Ruminal Starch Digestion Research Articles

Effect of expander processing on fractional rate of maize and barley starch degradation in the rumen of dairy cows estimated using rumen evacuation and in situ techniques

Effects of heat treatment (expanding) on ruminal and intestinal digestibility of starch in barley and maize grains were studied in an extended 4×4 Latin square experiment. Four lactating Danish Holstein Friesian cows fitted with ruminal, duodenal and ileal cannulae were offered grass-clover silage and grass-clover hay based diets supplemented with soybean meal and either untreated barley, expanded barley (105 °C), untreated maize or expanded maize (95 °C). Ruminal degradation characteristics of starch for untreated and expanded grains were determined in situ using nylon bags with two pore sizes (15 or 36 μm). Rate of starch degradation in the rumen was also determined based on series of total rumen evacuations. In vivo digestibility was estimated by sampling duodenal and ileal contents and faeces. Ruminal degradation of starch determined in situ was higher for barley than maize regardless of heat treatment. In situ studies (36 μm) showed expanding increased effective maize starch degradability in the rumen from 0.60 to 0.72, mainly due to an increased soluble fraction. Effective barley starch degradability, however, was unchanged at 0.96 as an increase in the soluble fraction was counterbalanced by a decrease in rate of degradation from 0.63 to 0.36 h −1 with 36 μm nylon bags. In vivo degradation characteristics based on rumen evacuations showed that heat treatment increased fractional rate of degradation of starch for both barley and maize, resulting in a slight increase in the effective degradability of barley starch from 0.81 to 0.85 and an increase in rumen effective degradability of maize starch from 0.71 to 0.78, when rumen starch pools were corrected for rumen starch outflow. In situ studies seemed to overestimate ruminal degradation of rapidly fermentable starch in barley, and underestimate degradation of slowly fermentable starch in maize, although in situ results were highly dependant on assumptions made on digestion and passage of the soluble fraction. Total tract digestibility of barley starch was not affected by heat treatment (0.99), whereas total digestibility of starch in maize increased from 0.84 to 0.96. Apparent rumen digestibility of starch was higher for barley than maize. Duodenal flow of starch in barley was highest 4 h post feeding, whereas a much larger peak was found for maize at 10–12 h post feeding, which indicates a passage time lag for undegraded maize starch in the rumen, or possibly the abomasum. Fractional rate of passage of starch from the rumen was not constant, indicating that passage of starch does not follow first order kinetics.

THE EFFECT OF NITROGEN FERTILIZATION OF MAIZE ON PROTEIN CONCENTRATION AND IN VITRO FEMENTABILITY OF GRAIN

The effect of nitrogen fertilization of maize on fermentability of maize grain in the rumen was studied by means of in vitro method based on the measurement of gas produced during the incubation of samples with rumen liquor. Gas production was recorded continuously up to 72 h incubation time and cumulative gas production was described by the Gompertz equation Y=A*exp(-exp(-d*(t-tm))). Seven treatments, one of them unfertilized and others fertilized with 100 to 250 kg N ha–1, were compared. Grain yield and concentration of crude protein (CP) in grain increased linearly with nitrogen fertilization. Grain yield increased for 25 kg dry matter (DM) ha–1 and CP concentration for 0.13 g kg–1 DM per each additional kg of N. Concentration of CP in grain, which varied from 83 to 115 g kg–1 DM, was closely related to the dynamics of gas production. The maximal gas production rate (MPR) was negatively related to CP concentration in the grain (R2 = 0.53; p < 0.10) and the time of MPR (tm) was positively related to the amount of added N (R2 = 0.74; p < 0.05) and concentration of CP in the grain (R2 = 0.88; p < 0.01). It is likely that intensive N fertilization of maize limits ruminal digestion of maize starch. Due to the shift of starch digestion from the rumen to lower gastrointestinal tract better utilization of energy can be expected in maize grain of extensively fertilized maize than in the grain of maize, in which supply of N is sub-optimal.

