Dietary trehalose enhances virulence of epidemic Clostridium difficile.

Clostridium difficile disease has recently increased to become a dominant nosocomial pathogen in North America and Europe, although little is known about what has driven this emergence. Here we show that two epidemic ribotypes (RT027 and RT078) have acquired unique mechanisms to metabolize low concentrations of the disaccharide trehalose. RT027 strains contain a single point mutation in the trehalose repressor that increases the sensitivity of this ribotype to trehalose by more than 500-fold. Furthermore, dietary trehalose increases the virulence of a RT027 strain in a mouse model of infection. RT078 strains acquired a cluster of four genes involved in trehalose metabolism, including a PTS permease that is both necessary and sufficient for growth on low concentrations of trehalose. We propose that the implementation of trehalose as a food additive into the human diet, shortly before the emergence of these two epidemic lineages, helped select for their emergence and contributed to hypervirulence.

Isolation and preliminary characterization of the human and mouse homologues of the bacterial cell cycle gene era.

Era is an essential GTPase that is required for proper cell cycle progression and cell division in Escherichia coli and is found in nearly all bacteria sequenced to date. To determine whether Era is also present in eukaryotic organisms, we searched the dbEST database and found EST clones coding for proteins that were similar to Era. Full sequencing of these ESTs from human and mouse identified a conserved homologue, ERAL1 (Era-like 1). ERAL1 maps to 17q11.2 in human and is located in the syntenic region of mouse chromosome 11. ERAL1 may be an attractive candidate for a tumor suppressor gene since ERAL1 is located in a chromosomal region where loss of heterozygosity is often associated with various types of cancer.

Synthetic lethal phenotypes caused by mutations affecting chromosome partitioning in Bacillus subtilis.

We investigated the genetic interactions between mutations affecting chromosome structure and partitioning in Bacillus subtilis. Loss-of-function mutations in spoIIIE (encoding a putative DNA translocase) and smc (involved in chromosome structure and partitioning) caused a synthetic lethal phenotype. We constructed a conditional mutation in smc and found that many of the spoIIIE smc double-mutant cells had a chromosome bisected by a division septum. The growth defect of the double mutant was exacerbated by a null mutation in the chromosome partitioning gene spo0J. These results suggest that mutants defective in nucleoid structure are unable to move chromosomes out of the way of the invaginating septum and that SpoIIIE is involved in repositioning these bisected chromosomes during vegetative growth.

Characterization of a prokaryotic SMC protein involved in chromosome partitioning.

smc of Bacillus subtilis encodes a homolog of eukaryotic SMC proteins involved in chromosome condensation, pairing, and partitioning. A null mutation in B. subtilis smc caused a temperature-sensitive-lethal phenotype in rich medium. Under permissive conditions, the mutant had abnormal nucleoids, approximately 10% of the cells were anucleate, and assembly of foci of the chromosome partitioning protein Spo0J was altered. In combination with a null mutation in spo0J, the smc mutation caused a synthetic phenotype; cell growth was slower and approximately 25% of the cells were anucleate. Our results demonstrate that the B. subtilis Smc protein, like its eukaryotic counterpart, plays an important role in chromosome structure and partitioning.

Cell cycle arrest in Era GTPase mutants: a potential growth rate-regulated checkpoint in Escherichia coli.

Era is a low-molecular-weight GTPase essential for Escherichia coli viability. The gene encoding Era is found in the rnc operon, and the synthesis of both RNase III and Era increases with growth rate. Mutants that are partially defective in Era GTPase activity or that are reduced in the synthesis of wild-type Era become arrested in the cell cycle at the predivisional two-cell stage. The partially defective Era GTPase mutation (era1) suppresses several temperature-sensitive lethal alleles that affect chromosome replication and chromosome partitioning but not cell division. Our results suggest that Era plays an important role in cell cycle progression at a specific point in the cycle, after chromosome partitioning but before cytokinesis. Possible functions for Era in cell cycle progression and the initiation of cell division are discussed.

Characterization of mutations affecting the Escherichia coli essential GTPase era that suppress two temperature-sensitive dnaG alleles.

