Fibrolytic enzyme and ammonia application effects on the nutritive value, intake, and digestion kinetics of bermudagrass hay in beef cattle

The objectives were to compare the effect of exogenous fibrolytic enzyme (Biocellulase A20) or anhydrous ammonia (4% DM) treatment on the nutritive value, voluntary intake, and digestion kinetics of bermudagrass (Cynodon dactylon cultivar Coastal) hay harvested after 2 maturities (5- and 13-wk regrowths). Six individually housed, ruminally cannulated Brangus steers (BW 325 ± 10 kg) were used in an experiment with a 6 × 6 Latin square design with a 3 (additives) × 2 (maturities) factorial arrangement of treatments. Each period consisted of 14 d of adaptation and 7, 4, 1, 1, and 4 d for measuring in vivo digestibility, in situ degradability, no measurements, rumen liquid fermentation and passage indices, and rate of solid passage, respectively. Steers were fed hay for ad libitum intake and supplemented with sugarcane molasses and distillers grain (supplement total of 2.88 kg DM/d). Enzyme did not affect the nutritional composition of hay but ammonia treatment decreased hay NDF, hemicellulose, and ADL concentrations and increased the CP concentration particularly for the mature lignified 13-wk hay. The enzyme increased NDF and hemicellulose digestibility of the 5-wk hay but decreased those of the 13-wk hay. Ammoniation decreased intake of hay but increased digestibility of DM, OM, NDF, hemicellulose, ADF, and cellulose and increased the ruminal in situ soluble and potentially digestible fractions and the rate of DM degradation of the 13-wk hay. Also, ammoniation increased the concentrations of ruminal NH3, total VFA, acetate, and butyrate but enzyme treatment did not. Neither enzyme addition nor ammoniation affected rate of liquid and solid passage. In conclusion, ammoniation decreased the concentration of most fiber fractions, decreased the intake of hays, and increased their CP concentration, in vivo digestibility, and in situ degradability at both maturities whereas enzyme application increased fiber digestibility of the 5-wk hay but decreased it in the case of the 13-wk hay.

Estimation of feeding value of four tropical forage species at two stages of maturity1,2

The feeding value of four tropical grasses was assessed through voluntary intake and digestibility studies using yearling Brahman x British steers (average BW = 256 +/- 34 kg). The digestibility of OM was estimated using total fecal collection (TFC), in vitro OM digestibility (IVOMD), and by estimating fecal production using insoluble acid detergent fiber (IADF) as an indigestible marker. The four grasses consisted of bahiagrass (Paspalum notatum), limpograss (Hemarthria altissima), bermudagrass (Cynodon dactylon), and stargrass (Cynodon spp.). Grass was harvested at two stages of maturity (approximately 4 and 10 wk). Forages were ground (5 to 10 cm) and offered to steers ad libitum. Forage treatments were assigned randomly to steers over eight 28-d periods and repeated over two consecutive years. Total forage offered and refused was determined during a 14-d sample collection period. For determination of fecal output, steers were placed into metabolism crates for 7 d. Composited samples of forage offered, forage refused, and feces of each steer at each period were analyzed for DM, OM, NDF, ADF, IADF, IVOMD, and CP. All digestibility results were calculated on an OM basis. There were year x grass x maturity interactions (P < 0.01) for all measures of forage quality, except CP. Increased maturity resulted in a 37.8% decrease (P < 0.001) in CP concentration when averaged across all forages. Four-week bermudagrass contained the greatest (P < 0.05) concentration of CP compared with all other grasses at both maturities, except 4-wk stargrass. Bahiagrass IVOMD did not differ among 4- and 10-wk maturities in both years; however, the IVOMD content of both stargrass and bermudagrass decreased (P < 0.05) when these forages matured from 4 to 10 wk. Apparent OM digestibility, determined by TFC, was greater (P < 0.05) than OM digestibility determined by IVOMD and IADF for all forages except bahiagrass, for which IADF did not differ from TFC. In Year 1, OM intake (OMI) of 10-wk limpograss was less (P < 0.05) than all other 4-wk forages. In Year 2, voluntary OMI of 10-wk limpograss was less (P < 0.05) than all grass x maturity combinations, except for 10-wk bermudagrass. These data suggest that important differences exist in changes in nutrient quality associated with increased maturity in tropical forages. Among the forages assessed in this study, bahiagrass seems to better retain nutrient quality when maturing from 4 to 10 wk.

Urea and(or) feather meal supplementation for yearling steers grazing limpograss (Hemarthria altissima var. 'Floralta') pasture

The unique relationship between TDN and CP concentration (low CP relative to TDN) in the whole-plant of 'Floralta' limpograss (Hemarthria altissima) may provide an opportunity for improving cattle performance through protein supplementation. In each of three consecutive years, yearling Brahman x British crossbred steers (initial weight approximately 270 kg) grazed limpograss during the summer and fall (five steers per ha, three pasture replications per treatment) and were fed liquid cane molasses-based supplements (1.4 kg DM daily) alone, or containing urea and(or) hydrolyzed poultry feather meal. In yr 1 and 2, protein supplementation did not influence ADG. In these years, pasture availability was in excess at all times, and visual observations indicated that the upper canopy contained abundant leaf. Pasture samples collected in a manner to simulate grazing had in vitro organic matter disappearance (IVOMD):CP ratios ranging from 6.5 to 8.1, and plasma urea nitrogen concentration in the blood of steers fed no supplemental protein was high (10.6 to 15.9 mg/dL), both not suggestive of a situation where providing a protein supplement might improve animal performance. In yr 3, ADG was improved (P < 0.05) by protein supplementation. Forage availability was in excess at the beginning of the trial but declined significantly as the trial progressed. At the end of the trial, forage IVOMD:CP ratio (11.1) and plasma urea nitrogen values of steers fed no protein supplement (6.6 mg/dL) were both suggestive of a situation where providing supplemental protein might improve animal performance. Grazing management of limpograss pasture can affect canopy composition, thereby influencing cattle response to protein supplementation. In cases where limpograss is moderately grazed resulting in abundant leaf in the grazed horizon, dietary energy:protein ratio can be balanced, and positive responses to protein supplementation may not be observed. Where limpograss is grazed more intensively resulting in greater quantities of stem in the upper pasture canopy, an imbalance of dietary protein (low) relative to energy can develop, increasing the opportunity for enhancing cattle performance through protein supplementation.

