Forage-based Diets Research Articles

Effects of corn vs. corn plus wheat in forage-based diets containing broiler litter on feed intake, ruminal digesta characteristics and digestion in cattle

Cattle consuming low-to moderate-quality forage were supplemented with corn or a 1:1 corn:wheat mixture with or without broiler litter to determine effects on feed intake, ruminal digesta characteristics and digestion. In the first experiment, mature beef steers (529 ± 33 kg initial body weight) with cannulas in the rumen and duodenum were fed prairie hay and soybean meal alone (control) or with (dry matter basis) 0.3% body weight (BW) of ground corn (C), 0.15% BW of corn plus 0.15% BW of ground wheat (CW), corn plus 0.3% BW of broiler litter (C-L) or the corn-wheat mixture plus 0.3% BW of broiler litter (CW-L). Ruminal fluid ammonia nitrogen (N) concentration 2 h after feeding was increased ( P < 0.05) by supplementation and was greater ( P < 0.05) for C-L than for CW-L (8.9, 9.3, 11.4, 27.6 and 21.4 mg dl −1 for control, C, CW, C-L and CW-L, respectively). Neither duodenal microbial N flow nor efficiency of microbial growth was affected by treatment. In the second experiment, Holstein steers (129 ± 11 and 219 ± 17 kg initial and final BW, respectively) consumed ad libitum bermudagrass hay alone (control) or with (dry matter basis) 0.6% BW of corn (C), 0.3% BW of corn plus 0.3% BW of wheat (CW), corn plus 0.6% BW of broiler litter (C-L) or the corn-wheat mixture plus 0.6% BW of broiler litter (CW-L). Total organic matter (OM) intake was increased ( P < 0.05) by supplementation and inclusion of broiler litter in supplements (4.34, 4.91, 5.14, 5.27 and 5.32 kg day −1); total tract OM digestion was increased ( P < 0.05) by supplementation and was lower ( P < 0.05) for supplement treatments with than without broiler litter (57.2, 61.8, 63.0, 59.5 and 59.9%); and digestible OM intake was increased ( P < 0.05) by supplementation and was not altered by broiler litter inclusion in supplements (2.51, 3.05, 3.25, 3.14 and 3.20 kg day −1 for control, C, CW, C-L and CW-L, respectively). In summary, supplementation of a diet containing broiler litter with a corn-wheat mixture compared with corn alone decreased ruminal ammonia N concentration early after feeding but did not change duodenal microbial N flow or efficiency of microbial growth. Grain source did not alter total feed intake by growing Holstein steers consuming diets with broiler litter, and an increase in total feed intake when broiler litter was included in diets compensated for low digestibility of broiler litter.

Forage Quality for Ruminants: Plant and Animal Considerations

Forage quality is a function of nutrient concentration, intake, nutrient availability, and partitioning of metabolized products within animals. Of these factors, intake potential is the major determinant of production by animals fed forage-based diets; however, it is one of the most difficult aspects of forage quality to determine or predict because variation among animals has a large influence on intake. Physical fill limits intake of forages with high cell wall concentrations when fed to animals with high energy demand. Hence, grasses, with their higher cell wall concentration, typically have lower intake than legumes. Energy availability of forage is also limited by cell wall concentration because cell contents are almost completely digested, whereas forage cell walls are slowly digested. Thus, the proportion of cell walls to cell contents is a major determinant of energy availability in feeds. Protein digestion by ruminants is complex. When crude protein concentration in herbage drops below 7% of dry matter, ruminal fermentation of forages may be limited and protein requirements of animals may not be met. Additionally, inefficient use of protein in high quality forages may limit performance of high producing animals. Usually, only about 25% of the forage protein escapes degradation from the rumen. Efficiency would be improved if a larger portion of forage protein passed from the rumen undegraded so that it can be degraded in the intestines where absorption is more efficient. Another important plant factor influencing forage quality is herbage maturity. Systems are now available for determining maturity of both legumes and grasses that will become more important as aids for predicting forage quality before forages are harvested or grazed. Forage quality is also influenced by the environment in which forages are grown and by soil fertility and these cause year-to-year, seasonal, and geographical variation in forage quality even when herbage is harvested at the same stage of maturity.