Two suppressor mutations of the temperature-sensitive DNA primase mutant dnaG2903 have been characterized. The gene responsible for suppression, era, encodes an essential GTPase of Escherichia coli. One mutation, rnc-15, is an insertion of an IS1 element within the leader region of the rnc operon and causes a polar defect on the downstream genes of the operon. A previously described polar mutation, rnc-40, was also able to suppress dnaG2903. The other mutation, era-1, causes a single amino acid substitution (P17R) in the G1 region of the GTP-binding domain of Era. Analysis of the GTPase activity of the Era-1 mutant protein showed a four- to five-fold decrease in the ability to convert GTP to GDP. Thus, lowered expression of wild-type Era caused by the polar mutations and reduced GTPase activity caused by the era-1 mutation suppresses dnaG2903 as well as a second dnaG allele, parB. Phenotypic analysis of the era-1 mutant at 25 degrees C showed that 10% of the cells contain four segregated nucleoids, indicative of a delay in cell division. Possible mechanisms of suppression of dnaG and roles for Era are discussed.

Isolation and characterization of suppressors of two Escherichia coli dnaG mutations, dnaG2903 and parB.

The dnaG gene of Escherichia coli encodes the primase protein, which synthesizes a short pRNA that is essential for the initiation of both leading and lagging strand DNA synthesis. Two temperature-sensitive mutations in the 3' end of the dnaG gene, dnaG2903 and parB, cause a defect in chromosome partitioning at the nonpermissive temperature 42 degrees. We have characterized 24 cold-sensitive suppressor mutations of these two dnaG alleles. By genetic mapping and complementation, five different classes of suppressors have been assigned; sdgC, sdgD, sdgE, sdgG and sdgH. The genes responsible for suppression in four of the five classes have been determined. Four of the sdgC suppressor alleles are complemented by the dnaE gene, which encodes the enzymatic subunit of DNA polymerase III. The sdgE class are mutations in era, an essential GTPase of unknown function. The sdgG suppressor is likely a mutation in one of three genes: ubiC, ubiA or yjbI. The sdgH class affects rpsF, which encodes the ribosomal protein S6. Possible mechanisms of suppression by these different classes are discussed.

Effects of varying levels of duodenal or midjejunal glucose and 2-deoxyglucose infusion on small intestinal disappearance and net portal glucose flux in steers.

Six crossbred steers (261 +/- 18 kg BW) fitted with hepatic portal, mesenteric venous and arterial catheters, and duodenal, midjejunal, and ileal cannulas were used in a replicated 3 x 3 Latin square design to determine the effect of varying levels and site of glucose plus 2-deoxyglucose (2DG) infusion on net portal-drained visceral flux. Steers were fed chopped alfalfa in six equal portions daily at 1.5% of BW. Glucose (0, 9, or 18 g/h) and 2DG (0, 1, or 2 g/h) were infused continuously through the duodenal or midjejunal cannula (two infusion sites) at total glucose plus 2DG infusion rates of 0, 10, or 20 g/h. Arterial and portal blood samples were taken simultaneously at 20-min intervals from 5 to 9 h of infusion. Portal blood flow was determined by continuous infusion of p-aminohippurate and net flux was calculated as venous-arterial concentration (PA) difference times blood flow. Arterial concentration of glucose was not affected (P > .10) by glucose plus 2DG infusion, whereas arterial concentration of 2DG was greater (P < .05) when glucose plus 2DG was infused into the duodenum and increased (linear, P < .10) as amount of glucose plus 2DG infused into both the duodenum and midjejunum increased. Net portal flux and PA difference of glucose and 2DG were greater (P < .05) when glucose plus 2DG was infused into the duodenum. Although 2DG was infused at 10% of the total glucose plus 2DG infusion, it accounted for only 1.7 and .7% of the glucose plus 2DG appearing in portal blood when glucose plus 2DG was infused at 10 and 20 g/h, respectively. We conclude that glucose is more readily absorbed across the proximal-half than the distal-half of the small intestine, and that passive diffusion is a minor route of glucose absorption.

Efficacy of laidlomycin propionate to reduce ruminal acidosis in cattle.