Contractile properties of human motor units in health, aging, and disease

The primary function of skeletal muscle is to produce force for postural control and movement. Although the contractile properties of the whole muscle are useful functional indicators, they do not accurately reflect the heterogeneity of the constituent motor units (MUs) and their changes in health and disease. However, data on the contractile properties of human MUs, in comparison to other animal species, are relatively sparse. This, in part, is due to greater methodological challenges of in vivo studies of MUs in the human. The purpose of this review is to critically appraise the methods used in humans; to describe the normative data from different muscle groups; to discuss differences between data from healthy humans and other animal species; and, last, to characterize changes of the MU contractile properties in aging, disease, and in response to intervention. Because the spike-triggered averaging technique can only be used to study the twitch properties, other methods were subsequently developed to measure a wider range of contractile properties. Although there is general agreement between human data and those from other animal species, major differences do exist. Potential reasons for these discrepancies include true biological differences, but differences in the techniques used may also be responsible. Although limited, measurement of MU contractile properties in humans has provided insight into the changes associated with aging and motoneuronal diseases and provides a means of gauging their adaptive capacity for training and immobilization.

Human motor units in health and disease

Recent advances in clinical neurophysiology have made it possible to non-invasively stimulate single motor axons and determine the physiological characteristics of the associated motor units. Some motor units lend themselves to longitudinal studies of their electrical and contractile characteristics. The former include the conduction velocities of their motor axons and the sizes and shapes of their motor unit action potentials and the latter such contractile characteristics of the motor unit as their contractile speeds, twitch and tetanic tensions, and resistance to fatigue. The feasibility of serially examining the same motor unit has made it possible to study the responses of single motor units to conditioning as well as changes in the responses of single motor units to diseases such as amyotrophic lateral sclerosis. The non-invasive character of these approaches offers an attractive means of studying the responses of single human cells, in these cases motor neurons, in health and disease.

Source and level of energy supplementation for yearling cattle fed ammoniated hay

Brahman x British crossbred steers were used in growth and digestion trials to evaluate the response of source (corn, sugar cane molasses, or soybean hulls) and feeding rate (0, 1.4, or 2.8 kg DM per steer daily in the growth trials; 0, 15, or 30% of the ration DM in the digestion trial) of energy supplementation in cattle fed ammoniated (4% of forage DM) stargrass (Cynodon nlemfuensis Vanderyst var. nlemfuensis) hay. Cattle on all treatments were fed 0.5 kg cottonseed meal daily. In the growth trials, steers grazed dormant bahiagrass (Paspalum notatum) pasture. Increasing the levels of supplementation decreased hay intake but increased total dietary intake for all diets (P < 0.07). Daily gain and feed efficiency of steers were improved (P < 0.03) with supplementation. Steers supplemented with corn or soybean hulls at 2.8 kg DM/d had a higher ADG (0.92 kg) and gain/feed (0.103) than steers supplemented with molasses (0.78 kg, 0.08, respectively) at the same level. Seven crossbred steers (200 kg) were used in a five-period digestion trial to evaluate apparent OM, NDF, ADF, and hemicellulose digestibility. Apparent OM digestibility of all diets increased linearly (P = 0.02) as the level of supplementation increased. Apparent NDF and ADF digestibility decreased (P < 0.03) as the level of supplementation with corn or molasses increased, whereas increasing the level of soybean hulls in the diet increased (P < 0.06) apparent NDF and ADF digestibility. Four ruminally fistulated crossbred steers (472 kg) were used in a 4 x 4 latin square design to investigate ruminal characteristics with energy supplementation at 30% of ration DM. Ruminal pH in steers supplemented with soybean hulls or corn declined after feeding. Ruminal pH decreased more rapidly with corn supplementation and remained below 6.2 for a longer period of time than with the other diets. Ruminal pH did not change within 24 h after feeding for steers fed the control or molasses diets. No change in total VFA concentration was observed in steers fed molasses or corn. Total ruminal VFA concentration in steers supplemented with soybean hulls increased initially after feeding and then declined within 24 h after feeding. Soybean hulls produced fewer negative associative effects than corn when fed with ammoniated stargrass hay at 2.8 kg DM/d. The reduced gain/feed of steers supplemented with molasses compared to soybean hulls or corn indicates that molasses was not utilized as efficiently as the other energy sources.

Multifocal motor neuropathy improved by IVIg: randomized, double-blind, placebo-controlled study

OBJECTIVE

To determine the effect of IV immunoglobulin (IVIg) on neurologic function and electrophysiologic studies in multifocal motor neuropathy with conduction block (MMN).

BACKGROUND

MMN is characterized by progressive, asymmetric, lower motor neuron weakness and is probably immune-mediated. IVIg treatment has been shown to have beneficial effects in several open-label studies and in one small controlled trial. However, larger randomized controlled studies are lacking.

METHODS

The authors recruited 16 patients with MMN. All subjects were given each of two treatments (IVIg [0.4 g/kg/d for 5 consecutive days] or placebo [dextrose or saline]) that were assigned according to a randomized, crossover design under double-blind conditions. Patients were evaluated before and about 28 days after trial treatment for subjective functional improvement, neurologic disability score, grip strength, distal and proximal compound muscle action potential amplitude, and conduction block.

RESULTS

Subjective functional improvement with IVIg treatment was rated as dramatic or very good in nine patients, moderate in one, mild in one, and absent in five patients. This improvement was absent after placebo. The neurologic disability score improved by 6.7+/-3.3 points with IVIg treatment, whereas it decreased by 2.1+/-3.0 with placebo (p = 0.038). Grip strength on the weaker side was increased by 6.4+/-1.9 kg with IVIg treatment; it decreased by 1.0+/-0.8 kg with placebo (p = 0.0021). Conduction block worsened by 12.98+/-6.52 % with placebo, but improved by 12.68+/-5.62 % with IVIg treatment (p = 0.037). Conduction block was reversed in five patients with IVIg but not placebo.

CONCLUSION

IVIg improved conduction block as well as subjective and objective clinical measures of function in patients with MMN.

