminant performance if incorporated into the ration. Four corn cultivars were evaluated in an in vitro ruminal fermentation where the digestion of starch was measured after 6 h. The cultivars included a flint corn, an opaque corn, CA3272, and its near-isogenic counterpart (IC). The flint corn produced less total volatile fatty acids (18.4 mM) than the other 3 corns (average of 25.3 mM), supporting the fact that it had the highest concentration of prolamins, which are negatively associated with starch availability. A second 6-h in vitro ruminal fermentation evaluated mixtures of the CA3272 and IC corns (0, 25, 50, 75, and 100% concentrations of CA3272). Total volatile fatty acid production was not different among treatments for any proportions of CA3272. In a third in vitro experiment, there was a small but significant difference in starch degradation of CA3272 compared with IC (90.6 vs. 89.7%) but this difference is most likely not biologically relevant. In a fourth in vitro experiment, CA3272 and IC were incubated in water at 40 and 65°C for 24 h. Degradation of starch from native amylase activity at 40°C was 1.99 and 1.60% for CA3272 and IC, respectively, but when they were incubated at 65°C, starch degradation was 10.56 and 0.85% for CA3272 and IC, respectively. These data demonstrate that amylase activity in CA3272 is expressed at a high temperature (65°C) but at the physiological temperature expected in a rumen of a cow (39-40°C), expression of amylase activity does not appear to be sufficient to have any positive (or negative) effects on ruminal metabolism.     

Effects of corn grain endosperm type and conservation method on feed intake,feeding behavior,and productive performance of lactating dairy cows

Our objective was to evaluate the effects of corn grain varying in endosperm type and conserved as high-moisture or dry ground corn on dry matter intake (DMI), feeding behavior, ruminal fermentation, and yields of milk and milk components of cows in early to mid-lactation. Seven ruminally and duodenally cannulated Holstein cows (73 ± 39 d in milk; mean ± SD) were used in a duplicated 4 × 4 Latin square design with 21-d periods. A 2 × 2 factorial arrangement of treatments was used with main effects of corn grain endosperm type (floury or vitreous) conserved as high-moisture corn (HMC) or dry ground corn (DGC). Rations were formulated to contain 27.0% starch, 26.6% neutral detergent fiber (NDF), 19.1% forage NDF, and 16.5% crude protein. Corn grain treatments supplied 86.6% of dietary starch and contained alfalfa silage as the sole forage. Dry matter intake was increased 1.3 kg/d by DGC compared with HMC. The increase in DMI by DGC was related to a shorter intermeal interval (104.4 vs. 118.2 min/d), and meal size was not affected by treatment. Dry ground corn decreased rumination bout length and number of chews per bout compared with HMC. No differences were detected between endosperm treatments for DMI, yields of milk, 3.5% fat-corrected milk (FCM), milk fat, protein, lactose, or solids-not-fat (SNF). Mean yield of 3.5% FCM across treatments was 47.5 kg/d. However, a tendency for an interaction was observed for feed efficiency; floury endosperm increased efficiency 0.05 kg 3.5% FCM per kg of DMI for DGC but decreased it by 0.14 kg 3.5% FCM per kg of DMI for HMC relative to vitreous endosperm. Vitreous compared with floury corn tended to increase true protein concentration in milk when conserved as DGC (2.68% vs. 2.62%) but not as HMC. Concentration of SNF was increased by DGC compared with HMC (8.45 vs. 8.37%) due, in part, to the effect of treatment on milk protein concentration. Body weight was not affected by treatment, but vitreous endosperm tended to increase loss of body condition compared with floury endosperm. Corn endosperm type and conservation method had little effect on productive performance of high-producing cows.     

Effects of corn grain endosperm type and conservation method on site of digestion,ruminal digestion kinetics,and flow of nitrogen fractions to the duodenum in lactating dairy cows