Three trials were conducted to evaluate the efficacy of laidlomycin propionate (LP) to reduce the incidence and severity of ruminal acidosis in cattle fed high-grain finishing diets. In each trial, LP was fed at 0, 6, or 12 mg/kg of diet DM. In two acidosis-challenge trials, ruminally fistulated steers were fed (DM basis) a 50% concentrate diet and then fed a 95% concentrate diet at a specific intake (2.75% BW) or steers were dosed intraruminally with a 100% concentrate diet. Laidlomycin propionate did not alter ruminal pH or total acid concentrations, but in Trial 1 the 6 mg/kg level altered (P < .10) the molar proportions of the acids, increasing total ruminal VFA and decreasing ruminal lactate. In Trial 3, a finishing trial, LP reduced (P < .10) intake day-to-day variation of individually fed steers during a 13-d adaptation period from a 65 to a 100% concentrate diet, suggesting reduced incidence of subacute acidosis. Feed intake was lower (P < .05) during the first 13 d of the trial due to LP but was not affected over the entire trial. Laidlomycin propionate improved feed efficiency (gain/feed) when calculated on a live weight basis (linear, P = .05) or carcass weight basis (linear, P = .20). Laidlomycin propionate does not prevent ruminal acidosis, but it may reduce the severity of ruminal acidosis during adaptation to a 100% concentrate diet.

The effects of ruminal acidosis on volatile fatty acid absorption and plasma activities of pancreatic enzymes in lambs.

Twenty crossbred wethers (41.9 +/- 4.0 kg BW), each fitted with a ruminal cannula and a jugular catheter, were used in a completely randomized design to examine the effects of ruminal acidosis on plasma activities of pancreatic enzymes and fractional rates of VFA absorption. Lambs had ad libitum access to a 50% concentrate diet. Acidosis was induced by an intraruminal dose of glucose at 0, 6, 12, or 18 g/kg BW via the ruminal cannula. Ruminal fluid and plasma were collected 0, 4, 8, 12, 18, 24, 36, 48, and 72 h after dosing. Ruminal fluid pH was reduced (linear, P < .001) with increasing ruminal glucose. Total ruminal VFA concentration decreased (linear, P < .01) and D(-)-lactate (linear, P < .01) and L(+)- lactate (linear, P = .07) concentrations increased with increasing ruminal glucose. Activities of amylase and lipase in plasma were not affected by ruminal glucose (P > .10). Ten days after the acidosis insult, rumens were evacuated and contents were replaced with an isotonic Cr:VFA solution to measure ruminal VFA absorption. Ruminal fluid was collected hourly from 0 to 6 h. Fractional rate of acetate absorption was 13% lower for lambs receiving 18 g/kg BW glucose than for control lambs. In addition, fractional liquid passage rate was lower (P < .05) in lambs receiving 18 g/kg BW glucose 6 mo after the insult of acidosis. These data suggest that a short-term, severe insult of acute acidosis does not result in pancreatic tissue damage but may result in reduced ruminal VFA absorption for an extended period of time.

Effect of level and type of fat on subacute acidosis in cattle fed dry-rolled corn finishing diets.

Five experiments were conducted to determine the effect of fat addition to dry-rolled corn (DRC) finishing diets on subacute acidosis. In Exp. 1, five ruminally fistulated steers (410 +/- 12 kg BW) were used in a 5 x 5 Latin square design. Treatments consisted of 0, 2, 4, 6, or 8% tallow added to a 50% fine-ground corn: 50% dry-rolled wheat basal challenge diet and dosed intraruminally as an acidosis challenge. Area below pH 6 was determined to quantify the total decrease in ruminal pH over a 24-h period. Area below pH 6 responded quadratically (P < .05); greatest time below pH 6 occurred with diets containing 2, 4, and 6% tallow. In Exp. 2, six ruminally fistulated steers (527 +/- 47 kg BW) were used in a 6 x 6 Latin square design and intraruminally dosed with 0, 4, 6, or 8% tallow or 4 or 8% yellow grease added to a 50% fine-ground corn:50% dry-rolled wheat basal challenge diet. Area below pH 6 responded quadratically for both tallow (P = .10) and yellow grease (P < .05) and was greatest for steers dosed with 4% tallow or yellow grease and decreased as tallow or yellow grease increased from 4 to 8%. Experiment 3 was a metabolism study using six ruminally fistulated steers (469 +/- 68 kg BW) in a 6 x 6 Latin square design. Cattle were fed a DRC finishing diet containing 0, 4, 6, or 8% tallow or 4 or 8% yellow grease.(ABSTRACT TRUNCATED AT 250 WORDS)

Differential effects of plane of protein or energy nutrition on visceral organs and hormones in lambs.