Evaluation of a Forage-Fat Blend as an Isocaloric Substitute for Steam-Flaked Wheat in Finishing Diets for Feedlot Cattle: Growth Performance and Digestive Function

Two trials were conducted to evaluate the addition of a forage-fat blend (FFB) as a substitute for grain in finishing diets for feedlot cattle. Treatments consisted of a steam-flaked wheat-based finishing diet containing 15, 29, or 45% FFB. The FFB contained 80% chopped alfalfa hay and 20% yellow grease and was formulated to have NEm and NEg values similar to that of wheat. In Trial 1, 126 crossbred steers (225 ± 5.4 kg) were used to evaluate treatment effects on growth performance and dietary NE. In Trial 2, three Holstein steers (448 ± 21 kg) with cannulas in the rumen and proximal duodenum were used to evaluate treatment effects on characteristics of digestion. Increasing the FFB did not affect (P>0.10) ADG, but decreased gain efficiency (linear effect, P<0.05) and dietary NE concentration (linear effect, P<0.01). Increasing the FFB did not affect (P>0.10) ruminal digestion of starch, N, or microbial N (MN) efficiency, but decreased (linear effect, P<0.10) ruminal digestion of OM and increased (linear effect, P<0.10) ruminal digestion of ADF. Increasing the FFB did not affect (P>0.10) postruminal digestion of OM, starch, and N, but decreased postruminal digestion of fatty acids (linear effect, P<0.05). Increasing the FFB did not affect (P>0.10) percentage of total tract starch, N, and ADF digestion, but decreased the percentage of total tract digestion of OM (linear effect, P<0.01) and DE (linear effect, P<0.05). We conclude that an isocaloric FFB can replace grain at levels of up to 45% of dietary DM without affecting ADG in feedlot cattle. However, when dietary inclusion rates are > 15%, dietary NE and, hence, BW gain efficiency may decrease. The magnitude of the effect of FFB inclusion rate on energy recovery is a predictable function of the relationship between fatty acid intake and intestinal fatty acid digestion.

Effect of Roughage Source on Ruminal Kinetics and Passage of Individual Feed Components in Finishing Diets for Steers

Bárcena-Gama, R., Swingle, R.S., Moore, J.A. and Poore, M.H. 2002. Effect of roughage source on ruminal kinetics and passage of individual feed components in finishing diets for steers. J. Appl. Anim. Res., 21: 109–121. Two 4 x 4 Latin square experiments were conducted to determine the effect of substituting chopped alfalfa hay (AH) in a diet containing 10% AH (DM basis) for chopped wheat straw (WS), chopped bermudagrass straw (BS) or cottonseed hulls (CSH), on diet utilization and kinetics of ruminal digestion and passage of roughage and grain. In experiment 1, total tract digestion coefficients for dry matter (DM), neutral detergent fiber (NDF) and starch were determined. Particulate passage rates for grain and roughages in each diet (rare earth metals) and liquid dilution rate (Co-EDTA) were also measured. In experiment 2, four mature ruminally cannulated steers were used to determine kinetics of in situ ruminal digestion of DM, NDF and starch for milo and roughage components of the diets. Replacing AH by low quality roughages depressed (P>0.05) total tract digestion of DM and NDF but not for starch. Potential extent of digestion (72 h in situ) of DM for milo was lower (P>0.05) in the CSH diet. The extent of digestion for DM and NDF were higher (P>0.05) for AH than for the lower quality roughages. Diets containing WS or BS promoted a higher (P>0.05) raft formation than AH or CSH diets. The AERD for DM and NDF from milo was not affected (P>0.05) by roughage source and ruminal pH did not differ (P>0.05) among diets. These results suggest that substitution of AH for low quality roughages depresses total tract digestibility and that the effect on kinetics of ruminal digestion and passage for the grain fraction was minimal. However, the data also suggest that inclusion of WS in 90% concentrate diets may function to improve rumen conditions for NDF digestion and to reduce the incidence of metabolic acidosis.