Our objective was to evaluate the relative effects of endosperm type and conservation method of corn grain on ruminal kinetics, site of nutrient digestion, and flow of nitrogen fractions to the duodenum in lactating dairy cows. Seven ruminally and duodenally cannulated Holstein cows (73 ± 39 d in milk; mean ± SD) were used in a duplicated 4 × 4 Latin square design with 21-d periods. A 2 × 2 factorial arrangement of treatments was used, with main effects of corn grain endosperm type (floury or vitreous) and conserved as dry ground corn (DGC) or high-moisture corn (HMC). Rations were formulated to contain 27.0% starch, 26.6% neutral detergent fiber (NDF), 19.1% forage NDF, and 16.5% crude protein. Corn grain treatments supplied 86.6% of dietary starch, and alfalfa silage was the sole forage. True ruminal starch digestibility was increased by HMC compared with DGC (87.2 vs. 64.3%) and by floury compared with vitreous corn grain (83.7 vs. 67.7%). The increase for HMC compared with DGC was because of an increase in the degradation rate (33.8 vs. 23.1%/h) and a decrease in passage rate of starch (7.6 vs. 15.2%/h). The increase for floury compared with vitreous corn grain was because of an increase in the degradation rate (31.5 vs. 25.4%/h) and a decrease in rate of starch passage from the rumen (7.9 vs. 14.9%/h). Apparent total-tract starch digestibility was increased by HMC compared with DGC and by floury compared with vitreous corn, but the increase for floury corn was greater for the DGC treatment. Dry ground corn compared with HMC tended to increase nonammonia N flow to the duodenum (466 vs. 431 g/d) by increasing flow of nonammonia nonmicrobial N (211 vs. 111 g/d) despite a decrease in microbial N flow (255 vs. 320 g/d). Vitreous corn increased nonammonia nonmicrobial N flow to the duodenum (187 vs. 135 g/d) compared with floury corn, but microbial N flow to the duodenum was not affected by endosperm type. Efficiency of microbial N production was not affected by treatment. Endosperm type and conservation method of corn grain greatly affect digestion kinetics and ruminal digestibility of starch as well as flow of N fractions to the duodenum and should be considered during diet formulation for lactating cows.     

Effect of endosperm type on texture and in vitro starch digestibility of maize tortillas

Tortilla is the main staple of Mexico and it is made using diverse maize varieties, which have different endosperm types. Three maize varieties with vitreous, intermediate and floury endosperms were used. Texture and starch digestibility were evaluated in freshly prepared and stored tortillas for 24, 48 and 72 h. Tortilla made with maize of vitreous endosperm had the highest force to rupture and the lowest distance of elongation, indicating more rigid texture. Stored tortillas had lower available starch content and higher effect was shown by tortilla of vitreous endosperm, pattern that agrees with the higher increase in the resistant starch content with the storage time. Fresh tortilla of floury endosperm showed the highest hydrolysis rate during the first 15 min followed by tortillas of intermediate and vitreous endosperms. Starch hydrolysis values decreased when storage time increased, in agreement with the resistant starch content in the stored tortillas. At the longest storage time (72 h) tortilla of floury endosperm presented higher hydrolysis rate, followed by tortilla of intermediate and vitreous endosperms. The endosperm type plays an important role in the textural and starch digestibility of fresh and stored tortillas.     

Corn grain endosperm type and brown midrib 3 corn silage: site of digestion and ruminal digestion kinetics in lactating cows

Interactions of endosperm type of corn grain and the brown midrib 3 (bm3) mutation in corn silage on ruminal kinetics and site of nutrient digestion of lactating dairy cows were evaluated. Eight ruminally and duodenally cannulated cows (72 +/- 8 d in milk; mean +/- SD) were used in a duplicated 4 x 4 Latin square design experiment with a 2 x 2 factorial arrangement of treatments. Treatments were corn grain endosperm type (floury or vitreous) and corn silage type (bm3 or isogenic normal). Diets contained 26% neutral detergent fiber (NDF) and 30% starch. Interactions of treatments were not observed for any measure of digestibility, but digestion kinetics of starch and fiber did interact to affect digestible organic matter intake by affecting dry matter intake. Rate of ruminal starch digestion was faster and rate of ruminal starch passage tended to be slower in diets containing corn grain with floury vs. vitreous endosperm, resulting in a mean increase of 22 units for ruminal starch digestibility. Although compensatory postruminal starch digestion decreased differences among treatments for total tract starch digestibility, starch entering the duodenum was more digestible for grain with floury endosperm compared with vitreous grain, resulting in greater total tract starch digestibility for floury compared with vitreous corn grain. Fermentation rate of potentially digestible NDF was not affected by either bm3 corn silage or greater ruminal starch digestion of floury grain. Brown midrib corn silage increased total tract NDF digestibility vs. control silage by numerically increasing ruminal and postruminal digestibility of NDF. Endosperm type of corn grain greatly influences site of starch digestion and should be considered when formulating diets.     