The effect of supplementation with Leucaena leucocephala and maize bran on voluntary food intake, digestibility, live weight and milk yield of Bos indicus × Bos taurus dairy cows and rumen fermentation in steers offered Pennisetum purpureum ad libitum in the semi-humid tropics

AbstractAn experiment was carried out to evaluate dairy performance and rumen fermentation from a forage-based diet supplemented with Lucaena leococephala (leucaena) and maize bran. Bos indicus (Ayrshire/Brown Swiss) х Bos taurus (Sahiwal) cattle were offered Pennisetum purpureum (napier grass) ad libitum either unsupplemented (N) or supplemented on a dry-matter (DM) basis with 1 kg (LL) or 2 kg leucaena (LH) or 2 kg leucaena together with 1 kg DM maize bran (LHM). Food intake, milk yield, diet apparent digestibility and nitrogen balance were measured using eight cows (mean live weight 384 (s.d. 41) kg in two 4х4 Latin squares. Rumen fermentation was measured using four rumen fistulated steers (mean live weight 352 (s.d. 12) kg in a 4 х 4 Latin square. Performance was recorded during the last 7 days of each 21-day experimental period. Supplementation increased food intake (6·3, 7·6, 7·9 and 8·7 kg DM per day; P &lt; 0·01; s.e.d. 0·24) and milk yield (5·1, 5·4, 5·5 and 6·5 kg/day; P &lt; 0·01; s.e.d. 0·28) for N, LL, LH and LHM respectively. Supplemented diets tended to be more digestible compared with napier grass as the sole food (organic matter apparent digestibility coefficients 0·54, 0·55, 0·57 and 0·57; s.e.d. 0·020; N, LL, LH and LHM, respectively) and N balance increased progressively with supplementation.Supplementation progressively increased rumen ammonia-nitrogen concentrations in steers and the rate of rumen degradation of napier grass increased when leucaena (diets LL and LH) was offered. The results suggest that supplementation of napier grass with leucaena increased DM intake owing to increased ammonia concentrations and rates of napier degradation in the rumen. Supplementation of the forage diet with 1 kg DM maize bran did not significantly reduce the rumen degradation of napier grass and increased the molar proportions of propionate which may have increased the efficiency of utilization of metabolizable energy and therefore milk production.

Influence of production system on carcass characteristics of F 1 Wagyu × Angus steers and heifers

American Wagyu × Angus steers ( n = 15) and heifers ( n = 26) were finished to typical Japanese market weight and degree of finish using two different feeding methods. The first method (deferred) consisted of two growing/ finishing phases: a forage-based diet for approximately 8 months followed by a high concentrate diet fed ad libitum for an additional 8 months while the second finishing method (linear) was designed to produce a linear rate of gain for the entire 16 months that the cattle were on feed. Even though there were substantial differences in daily weight gain ( P < 0.05) within the two growing/finishing phases, total weight gain for the entire 16 months was not different between the two feeding methods ( P > 0.05). Cattle produced by the linear growth method were superior to deferred growth cattle for carcass weight (as estimated by cold left side weight), rib thickness, dressing percentage, marbling score, fat color, fat luster, fat quality, as well as in scores for meat color, brightness, firmness and texture ( P < 0.05). Fat thickness was not affected by treatment ( P > 0.05). These data indicate that the linear method of production is more consistent with producing carcasses for the Japanese beef market.

Fibrolytic enzymes improve growth of steers fed forage-based diets

Fibrolytic enzymes improve growth of steers fed forage-based diets

Effect of extended underfeeding on digestion and nitrogen balance in nonlactating cows.

The effect of extended underfeeding on digestion was studied in dairy cows. Four nonlactating cows (BW = 747 kg) were first fed a forage-based diet at a level above energy maintenance requirements for 7 wk (9.4 kg DM/d) then were restricted at a low level of intake of the same diet for 5 mo (5.2 kg DM/d), then refed at the first level. Digestion measurements were made before and after the underfeeding period, and at 1, 5, 9, and 19 wk of underfeeding. Organic matter digestibility decreased with underfeeding then increased (62.7, 56.2, and 61.5% before, 1 wk after, and 19 wk after underfeeding, respectively). Differences in ruminal apparent OM digestion were nonsignificant (P > .05). This lack of difference was related to the absence of variation of ruminal particle passage rate and DM degradability measured in situ. However, the decrease in feed intake decreased ruminal (P < .01) and intestinal (P < .05) liquid dilution rates, ruminal DM pool size and DM content (P < .01), and protozoa concentration (P < .01). The decrease (P < .01) in N retention with underfeeding was followed by an increase (P < .05) during the underfeeding period, due to a decrease in fecal and urine N losses. This experiment has shown an unusual and temporary response of digestion to underfeeding. Knowledge of adaptation of digestion to low intakes needs to be improved.