Modulation of somatotrophic and homeorhetic hormones, along with changes in visceral mass and metabolic activity, were measured in growing lambs restricted in energy (ER) or metabolizable protein (PR) to maintain BW for 7 wk and then repleted for 2 wk. Control lambs were fed an adequate diet for 9 wk. Serum IGF-I decreased more rapidly in PR, but both ER and PR were 70% of controls by wk 7 of restriction (P < .05) and increased above controls by d 14 of repletion. Somatotropin, increased by PR, returned to control levels upon repletion (P < .05). Insulin was decreased by PR (P < .02) but was transiently elevated above controls by repletion in ER and PR at d 2 (P < .01). Serum triiodothyronine, reduced to 70% of controls by PR and ER, returned to control levels after d 6 of repletion (P < .05). Thyroxine declined gradually to 65% of controls in ER and PR (P < .07) but did not respond to repletion. By wk 7 of restriction, liver mass in ER and PR was decreased to 50% of controls (P < .05). Return of liver mass, on an empty body weight basis, occurred by d 2 of repletion (P < .01). In vitro O2 consumption per gram of liver tissue was increased to 125% of controls by ER and PR (P < .05). Calculated whole liver O2 consumption in ER and PR was 68% of controls at wk 7 of restriction (P < .10). Protein restriction had a more immediate impact on hormones but not on visceral mass or activity compared with energy restriction. Elevated IGF-I levels, as observed in previously restricted lambs, may mediate compensatory growth in ruminants.

Functional analysis of mutations in the transcription terminator T1 that suppress two dnaG alleles in Escherichia coli.

The mutations dnaG2903 and parB are both temperature-sensitive conditional lethal alleles of the Escherichia coli dnaG gene, which encodes the protein primase. The lesions are located in the 3' end of the gene, 9 basepairs apart, and both cause Glu-to-Lys substitutions in the carboxy terminus of primase. Previously, it was shown that dnaG2903 can be suppressed by point mutations in the rho-independent transcription terminator T1, which is located just upstream of dnaG in the rpsU-dnaG-rpoD macromolecular synthesis operon. We report here that parB can also be suppressed by point mutations in T1, demonstrating that parB can be suppressed in the same manner as dnaG2903. We also identified additional suppressors of dnaG2903 that are point mutations in T1, suggesting that defective transcription termination leading to overexpression of dnaG2903 and parB suppresses the temperature-sensitive phenotype of strains harboring these mutations. Utilizing two mutant rpoB alleles whose transcription termination phenotypes at rho-independent terminators have been previously characterized, we demonstrate that defective transcription termination leading to the overexpression of dnaG does indeed suppress dnaG2903 and parB. The point mutations in T1 identified in this study were analyzed for their effects on termination efficiency at T1. Our results indicate that the thermodynamic stability of the hairpin structures may not be the sole determinant of termination efficiency in vivo.

Effect of monensin and monensin and tylosin combination on feed intake variation of feedlot steers.

A trial involving four commercial feedlots and an individual feeding trial evaluated the effect of monensin and monensin/tylosin on intake variation and deaths from digestive disorders. Four commercial feedlots in Texas and Colorado fed 2,904 yearling crossbred steers (340 kg) high-grain diets containing approximately 82% grain, 8% silage and alfalfa hay, 4% fat, and 6% supplement (DM basis). Steers were allotted randomly to one of three monensin/tylosin levels: 1) no monensin or tylosin (control); 2) 22 mg/kg of monensin and 11 mg/kg of tylosin; or 3) 33 mg/kg of monensin and 11 mg/kg of tylosin. Monensin/tylosin reduced DMI (P < .05) and improved ADG (P < .05) and feed efficiency (P < .01). Intake variation associated with dry matter offered per pen was not different among treatments. In the individual feeding trial, feeding 27 mg/kg of monensin reduced (P < .10) DMI variation during grain adaptation and during d 57 to 70 and d 97 to 110 compared with the control (no monensin) diet. The magnitude of intake variance was 5 to 10 times greater with individually fed steers than with steers fed in the commercial feedlot pens. When the DMI of the individually fed steers were averaged and treated as a pen of steers, DMI variance was reduced drastically and was not different between treatments. We interpret these data to indicate that monensin and monensin/tylosin reduce feed intake variation among individual steers within a pen of steers. Pen means mask individual animal variation to the point that it is difficult to detect treatment differences.

Evaluation of acid detergent insoluble nitrogen as an indicator of protein quality in nonforage proteins.

