Grain feeding and the dissemination of acid-resistant Escherichia coli from cattle

The gastric stomach of humans is a barrier to food-borne pathogens, but Escherichia coli can survive at pH 2.0 if it is grown under mildly acidic conditions. Cattle are a natural reservoir for pathogenic E. coli, and cattle fed mostly grain had lower colonic pH and more acid-resistant E. coli than cattle fed only hay. On the basis of numbers and survival after acid shock, cattle that were fed grain had 10(6)-fold more acid-resistant E. coli than cattle fed hay, but a brief period of hay feeding decreased the acid-resistant count substantially.     

Basal medium for the selective enumeration of rumen bacteria utilizing specific energy sources

A 40% rumen fluid basal medium has been developed that without added substrate will support growth of about 10% or less of the total colony count obtained with 40% rumen fluid-glucose-cellobiose-starch-agar medium (RGCSA). The basal medium is prepared by anaerobic incubation of all ingredients in RGCSA medium except the carbohydrates, Na2CO3, and cysteine for 7 days at 38 degrees C. After incubation, substrate(s), Na2CO3 and cysteine are added and the medium is tubed and sterilized as in normal medium preparation. When xylose was included with glucose, cellobiose, and starch as added carbohydrates in the incubated medium, colony counts were comparable to those obtained with RGCSA medium. The addition of specific carbohydrates or other substrates as energy sources to the basal medium suggested that the percentage of the bacterial population capable of utilizing these energy sources was influenced by the ration of the animal; however, considerable animal variation and day-to-day variation in a given animal was observed. Comparison of the population in animals fed either orchardgrass hay or 60% corn-40% orchardgrass (60-40) indicated little or no difference for the percentage of bacteria utilizing glucose, pectin, xylan, or mannitol. Increases in the percentages of xylose-, cellobiose-, Glycerol-, and lactate-utilizing bacteria occurred with the orchardgrass hay ration, whereas the percentage of starch-digesting bacteria was increased significantly (P less than 0.01) in the animals fed the 60-40 ration. A limited number of bacterial strains were isolated from the basal medium without added substrate, most of which were atypical with respect to the predominant rumen bacteria. Growth of these strains, even in complex media, was very slow and limited. Based on these data with isolated strains and colony counts obtained in roll tube medium containing only minerals, resazurin, agar, Na2CO3, and cysteine, the selective medium overestimated the percentage of bacteria able to use a specific energy source. This overestimate was 6 to 7% of the total culturable count.     

The effects of starch and protein degradation rates, hay sources, and feeding frequency on rumen microbial fermentation in a continuous culture system

Six continuous culture fermenters were used in three experiments to study the effects of dietary starch and protein degradability combination, hay sources, and feeding frequency on fermentation by rumen microorganisms. Experiments 1 and 2 used a 3 x 2 factorial design in which six diets were formulated to contain low (LS), medium (MS), or high starch degradability (HS) in combination with low (LP) or high protein degradability (HP). The dietary combinations were (1) LS + HP, (2) LS + LP, (3) MS + HP, (4) MS + LP, (5) HS + HP, and (6) HS + LP. In experiment 1, pangola was used as the hay source, and in experiment 2, alfalfa hay was used. In experiment 3, two starch degradabilities (LS, MS) and two hay sources (alfalfa, A; pangola, P) were combined with two feeding frequencies (2 X/d, 12 X/d). The dietary combinations were (1) LS + A + 12 X/d, (2) MS + A + 12 X/d, (3) LS + A + 2 X/d, (4) MS + A + 2 X/d, (5) LS + P + 12 X/d, and (6) MS + P + 12 X/d. A CRD design was used for experiment 3. Two rumen-cannulated Holstein cows fed alfalfa hay ad lib were used as donors of rumen fluid for all experiments. Each period was 6 d in length, with 5 d for adaptation and 1 d for sampling. In experiments 1 and 2, the effects of starch degradability on the composition of rumen microorganisms were significant. The MS or HS with HP had the highest total bacterial and protozoal density (P < 0.05). As for VFA, pH and nitrogen products, the effects of starch and protein degradability were not significant. There was no interaction between starch and protein degradability on most of microbial composition (ammonia-N, microbial nitrogen). In experiment 3, 12 X/d feeding frequency (MS + A + 12 X/d vs. MS + A + 12 X/d) resulted in higher pH, which tended to increase bacterial and protozoal density and starch and protein digestibilities. Different hay sources altered the starch and protein synchronization effect on the ammonia-N concentration (mg/dl) and non-ammonia N content (% DM) in the continuous culture system.     