Genotype/phenotype correlations in X-linked dominant Charcot-Marie-Tooth disease

We have studied the relationship between genotype, clinical phenotype, and pathology in 13 families with dominant X-linked Charcot-Marie-Tooth (CMT) neuropathy. Connexin32 (Cx32) gene mutations were spread throughout the coding region and included eight missense mutations, one 8-bp deletion/4-bp insertion frame shifting mutation, two nonsense mutations, and one deletion of the entire coding sequence. One hundred sixteen affected CMTX patients (53 males and 63 females) and 63 unaffected, at-risk individuals were compared by neurological and electrophysiological examinations and analyzed by gender; nerve biopsies were available from seven index cases. It was found that mutations within all regions of the Cx32 gene coding sequence caused an identical clinical phenotype. Male CMTX patients were affected more severely and showed an age-dependent progression of clinical signs and of the pathology; there was, however, variability in the severity of disease expression, irrespective of age, among males within families of defined genotype. All but 10% of female CMTX patients had only mild signs. Motor nerve conduction velocities were moderately slowed (median nerve MNCV: males 34.5 +/- 6.2 m/sec; females 45.8 +/- 7.3 m/sec), and motor and sensory nerve amplitudes were reduced (median nerve CMAP: males 3.7 +/- 3.7 mV; females 7.8 +/- 3.4 mV), with electromyographic evidence of chronic denervation. Differences were significant between gender and between affected and unaffected individuals. In agreement with the electrophysiological observations, pathological studies showed evidence of paranodal demyelination and of a length-related axonal degeneration in motor and sensory nerve fibers. Correlations between genotype and clinical phenotype suggested that missense mutations located within the second transmembrane domain and/or cytoplasmic loop might be associated with milder clinical phenotype, and therefore might be less disruptive of connexin32 gap junction function. Missense, chain-terminating, or deletion mutations in all other locations of the connexin32 protein caused severe forms of CMTX and disease onset in the first decade. Observed variability of disease severity among males within kinships suggests the influence of other modifying factors.

The relationship of motor unit size, firing rate and force

OBJECTIVE

Using a clinical electromyographic (EMG) protocol, motor units were sampled from the quadriceps femoris during isometric contractions at fixed force levels to examine how average motor unit size and firing rate relate to force generation.

METHODS

Mean firing rates (mFRs) and sizes (mean surface-detected motor unit action potential (mS-MUAP) area) of samples of active motor units were assessed at various force levels in 79 subjects.

RESULTS

MS-MUAP size increased linearly with increased force generation, while mFR remained relatively constant up to 30% of a maximal force and increased appreciably only at higher force levels. A relationship was found between muscle force and mS-MUAP area (r2 = 0.67), mFR (r2 = 0.38), and the product of mS-MUAP area and mFR (mS-MUAP x mFR) (r2 = 0.70).

CONCLUSIONS

The results support the hypothesis that motor units are recruited in an orderly manner during forceful contractions, and that in large muscles only at higher levels of contraction ( > 30% MVC) do mFRs increase appreciably. MS-MUAP and mFR can be assessed using clinical EMG techniques and they may provide a physiological basis for analyzing the role of motor units during muscle force generation.

The effects of training through high-frequency electrical stimulation on the physiological properties of single human thenar motor units

The relative impact of training on motor units (MUs) with differing physiological characteristics remains controversial. To examine this issue, we longitudinally tracked the contractile and electrical characteristics of six human thenar MUs in 2 young healthy subjects before, during, and following an intermittent, high-frequency electrical stimulation program. Responses of MUs with differing baseline physiological characteristics varied widely. While the twitch and maximal tetanic tensions of the slower and fatigue-resistant MUs increased, tensions of the faster and more fatigable MUs declined. The fatigue resistance of the faster and more fatigable MUs, on the other hand, increased while that of the slower MUs remained unchanged. Although electrical stimulation of individual MUs allowed their training to be precisely controlled, it will be of practical importance to determine whether similar divergent MU contractile changes also occur with voluntary training.

A longitudinal study of the pathophysiological changes in single human thenar motor units in amyotrophic lateral sclerosis

The sequence of pathophysiological changes in amyotrophic lateral sclerosis (ALS) at the single motor unit (MU) level is not well understood. Using a recently described technique, a comprehensive range of physiological properties in two thenar MUs in ALS were intensively studied. In the first MU, despite a marked decline in the ability of the subject to voluntarily recruit the MU, the physiological properties of this MU remained remarkably stable over a 2-year period. In contrast, the physiological properties of the other MU declined rapidly over 5 months despite the fact that this MU could be recruited with ease throughout the study period. These differences between the progressively dysfunctional changes in these two MUs illustrates the value of such longitudinal studies of specific MUs in improving our understanding of the evolution of changes in single motoneurons in ALS. The broader application of longitudinally tracking the pathophysiological changes of the surviving MUs may prove to be a sensitive measure of disease progression and in evaluating the effectiveness of treatments.

Dissociation of the electrical and contractile properties in single human motor units during fatigue

The surface EMG area often exhibits progressive enlargement during a submaximal fatiguing contraction, but the underlying reasons still remain uncertain. Fatigue-induced changes in the surface-detected motor unit action potentials (S-MUAPs) of 10 human thenar motor units (MUs) with widely differing physiological properties were examined. After 2 min of repetitive 40-Hz stimulation, the size of the S-MUAPs of all MUs increased, the magnitude of which was negatively correlated with their tetanic tension changes. These findings suggest that during muscle fatigue, in addition to reflecting recruitment of new MUs and increases in firing rates of the active MUs, the surface EMG may also be markedly influenced by changes in the S-MUAPs, especially in fast fatigable muscles.

Firing rate analysis using decompostion-enhanced spike triggered averaging in the quadriceps femoris

Electromyographic signals detected from the quadriceps femoris during various constant force contractions were decomposed to identify individual motor unit discharges and mean firing rates (FRs). Subject and group mean FRs were calculated for each force level. Mean FR values and FR variability increased with force. Individual, subject, and group mean FRs showed slight increases until 30% of maximum voluntary contraction and larger increases thereafter. Findings are discussed in relation to motor unit recruitment, frequency modulation, and fatigue.