Milk production and ruminal digestion in lactating dairy cows grazing temperate pastures and supplemented with dry cracked corn or high moisture corn

We studied the effects of dry cracked corn (DC) replacement by high moisture corn (HMC) as energy supplement on ruminal digestion of dry matter (DM) components, food intake, milk production and composition, and live weight change (LWC) in lactating dairy cows grazing pastures. Treatments were: T1, 9.0 kg of HMC (74% DM) and T2, 6.8 kg of DC (85.9% DM). Cows grazed winter oats and ryegrass pasture (in vitro DM digestibility: 81.0% and crude protein: 21.3%). Six Holstein lactating cows were surgically fitted with permanent ruminal cannula and grouped in a crossover design to study ruminal digestion. Milk production and composition were assessed in 22 Holstein cows alloted to T1 ( n=12) and T2 ( n=10) in a completely randomized design corrected by covariate, using milk production and composition registered for 15 days prior to starting the experiment. Eight cows per treatment were used to estimate the total intake. Total dry matter intake and forage intake were not different between treatments ( P≥0.10). Ammonia N concentration was significantly lower ( P≤0.01) in T1 (12.87 mg dl −1) than in T2 (19.09 mg dl −1); however, ruminal pH and total volatile fatty acids were not different ( P≥0.10). The soluble fraction of starch was higher ( P≤0.01) for HMC (T1: 42.53%; T2: 1.29%), and the fractional rate of starch digestion in the rumen was also higher ( P≤0.01) for HMC (T1: 9.93% h −1; T2: 6.15% h −1). The ruminal digestion of neutral detergent fiber was not significantly different between treatments ( P≥0.10). Starch in feces tended ( P≤0.10) to be higher in T2 (514.9 g per day) than in T1 (410.0 g per day), in agreement with higher ( P≤0.05) starch digestibility in the total tract of high moisture corn (T1: 90.26%; T2: 86.87). Milk production and composition was not different ( P≥0.10) between treatments, although T1 tended ( P≤0.10) to have a higher protein percentage (T1: 3.39%; T2: 3.30%). No significant differences in LWCs ( P≥0.10) were found. Higher ruminal starch digestion of HMC could explain the lower ruminal ammonia concentration observed in T1. Except for the tendency to produce milk with a higher protein concentration, differences in rumen environment did not affect milk production and composition.

Effects of expander-treating a barley-based concentrate on ruminal fermentation, bacterial N synthesis, escape of dietary N, and performance of dairy cows

Three primiparous dairy cows in early lactation with cannulas in rumen, duodenum and ileum were used in a 3×3 Latin square design to study effects of expander treatment of a barley-based concentrate. The concentrate was either pelleted at 75–80°C or expander treated at 125–130°C prior to pelleting. The diets consisted of 6.7 kg DM of grass silage and 10 kg DM of (1) 100% pelleted, (2) 50% pelleted and 50% expanded or (3) 100% expanded concentrate. The diets were offered as a mixed ration in four equal meals daily. Ruminal fermentation, bacterial N synthesis, duodenal, ileal and faecal flow of nutrients, and animal performance were monitored. Expander treatment numerically increased ruminal digestion of starch, which explained the observed increase in ruminal VFA concentration and the lowered ruminal pH ( P<0.05). The proportion of butyrate in rumen liquid increased, whereas the proportion of propionate decreased in the expanded compared to the pelleted treatment ( P<0.05). Expander treatment tended to increase rumen volume and rumen NDF pool size. Ruminal digestion of NDF was numerically lower in the expanded than in the pelleted treatment. No differences in bacterial N synthesis or efficiency of synthesis were observed among treatments. Expander treatment numerically increased the duodenal flow of non-ammonia N (NAN) and amino acid N (AAN), and seemed to increase the flow of non-ammonia non-bacterial N (NANBN) to the duodenum to a similar extent as was indicated by nylon bag studies. Milk production and milk fat and protein content were increased by the expander treatment ( P<0.05), indicating that expander treatment increased the supply of nutrients for milk production.

Glucose uptake and regulation by intestinal tissues: Implications and whole-body energetics

The purpose of this review is to examine mechanisms of glucose absorption by the ruminant small intestine and to relate these processes to avail- able information on the theoretical advantages of shift- ing site of starch digestion in ruminants. The primary mechanism for glucose absorption across the brush- border membrane of enterocytes is the Na + -dependent glucose transporter, SGLT1. This transport protein is a high-affinity, concentrative, glucose transporter that couples glucose transport to an inwardly directed Na + gradient. This Na + gradient is maintained by the activ- ity of Na + /K + -ATPase in the basolateral membrane. The activity of SGLT1 is highest in the developing ruminant and declines after weaning. Glucose transporter activ- ity can be increased by intraluminal glucose; however, glucose absorption or metabolism is not necessary to induce transporter activity. Changes in SGLT1 activity are proportional to SGLT1 protein content. In contrast, SGLT1 mRNA levels are poorly correlated with SGLT1 activity, suggesting post-transcriptional regulation.