Effect of zinc supplementation on performance and zinc metabolism of lambs fed forage-based diets

SummaryExperiments were conducted to determine the effects of zinc (Zn) supplementation on the performance and mineral metabolism of lambs fed forage-based diets containing 15–23 mg Zn/kg. In Expt 1, 20 lambs were fed a good-quality orchardgrass (21·4 mg Zn/kg) or a low-quality tall fescue (14·7 mg Zn/kg) hay and supplemental Zn (as ZnO) at 0 or 30 mg/day in a 2 x 2 factorial arrangement of treatments. Forage was fed ad libitum and all lambs received 92 g dry matter/day of a corn-based supplement which served as the carrier of the supplemental Zn. Lambs fed orchardgrass hay had a greater (P &lt; 0·01) dry matter intake and average daily gain for the 42-day study. Zinc supplementation did not affect performance of lambs fed tall fescue but tended to improve performance in those fed orchardgrass hay. At the end of the 42-day growth phase, lambs were placed in metabolism crates for a 7-day total collection of urine and faeces. Supplemental Zn increased intake (P &lt;0·01) and faecal excretion (P &lt;0·01) of Zn. Absorbed Zn was greater (P &lt; 0·05) for lambs fed supplemental Zn. There was a tendency for a forage × Zn interaction (P &lt; 0·10) for urinary Zn excretion and retention. Urinary Zn excretion was highest in lambs fed tall fescue hay supplemented with Zn. In Expt 2, 24 lambs were fed diets consisting of ad libitum chopped tall fescue hay (23 mg Zn/kg) and 176 g/day of a corn and mineral supplement which served as the carrier of the Zn treatments. Treatments were no supplemental Zn or 30 mg/day supplemental Zn as ZnO, ZnSO4 or Zn methionine. Zinc oxide and ZnSO4 supplementation increased average daily gain (P &lt; 0·10) and decreased feed/gain (P &lt; 0·10) for the 56-day study when compared to control and Zn methionine-supplemented lambs.

Digestion in the Rumen and Total Tract of Forage-Based Diets with Starch or Dextrose Supplements Fed to Holstein Heifers1,2

Three diets were fed to six cannulated heifers in a replicated 3 × 3 Latin square design. Diets were a high forage control, a high forage diet with dextrose (5.6% of DM), and a medium concentrate (39.7% of DM) diet. Diets contained 13.3% CP and 1% NaHCO3 and were fed as a TMR twice daily. Mean ruminal pH (6.47), glucose concentration (.55mM), and reducing sugar concentration (.64mM) in heifers were similar across diets. Rate of orchardgrass NDF digestion in situ was faster for heifers fed the dextrose than for those fed the medium concentrate diet, but both were similar to that for heifers fed the control diet. Heifers fed the medium concentrate and dextrose diets had faster ruminal particulate fractional passage rates than those fed the control diet. True ruminal and apparent total tract digestion of OM and NDF were similar among diets, but ruminal NDF digestion tended to be higher with the control than with the medium concentrate diet. Total NAN and bacterial N flow to the duodenum and efficiency of bacterial protein synthesis in the rumen were greater with the medium concentrate diet than with the control and dextrose diets. The results were consistent with others that demonstrated that factors related to nonstructural carbohydrates in the diet other than just low ruminal pH affect ruminal fiber digestion; however, these results were not as strong as those of our previous in vitro work.

Replacement value of tree legumes for concentrates in forage-based diets. I. Replacement value of Gliricidia sepium for growing goats