Cottonseed meal or feather meal supplementation of ammoniated tropical grass hay for yearling cattle

Despite high N intake by cattle consuming ammoniated forages, improvements in ADG might be expected be feeding proteins that supply ruminally available and(or) undegraded intake protein. Growth studies with 220-kg steers were conducted to evaluate ammoniated hay plus a liquid cane molasses-based supplement containing urea or a combination of urea and .07, .14, or .21 kg of CP daily from cottonseed meal (CSM) or feather meal (FM). Steers grazed dormant pasture and were fed hay plus 1.36 kg of DM daily per steer of the supplement. In each of 3 yr, total DM intake was similar (P > .60) among treatments, averaging 3.0% of BW. Daily gain by steers supplemented with urea and maximum ADG were similar across years, ranging from .21 to .23 kg and .50 to .60 kg, respectively. In all years for CSM supplementation, and in two of the three years for FM supplementation, increasing level of CP supplementation resulted in linear (P < .01) increases in ADG and gain:feed ratio (GF), with no differences (P > .10) between the protein sources. In one year, ADG and GF by steers supplemented with FM were maximized at the .07 kg of CP level, suggesting greater efficiency of protein utilization in FM. Improved performance by cattle fed ammoniated tropical grass hay may be obtained by feeding a protein supplement that provides preformed protein that is either moderately or highly resistant to ruminal degradation. Ruminal degradation characteristics of protein sources may influence efficiency of protein utilization in cattle fed ammoniated tropical grass hay plus molasses-based supplements.     

A review of bloat in feedlot cattle

Improvements in feedlot management practices and the use of various feed additives have reduced, but not eliminated, the occurrence of bloat in feedlot cattle. Feedlot bloat reduces the profitability of production by compromising animal performance and more directly by causing fatalities. In feedlots, bloat is associated with the ingestion of large amounts of rapidly fermented cereal grain and destabilization of the microbial populations of the rumen. An abundance of rapidly fermented carbohydrate allows acid-tolerant bacteria (e.g., Streptococcus bovis and Lactobacillus spp.) to proliferate and produce excessive quantities of fermentation acids. As a result, ruminal pH becomes exceedingly low, and this impairs rumen motility. Further, the excessive production of mucopolysaccharide or "slime" increases the viscosity of ruminal fluid and stabilizes the foam implicated in frothy feedlot bloat. Although protocols have been developed to treat feedlot bloat, the most profitable approach is to use management strategies to reduce its likelihood. Amount of roughage, grain processing techniques, selection of cereal grain (e.g., corn, barley, and wheat), dietary adaptation periods, and various additives (e.g., ionophores) can influence the occurrence of bloat in feedlot cattle. Successful management of these factors depends on a thorough understanding of the behavioral, dietary, and microbial events that precipitate bloat in feedlot cattle.     

Significant contribution of spleen cells in mediating the lethal effects of endotoxin in vivo

Two closely related, histocompatible mouse strains that have marked differences in both in vitro and in vivo responses to endotoxin were used to evaluate the contribution of lymphoid cells to the lethal effect of endotoxin. C3H/HeJ mice are endotoxin resistant, whereas C3H/HeN mice are endotoxin sensitive. In vitro spleen cell mitogenic responses to endotoxin were similar in untreated mice and in mice that received sublethal irradiation (450 R) followed by reconstitution with autologous spleen cells. Reconstitution with spleen cells from the related strain produced chimeric animals with spleen cell mitogenic activity like that of the donor strain. When chimeric animals were subjected to a lethal challenge of endotoxin, their response was markedly altered by the transferred lymphoid cells. C3H/HeJ animals reconstituted with C3H/HeN cells became more endotoxin sensitive, whereas C3H/HeJ cells became more endotoxin resistant. These results indicate that spleen cells play a significant, detrimental role in endotoxin-induced lethality.     