Effect of the substitution of urea for soybean meal on digestion in steers

Four growing Holstein steers (305 ± 33 kg body weight) with ruminal and duodenal cannulae were used in a 4 × 4 Latin square experiment to assess the effect of level of dietary urea (0, 7.3, 14.7 and 22.0 g kg−1 of dry matter) on the site and extent of digestion of some feed components. The diets were isonitrogenous and consisted of 60% ryegrass hay and 40% concentrate and were offered to the animals three times daily in amounts limited to 24 g of dry matter kg−1 liveweight in order to avoid feed refusals. The addition of urea caused a linear increase in ruminal pH and in ruminal ammonia concentration during the first hours after feed ingestion (P &lt; 0.01), and linearly increased ruminal digestibility of cellulose (P &lt; 0.01) and apparent nitrogen (P &lt; 0.05). However, it had no significant effect on apparent total digestibility of feed components, nor did it affect ruminal digestibility of dry matter, organic matter or starch. Flow of microbial nitrogen to the small intestine decreased linearly (P &lt; 0.05), but the efficiency of microbial protein synthesis or the proportion of undegraded feed nitrogen in the rumen that flowed to the small intestine was not significantly affected (P &gt; 0.05). The increase in ruminal ammonia concentration above that necessary for optimal microbial growth increased ruminal nitrogen losses into the blood. However, excess ruminal ammonia concentration also increased ruminal fibre digestion. Key words: Non-protein nitrogen, microbial protein synthesis, ruminants, digestion

Influence of ruminal biohydrogenation on the feeding value of fat in finishing diets for feedlot cattle.

Four Holstein steers (212 kg) with cannulas in the rumen and proximal duodenum were used in a 4 x 4 Latin square experiment to study the influence of degree of ruminal biohydrogenation (BH) on the feeding value of supplemental fat. Treatments consisted of an 88% concentrate finishing diet supplemented with 1) 2% yellow grease (control); 2) 4% formaldehyde-protected fat (Rumentek), 2% yellow grease (LBH); 3) 2% Rumentek, 4% yellow grease (MBH); or 4) 6% yellow grease (HBH). Ruminal BH of HBH, MBH, and LBH diets was 74, 68, and 54%, respectively. High-fat supplementation decreased (7%, P < .05) intestinal digestibility of 18:0 but increased intestinal digestibility of 18:1 (3%, P < .10), 18:2 (14%, P < .01), and 18:3 (23%, P < .05). Increases in intestinal digestibility of 18:0 (quadratic effect, P < .05), 18:1 (linear effect, P < .01), 18:2 (linear effect, P < .01), 18:3 (linear effect, P < .05), and total fatty acids (linear effect, P < .05) were inversely related to BH. For every 1% increase in the proportion of 18:1 fat entering the small intestine, the digestibility of 18:0 increased 1%. High-fat supplementation depressed ruminal digestion of OM (11%, P < .05), NDF (16%, P < .05), starch (6%, P < .05), and feed N (12%, P < .01). Formaldehyde-protein protection of fat diminished its depressing effects on ruminal digestion of NDF (quadratic effect, P < .10) and enhanced ruminal escape of feed N (linear effect, P < .10). Postruminal digestion of OM was greater (4.6%, P < .10) for high-fat diets. High-fat diets decreased (P < .05) total tract digestion of OM (1.9%), NDF (7.4%), and starch (.5%). Postruminal and total tract digestibility of OM, NDF, N, and starch was not affected (P > .10) by BH. In a 125-d finishing trial, 100 yearling steers (362 kg) were used to evaluate treatment effects on growth performance. High-fat diets did not affect (P > .10) ADG but increased (P < .10) feed efficiency (9%, P < .10), dietary NEm (7.6%, P < .05), and dressing percentage (9%, P < .05). The magnitude of the increase in dressing percentage was inversely related (linear effect, P < .10) to BH. We conclude that decreasing ruminal BH will increase postruminal digestibility of fat, and hence the NE value of dietary fat. The synergistic effect of increasing the proportion of 18:1 on intestinal digestion of fat enables higher levels of fat supplementation. Protecting fat from BH minimizes the detrimental effects of supplemental fat on fiber digestion.