The usefulness of central motor conduction studies in the localization of cord involvement in cervical spondylytic myelopathy

Cervical spondylytic myelopathy (CSM) is common. Magnetic resonance imaging (MRI), although sensitive, often reveals extensive and sometimes clinically irrelevant findings. The purpose of this study was to investigate the usefulness of central motor conduction studies in localizing the rostral level of cord involvement in 6 patients with CSM. Central motor conduction was assessed using high-voltage stimulation for the spinal roots and magnetoelectrical stimulation for the motor cortex, recording from "marker muscles" innervated by successively higher cervical cord segments. Abnormal central motor conduction affected all subjects at C8-T1, 5 subjects at C7, but none at the C5-C6 levels. The MRI showed abnormalities at multiple levels as high as C4. Our results suggest that central motor conduction studies are helpful in localizing the clinically relevant levels of spinal cord compression in CSM and correlate well with motor abnormalities on clinical examination.

Longitudinal study of the contractile and electrical properties of single human thenar motor units

Serial motor unit number estimates have shed important light on the extent and rates of motoneuron losses in aging and amyotrophic lateral sclerosis. However, the estimates alone provide few clues to the health and functional status of surviving motor units. A reliable means for assessing the functional status of the surviving motor units would therefore by a welcome addition to our present tools for studying motor units. Examining the physiological properties of samples of motor units drawn at intervals during the course of a motoneuronal disease suffers from the important limitation that the samples may not be representative of one another. The latter problem could be circumvented by serially studying the same motor units. This study describes a noninvasive technique capable of longitudinally tracking the contractile and electrical properties of specific single thenar motor units in healthy subjects, in some instances over several years. The technique proved to be reasonably reliable and provided information on a wide range of contractile and electrical properties of motor units. Such an approach could serve as a potentially powerful and sensitive means of studying the life histories of single motor units in aging, diseases of the motoneuron, and in the latter instances, the responses of the motoneurons to treatment.

Quantitation in EMG

The neuromuscular system may be affected by disorders of the central nervous system as well as other disorders affecting motoneurons, axons, neuromuscular transmission, the sarcolemmal membrane, the contractile elements and other components of the muscle fibers themselves. One or a combination of these possibilities can present in patients in the critical care unit. This paper reviews various qualitative and quantitative methods for assessing the various components of the peripheral contributions to the electrical and force output as well as the central motor drive to motoneurons. These methods all have their own strengths and weaknesses but many are complementary and together, can provide important diagnostic and prognostic information to guide management.

Decomposition-enhanced spike-triggered averaging: contraction level effects

Decomposition-enhanced spike-triggered averaging (DE-STA) was applied to the vastus medialis muscle to examine size distributions of surface-detected motor-unit action potentials (S-MUAPs) at various force levels. Using DE-STA, 15-20 S-MUAPs were identified during 5%, 10%, 20%, and 30% of maximum voluntary contraction. Average S-MUAPs showed increase in peak to peak (and negative peak) amplitude with force (In microV): 5% = 37.9 +/- 6.1 (16.6 +/- 2.5), 10% = 44.0 +/- 4.0 (20.4 +/- 1.8), 20% = 80.7 +/- 9.3 (41.3 +/- 4.5), and 30% = 102.5 +/- 10.3 (53.6 +/- 5.0). Test-retest variability of peak to peak (and negative peak amplitude) between repeated trials was 0.10 (0.14), 0.14 (0.14), 0.17 (0.15), and 0.21 (0.20) at 5%, 10%, 20%, and 30% respectively. A relationship was found between the S-MUAP amplitude and force (r2 = 0.78, df = 90, F = 160, P < 0.001). Increase in average S-MUAP amplitude with force suggests that STA performed only at low levels of contraction may result in a biased sampling and small average S-MUAP amplitudes.

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.

Multifocal motor neuropathy presenting as ophthalmoplegia

A 45-year-old man developed ophthalmoplegia and subsequently multiple cranial nerve palsies in association with bibrachial paresis. Investigations revealed evidence of conduction block occurring at a very proximal location (i.e., the spinal roots) and seemingly sparing sensory fibers. Other causes were ruled out and a diagnosis of multifocal motor neuropathy with conduction block (MMN) was suggested. The patient responded to cyclophosphamide. Differentiating features between MMN and chronic inflammatory demyelinating polyradioneuropathy (CIDP) are discussed. This case demonstrates that MMN may rarely present with ophthalmoparesis and also demonstrates that features of MMN and CIDP may overlap.

Age-related changes in the twitch contractile properties of human thenar motor units

The purpose of this study was to examine the effects of aging on the contractile and electrophysiological properties of human thenar motor units (MUs). Percutaneous electrical stimulation of single motor axons within the median nerve was used to isolate and examine the twitch tensions, contractile speeds, and surface-detected MU action potential (S-MUAP) sizes of 48 thenar MUs in 17 younger subjects (25-53 yr) and 44 thenar MUs in 9 older subjects (64-77 yr). A wide range of twitch tensions, contractile speeds, and S-MUAP sizes was observed in both age groups. However, older subjects had significantly larger MU twitch tensions and slower MU twitch contraction and half-relaxation times. These changes were accompanied by increased S-MUAP sizes. These findings suggest that the human thenar MU pool undergoes significant age-related increase in MU size and slowing of contractile speed. Such adaptation may help to overcome previously reported age-related losses of thenar MUs.

Methods for estimating the numbers of motor units in human muscles

After the introduction by A. J. McComas of the original method for estimating the number of motor units based on manual incremental stimulation of a motor nerve, several new techniques have been developed, designed to correct for some of the errors inherent in the original technique. These methods incorporate algorithms to adjust for alternation and, to a greater or lesser extent, automate the methods, rendering the techniques less subject to operator bias and various physiological and technical errors. This review explores the advantages and drawbacks in the multiple-point stimulation (MPS), spike-triggered averaging (STA), and decomposition-enhanced STA techniques, illustrates some of the current applications of the techniques, and explores some tantalizing prospects for new studies of motor-unit physiology in the future.