Monocondylar fractures of the femur. Therapeutic strategy and clinical outcome]

Two groups of 3 120-160-kg Holstein steers were fed a diet high in carbohydrate and low in long fiber and either with or without added sodium sulfate. Prior to and during the course of feeding the experimental diet, the concentrations of rumen hydrogen sulfide gas and rumen fluid sulfide were determined by a simple sulfide detector tube method and by sulfide-selective electrode, respectively. Other measurements included rumen fluid pH, blood creatine kinase, and blood sulfhemoglobin. Two of the 3 steers fed the high-sulfate diet developed signs and lesions of polioencephalomalacia. Clinical signs included episodic ataxia and blunted or absent menace reaction. Increased ruminal H2S gas concentrations occurred in all 3 steers consuming the diet with added sulfate. The onset of clinical signs coincided with the onset of elevated H2S concentrations. These increases were 40-60 times the values measured in the steers consuming the diet without added sulfate. In contrast, increases in rumen fluid sulfide concentrations usually rose to 4 times that of control steers. The steers fed an identical diet but without added sulfate exhibited no signs or lesions of polioencephalomalacia and no elevations of sulfide in rumen gas or fluid. All steers had a modest decrease in rumen fluid pH associated with the transition to the concentrate diet. No significant changes were observed in any of the blood measurements of any of the steers. An additional pair of steers was fed the experimental diet with or without added sulfate to compare the ruminal H2S gas concentrations estimated by H2S detector tubes with those estimated by a different method of analysis utilizing charcoal trapping of H2S, conversion to sulfate, and measurement of the sulfate. Both methods yielded comparable estimates of H2S concentration. Overall, these data indicate that changes in rumen gas cap H2S concentrations are larger than changes in rumen fluid sulfide concentration and the estimation of rumen gas cap H2S concentration may be a practical approach to detecting pathologic increases in ruminal H2S gas. This simple, rapid, minimally invasive method should be useful for estimating the H2S content of ruminal gas under field conditions.     

Pathogenicity of K. ozaenae for mice and chick embryos

The authors tested the virulence of K. ozaenae--its old museum strains, the freshly isolated ones and those passaged on meat-peptone agar; experiments were carried out on mice and chick embryos. To mice the culture was administered intraperitoneally, subcutaneously, intranasally, and to embryos--into the allantoic cavity and on the chorioallantoic membrane. Irrespective of the method of administration, the freshly isolated strains were highly virulent both for mice and for chick embryos. The virulence of such strains decreased in the process of passaging on the nutrient medium. Old museum strains were of low virulence for albino mice and avirulent for chick embryos. In comparing the virulent and avirulent strains there were found no differences in the antigenic structure and toxicity of the Boiven complex, cytoplasm, membrane, capsular polysaccharide or whole virulent and avirulent bacteria killed by heating.     

Changes in factors affecting the rate of digesta passage during pregnancy and lactation in sheep fed on hay

The objective of this study was to assess feed intake and digesta passage characteristics in five Blackhead ewes fed hay ad libitum during pregnancy [I: d 60-80 post conceptionem (p conc); II: d 105-125 p conc; III: d 128-148 p conc] and lactation [IV: d 10-30 post partum (pp); V: d 35-55 pp]. During pregnancy, feed intake and rumination activity increased. The rumen fluid volume and the daily number of A-cycles did not change significantly. The mean retention time (MRT) of the fluid and particle markers in the reticulorumen (RR) and distal to the RR decreased by 14-32%. During lactation, the rumen fluid volume increased as compared to pregnancy by about 15%. Daily feed intake peaked during period V (83.7 g DM/kg BW0.75). The MRT of particle markers in the RR increased as compared with late pregnancy. Both during pregnancy and lactation, the increased passage rate of digesta was achieved predominantly by an increased amount of digesta passing through the reticulo-omasal orifice during each opening. Sieving of forestomach contents and faeces revealed that the breakdown rate of large feed particles did not limit digesta passage.     