Yeast culture supplementation prevented milk fat depression by a short-term dietary challenge with fermentable starch

Effects of yeast culture on responses to a fermentable starch challenge were evaluated in an experiment with a crossover arrangement of treatments for yeast culture supplementation with 28-d periods and a fermentable starch challenge on the last 2 d of each 28-d period as a split plot within period. Eight ruminally cannulated, midlactation, multiparous Holstein cows (96 ± 14 d in milk) were randomly assigned to treatment sequence. Treatments were yeast culture or control (mix of dry ground corn and soybean meal), top-dressed at 56 g per head per day throughout each period. Diets containing dry ground corn grain were fed from d 1 through 26 of each period. On the last 2 d of each period, the dry ground corn was replaced by finely ground high-moisture corn grain on an equivalent dry matter basis to abruptly increase ruminal fermentability of dietary starch. Response variables were averaged for d 25 and 26 for the dry corn treatment and for d 27 and 28 for the high-moisture corn treatment each period. The fermentable starch challenge decreased dry matter intake by 1.9 kg/d and tended to increase milk yield compared with the dry corn diet. However, effects of the fermentable starch challenge on yield of milk fat varied for the yeast culture and control diets; yield of milk fat decreased from 1.42 to 1.30 kg/d for the control treatment but increased from 1.40 to 1.47 kg/d for the yeast culture treatment. Milk fat concentration tended to decrease from 3.34 to 3.03% during the dietary challenge compared with the base diet for the control treatment but was not affected (mean = 3.32%) by the dietary challenge for the yeast culture treatment. An interaction of treatments was also detected for fat-corrected milk, which increased from 41.0 to 43.0 kg/d for the yeast culture treatment but decreased from 41.6 to 39.8 kg/d for the control diet with the fermentable starch challenge. Frequency of ruminating bouts was decreased by yeast culture compared with control (12.8 vs. 15.7 bouts/d) but not the fermentable starch challenge. No treatment interactions were observed for any measure of ruminal pH, total or individual volatile fatty acid concentration in ruminal fluid, acetate:propionate ratio, or individual fatty acid isomers in milk fat. Yeast culture supplementation may help prevent depression in milk fat during transition to a diet with highly fermentable starch, but the mechanism responsible remains to be elucidated.     

Properties and Uses of Horny and Floury Endosperms of Corn

Ordinary corn kernel endosperm is composed of horny and floury portions. Corn varieties having different endosperm were investigated. Their chemical composition was almost identical, but in tissue structure the floury endosperm is soft and the horny endosperm is hard. The starch isolated from floury endosperm is easier to gelatinize, and higher in viscosity, swelling value, and α-amylase digestibility than the starch from horny endosperm. The floury endosperm is superior to the horny endosperm in such baking products as bread and cookies.     

Influence of ensiling time and inoculation on alteration of the starch-protein matrix in high-moisture corn

The fates of hydrophobic zein proteins, which encapsulate corn starch to create vitreous endosperm, have not been investigated in high-moisture corn (HMC). To assess influences of ensiling time and inoculation on zein proteins in HMC, quadruplicate samples of 2 random corn hybrids (A and B), containing 25.7 and 29.3% moisture, were ground, inoculated with (I) or without 600,000 cfu/g of Lactobacillus buchneri 40788 (Lallemand Animal Nutrition, Milwaukee, WI), and ensiled for 0, 15, 30, 60, 120, and 240 d. Nutrient composition [crude protein (CP), starch, acid detergent fiber, and neutral detergent fiber], fermentation (pH, lactate, and acetate), and protein degradation markers (buffer-soluble CP, isopropanol-soluble CP, and NH₃-N) were evaluated. At 0 and 240 d, α, γ, δ, and β zein subunits were profiled using HPLC. Data were evaluated as a split-split plot using the PROC MIXED procedures of SAS. Ensiling time and inoculation decreased pH, and altered lactate and acetate contents of HMC. Lactate and acetate contents of A, AI, B, and BI at 240 d were 0.40, 0.32, 1.11, 0.73, and 0, 0.35, 0.30, and 0.87% of DM, respectively. Buffer-soluble CP in HMC increased from 1.5 to 2.0% of DM at 0 d to >4.0% of DM at 240 d. Inoculation had no effect on buffer-soluble CP but increased NH₃-N content of HMC. Corn A contained more isopropanol-soluble CP than did corn B and peak areas for 6 α, and all γ and δ zein regions were greater for corn A. Ensiling (0 vs. 240 d) decreased all zein subunits with the exception of 2 α and 1 δ subunit. Ensiling decreased (42.2-73.2%) γ zeins, which are primarily responsible for cross-linking in the starch-protein matrix. Despite altering lactate and acetate contents, inoculation had no effect on degrading hydrophobic zein proteins in HMC. Data suggest that hydrophobic zein proteins in the starch-protein matrix of HMC are degraded by proteolytic activity over an extended ensiling time.     