Urea ammoniation effects on the feeding value of guineagrass (Panicum maximum) hay

Laboratory, digestion, and growth studies evaluated urea as a source of ammoniation for quality improvement in guineagrass (Panicum maximum) hay. In a laboratory trial, 5.0-kg portions of hay were reconstituted with water to yield final forage moisture concentrations or 25 of 40% and treated with urea at 0, 4, 6, or 8% of the forage DM, with or without urease addition. Main effects of forage moisture or urease addition did not influence (P > .10) CP or NDF concentration or in vitro OM disappearance (IVOMD) of the guineagrass hay. Hay CP concentration and IVOMD increased linearly (P < .01), whereas concentrations of hemicellulose and ADL decreased linearly (P < .05) with increasing urea level. In other experiments, round bales of hay (320 kg) were reconstituted with water to yield final forage moisture concentrations of 25 or 40% and treated with urea at 0, 4, or 6% of the forage DM. The urea solution was applied as a spray onto the cut edges of the bales, or by low pressure (10 psi) injection. Two- and three-way interactions (P < .05) existed among forage moisture concentration, urea application method, and urea level for CP and NDF concentration and IVOMD of the guineagrass hay. Greatest enhancements in these forage quality characteristics were obtained when the urea solution was sprayed onto the hay at the 25% forage moisture concentration. In two digestion and two growth trials, round bales of hay were treated with 0, 4, and 6% urea sprayed onto the hay at the 25% forage moisture level. In each growth trial, 30 St. Croix white hair castrated male sheep (Trial 1:34 +/- 5.5 kg, Trial 2: 17 +/- 3.5 kg) were allotted to six pens of five head each, resulting in two pens per treatment. In the digestion trials, six similar sheep were used in a replicated 3 x 3 Latin square design. In the digestion and growth trials, hay intake increased in a quadratic (P < .05) manner with increasing urea level. Apparent NDF and ADF digestibilities increased linearly (P < .05) with increasing urea level. Linear improvements in ADG (P < .05) and gain/feed (P < .07) were observed with increasing urea level. Urea ammoniation offers potential for improving the feeding value of tropical forages and provides an option for quality forage during the dry season.

Value of feather meal in a molasses-based liquid supplement fed to yearling cattle consuming a forage diet

Hydrolyzed feather meal (FM) was compared to other sources of CP to determine its value as a protein source in a molasses-based liquid supplement. Ruminal N escape values (measured in situ) for FM, ring-dried blood meal, cottonseed meal, and soybean meal approximated reported values. Ruminal N escape value for catfish meal was lower than values reported for other fish meals. In two trials (194 d), 84 yearling heifers were allotted to 12 pastures (3 pastures/treatment) and fed one of four supplements (1.7 kg of DM.heifer-1.d-1) containing either molasses and urea; molasses, urea,and FM; molasses, urea, FM, and catfish meal; or molasses, urea, FM, and catfish oil. Heifers were exposed to bulls for 60 d. In two trials, 112 steers were allotted to 16 pastures (4 Pastures/treatment) and fed one of four supplements (1.7 kg of DM.steer-1.d-1) containing molasses and urea; molasses, urea and FM; molasses, urea, FM and ring-dried poultry blood meal; or molasses, urea, and poultry feathers and blood hydrolyzed together. In all trials, cattle fed molasses containing FM had faster gains (P < .05) and heifers had heavier live weights at breeding (P < .05) and higher pregnancy rates (P < .05) than cattle fed molasses and urea. Combining poultry blood with molasses, urea, and FM improved (P < .05) steer gains in one of two trials. Combining catfish meal with molasses, urea, and FM did not improve (P > .05) ADG of pregnancy rate of heifers. Combining catfish oil with molasses, urea, and FM increased (P < .05) ADG in one trial and blood cholesterol and live weight of heifers at breeding in both trials. It is concluded that protein feeds, such as FM, that contain a large portion of ruminally undegradable protein may provide much of the CP in liquid supplements fed to growing cattle consuming moderate-quality forage. Adding catfish oil to a liquid supplement may improve ADG and live weight of yearling heifers at breeding.

Effect of molasses-based liquid supplements on digestibility of creeping bluestem and performance of mature cows on winter range

Poor quality of tropical range forage leads to excessive weight loss and poor reproductive performance of beef cows. This research measured 1) the digestibility by steers fed creeping bluestem (Schizachyrium scoparium var. stoloniferum) diets supplemented with cane molasses (0 or 20% of diet DM) and(or) added CP (no added CP, urea, or soybean meal) and 2) the performance of mature cows grazing creeping bluestem range and supplemented with 1.6 kg/(cow.d) (DM basis) of either molasses-urea or molasses-cottonseed meal-urea, each containing 30% CP (DM basis). Bluestem averaged 4.7% CP and 37.0% in vitro OM digestion. In the digestion trial, diets supplemented with molasses had greater (P < .01) apparent OM digestibility but lower (P < .01) apparent NDF, ADF, and hemicellulose digestibilities than diets not supplemented with molasses. Apparent OM digestibility of diets supplemented with soybean meal was greater (P < .05) than that of diets supplemented with urea but not different (P > .05) from the control. While grazing range, mature cows supplemented with molasses-urea lost less (P < .05) body condition (-1.7 vs -1.3) than cows supplemented with molasses-cottonseed meal-urea. Treatment did not affect cow weight loss on range (P = .85) or pregnancy rate (P = .51). Cows supplemented with molasses-urea tended to wean a heavier calf (P = .09). When fed at 1.6 kg/(cow.d) to mature cows grazing range, a molasses-based supplement containing urea was of equal value to one containing a natural protein.

Pyridoxine dependent epilepsy with iatrogenic sensory neuronopathy

An 18-year-old man was treated from birth with chronic high dose pyridoxine (vitamin B6) up to 2000 mg per day for pyridoxine-dependent seizures. Within two years of onset of treatment, he developed a sensory neuropathy which did not progress over the following 16 years. Electrophysiological studies were consistent with a pure sensory neuronopathy expressed as centripetal degeneration of processes of the dorsal root ganglion cells.