Effects of corn processing on the site and extent of digestion in lactating cows

Three multiparous Holstein cows in midlactation were fitted with ruminal and duodenal cannulas. Cows were used in an experiment with a 3 x 3 Latin square design to study the effect of corn processing on nutrient flow from the rumen to the duodenum and on ruminal fermentation in lactating cows. Cows were fed diets consisting of 40% forage and 60% concentrate. The only difference in dietary ingredients was the type of processed corn included at 24% of the total diet (as-fed basis). Treatments were dry-rolled corn with a bulk density of 0.54 kg/L and steam-flaked corn with a bulk density of either 0.39 kg/L or 0.31 kg/L. Ruminal fluid pH was not affected by corn processing, but steam-flaking decreased the molar percentage of acetate and increased the molar percentage of propionate. Digestibility of starch in the rumen was not affected by processing. Digestibility of starch entering the duodenum as well as apparent digestibility of starch in the total tract were increased by steam-flaking. Flow of feed and microbial N from the rumen and microbial N efficiency were not affected by grain processing. Yields of milk and milk components as well as composition of milk were not affected by grain processing.     

Effect of dietary monensin on ovarian response following gonadotropin treatment in prepuberal heifers

Twenty prepuberal Charolais X Brahman-Hereford heifers were randomly assigned to be fed a concentrate containing either 0 mg (C) or 200 mg (M) monensin sodium/head/day. Coastal bermudagrass hay was fed ad libitum. Average daily gain was similar for the two groups. Each heifer received 1 mg of porcine follicle stimulating hormone (FSH-P) (Armour) at 0800 and 2000 hr on days 22 through 26 (10 mg total) and 2,500 IU human chorionic gonadotropin (HCG) on day 27. Flank laparotomy was performed on day 30, for examination of ovaries, and ovariectomy was performed on day 37. The average ovarian size +/- standard error at day 15 ws 3,730 +/- 66 mm3 and 1,848 +/- 55 mm3 for groups M and C, respectively (P < .025), as measured by rectal palpation. Numbers of ovulation sites measured on day 30 were 9.1 +/- 2.2 and 4.9 +/- 1.8 per heifer for groups M and C, respectively (P < .01). After ovariectomy on day 37, heifers fed M were found to have greater ovarian weight (P < .05), more corpora lutea (CL) (P < .05), greater total luteal weight (P < .05), more follicles (P < .01) and greater weight of follicular fluid (P < .05) and stroma (P < .025) than controls. CL were analyzed for progesterone content by spectrophotometric procedures. Heifers fed M had slightly larger CL (P < .10) with progesterone concentrations similar to those in CL from controls. This resulted in more luteal progesterone per CL and more luteal progesterone per heifer in the M heifers than in the controls. Prepuberal heifers fed M, which caused the expected shifts in rumen fermentation and volatile fatty acid production, exhibited an enhanced ovarian response to gonadotropins compared to that exhibited by controls.     

Embryotoxicity of leukocyte extracts and its relationship to intrauterine contraception in humans

Twelve human uteri containing intrauterine contraceptive devices (IUDs) and ten uteri without IUDs were obtained at hysterectomy. Samples of fluid were collected from the uterine lumina by absorbing the fluid in small pieces of lens paper. In the samples of luminal fluid we measured the concentration of beta-galactosidase, an enzyme which is present in human neutrophilic leukocytes and whose concentration in luminal fluid should correlate with the local inflammatory response to the intrauterine foreign body. In the samples of fluid from IUD-bearing uteri, the concentration of beta-galactosidase was significantly (P less than 0.0005) greater than that in luminal fluid from control uteri, the averages of the two groups differing by 3.8 units. To determine whether a foreign-body response of this magnitude could have any effect on preimplantation embryos, we cultured mouse embryos from day 4 to day 7 of development in culture media to which extracts of human leukocytes were added. All mouse embryos were killed when the culture media contained enough leukocyte extract to give beta-galactosidase concentrations of 0.5 unit or higher. Thus mouse embryos were killed by leukocyte extracts whose beta-galactosidase concentrations were actually less than the concentration of this marker enzyme measured in IUD uterine fluid. This comparison indicates that the luminal fluid in IUD-bearing uteri contains leukocyte break-down products in sufficient concentration to be lethal for preimplantation embryos.     