Digestion, growth and laboratory studies evaluated the replacement value of the tropical tree legume Gliricidia sepium for a concentrate feed in kinggrass ( Pennisetum purpureum) based diets for growing goats. In the growth trial, 24 intact male goats (10–18 kg) were allotted to three treatments in a randomized design. Nine additional goats used to study digestibility and N balance of the diets were allotted to the treatments in a randomized complete block design with two periods giving six observations per treatment. The (positive) control diet contained 40% concentrate, and gliricidia replaced 0, 50 or 100% of the concentrate, yielding diets containing 0% (G0), 20% (G20) and 40% (G40) gliricidia. Gliricidia was greater in total N concentration than kinggrass, and a greater percentage of the N in gliricidia was potentially ruminally degradable than that in kinggrass. The ruminally degradable N fraction in gliricidia was degraded in situ at a faster rate than that in kinggrass, resulting in a greater estimated pool of N available for rumen function. In the digestion trial, apparent dietary organic matter (OM) and fiber digestibilities, dietary N retained and absorbed, and N utilization efficiency declined in a linear ( P < 0.05) manner with increasing gliricidia level in the diet. In the growth trial, OM intake was similar ( P = 0.64) among treatments. Differences in daily gain and gain feed ratio were greater ( P < 0.06) between the G0 (110 g, 0.19) and G20 (75 g, 0.13) diets than between the G20 and G40 (75 g, 0.13) diets. Lower animal performance on gliricidia-supplemented diets was likely due to lower available dietary energy resulting in lower N digestion and assimilation. All goats on gliricidia-supplemented diets gained weight and maintained a positive N balance, suggesting that gliricidia may replace some of the concentrate used in kinggrass-based diets for growing goats. High costs of grain imports may economically favor lower rates of gain in tropical areas of the world.

Replacement value of tree legumes for concentrates in forage-based diets. II. Replacement value of Leucaena leucocephala and Gliricidia sepium for lactating goats

Laboratory, digestion and lactation trials investigated the replacement value of the tree legumes Gliricidia sepium and Leucaena leucocephala for a concentrate supplement in kinggrass ( Pennisetum purpureum) based diets. In the lactation trial, 15 does in mid-lactation were allocated to three dietary treatments in a 3 × 3 Latin square design with five square replications. In the digestion trial, six intact yearling male goats were assigned to the same treatments in a replicated 3 × 3 Latin square design. Diets were based on kinggrass and supplemented with either a commercial concentrate feed, gliricidia or leucaena. In the control diet, 60% of the total dietary N was supplied by the concentrate. In the legume-supplemented diets, gliricidia or leucaena replaced approximately 50% of the N supplied by the concentrate. Dried banana fruit ( Musa×paradisiaca) was used in the legume-supplemented diets to equal the energy content of the control diet. Diets contained approximately 2.2% N and 73% total digestible nutrients. Legumes were greater in total N concentration than kinggrass, with leucaena containing more N than gliricidia ( P<0.05). Size and degradation rate of the potentially ruminally degradable N fraction were greatest for gliricidia and least for kinggrass, with values for leucaena being intermediate ( P<0.05). In vitro organic matter (OM) digestion was greater ( P<0.05) for the legumes than for kinggrass, but the extent of in vitro cell wall digestion was greater ( P<0.05) for kinggrass than for the legumes. In vitro OM and cell wall digestion was greatest ( P<0.05) for banana. In the digestion trial, apparent dietary OM and cell wall digestibilities were similar ( P>0.10) across treatments. Fecal N production was greater ( P<0.05) for legume-supplemented diets than the control, leading to lower ( P<0.05) N digestibility for legume-supplemented diets. In the lactation trial, OM intake was greatest ( P<0.01) for the control diet and least ( P<0.01) for the gliricidia-supplemented diet, but milk production characteristics were similar ( P>0.10) for all treatments. For iso-energetic diets, up to 50% of the concentrate N may be replaced by the tropical tree legumes gliricidia and leucaena without a reduction in milk production.

Whole-body fat metabolism in cattle fed forage-based diets.

The production performance of cattle fed forage-based diets, particularly conserved forages, is poor and unpredictable. It has been shown that protein deposition is limiting in silage-fed cattle (Gill et al., 1987). It has also frequently been reported that the ratio of carcass fat:protein in silage-fed cattle is high (Baker, Young &amp; Laws, 1992). There are few comparative dietary studies on whole-body fat metabolism in cattle. It was therefore the aim of this study to measure some of the parameters of whole-body fat metabolism in cattle fed forage-based diets and thus to determine if the high fat:protein ratio of silage-fed cattle is due to altered rates of whole-body fat metabolism. It was also our aim to determine whether the well-documented effects of β-agonists on fat metabolism are dependent on dietary status.