Modelos matemáticos para evaluar la tasa de digestión in vitro del almidón

Mendoza MGD, Ortega CME, Ricalde VR, Martinez GJA. Tec Pecu Mex 2000;38(1)51-65. The objective was to compare mathematical models to describe ruminal starch digestion. Information of ruminal starch degradation in vitro from sorghum, corn, high moisture corn and wheat were analyzed. The first order kinetic model (FOM), with lag time (FOM-L), with indigestible fraction (FOM-I), two compartmental models, and the saturation kinetics model (SKM) were compared by analyses of residual sum squares and the biological meaning of the parameter derived. Compartmental models did not fit the data and the rest of the models detected the differences of the rate of starch digestion of the grains. The SKM had the lowerst residual sum of squares followed by the FOM. However, SKM estimated some parameters without biological meaning. The inclusion of lag time and indigestible fraction did not improve the estimation of the FOM. It was concluded that the first order model is the most appropriate to describe ruminal starch digestion.

Local e extensão da digestão em terneiros desmamados alimentados "Ad Libitum" com dietas ricas em concentrado contendo diferentes fontes de proteína suplementar

Foram utilizados nove terneiros da raça Holandesa (139 ± 2,4kg), fistulados no duodeno, em um delineamento experimental completamente casualizado para estudar o efeito da suplementação com diferentes fontes protéicas (2% de uréia ou 10% de farinha de carne na dieta total) de dietas ricas em concentrado (milho e farelo de soja) sobre o local e extensão da digestão do alimento, em condições de consumo ad libitum. A relação volumoso:concentrado das dietas foi de 30:70. A digestibilidade ruminal e total da matéria seca, matéria orgânica e nitrogênio, assim como o fluxo duodenal de nitrogênio microbiano e residual do alimento, e a eficiência da síntese protéica microbiana foram semelhantes nos dois tratamentos (P&gt;0,10). A digestibilidade ruminal do amido também foi semelhante, mas a digestibilidade total foi menor no tratamento com uréia (P&lt;0,10). No entanto, é provável que isso seja devido mais a limitações dos ruminantes em digerir amido no intestino delgado do que a uma influência do suplemento protéico. O uso de uréia ou de farinha de carne, como fontes de proteína suplementar de dietas à base de milho e farelo de soja, balanceadas para suprir a demanda de crescimento de terneiros jovens e fornecidas ad libitum, não influencia significativamente o processo de digestão nestes animais. Deste modo, a escolha por um outro suplemento depende mais de outros critérios do que dos nutricionais.

Effect of feeding mixtures of high moisture corn and dry-rolled grain sorghum on ruminal fermentation and starch digestion

This experiment was conducted to study the effects of feeding mixtures of high moisture corn (HMC) and dry-rolled grain sorghum (DRGS) on ruminal fermentation and site and extent of starch digestion. Twelve ruminally, duodenally and ileally fistulated sheep were assigned to the following treatments: T 1 100% HMC; T 2 67% HMC:33% DRGS; T 3 33% HMC:67% DRGS; and T 4 100% DRGS. Starch and DM intake increased (quadratic, p<0.05) with increasing DRGS. Ruminal starch digestibility (%) decreased (linear, p<0.01) as DRGS was added to the diet (T 1 89.6; T 2 75.4; T 3 70.2; and T 4 51.3) whereas digestion in the small intestine (percentage of intake) increased (linear, p<0.01; T 1 9.2; T 2 22.0; T 3 28.7; and T 4 47.1). Numbers (organisms × 10 3) of total protozoa (quadratic p<0.20; T 1 184.0; T 2 558.5; T 3 250.2; and T 4 130.8) and Entodinium (quadratic, p<0.20; T 1 183.7; T 2 555.9; T 3 244.6; and T 4 118.7) tended to be higher for the grain mixtures. The numbers of Holotrichs ( p<0.05) and ruminal pH decreased linearly ( p<0.05) with increasing dietary HMC level. The molar proportion of propionate decreased linearly ( p<.01) as HMC increased in the diet. No associative effects were detected in ruminal starch digestion when both DRGS and HMC were in the diet. However, the elevated number of protozoa observed when HMC and DRGS were combined may have an effect on the site of starch digestion.