Effect of ruminal cellulolytic bacterial concentrations on in situ digestion of forage cellulose

To evaluate the effects of ruminal cellulolytic bacterial concentrations on in vivo cellulose digestion, varying percentages of flaked soybean hulls were substituted for orchardgrass hay in high-forage diets fed to sheep. In two experiments, total and cellulolytic ruminal bacterial concentrations were not affected by diet. No differences were found for in situ digestion of forage cellulose in the first experiment; however, in Exp. 2, ruminal pH and in situ cellulose digestion were lower (P<.01) with a 40% soybean hull diet. In Exp. 3 with four sheep, two diets were compared, one containing 19.6% cellulose from alfalfa meal and the other 64.3% purified wood cellulose. Ruminal pH was lower (P<.02), 9 and 24 h after feeding, for the high-cellulose diet. Total bacterial concentrations did not change with diet; however, the concentration of cellulolytic bacteria increased (P<.05) when the higher cellulose diet was fed. In situ cellulose digestion was not different between diets. In Exp. 4, 3% sodium bicarbonate was added to the high-cellulose diet, and it was fed twice a day. No differences were observed in pH between diets (P>.42). However, the concentration of total ruminal bacteria increased (P<.06), the concentration of cellulolytic bacteria increased (P<.03), and the percentage of cellulolytic bacteria increased (P<.04) when the buffered high-cellulose diet was fed. In situ digestion of alfalfa cellulose at 30 h was not different between diets (P>.60). These data indicate that the concentration of cellulolytic bacteria is not the limiting factor in the digestion of cellulose in the rumen.     

Nonstructural carbohydrate and protein effects on rumen fermentation, nutrient flow, and performance of dairy cows

Four multiparous Holstein cows fitted with rumen and duodenal cannulas were used in a 4 x 4 Latin square with 20-d periods. Four diets were formulated for high and low rumen availabilities of nonstructural carbohydrate and protein. Cows were milked and fed three times daily. Milk production averaged 39 kg/d and was unaffected by treatment. Dry matter intake and 4% FCM production were increased by 1 kg/d for cows fed the low rumen-available nonstructural carbohydrate diets. Milk protein percentage was elevated when either the high rumen-available nonstructural carbohydrate or high rumen-available protein diets were fed. Low rumen-available protein diets increased duodenal passage of total essential AA but did not increase passage of Arg, Ile, and Met. Passage of bacterial N was highest (262 g/d) when high rumen-available nonstructural carbohydrate was combined with high rumen-available protein and was lowest when high rumen-available nonstructural carbohydrate was combined with low rumen-available protein (214 g/d). Diets with low rumen availabilities of protein were not advantageous, possibly because duodenal passage of one or more of the limiting AA was not increased. Passage of bacterial N to the duodenum was highest when rumen availabilities of both nonstructural carbohydrate and protein were high.     

Tumor inhibition in mice by lipopolysaccharide-induced peritoneal cells and an induced soluble factor

Lipopolysaccharide (LPS) was shown to prevent tumor growth in BALB/c mice when administered either prior to or after the inoculation of lethal doses of tumor cells. An attempt to elucidate the mechanism of this phenomenon utilizing in vivo protocols was made by the adoptive transfer of tumor protection with peritoneal cells as well as with cell-free peritoneal fluids obtained from non-tumor-bearing, LPS-stimulated syngeneic mice. The in vivo-activated peritoneal cells from LPS-treated mice were capable of adoptively transferring tumor protection at peritoneal cell to tumor cell ratios ranging from 1,000:1 to 100:1. Experiments were also performed that indicate that: (i) LPS exerts no direct toxic or inhibitory effect on the tumor cells, and (ii) that residual LPS present in cell and fluid preparations was not responsible for such protection.     

Bacterial infection and endotoxin in female reproductive tract in rats: correlation with the developmental status of preimplantation embryos