Depression in feed intake by a highly fermentable diet is related to plasma insulin concentration and insulin response to glucose infusion

The effects of dietary starch fermentability on feed intake and nutrient digestibility were evaluated in a crossover study, which was also designed to find factors that predict individual variation in feed intake response to starch fermentability. Thirty-two multiparous Holstein cows (121 ± 48 d in milk, 44 ± 7 kg/d of milk yield; mean ± SD) were randomly assigned to treatment sequence and were fed a diet intermediate to the treatments during a preliminary 28-d period. Treatments were dry ground corn grain and high-moisture corn harvested from the same field. Treatment periods were 14 d, with the final 4 d used for data and sample collection. Diets included corn silage and alfalfa haylage at a 2:1 ratio and were 26% neutral detergent fiber, 17% crude protein, 32% starch, and 3.5% fatty acids. High-moisture corn decreased dry matter intake (DMI) by 8%, but did not significantly alter digestible DMI. Individual DMI responses were highly variable, and variables from preliminary plasma analyses, propionate challenge tests, glucose tolerance tests, and hepatic mRNA analysis were assessed as potential predictors of DMI response to increased dietary starch fermentability. Of the covariates tested, only preliminary plasma insulin concentration and insulin response to glucose infusion were significant predictors of DMI response. High preliminary plasma insulin concentration was correlated with greater depression in DMI with increased fermentability; conversely, greater insulin secretion in response to glucose infusion was associated with minimal depression in DMI. These insulin variables were not significantly correlated. Consistent with past results, increased dietary starch fermentability decreased DMI. Significant correlations between insulin variables and individual DMI responses may warrant further investigation.     

Is flint corn naturally resistant to Sitophilus zeamais infestation?

Sitophilus zeamais (maize weevil) is one of the most destructive pests of maize stored in tropical and subtropical regions. This study determined the resistance of flint corn and dent corn to infestation by S. zeamais (Motschulsky), the maize weevil. Improved King Philip hybrid flint corn and Fontanelle 6T-510 hybrid dent corn were used in this experiment. Two temperature conditions (10 °C and 27 °C) and two storage times (15 days and 30 days) were used. Results showed that flint corn was more resistant to insect damage than dent corn at 27 °C and 30 day storage time. After 30 days storage time and 27 °C death rate was significantly higher in flint corn (R² = 0.945) compared to (R² = 0.634) in dent corn. Damaged seed was 10% higher in dent corn then in flint corn at 27 °C and 30 days. However, no significant difference was observed for seed weight loss between flint corn and dent corn at the same storage conditions. Both dent and flint corn were extensively cultivated in developing countries It appears that storage of flint corn may be one promising solution to reducing corn damage infestation problems in the tropics and in developing countries, but more research is needed.     

Diet fermentability influences lactational performance responses to corn distillers grains: a meta-analysis