The effect of chemical treatment of barley on starch digestion in ruminants

Two experiments were conducted with sheep and Jersey cows to study the effects of formaldehyde (HCHO) treatment of barley on rumen fermentation, flow of starch to small intestine and its subsequent apparent digestion. HCHO was applied to barley at a rate of 30 g HCHO kg −1 barley crude protein (CP). Diets containing either untreated barley (UB) or HCHO treated barley (TB) were fed to sheep and cattle for a period of 4 weeks in two separate cross-over design experiments. Rumen degradability of DM, starch (S) and total N was assessed by the in sacco technique, flow of nutrients to intestine and microbial protein reaching the duodenum were also determined. Treatment of barley with HCHO did confer some resistance to degradation on the starch and protein components of barley as reflected in the results from the in sacco experiment. However this resistance was not enough to increase S or total N flow to the small intestine, or to alter the concentrations of rumen metabolites or microbial protein reaching the intestines in either sheep or cattle.

Influence of grain source on ruminal characteristics and rate, site, and extent of digestion in beef steers.

Six cannulated Salers steers (305 +/- 17 kg initial BW) were used in a double 3 x 3 Latin square design to compare the effects of the nature of the cereal (wheat vs corn) and the corn genotype (dent vs flint) on rate, site, and extent of digestion of high-concentrate diets. The cereals were coarsely cracked, and the diets were balanced to have the same percentage of starch (47.7 +/- 2.3%) and CP (14.6 +/- .7%). Differences in ruminal starch digestion were observed between wheat- and corn-based diets (86.6 vs 47.8%; P < .001) and between corn genotypes (60.8 vs 34.8% for dent and flint corns; P < .001). For flint corn, more than half the starch was digested in the hindgut. Total tract digestion of starch was greater (P < .001) by steers fed wheat than by those fed corn and did not differ (P > .1) between the two corn genotypes. Ruminal mean pH (P < .01) was lower and total VFA concentration (P < .1) was higher for wheat- than for corn-based diets. Ruminal acetate:propionate tended to increase with the decrease in the amount of starch degraded in the rumen, but differences were not significant (P > .1). When wheat replaced corn, nonammonia, nonmicrobial N duodenal flow decreased (P < .01), and microbial duodenal flow increased (P < .05), so there were no differences in the duodenal flow of nonammonia N duodenal flow (P > .1). The lower nonammonia N duodenal flow for the dent corn- than for the flint corn-based diet (P < .05) was related to a lower passage of nonammonia, nonmicrobial N into the duodenum. Efficiency of microbial protein synthesis was inversely correlated with the amount of starch degraded in the rumen. Nature of the cereal, wheat vs corn, and genotype of the corn, dent vs flint, alter the site and extent of starch digestion.

Influence of malic acid supplementation on ruminal pH, lactic acid utilization, and digestive function in steers fed high-concentrate finishing diets.

Two trials were conducted to evaluate the influence of malic acid supplementation on ruminal fermentation. In Trial 1, six Holstein steers (300 kg) with ruminal cannulas were used in a crossover design experiment to study the influence of malic acid (MA) on ruminal metabolism during glucose-induced lactic acidosis. Treatments consisted of a 77% steam-flaked barley-based finishing diet supplemented to provide 0 or 80 g/d of MA. After a 13-d dietary adjustment period, 1 kg of glucose was infused into the rumen 1 h after the morning feeding. Ruminal pH was closely associated (R2 = .70) with ruminal DL-lactate concentration. Malic acid supplementation increased (P < .01) ruminal pH 3 h after the glucose infusion. However, there were no treatment effects (P > .10) on ruminal VFA molar proportions or ruminal and plasma DL-lactate concentrations. In Trial 2, four Holstein steers (150 kg) with cannulas in the rumen and proximal duodenum were used in a crossover design experiment to evaluate the influence of MA supplementation on characteristics of digestion. Treatments consisted of an 81% steam-flaked barley-based finishing diet supplemented to provide 0 or 80 g/d of MA. There were no treatment effects (P > .10) on ruminal and total tract digestion of OM, ADF, starch, and feed N or on ruminal microbial efficiency. Malic acid supplementation increased (P < .05) ruminal pH 2 h after feeding. As with Trial 1, there were no treatment effects (P > .10) on ruminal VFA and DL-lactate concentrations. We conclude that supplementation of high-grain finishing diets with MA may be beneficial in promoting a higher ruminal pH during periods of peak acid production without detrimental effects on ruminal microbial efficiency or starch, fiber, and protein digestion. There were no detectable beneficial effects of MA supplementation on ruminal and plasma lactic acid concentrations in cattle fed high-grain diets.