Continuous-culture fermentation as a tool for forage evaluation (1994)

Ruminal degradation of organic matter and protein in alfalfa and prairie hay were evaluated in vivo, using cannulated cows, and in vitro, using a continuous-culture fermenter to simulate ruminal fermentation. Estimates of organic matter degradability, microbial N flow per unit feed N input, and efficiency of microbial growth were not different (P>.10) between the in vivo and in vitro systems. However, for both forages, estimates of nitrogen degradability were greater with the in vitro system. Despite the differences between in vivo and in vitro techniques for some variables, continuous-culture fermentation will allow us to compare the effects of dietary treatments on forage digestion and will aid in the formulation of supplements to meet specific nutrient requirements for cattle consuming forage-based diets.

Effects of supplementing growing steers with high levels of partially hydrogenated tallow on feed intake, digestibility, live weight gain, and carcass characteristics.

Effects of supplementing growing steers consuming forage-based diets with high levels of partially hydrogenated tallow on feed intake, digestibility, live weight gain, and carcass characteristics were determined in this study. In Exp. 1, Holstein steer calves were fed bermudagrass hay alone (Control) and with a ground corn-based concentrate at .95% BW (DM basis) plus partially hydrogenated tallow at 0 (Basal), .33 (low fat; LF), or .67% BW (high fat; HF) in a Latin square. Total DMI was increased by concentrate supplementation and was lower for HF than for LF (P < .05; 3.18, 3.83, 4.25, and 3.17 kg/d for Control, Basal, LF, and HF, respectively). In Exp. 2, grazing Angus x Hereford steers (270 kg +/- .4 initial shrunk BW) were fed the same supplements as in Exp. 1 for 84 or 98 d and slaughtered. Live weight gain was increased (P < .05) by concentrate supplementation (1.01, 1.34, 1.41, and 1.30 kg/d for Control, Basal, Low, and High, respectively). The concentration of total lipids in longissimus muscle was 2.51, 2.53, 3.05, and 3.03% of wet tissue for Control, Basal, LF, and HF, respectively (Basal > the mean of LF and HF; P < .07); the proportion of palmitic acid in total fatty acids was similar among treatments. Fat supplementation did not markedly affect sensory, taste, or tenderness characteristics of longissimus muscle. In conclusion, supplementing grazing beef steers with high levels of partially hydrogenated tallow, with slaughter at approximately 400-kg shrunk BW, tended to increase fat in longissimus muscle without altering the palmitic acid level in fatty acids, although sensory, taste, and tenderness characteristics were not modified.

Quantitative ruminant nutrition — a green science

Knowledge of quantitative digestion and metabolism in ruminants was developed most rapidly when isotope dilution techniques became easy to apply, facilitated by improved instrumentation and mathematical approaches. The Armidale group led by Professor E. F. Annison and Dr D. B. Lindsay were at the forefront of these developments in the late 1950's. Since then knowledge in this area has developed at an ever increasing rate. The data that accumulated from the quantitative approach led to simple or complex models of animal digestion, metabolism and growth. These in turn led to much questioning of the dogma of feed evaluation and feeding standards as they applied in practice, especially for ruminants fed on poor quality forages. The knowledge that developed has clearly shown that the way toward substantial increases in productivity of ruminants on forage based diets is through the balanced nutrient approach that considers the efficiency of the rumen ecosystem and the availability of dietary nutrients post-ruminally. With increasing emphasis on quality-beef markets at the present time, it seems likely that the time is ripe for application of much of this knowledge. The major breakthroughs have come about by recognition of the nutrients required to balance a ruminant's diet where the animal depends on the end-products of rumen fermentation (i.e. on a forage-based diet). When this is achieved, the increase in efficiency of use of nutrients lifts the overall nutrition of the animal to a level that is well above that predicted from feeding standards, based on the metabolizable energy content of the supplement or the total diet. This understanding, together with the stoichiometry of rumen fermentation, has indicated an important approach to help ameliorate the greenhouse effect, that is, lowering of enteric methane production per unit of feed intake or per unit of animal products from ruminants by strategic supplementation.