Two trials were conducted to determine the adequacy of ADIN as an indicator of N digestibility. In Trial 1, eight nonforage plant protein sources were heated at 150 degrees C for 90 min in the presence of xylose (12.8% of CP, DM basis) to produce heat damage. Thirty-four wethers (average BW 40 kg +/- 9.9) were used to determine the effect of heat on N digestibility. Differences in ADIN were evident among the protein sources, and no significant heat x protein source interaction was observed for N digestibility. Apparent N digestibilities were reduced (P < .001) for all protein sources by heat treatment. Acid detergent insoluble N and N digestibility were correlated (r2 = .66). However, the assumption that ADIN was completely indigestible led to underestimation of N digestibility: approximately 58% of the ADIN was digestible in these feeds. In Trial 2, seven dried distillers grains from different distilling plants were tested for N digestibility using 24 wethers (average BW 35 kg +/- 3.6). Visual differences in color indicated possible differences in degree of heating in these feeds. The ADIN contents were quite variable among these feeds; however, there were no differences in N digestibility. The correlation between ADIN and N digestibility was weak (r2 = .24). These results indicate that ADIN values in nonforage protein sources predicted more protein damage than that estimated by in vivo N digestibility values.

Growth efficiency and digestibility of heated protein fed to growing ruminants.

Four trials were conducted to evaluate digestibility and growth efficiency caused by feeding heat-damaged protein. In Trial 1, 60 lambs (18.6 kg) were fed diets containing corn gluten meal (CGM) at five levels either of control (CGM-C) or heat-damaged (CGM-H), along with urea as the main supplemental N source. Efficiency of protein used for growth was determined by the slope-ratio technique. The heat damage to CGM decreased (P < .001) protein efficiency by 46%. In Trial 2, diets with the three highest CGM levels from Trial 1 were fed to 18 of the same lambs in a digestion trial. True N digestibility (TND) was 108% for CGM-C and was decreased (P < .05) 22% by heat damage. In Trial 3, 90 growing cattle (219 kg) were individually fed one of three protein supplements for 56 d. The protein supplement contained either a control source of dried distillers grains (DDG-C) or a heat-damaged source (DDG-H) at five levels, and a urea treatment was used as a negative control. Protein efficiency of DDG protein determined by the slope-ratio technique was decreased (P < .05) 34% by heat damage. In Trial 4, four yearling heifers (265 kg) were used in a 4 x 4 Latin square design to determine N digestibility of three diets used in Trial 3 (plus a diet not reported herein). True N digestibility averaged 98% for DDG-C and was decreased 7% by heat damage. These data suggest that some of the N in heat-damaged protein was absorbed postruminally but was not used for growth by growing ruminants.

Metabolizable protein and amino acid requirements of growing cattle.

Metabolizable protein and amino acid requirements for growing cattle were estimated using data from 11 research trials. A total of 543 steers were individually fed a high-roughage diet supplemented with protein at several levels above a urea supplement control. The mean weight for all animals was 253 kg, with a range in mean initial to final weights of 200 to 316 kg, respectively. Daily gain ranged from -.04 to .89 kg. Metabolizable protein for each treatment group was calculated at the point at which the protein requirement was met. The sum of dietary escape protein (basal and supplemental) and calculated microbial protein represented metabolizable protein supplied per test protein source analyzed in each trial. Daily gain was regressed against calculated metabolizable protein flow using weighted regression analysis (r2 = .69, n = 45) to determine the metabolizable protein requirements for maintenance (3.8 x BW.75 g/d, where BW is expressed in kilograms) and growth (305 g/kg of live weight gain). Calculated metabolizable amino acid requirements as a percentage of metabolizable protein for a 253-kg animal gaining .49 kg/d were as follows: methionine, 3.0%; total sulfur amino acids, 5.8%; lysine, 8.0%; tryptophan, 1.0%; threonine, 5.2%; valine, 5.7%; isoleucine, 5.6%; leucine, 6.9%; phenylalanine, 3.9%; and histidine, 1.6%. The proposed requirements were based on live animal gain and intake of metabolizable protein and should represent the needs of the growing beef animal.

Influence of ruminal protozoa on site and extent of starch digestion and ruminal fermentation.