Increasing supply of corn distillers grains (CDG) raises questions about the extent to which they can be used in diets of lactating dairy cows. A database of treatment means (n = 44) reported in 16 peer-reviewed journal articles published from 1985 to 2008 was developed. The database included response (within study) to a CDG diet compared with the control (no CDG) for milk yield (MY), milk fat concentration and yield, CDG content of the diet, and dietary composition of control and CDG diets (% of dietary dry matter). Additionally, corn grain fermentability was classified as high moisture (n = 7) or dry (n = 37). Data from studies with diets including more than one grain source (n = 8) had been eliminated from the analysis. Dietary concentrations of CDG ranged from 4.2 to 42% across studies. Dietary concentrations in diets containing CDG were 16.8 ± 1.91% (mean ± standard deviation) crude protein, 36 ± 15.5% corn silage, 23 ± 8.8% corn grain, and 28 ± 5.8% starch. Responses to CDG were 0.5 ± 2.10 kg/cow per day (mean ± standard deviation) for MY, 0.05 ± 0.178 percentage units for milk fat concentration, and 26 ± 77.6 g/cow per day for milk fat yield. Only MY response was related to increasing concentrations of CDG in diets and peaked at 1.2 kg/cow per day for 21% CDG. Diet fermentability was associated with responses. The greatest MY response to CDG was with 24% corn silage or 23% starch, and concentrations greater than 47% corn silage or 32% starch resulted in negative MY responses. Responses in MY differed by level of MY and were often more evident in higher- (>30.0 kg MY/d) than in lower-producing cows. Milk fat concentration response was not related to dietary CDG, but was correlated linearly with milk fat concentration of cows fed the control diet. Milk fat concentration greater than 3.6% for the control treatment was related to a negative milk fat concentration response to CDG, regardless of dietary concentration of CDG. Partially replacing high-moisture corn with CDG increased milk fat concentration by 0.16 percentage units compared with that from dry corn. When formulating diets with CDG, diet fermentability and level of MY (higher vs. lower) must be considered. Concentrations of corn silage and starch must be moderate to optimize lactational responses to CDG. Overall, lactational response to CDG in this database was dependent on diet fermentability and milk fat concentration in the control.     

Endosperm Structure and Physicochemical Properties of Starches from Normal,Waxy, and Super-Sweet Maize

Maize is a main botanical source used for extraction of starch in the world market. New maize cultivars with different amylose contents and special starch metabolism characteristics have been generated. Three types of maize cultivars, namely, normal maize, waxy maize (wxwx homozygous mutant), and super-sweet maize (sh2sh2 homozygous mutant), were investigated to determine differences in endosperm structures, morphologies, and physicochemical properties of starches. Maize kernels exhibited significantly different contents of total starch, soluble sugar, and amylose. Normal maize kernels contained the largest proportion of floury endosperm, followed by waxy maize and then super-sweet maize. Normal maize starch and waxy maize starch were larger in size than super-sweet maize starch. Normal maize starch and waxy maize starch were spherical and polygonal in floury and vitreous endosperms, respectively. Super-sweet maize starch was spherical both in floury and vitreous endosperms. Waxy maize starch showed the strongest birefringence patterns, the highest crystallinity and the largest proportion of ordered structure in external region of granules, and the largest proportion of double helix components, followed by normal maize starch and then super-sweet maize starch. Waxy maize starch showed the highest peak viscosity, trough viscosity, breakdown viscosity, gelatinization temperatures (i.e., gelatinization conclusion temperature, gelatinization onset temperature, gelatinization peak temperature, and gelatinization enthalpy). By contrast, super-sweet maize starch showed the lowest corresponding values for these parameters.     

An evaluation of exogenous enzymes with amylolytic activity for dairy cows

An experimental (7B) and a commercial (AMA) formulation of enzymes, both primarily with α-amylase activity, were evaluated for activity at various pH values, stability in ruminal fluid, the potential to improve in vitro ruminal fermentations, and the potential to improve production performance of lactating cows. When incubated (40°C) in buffer with a pH between 5.4 and 6.0, 7B had about 10 to 25 times greater amylase activity than AMA, and enzyme activity in this range increased by 100% for 7B, whereas activity decreased by about 26% for AMA. Both formulations maintained enzyme activity when they were incubated in in vitro ruminal fermentations for 24 h. After 6 h of ruminal in vitro fermentation, additions of 7B resulted in linear increases in apparent total volatile fatty acid production for flint and dent corn but had no effect on floury corn. In a lactation trial, 28 Holstein cows (68 ± 31 d in milk, 46.9 ± 9.1 kg of milk/d) were fed a total mixed ration (TMR) supplemented with nothing (CON), a low dose of 7B [7BL, 0.88 mL/kg of TMR dry matter (DM)], a high dose of 7B (7BH, 4.4 mL/kg of TMR DM), or AMA (0.4 g/kg of TMR DM). The experiment was conducted as a 4. 4 Latin square design with 21-d periods. Cows fed 7BL, 7BH, and AMA ate similar amounts of DM, and cows fed the latter 2 diets consumed more DM than did cows fed CON. Cows fed 7BL produced more milk than cows fed CON and 7BH, but produced similar amounts to cows fed AMA. The production of 3.5% fat-corrected milk was greater from cows fed 7BL and AMA compared with cows fed CON. The percentages of milk fat and milk protein were unaffected by treatment. Total-tract digestion of DM and organic matter were greater for cows fed 7BL compared with those fed CON. The addition of exogenous amylase enzymes to the diets of lactating dairy cows has the potential to improve animal productivity.     