During mammalian preimplantation development, a substantial numbers of embryos are believed to be lost for reasons that are unclear. Using female rats, we investigated whether the developmental status of embryos is influenced by bacterial infection and endotoxin in the reproductive tract. From the vagina of cycling rats (n = 11), 21 bacterial isolates were identified; they were Streptococcus faecalis (S. faecalis; 38%), Escherichia coli (E. coli; 19%), Acinetobactor calcoaceticus (A. calcoaceticus; 14%), and coagulase negative staphylococcus (14%), Micrococcus sp. (5%), Bacillus subtilis (B. subtilis; 5%) and Proteus vulgaris (P. vulgaris; 5%). From the vagina of day 4 pregnant rats (n = 12), 26 isolates were identified; they were S. faecalis (23%), A. calcoaceticus (23%), E. coli (15%), Micrococcus sp. (15%), B. subtilis (8%), P. vulgaris (4%), Staphylococcus aureus (4%), beta-hemolytic streptococcus (4%) and Pseudomonas aeruginosa (4%). Gram negative bacteria found in the vagina of cycling and day 4 pregnant rats were 38% and 46%, respectively. In both, bacterial load was 10(3)-10(5) colony forming units and there was no association with the abnormality of the recovered embryos. However, in two day 4 pregnant animals, pathogenic bacteria (Staphylococcus aureus and beta-hemolytic streptococcus) were isolated and embryos recovered from them were degenerated and deformed. The vagina of day 9 pregnant animals (n = 7) were, however, sterile. Consistently, in all animals, the upper reproductive tract (uterus and oviduct) was devoid of any bacteria and no anaerobic bacteria were isolated from any part of the tract. The levels of endotoxin in the vagina of cycling and day 4 pregnant rats were 1.35 +/- 0.1 and 1.17 +/- 0.1 endotoxin units (EU), respectively. It was undetectable in the oviduct and uterus of all animals (n = 5) except one which showed high levels of endotoxin in uterus (4.5 EU) and oviduct (2.2 EU) and the animal also produced degenerated and deformed embryos. These results indicate that common bacterial flora of vagina may not affect embryo development and the presence of pathogenic bacteria in the vagina and/or endotoxin in reproductive tract could be detrimental to viability of gametes and preimplantation embryos in rats.     

Characterization of proteolytic activities of rumen bacterial isolates from forage-fed cattle

The proteolytic activities of eight strains of ruminal bacteria isolated from New Zealand cattle were characterized with respect to their cellular location, response to proteinase inhibitors and hydrolysis of artificial proteinase substrates. The Streptococcus bovis strains had predominantly cell-bound activity, which included a mixture of serine and cysteine-type proteinases which had high activity against leucine p-nitroanilide (LPNA). The Eubacterium strains had a mainly cell-associated activity with serine and metallo-type proteinases which showed high activity against the chymotrypsin substrate, N-succinyl alanine alanine phenylalanine proline p-nitroanilide (NSAAPPPNA) and some LPNA activity. A Butyrivibrio strain, C211, had a cell-bound mixture of cysteine and metallo-proteinase activities and strongly hydrolysed NSAAPPPNA and LPNA while the high activity Butyrivibrio-like strain, B316, had a cell-bound, mainly serine proteinase activity which strongly hydrolysed NSAAPPPNA. A Prevotella-like strain, C21a, had a mixture of cysteine, serine and metallo-proteinase activities which were cell-bound and hydrolysed LPNA. The activities of these strains did not match those of the bacterial fraction of rumen fluid, which contained activities mainly of the cysteine type with specificity towards the substrate N-succinyl phenylalanine p-nitroanilide. The contribution of these strains to proteolysis in the rumen is discussed.     

Biogenic amines in silage, apparent postruminal passage, and the relationship between biogenic amines and digestive function and intake by steers

A 4 x 4 Latin square experiment was conducted to examine abomasal passage of biogenic amines in steers fed silage and their related effects on intake, digestibility, and digestive function. Thirty percent of the dry matter (DM) in the diets consisted of alfalfa forage, which was fed as either hay or silage. The DM from alfalfa silage DM was substituted at 0, 33, 67, and 100% for DM from alfalfa hay and was fed to four ruminally and abomasally cannulated steers. The roughage component of the diet constituted 50% of the DM and consisted of 60% alfalfa silage or hay and 40% tropical corn silage. The concentrate was composed mainly of ground corn. The concentrations of putrescine and cadaverine in abomasal digesta increased as alfalfa silage in the diet increased. Abomasal recovery of biogenic amines, a product of their concentration in abomasal digesta and the passage of DM through the abomasum, was negatively correlated with intake. Abomasal recovery of most amines was 5 to 20% of intake. Abomasal recovery of cadaverine was correlated with depressed intake. Total DM intake was reduced 8.3 to 25.8% as the proportion of alfalfa silage in the diet increased. Frequency of reticular contractions, intake, ruminal DM digestibility, ruminal outflow, volatile fatty acids, and total tract DM digestibility decreased in steers fed diets that contained more alfalfa silage. Ruminal fluid pH and NH3 concentration increased in steers fed more alfalfa silage; however, mass and the DM percentage of ruminal contents decreased linearly. Postprandial insulin concentrations were quadratically related to the proportion of alfalfa hay or silage in the diet. Intraruminal metabolism of biogenic amines is extensive based on the relatively low quantities recovered in abomasal digesta; however, the amounts recovered in abomasal digesta were related to intake depression and associated physiological effects.     