Electrodiagnosis in the management of focal neuropathies: the "WOG" syndrome

The role of electrodiagnosis in managing patients with focal neuropathies is discussed from the differing perspectives of a peripheral nerve surgeon and a practitioner of electrodiagnostic medicine. Both clinical evaluation and electrodiagnosis are useful methodologies, each having limitations. Dr. Dellon labels the overreliance on electrodiagnosis and the "WOG" (Word of God) syndrome, and describes its signs, symptoms, and treatment. Dr. Brown contends Dr. Dellon's crusade is misdirected. The exchange is an eloquent polemic on the virtues and foibles of these different approaches to evaluating peripheral nerve function and the imperative to practice them in a complementary rather than a contentious manner.

A method for the longitudinal study of human thenar motor units

Methods currently available to study the electrophysiological and contractile properties of single human motor units (MUs) preclude the same MU from being studied on repeated occasions. We have developed a method which allows single thenar MUs to be studied longitudinally. Sites were located along the median nerve where, using percutaneous stimulation, it was possible to selectively activate a single thenar motor axon as determined by: (a) the presence of an "all-or-nothing" surface-detected motor unit action potential (S-MUAP); (b) the occasional presence of F-responses identical in size and shape to the direct S-MUAP; (c) excitation thresholds widely separated from the next highest threshold motor axon so as to allow high frequency stimulation. To ensure that the same motor axon had been located and stimulated in successive studies, additional criteria included: (a) the motor axon was found at approximately the same site along the nerve; (b) the threshold for excitation remained widely separated from the next highest threshold motor axon; (c) the shape of the S-MUAP was almost identical on repeated studies; (d) S-MUAP and F-response latencies were similar. This method provides, for the first time, the ability to track longitudinally the electrical and contractile properties of single MUs in health and during the course and treatment of disease.

Motor unit number estimates based on the automated analysis of F-responses

An automated technique for estimating the number of motor units based on single motor unit action potentials in the F-response is described. The average surface detected motor unit action potential (S-MUAP) was calculated from the datapoint-by-datapoint average of a sample of S-MUAPs automatically selected from a population of F-responses. The technique was applied to the thenar muscles of young (n = 18, aged 31 +/- 11 years) and older (n = 15, aged 68 +/- 3) subjects. Motor unit number estimates based on the automated selection of S-MUAPs from the F-responses compared well with those derived using a computer-assisted manual method for selecting S-MUAPs from the F-response (automated 245 +/- 105 vs. manual 241 +/- 100, r = 0.93) and were similar to estimates obtained using multiple point stimulation (219 +/- 77). The advantages of the automated technique for collecting S-MUAPs from the F-response include the ready tolerance of the technique by subjects, the minimal amount of operator interaction required, and the additional information relating to the conduction velocities and latencies of single motor axons.

Physiological properties of single thenar motor units in the F-response of younger and older adults

The purpose of this study was to characterize the properties of single thenar motor units in the F-response of healthy younger (n = 15; age 33 +/- 11 years) and older subjects (n = 15; age 68 +/- 3 years). Trains of 300 stimuli at intensities evoking M-potentials 10%, 20%, and 30% of the peak-to-peak amplitude of the maximum M-potential, were delivered to the median nerve. In the young, observed firing probabilities of surface-detected motor unit action potentials (S-MUAPs) extracted from the F-response ranged from less than 1-10%, the S-MUAPs varied in size from 0.015% to 5.3% of the maximum M-potential negative peak area, and they were similar in size to the population of S-MUAPs collected by multiple point stimulation of the median nerve. The percentage difference between the slowest and fastest conducting fibers for individual subjects ranged from 8% to 20%, which translated to conduction velocities (CVs) of 48-68 m.s-1 (mean 59 +/- 4). The preceding were all independent of stimulus intensity. The S-MUAP sizes were significantly larger in older subjects (39%), and the range and distribution of motor unit CVs (38-61 m.s-1; mean 52 +/- 3) were markedly shifted to reflect a slower population of motor fibers. These findings suggest that age-related axonal slowing may uniformly affect all median motor fibers.

AAEM minimonograph #42: intraoperative monitoring of peripheral and cranial nerves

Intraoperative studies of focal neuropathies have become increasingly common both as an aid to the localization of the neuropathy and a means of monitoring the integrity of the nerve in the course of surgery. Success very often depends on careful attention to the technical problems presented by working in the operating theater. Despite these difficulties, assessment of conduction directly from the exposed nerve offers opportunities for better understanding the pathophysiology of these neuropathies and correlating these findings with conventional electrodiagnostic studies.

Cane molasses and cottonseed meal supplementation of ammoniated tropical grass hay for yearling cattle

Laboratory, digestion, and growth studies were used to evaluate liquid cane molasses (MOL) and(or) cottonseed meal (CSM) supplementation of ammoniated (4% of the forage DM) stargrass (Cynodon nlemfuensis Vanderyst var. nlemfuensis) hay. Ammoniation increased (P < .01) total N concentration (1.0 to 1.4% vs 1.7 to 2.8%) and in vitro digestion of OM, NDF, and ADF and decreased (P < .01) NDF concentration of stargrass hay. Two digestion (4 x 4 Latin square, 250-kg steers) and two growth (230-kg Brahman crossbred steers, seven to eight steers per pasture, three to four pastures per treatment, October through February) trials evaluated MOL and(or) CSM supplementation of ammoniated hay. Supplementation with CSM alone did not influence (P > .05) apparent digestibilities of OM or NDF, whereas supplementation with MOL either alone or with CSM increased (P < .05) apparent OM digestibility, but decreased (P < .05) apparent NDF digestibility. In the growth trials, hay intake was not affected (P > .05) by supplementation with CSM alone and was decreased (P < .05) by supplementation with MOL either alone or with CSM; however, total feed intake was increased (P < .05) by MOL supplementation. Cattle fed only ammoniated hay gained approximately .20 kg/d. In both trials, daily gain and gain/feed were improved (P < .05) by CSM (.39 to .47 kg; .062 to .071) or MOL (.34 to .35 kg; .047 to .048) supplementation. Improvements (P < .05) in daily gain (.54 to .76 kg) and gain/feed (.077 to .083) by supplementation with MOL plus CSM were additive to responses from supplementation with MOL or CSM individually.(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of ageing on the motor unit: a brief review

This review briefly summarizes the current state of knowledge regarding age related changes in skeletal muscle, followed by a more in-depth review of ageing effects on animal and human motor units (MUs). Ageing in humans is generally associated with reductions in muscle mass (atrophy), leading to reduced voluntary and electrically evoked contractile strength by the 7th decade for most muscle groups studied. As well, contraction and one-half relaxation times are typically prolonged in muscles of the elderly. Evidence from animal and human studies points toward age associated MU loss as the primary mechanism for muscle atrophy, and such losses may be greatest among the largest and fastest MUs. However, based on studies in animals and humans, it appears that at least some of the surviving MUs are able to partially compensate for MU losses, as indicated by an increase in the average MU size with age. The fact that muscles in the elderly have fewer, but on average larger and slower, MUs has important implications for motor control and function in this population.