Eight ruminally, duodenally, and ileally fistulated sheep were used to study the effects of protozoa on ruminal fermentation and starch digestion in the rumen and intestines. The experimental diet (75% grain DM basis) was based on a mixture of 67% high-moisture corn (HMC) and 33% dry-rolled grain sorghum (DRGS). Protozoa were reduced from 51,286 to 13,987 organisms/mL of ruminal fluid by feeding a diet (13 d) containing 9% tallow and monensin at 27 mg/kg (DM basis). Three sheep were defaunated by intraruminal infusions of lactic acid (20 to 30 g/d) and one sheep by washing the rumen and heating ruminal contents (60 degrees C for 20 min). No differences were observed in DM or starch intake, ruminal fluid pH, lactate concentration, or total tract starch digestibility. Molar proportion of acetate was reduced (48.6 vs 58.3%; P < .01) and propionate was increased (32.2 vs 23.4%; P < .03) by defaunation. Total VFA tended (P = .20) to be lower in faunated sheep (118.5 vs 139.2 mM). In situ rate of starch digestion of HMC (22.3 vs 14.7 %/h; P < .02) and DRGS (5.1 vs 3.3 %/h; P < .009) was increased by defaunation. Starch digestibility (percentage of intake) in the rumen was increased (P < .001) by defaunation (84.2 vs 93.7%) and was reduced (P < .002) in the small intestine (5.2 vs 13.6%). Defaunation increased (P < .03) amylolytic activity (.40 vs .17 units/mg of protein; P < .03) and osmotic pressure (321 vs 245 mOsm/kg; P < .006).(ABSTRACT TRUNCATED AT 250 WORDS)

Genetic variation in liver mass, body mass, and liver:body mass in mice.

Genetic variation for liver mass (LM), body mass (BM), and liver:body mass (LM/BM) was examined for outbred populations of laboratory mice. Liver mass and body mass data were collected on 170 pureline sires at 12 wk of age, representing four outbred stocks of laboratory mice; 523 of their male and female two-way-cross progeny at 9 or 12 wk; and 214 four-way-cross offspring at 12, 14, or 16 wk. Genetic differences for LM, BM, and LM/BM were found among the base sire lines and between two-way crosses. Heritabilities and genetic correlations for LM, BM, LM/BM, and LM/MBM (MBM = BM.75) were estimated using offspring-sire regression within and across characteristics. Estimates of heritabilities and genetic correlations were also derived from full-sib covariances in the two-way-cross generation. Heritability estimates pooled over all analyses were .53, .54, .36, and .40 for LM, BM, LM/BM, and LM/MBM, respectively. Body mass was highly genetically correlated (.87) with LM and lowly correlated with LM/BM. Previous research has indicated possible positive relationships between LM/BM and maintenance energy requirements in mature, nonlactating, nonpregnant animals. A selection index was developed for increasing BM but restricting genetic change in LM to zero. Selection using this index would be 40% as efficient in increasing BM as selection on BM alone but may hold maintenance energy requirements at a stable level.

Effect of grain sorghum hybrid on in vitro rate of starch disappearance and finishing performance of ruminants.

Forty-eight commercial grain sorghum hybrids were ranked on the basis of in vitro starch disappearance (IVSD) and starch content. Starch content ranged from 64.3 to 70.3% (P less than .01) and IVSD ranged from 5.2 to 6.3%/h (P less than .01). In the next year, 20 experimental grain sorghum hybrids consisting of 17 hybrids being developed for livestock diets and three for human diets were ranked according to IVSD, starch content, and CP content. In these samples, IVSD varied from 6.0 to 9.1%/h (P less than .05). Starch content and CP were not related to IVSD. Starch content was not correlated to CP content. Four of the original 48 grain sorghum hybrids, selected on the basis of IVSD (two fast and two slow), that differed in IVSD by 7.0% (6.5 to 7.0%/h), were fed for 133 d to steers (mean initial BW of 326 kg). The ADG of steers fed Hybrid A (fastest IVSD) was 9.0% faster than that of steers fed Hybrid D (slowest IVSD; 1.33 vs 1.22 kg, P = .06). Gain:feed ratio was positively correlated with IVSD across all treatments (R2 = .94). Hybrids A and D, another Hybrid, A1, and a bird-resistant hybrid (BR) were fed for 85 d to finishing lambs (mean initial BW of 28 kg). Lambs fed Hybrid A gained more efficiently (gain:feed) than those fed BR or A1 (.210 vs .188 and .184, P less than .05), and those fed D were intermediate (.200). Performance of sheep fed A1, with the fastest IVSD, and those fed BR, with the lowest IVSD, were similar, suggesting that factors other than IVSD affected lamb performance. Our data indicate that rate of grain sorghum starch digestion may influence feeding value of grain sorghum fed to cattle.