A query for effective mean particle size in dry and high-moisture corns

The objective of this study was to investigate whether prediction of fermentation potential (FP) of dry and high-moisture (HM) corns could be improved by using a concept of effective (e) mean particle size (MPS). A set of FP standards was created by processing a single lot of Reid Yellow Dent (RYD) corn to achieve MPS of 3,778, 2,786, 2,282, 1,808, 1,410, 806, 586, 378, 308, 226, and 105 μm. In vitro gas production of RYD standards was measured, and peak absolute rate (PAR) of gas production (mL/0.2 g of DM/h) was used to establish a standard relationship between PAR and MPS. To identify factors other than MPS affecting FP, the MPS and nutrient composition of 36 diverse samples of dry (n = 18) and HM (n = 18) corns were determined. Composition included dry matter (DM), crude protein, soluble crude protein, neutral detergent fiber, starch, NH₃-N, prolamin protein, and fat. In vitro gas production of undried, unground dry and HM corns was measured, and PAR, time of peak absolute rate (h), maximum cumulative gas production (mL/0.2 g of DM), gas production fractional rate (h^?1), and lag (h) were determined. Nonlinear relationships between MPS, defined as the dependent variable, and PAR, as an independent variable, were used to identify FP deviations unexplained by MPS. When no variation in nutritional composition was present (RYD standards), the relationship between PAR and MPS was described by an exponential decay model [RYD_MPS = 9,006 × e^{(?0.452×PAR)}; R² = 0.96]. For diverse dry and HM corn populations, the variation in MPS explained by PAR was diminished (R² = 0.50). To investigate factors that diminish the relationship between MPS and PAR in diverse corns, relative residual (rr) MPS was determined [rrMPS = (MPS – RYD_MPS)/MPS], where RYD_MPS was predicted from the PAR of diverse dry and HM corn. The rrMPS was most highly related to prolamin protein [rrMPS_dry = 0.58 ? 0.15 × (prolamin protein, % of DM); R² = 0.43] and NH₃-N [rrMPS_HM = 0.21 + 0.08 × (NH₃-N, % of total N); R² = 0.46] for dry and HM corns, respectively. An eMPS was calculated as eMPS = MPS – MPS × rrMPS, where rrMPS was predicted from prolamin protein or NH₃-N concentration in dry and HM corn, respectively. The natural logarithm of eMPS accounted for 84% of the variability in PAR and 53% of the variability in the fractional rate of gas production. Calculating eMPS by adjusting the MPS of dry corn for prolamin and HM corn for NH₃-N concentration improved the assessment of industry corn FP.     

Effect of nylon bag and protozoa on in vitro corn starch disappearance

An in vitro experiment was carried out to study whether the presence of protozoa in nylon bags can explain the underestimation of the in situ degradation of slowly degradable starch. Corn of a high (flint) and a low (dent) vitreousness variety was ground over a 3-mm screen, weighed in nylon bags with a pore size of 37 μ m, and washed in cold water. Samples of washed cornstarch were incubated in 40-mL tubes with faunated and defaunated ruminal fluid. An additional amount of washed corn, in nylon bags, was inserted in each incubation tube. Incubations were carried out for 0, 2, 4, 6, 12, and 24 h, and starch residue in tube and nylon bag was determined. In general, starch disappearance from the nylon bag was less than from the tube, and was less with faunated than defaunated rumen fluid, but corn variety did not affect starch disappearance. When no protozoa were present, the disappearance of starch from the bags was higher after 6 and 12 h incubation compared with presence of protozoa. However, in the tubes, there was no difference in starch disappearance due to presence or absence of protozoa. Estimated lag time was higher in presence (4.6 h) then absence (3.6 h) of protozoa. It was concluded that the effect of presence or absence of protozoa on starch disappearance differs within or outside nylon bags. The reduced disappearance rate of starch inside the nylon bags in the presence of protozoa helps to explain the underestimation of starch degradation based on the in sacco procedure when compared with in vivo data upon incubation of slowly degradable starch sources.