THE EFFECT OF MAIZE GRAIN TYPE ON DIGESTIBILITY OF STARCH IN THE RUMEN OF SHEEP

Ruminal starch digestibility of dried maize grain and whole plant maize silage was determined by the in sacco method. It was found out that starch of dent type maize hybrid is more extensively digested in the rumen than starch of flint type hybrid. Digestibilities of dried maize grain from dent and flint type hybrids were 683 and 554 g kg-1 respectively. Ruminal digestibilities of corresponding silages were 915 and 743 g kg-1. Ruminal digestibility of starch in whole plant maize silage was on average about 200 g kg-1 higher than in dried grain samples. Ruminal starch digestibility of maize silages can not be estimated directly on the basis of measurements done on dried grain samples. Some practical implications of differences among hybrids and between dried and ensiled maize are discussed.

Ruminal fermentation and in situ starch digestion with high moisture corn, dry rolled grain sorghum or a mixture of these grains

An experiment was conducted to study the effects of feeding mixtures of high moisture corn (HMC) and dry-rolled grain sorghum (DRGS) on ruminal fermentation and site and the extent of starch digestion. Three ruminally fistulated steers were used in a replicated Latin square design. Dietary grain treatments were:(1) 100% HMC;(2) 67% HMC:33% DRGS; and (3) 100% DRGS. Starch and DM intake ( P<0.01), and in situ rate of starch disappearance of DRGS ( P<0.05) increased linearly as sorghum was added to the diet. Entodinium counts and total amylolytic activity tended to be higher (quadratic, P=0.20) in the mixture. VFA and molar proportion were not affected by the treatments. No associative effects were detected in ruminal starch digestion. Ruminal protozoa numbers were increased when DRGS and HMC were combined.

In vitro ruminal starch digestibility in opaque-2 and regular corn hybrids

Opaque-2 corn ( Zea mays L.), more commonly known as high lysine corn, contains more lysine than normal corn. However, little is known about the digestibility in ruminants of different high lysine hybrids. Objectives were to determine in vitro ruminal starch digestibility of corn grain from high lysine and normal hybrids. Samples included grain from seven high lysine and one normal hybrid harvested at physiological maturity, and five high lysine and five normal hybrids harvested after field drying. All grain was ground prior to starch and in vitro analyses; dry grain was both coarsely and finely ground to examine the interaction between particle size and corn type. Starch content of normal corn was slightly higher than high lysine for both blacklayer (67.1% vs. 65.0%; P<0.01) and dry corn (70.9% vs. 66.9%; P<0.03). Starch digestibility of high lysine and normal hybrids at blacklayer was 55.8% and 39.1%, respectively, following 6 h of fermentation ( P<0.01) and 95.8% and 89.2% after 12 h ( P<0.01). For fine-ground dry corn, starch digestibility of high lysine and normal hybrids was 40.2% and 29.6%, respectively, after 6 h ( P<0.01) and 89.0% and 78.5% after 12 h ( P<0.01). For coarse-ground dry corn, no difference in digestibility between hybrids was observed after 6 h, however, high lysine corn was 48% more digestible than normal corn after 12 h (70.6% vs. 47.7%; P<0.01). Although digestibility was variable between different opaque-2 corn hybrids, in vitro starch digestibility was consistently higher for all opaque-2 hybrids compared with normal corn.