The Influence of Forage Type on the Production Response of Lactating Dairy Cows Supplemented with Different Types of Dietary Fat

Research has demonstrated a difference in fat utilization by lactating dairy cows with different dietary forage types. Responses appear to be greatest on alfalfa-based diets and poorest on all corn silage-based diets. The addition of extruded soybeans to dairy cow diets containing corn silage and alfalfa hay increased fat-corrected milk (FCM) production by an average of 2.4% compared to 10% for all alfalfa silage-based diets. In 11 experiments, the addition of whole cottonseed (WCS) to corn silage-based diets decreased FCM production by an average of 4% whereas the addition of WCS to alfalfa hay-based diets increased average milk fat percent and FCM production by 11 and 6%, respectively. When WCS was included in diets with corn silage as the primary forage and alfalfa hay or bermudagrass hay as a secondary forage, the fatinduced milk fat depression found on corn silagebased diets appeared to be alleviated. Alfalfa diets supplemented with yellow grease increased average milk production by 6.6% with milk fat percentage unchanged. Results supported the inclusion of tallow at 500g/cow/day in diets based on ryegrass silage whereas the inclusion of tallow or blended animal-vegetable fats on corn silage- or cottonseed hull-based diets was not supported by summarized experiments. Supplementing corn silage/alfalfa silage-based diets with prilled fat increased FCM production by an average of 6.2% whereas the inclusion of prilled fat in alfalfa silage or corn silage based diets had inconsistent effects on production responses. The supplementation of different forage-based diets with Ca-salts of fatty acids resulted in an average FCM production increase of approximately 5%.

Effects of feed intake on particle distribution, passage of digesta, and extent of digestion in the gastrointestinal tract of cattle

Four nonlactating Holstein dairy cows (means +/- SD BW = 692 +/- 49 kg) were used in a 4 x 4 Latin square design experiment to determine changes in distribution of particles within the ruminoreticulum (RR) and total digestive tract in cattle fed a forage-based diet at four intake levels. Relationships between chewing activities and rates of particle breakdown, passage, and digestion were also determined. Percentage of large particles increased linearly in the dorsal rumen (P = .001), ventral rumen (P = .004), reticulum (P = .007), duodenum (P = .007), and feces (P = .006) as DMI increased. Particles of sizes less than or equal to 2,000 microns, eligible to pass from the RR, constituted 60 to 92% of particle DM in the RR. Increased feed intake resulted in a longer (P = .003) eating but a shorter (P = .008) ruminating time per kilogram of DM intake, whereas total chewing time per kilogram of DMI was not affected (P = .12). Passage rate constants of NDF from the RR increased (P = .03) with intake. There was no change (P = .87) in the rate constant for particle breakdown in the dorsal rumen with increased intake. Neither fractional passage rate of NDF nor the rate constant for particle breakdown was related to time spent eating (P + .12; P = .34) or time spent ruminating (P = .11; P = .55). It was concluded that rate of passage of small particles from the RR was a determinant of passage from the RR and that changes in rates of passage and breakdown of particles could only be partially explained by changes in chewing activities.

Reticular contraction attributes and passage of digesta from the ruminoreticulum in cattle fed roughage diets.

Four nonlactating Holstein dairy cows (BW = 692 +/- 49 kg) were used in a 4 x 4 Latin square design experiment to determine how changes in attributes of reticular contractions were related to changes in passage of digesta from the ruminoreticulum in cattle fed a forage-based diet. Frequencies of reticular contraction during eating, ruminating, and resting phases of the feeding cycle were not affected (P = .09; P = .07; P = .09, respectively) by feeding level. Duration and amplitude of reticular contractions both increased linearly during eating (P = .03; P = .01), ruminating (P = .01; P = .02), and resting (P = .04; P = .02), respectively, as feed intake level increased. After removing the effects of intake, squared partial correlations computed within analyses of covariance indicated that NDF flow was not related to frequency (r2 = .15, P = .20) but was positively correlated with duration (r2 = .76, P = .0001) and amplitude (r2 = .56, P = .003) of contraction, indicating that duration and amplitude of reticular contraction were more associated with duodenal NDF flow than frequency. However, duration of reticular contraction (r2 = .47, P = .014) explained a greater variation in duodenal NDF flow than amplitude (r2 = .011, P = .74). Stepwise multiple regression also indicated that duration of reticular contraction was the attribute most associated (r2 = .76, P = .0001) with duodenal NDF flow. It was concluded that the changes in digesta passage from the ruminoreticulum were associated primarily with changes in the duration of reticular contraction.