Determinants of mean motor unit size: impact on estimates of motor unit number

The purpose of this study was to compare two fundamentally different methods of deriving the average surface-detected motor unit action potential (S-MUAP) size from which to calculate a motor unit number estimate (MUNE), namely: (1) the simple arithmetic average of S-MUAP parameter values; and (2) a computer-derived datapoint by datapoint average waveform which takes account of differences in S-MUAP shapes and durations. Multiple point stimulation was used to collect representative samples of between 11 and 20 S-MUAPs (mean 15 +/- 2 SD) from the median-innervated thenar muscles of 20 healthy control subjects between 20 and 76 years of age (mean 48 +/- 19 SD). The average S-MUAP size based on peak-to-peak amplitude, negative peak amplitude, and negative peak area measurements was calculated using the two different methods. The mean S-MUAP sizes based on the average waveform were significantly lower in all cases than those based on the simple average of S-MUAP parameter values. Differences tended to be greatest for MUNEs based on peak-to-peak amplitude (35%), less for negative peak amplitude (20%), and least for negative peak area (16%).

AAEM case report #27: acute retrohumeral radial neuropathies

Acute radial neuropathies localized to the retrohumeral course of the radial nerve are common. Most individuals fully recover within a matter of days or, at the most, a few weeks. In a few, recovery may take longer and occasionally remains incomplete. In almost all instances the site of injury to the radial nerve can be accurately localized to the region of the spiral groove and the relative contributions of conduction block and axonal degeneration assessed using electrophysiologic techniques.

Severe axonal degeneration in acute Guillain-Barré syndrome: evidence of two different mechanisms?

Four cases of severe acute Guillain-Barré syndrome (GBS) characterized by severe axonal degeneration are presented. All had electrically inexcitable motor nerves as early as 4 days after onset. The disease was rapid in onset and the residual disability was severe. Two different types of pathology were seen. Nerve biopsies in 3 cases showed severe axonal degeneration without inflammation or demyelination. Autopsy in one of these cases showed that the dorsal and ventral roots were also significantly affected. These cases illustrate the primary axonal form of GBS. Nerve biopsy in the fourth case at day 15 showed marked inflammation and demyelination with axonal degeneration. Contralateral nerve biopsy at day 75 showed almost complete loss of axons. This case illustrates another type of axonal degeneration, that which occurs secondary to inflammation and demyelination.

Right phrenic nerve injury in orthotopic liver transplantation

Right hemidiaphragm paralysis has been previously documented in patients after orthotopic liver transplantation (OLT) and it may contribute to the development of postoperative pulmonary problems. It has been postulated that a crush injury to the right phrenic nerve during OLT is the cause of dysfunction of the right hemidiaphragm. To assess the incidence and effect of right phrenic nerve injury after OLT, we prospectively studied 48 adult liver recipients. Twelve patients who underwent liver resection (LR), in whom the suprahepatic vena cava was not clamped, were used as a comparison group. Diaphragm excursion by ultrasound and pulmonary function were performed preoperatively and postoperatively; transcutaneous phrenic nerve conduction studies were performed postoperatively. Right phrenic nerve injury and hemidiaphragm paralysis occurred in 79% and 38% of the liver recipients but not after LR. Conduction along the right phrenic nerve was absent in 53% and reduced in another 26%. Left phrenic nerve conduction and left hemidiaphragm excursion were normal in both liver recipients and the patients who had LR. Liver recipients with no conduction in the right phrenic nerve had a significantly greater decrease in vital capacity in the supine position (29 +/- 9.8%) compared with those with some conduction (14 +/- 6.9%, P < 0.001). However, neither the time on the ventilator nor the hospital stay was significantly different in the latter two groups. Complete recovery of phrenic nerve conduction and diaphragm function took until nine months in some patients. Right phrenic nerve injury is common after OLT and it is the cause of right hemidiaphragm dysfunction.

The estimated numbers and relative sizes of thenar motor units as selected by multiple point stimulation in young and older adults

Multiple point stimulation (MPS) is described as a method of estimating the numbers of motor units in the median innervated thenar muscles of young and older control subjects. Stimulation at multiple sites along the course of the median nerve was employed to collect a sample of the lowest threshold, all-or-nothing surface-recorded motor unit action potentials (S-MUAPs). The average, negative peak area, and peak-to-peak amplitude of the sample of S-MUAPs was determined and divided into the corresponding value for the maximal compound muscle action potential to derive the motor unit estimate (MUE). In 37 trials from 17 younger subjects (20-40 years), the mean MUE was 288 +/- 95 SD based on negative peak area and, in 33 trials from 20 older subjects, mean values were 139 +/- 68. In 23 young and older subjects, MPS was performed on at least two occasions and the MUEs were found to be highly correlated (r = 0.88).

Effects of motor unit losses on strength in older men and women

The influence of age-associated motor unit loss on contractile strength was investigated in a representative sample of healthy, active young and older men and women. In 24 younger subjects (22-38 yr) and 20 older subjects (60-81 yr) spike-triggered averaging was employed to extract a sample of surface-recorded single motor unit action potentials (S-MUAPs) from the biceps brachii and brachialis muscles. The amplitude of the maximum compound muscle action potential of the biceps brachii and brachialis muscles was divided by the mean S-MUAP amplitude to estimate the numbers of motor units present. The maximum isometric twitch contraction (MTC) and maximum voluntary contraction (MVC) of the elbow flexors were also recorded in 18 of the younger subjects and in all older subjects. The estimated numbers of motor units were significantly reduced (47%, P < 0.001) in older subjects with a mean value of 189 +/- 77 compared with a mean of 357 +/- 97 in younger subjects. The sizes of the S-MUAPs, however, were significantly larger in older subjects (23%, P < 0.01). Significant but less marked age-associated reductions in the MTC (33%, P < 0.05) and MVC (33%, P < 0.001) were also found and were similar for both men and women. These results suggest that motor unit losses, even in healthy active individuals, are a primary factor in the age-associated reductions in contractile strength.