Ruminal microbial and fermentative changes associated with experimentally induced subacute acidosis in steers

We used six ruminally cannulated steers in a two-period crossover design to study ruminal fermentative and microbial changes associated with induced subacute acidosis. Steers were adapted to either an 80% alfalfa hay (hay-adapted)- or corn grain (grain-adapted)-based concentrate diet. After feed was withheld for 24 h, steers were overfed with an all-grain diet at 3.5 x NEm daily for 3 d. Ruminal contents and jugular blood samples were collected before withholding feed and at 0 and 12 h daily for 3 d during the overfeeding period. Ruminal samples were analyzed for pH, lactate, VFA concentrations, and counts of total anaerobic, amylolytic, lactic acid-producing and -fermenting bacteria, and ciliated protozoa. Blood samples were analyzed to assess acid-base status. Ruminal pH declined to a range of 5.5 to 5.0 with increased VFA concentrations, but normal lactate concentrations (<5 mM) were indicative of subacute acidosis. Total viable and amylolytic bacterial counts were higher (P < .05) in grain-adapted than hay-adapted steers. Anaerobic lactobacilli counts increased over time (P < .01) in both groups and were generally higher in grain-adapted than hay-adapted steers. Lactate-utilizing bacteria were initially greater in grain-adapted than hay-adapted steers and increased over time in both groups following grain challenge. Total ciliates were initially higher (P < .05) in grain-adapted than hay-adapted steers and decreased after 48 h in both groups. Blood acid-base changes were minimal. Bacterial changes associated with subacute acidosis resemble those reported during adaptation to grain feeding, and the decline in ciliated protozoa may be the only microbial indicator of a potentially acidotic condition in the rumen.     

Silage or limit-fed grain growing diets for steers: II. Empty body and carcass composition

The influence of energy source (silage- or grain-based) on empty body and carcass composition and adipocyte cellularity independent of rate of gain was tested. Sixty-four Angus steers were allotted to either a forage (ad libitum) or grain (limit-fed) diet for a growing phase (145 d) followed by 45, 75, or 105 d of ad libitum access to a grain-based diet. Eight steers were slaughtered initially and eight from each treatment were slaughtered at the end of the growing phase, and at each of the termination dates. The silage growing diet consisted (DM basis) of 55% sorghum silage (approximately 24% dry matter), 22% alfalfa hay, 11% ground shelled corn, and 11% soybean meal. The grain-based growing diet was composed of 77% ground shelled corn, 5% soybean meal, 14% cottonseed hulls, 3% molasses, and 1% salt and mineral; it was limit-fed to produce the same rate of gain as the silage diet. No implants or ionophores were used. At the end of the growing phase, the steers fed grain were heavier and had a higher percentage of fat in the empty body (24 vs 19% fat) and the carcass (26 vs 21% fat) than did steers fed forage. Rate of gain during the growth phase was related positively to percentage of carcass fat; when corrected for fill, data for both diets fit one regression line for fat vs rate of gain. When adjusted for gain during the growing phase, fat content was not different in empty body or carcass, but internal fat was higher (P < .10) for steers fed grain. After 45 d on the finishing diet, carcass fat remained low (23%), but after 75 and 105 d, fat content reached 27%. Source of energy did not detectably affect carcass composition independent of rate of gain. Cell size of adipocytes from four adipose depots increased with time on feed but were not affected by diet during the growing phase. Lean Choice beef can be produced in only 45 d in the feedlot with medium-framed Angus cattle.