Effect of dietary level of barley-based supplements and ruminal buffer on digestion and growth by beef cattle1

Six ruminally cannulated beef steers were used in a 6 x 6 Latin square experiment with a 3 x 2 factorial arrangement of treatments to evaluate the effects of barley supplementation (BS; 10, 30 or 50% of diet DM) and ruminal buffer (RB; Na sesquicarbonate at 0 or 4% of BS DM) addition to bromegrass hay-based diets on digestion. When early- (boot) and late- (full maturity) havested bromegrass and wheat straw substrates were incubated in situ, no interactions (P greater than .10) involving substrate with dietary BS or RB were observed, indicating that forages differing in fermentability responded similarly to different ruminal environments. Averaged across substrates, RB had no effect with 10% BS and a positive effect with 30% BS, but a negative effect with 50% BS diets (BS x RB, quadratic; P less than .05) for in situ DM and NDF disappearance for 18 and 24 h of incubation and for rate of disappearance of potentially degraded DM and NDF. Intakes of DM and digested DM were greater (P less than .01) for RB diets; however, RB had no effect (P greater than .10) on total tract DM and NDF digestibility. Intake and digestibility of DM increased linearly (P less than .01), whereas NDF digestibility decreased linearly (P less than .01) as BS percentage was increased in the diet. Sixty beef steers (avg initial wt 302 kg) were fed the same dietary treatments in a growth experiment. A numerical improvement in DM intake (P = .20) and ADG (P = .06) was observed when RB was provided with the 50% BS diet. Results of these experiments indicate that RB may moderate negative effects occurring on ruminal fiber digestion when grains are used to supplement forage-based diets; however, improvements in ruminal digestion were not translated effectively to improved animal productivity.

Manipulation of the Functional Activity of the Gut by Dietary and Other Means (Antibiotics/Probiotics) in Ruminants

The mucosa of the gut is some of the most metabolically active tissue in the body. This paper discusses the methodology used to assess enterocyte cell metabolism and nutrient uptake in the reticulorumen and small intestine of ruminant species. Metabolism of volatile fatty acids and glucose by this tissue may limit the availability of essential nutrients to peripheral tissues, and the extent to which this may vary between concentrate-based and forage-based diets is discussed. Factors that affect the development and expression of metabolite uptake by the enterocyte are considered in addition to the influence that manipulation of the microbial flora of the gut by the use of antibiotic growth promoters or probiotics may have upon this process. Data are presented to show that the use of antibiotic compounds in ruminant feeds can influence the rate of cell turnover in the small intestine and the rate of glucose uptake by isolated brush border vesicles.

A comparison of silage-based and dried forage-based diets, and the effect of protein supplementation of a silage-based diet for finishing beef cattle

ABSTRACTAn experiment was carried out to compare silage-based and dried forage-based diets for finishing beef cattle and to examine the effects of protein supplementation and formaldehyde treatment of silage on performance and carcass composition. The four diets used consisted, on a dry matter basis, of (1) 700 g/kg formic acid-treated grass silage and 300 g/kg low protein cereal-based concentrate (LPC), (2) 720 g/kg formic acid-treated silage and 280 g/kg high protein cereal/fish meal concentrate, (3) 600 g/kg formaldehyde-treated silage and 400 g/kg LPC, and (4) 480 g/kg artificially dried grass and grass hay and 520 g/kg LPC. The silages were well preserved with 33 to 40 g ammonia N per kg total nitrogen. The diets were offered to 40 British Friesian castrated male cattle which were initially 387 (s.e. 2·9) kg live weight. For diets 1 to 4 respectively metabolizable energy intakes were 91·8, 94·7, 94·9 and 91·8 MJ/day; total nitrogen intakes 192, 234, 189 and 191 g/day; live-weight gains 0/89, 0/93, 0/86 and 0/82 (s.e. 0/045) kg/day; carcass gains 0·51, 0·52, 0·52, 0·52 and 0·50 (s.e. 0·33) kg/day; mean subcutaneous fat depths 5·6, 5·4, 5·3 and 6·0 (s.e. 0·41) mm; marbling scores 3·0, 3·3, 3·2 and 2·6 (s.e. 0·19) and areas of m. longissimus dorsi 65·7, 66·4, 64·7 and 64·3 (s.e. 1·66) cm2. It is concluded that performance, efficiency of energy utilization and carcass fatness were similar for a diet containing 700 g/kg well preserved grass silage and a dried forage-based diet with a similar intake of energy and protein. Protein supplementation of a diet based on formic acid-treated silage or formaldehyde treatment of silage did not affect performance or carcass fatness.