Effects of motor unit losses on strength in older men and women

The influence of age-associated motor unit loss on contractile strength was investigated in a representative sample of healthy, active young and older men and women. In 24 younger subjects (22-38 yr) and 20 older subjects (60-81 yr) spike-triggered averaging was employed to extract a sample of surface-recorded single motor unit action potentials (S-MUAPs) from the biceps brachii and brachialis muscles. The amplitude of the maximum compound muscle action potential of the biceps brachii and brachialis muscles was divided by the mean S-MUAP amplitude to estimate the numbers of motor units present. The maximum isometric twitch contraction (MTC) and maximum voluntary contraction (MVC) of the elbow flexors were also recorded in 18 of the younger subjects and in all older subjects. The estimated numbers of motor units were significantly reduced (47%, P < 0.001) in older subjects with a mean value of 189 +/- 77 compared with a mean of 357 +/- 97 in younger subjects. The sizes of the S-MUAPs, however, were significantly larger in older subjects (23%, P < 0.01). Significant but less marked age-associated reductions in the MTC (33%, P < 0.05) and MVC (33%, P < 0.001) were also found and were similar for both men and women. These results suggest that motor unit losses, even in healthy active individuals, are a primary factor in the age-associated reductions in contractile strength.

Electrophysiological changes in the acute "axonal" form of Guillain-Barre syndrome

The acute "axonal" form of Guillain-Barre syndrome is characterized by rapid progression to severe widespread paralysis and respiratory dependence within 2-5 days of the onset of weakness with very poor and delayed recovery. In 3 cases studied within the first 7 days, the maximum thenar, hypothenar, tibialis anterior, and extensor digitorum brevis "M" potentials were either very reduced in size or absent in response to stimulation at the usual most distal sites of stimulation at the wrist, fibular head, and/or ankle. In the latter instances, advancing the site of stimulation closer to the motor point often evoked an M response. Furthermore, continued distal advance of the site of stimulation evoked progressively larger sized M potentials. Over succeeding days even these very distally evoked M potentials disappeared. Maximum conduction velocities in motor nerve fibers just prior to total loss of excitability were often very reduced. The pattern in these cases is most consistent with progressive loss of excitability and conduction in nerve fibers undergoing axonal degeneration, although coexisting primary demyelination in the terminal segment could not be excluded as the basis for the sometimes very slowed conduction velocities.

Clinicopathological features of primary lateral sclerosis are different from amyotrophic lateral sclerosis

Primary lateral sclerosis (PLS) bears close resemblance to cases of amyotrophic lateral sclerosis (ALS) presenting with spasticity, but histopathological studies have shown significant difference between the two conditions. When the lower motor neurons in cases of ALS and PLS are compared with the equivalent cells of control subjects, morphometric studies indicate significantly decreased size and increased convexity (rounding) of the cell bodies only in ALS. In both disorders there is loss or shrinkage of the largest cortical motor neurons (Betz cells) in the primary motor cortex, though this change is not conspicuous in all cases of ALS. Morphometry reveals in both diseases a general reduction in the sizes of pyramidal cells in the precentral gyrus, indicating that smaller neurons are involved. The cortical motor neurons shrink more in PLS than in ALS. It is concluded that there is clear difference between ALS and PLS. In PLS, quantitative histopathological data show that the neuronal degeneration is confined to long descending pathways, notably the corticospinal system, with no concomitant involvement of lower motor neurons. In ALS, lower motor neuron degeneration occurs in all cases, whereas involvement of the motor cortex is variable.

Detection of hereditary motor sensory neuropathy type I in childhood

Clinical signs and slowed motor nerve conduction velocities were found in 17 of 36 children under 10 years of age who had one parent with hereditary motor sensory neuropathy type I (HMSN I). Four children had slowed conduction velocities at one year or less. Clinical signs were subtle and included pes planus, distal foot wasting, weakness of ankle eversion and dorsiflexion and areflexia. HMSN I can be detected reliably in children, even before one year of age.

Quantitation of axon loss and conduction block in acute radial nerve palsies

Eleven acute radial nerve palsies were examined between 3 days and 14 weeks following the onset of the neuropathy. Our objective was to quantify the relative extent of axon loss and conduction block in radial motor fibers supplying the extensor and abductor pollicis longus (EPL/APL) muscles. In 10 of 11 cases, conduction block exceeded axon loss. Maximum motor and sensory conduction velocities were normal distal to the spiral groove, suggesting that the larger myelinated fibers were not selectively involved in this acute neuropathy. The localization of the conduction block and slowing was, in every case, across the spiral groove. This method provides a relatively simple way of assessing the approximate contributions of axon loss and conduction block, and fits well with the early and usually complete clinical recovery in these cases.

Early postoperative ulnar neuropathies following coronary artery bypass surgery

Ulnar neuropathies following surgery are common. However, they often go undetected during the early postoperative period, because the patient may be unaware of symptoms related to the neuropathy. Nerve conduction studies are useful in localizing the lesion, but are usually employed only in cases developing signs and symptoms. We undertook this study to determine the incidence, time of onset, and outcome of clinical and subclinical ulnar neuropathies. Electrophysiological studies were carried out preoperatively, immediately following surgery, and 4 to 6 weeks postoperatively in 20 coronary artery bypass patients. Conduction velocity across the elbow was reduced in 3 limbs (8%) postoperatively, all of which were detected immediately following surgery. One patient developed conduction block and weakness in ulnar supplied intrinsic hand muscles. Denervation was seen in 2 cases and, in 1 case (5%), a right brachial plexus injury was clinically evident 5 days following surgery. All newly developing ulnar neuropathies were asymptomatic, with most recovering to their preoperative electrophysiological status at follow-up.