Influence of dietary magnesium level on growth-performance and metabolic responses of Holstein steers to laidlomycin propionate.

We used 216 Holstein steers (151 kg) in a 262-d trial to evaluate the influence of dietary magnesium level (.19, .25, and .32%) and laidlomycin propionate (LP; 0 vs 11 ppm, air-dry basis) on growth performance and NE value of the diet. During the initial 112 d of the trial, LP increased (P < .01) ADG (6.3%) and feed efficiency (4.2%). From d 112 until slaughter, LP increased (P < .05) ADG (9.7%) and feed efficiency (4.5%). Across the 262-d feeding period, LP supplementation enhanced (P < .01) ADG (8.9%) and feed efficiency (6.3%). There was an interaction (P < .05) between dietary Mg and LP on NE value of the diet. The enhancement in NE value of the diets owing to LP with .19, .25, and .32% dietary Mg were .5, 3.0, and 5.9%, respectively. Six Holstein steers (302 kg) were used in a 6 x 6 Latin square experiment to evaluate treatment effects on characteristics of ruminal and total tract digestion. There were no treatment interactions (P > .10) on site and extent of digestion of OM, starch, and N. Supplemental Mg increased (quadratic effect, P < .10) ruminal OM digestion. Neither LP nor dietary Mg level affected (P > .10) ruminal digestion of starch and feed N. Supplemental LP decreased (15%, P < .05) ruminal microbial efficiency. Total tract digestion of OM and N increased (linear effect, P < .01) with increasing dietary Mg level. There were interactions between LP and dietary Mg level on ruminal soluble-Mg concentration (linear effect, P < .01) and Mg absorption (quadratic effect, P < .05). Apparent total tract Mg digestion increased owing to LP (P < .01) and dietary Mg level (linear effect, P < .01). There were no treatment effects (P > .10) on ruminal pH. Dietary Mg level did not influence (P > .10) ruminal VFA concentrations or molar proportions. Supplemental LP increased (14%; P < .10) total ruminal VFA concentration but did not affect (P > .10) VFA molar proportions. We conclude that LP will increase daily weight gain and feed efficiency of calf-fed Holstein steers and that this response may be enhanced by increasing dietary Mg level.

The feeding value of dry-rolled and steam-flaked corn in finishing diets for feedlot cattle: influence of protein supplementation.

We used 80 medium-framed yearling crossbred heifers (357 kg) in a 110-d trial to evaluate the influence of dietary protein level (11 vs 14%) on the feeding value of dry-rolled (DRC) and steam-flaked corn (SFC). All diets contained 1% urea; cottonseed meal (CSM) was the source of supplemental undegradable intake protein (UIP). Steam flaking corn reduced DMI (9%, P < .10) and increased (P < .01) feed efficiency (14%), dietary NEm (13%), and NEg (15%). Steam flaking increased the NEm by 17% and NEg by 19%. Supplemental CSM decreased (P < .10) feed efficiency (7%) and dietary NEm (4%) and NEg (6%). There were no treatment effects (P > .10) on carcass characteristics. Steam flaking corn increased (P < .05) fecal pH and reduced (P < .01) fecal starch. Supplemental CSM increased (P < .01) fecal pH and reduced (P < .01) fecal starch. Four Holstein steers (413 kg) were used in a 4 x 4 Latin square experiment to evaluate treatment effects on digestive function. Steam flaking corn increased (P < .05) flow of nonammonia N (11%, P < .05) and microbial N (15%, P < .01) to the duodenum. Supplemental CSM increased the flow of microbial N (6%, P < .01), feed N (21%, P < .10), and nonammonia N (12%, P < .05) to the duodenum. The UIP value of CSM was 28% for the DRC diet and 52% for the SFC diet. Steam flaking corn increased (P < .01) ruminal starch digestion (26%) and total tract digestibility of OM (17%), N (15%), starch (19%), and GE (17%). Steam flaking increased the DE value of corn by 21%. Supplemental CSM did not influence (P > .10) postruminal or total tract starch digestion. Supplemental CSM decreased (7%, P < .10) the DE value of the diet. We conclude that increasing the postruminal protein supply of a corn-based finishing diet beyond that provided by urea supplementation, alone, will not enhance starch digestion or the energy value of the diet.