Evaluation of the sample needed to accurately estimate outcome-based measurements of dairy welfare on farm.

Dairy welfare assessment programs are becoming more common on US farms. Outcome-based measurements, such as locomotion, hock lesion, hygiene, and body condition scores (BCS), are included in these assessments. The objective of the current study was to investigate the proportion of cows in the pen or subsamples of pens on a farm needed to provide an accurate estimate of the previously mentioned measurements. In experiment 1, we evaluated cows in 52 high pens (50 farms) for lameness using a 1- to 5-scale locomotion scoring system (1 = normal and 5 = severely lame; 24.4 and 6% of animals were scored ≥ 3 or ≥ 4, respectively). Cows were also given a BCS using a 1- to 5-scale, where 1 = emaciated and 5 = obese; cows were rarely thin (BCS ≤ 2; 0.10% of cows) or fat (BCS ≥ 4; 0.11% of cows). Hygiene scores were assessed on a 1- to 5-scale with 1 = clean and 5 = severely dirty; 54.9% of cows had a hygiene score ≥ 3. Hock injuries were classified as 1 = no lesion, 2 = mild lesion, and 3 = severe lesion; 10.6% of cows had a score of 3. Subsets of data were created with 10 replicates of random sampling that represented 100, 90, 80, 70, 60, 50, 40, 30, 20, 15, 10, 5, and 3% of the cows measured/pen. In experiment 2, we scored the same outcome measures on all cows in lactating pens from 12 farms and evaluated using pen subsamples: high; high and fresh; high, fresh, and hospital; and high, low, and hospital. For both experiments, the association between the estimates derived from all subsamples and entire pen (experiment 1) or herd (experiment 2) prevalence was evaluated using linear regression. To be considered a good estimate, 3 criteria must be met: R(2)>0.9, slope = 1, and intercept = 0. In experiment 1, on average, recording 15% of the pen represented the percentage of clinically lame cows (score ≥ 3), whereas 30% needed to be measured to estimate severe lameness (score ≥ 4). Only 15% of the pen was needed to estimate the percentage of the herd with a hygiene score ≥ 3, whereas 30% to estimate the prevalence of severe hock lesions. Estimating very thin and fat cows required that 70 to 80% of the pen be measured. In experiment 2, none of the pen subsamples met our criteria for accurate estimates of herd prevalence. In conclusion, we found that both a higher percentage of the pen must be sampled to generate accurate values for relatively rare parameters and that the population measured plays an important role in prevalence estimates.

Effect of slope and sciatic nerve injury on ankle muscle recruitment and hindlimb kinematics during walking in the rat.

Slope-related differences in hindlimb movements and activation of the soleus and tibialis anterior muscles were studied during treadmill locomotion in intact rats and in rats 4 and 10 weeks following transection and surgical repair of the sciatic nerve. In intact rats, the tibialis anterior and soleus muscles were activated reciprocally at all slopes, and the overall intensity of activity in tibialis anterior and the mid-step activity in soleus increased with increasing slope. Based on the results of principal components analysis, the pattern of activation of soleus, but not of tibialis anterior, changed significantly with slope. Slope-related differences in hindlimb kinematics were found in intact rats, and these correlated well with the demands of walking up or down slopes. Following recovery from sciatic nerve injury, the soleus and tibialis anterior were co-activated throughout much of the step cycle and there was no difference in intensity or pattern of activation with slope for either muscle. Unlike intact rats, these animals walked with their feet flat on the treadmill belt through most of the stance phase. Even so, during downslope walking limb length and limb orientation throughout the step cycle were not significantly changed from values found in intact rats. This conservation of hindlimb kinematics was not observed during level or upslope walking. These findings are interpreted as evidence that the recovering animals adopt a novel locomotor strategy that involves stiffening of the ankle joint by antagonist co-activation and compensation at more proximal joints. Their movements are most suitable to the requirements of downslope walking but the recovering rats lack the ability to adapt to the demands of level or upslope walking.

Inverse dynamics analysis of the pelvic limbs in Labrador Retrievers with and without cranial cruciate ligament disease.

OBJECTIVES: To quantify net joint moments, joint powers, and joint reaction forces (JRF) across the hock, stifle, and hip joints in Labrador Retrievers with and without cranial cruciate ligament (CCL) disease. To investigate differences in joint mechanics between normal, CCL deficient, and contralateral pelvic limbs. STUDY DESIGN: Cross-sectional clinical study. ANIMALS: Clinically normal (n=14) and CCL-deficient (n=9) Labrador Retrievers. METHODS: Each limb was analyzed separately and classified as normal, CCL-deficient or sound contralateral limb. Kinematic, ground reaction force (GRF), and morphometric data were combined in an inverse dynamic approach to compute hock, stifle and hip net moments, powers and JRF, while trotting. RESULTS: Vertical and braking GRF and JRF were significantly decreased in CCL-deficient limbs. In affected limbs, extensor moments at the hock and hip, flexor moment at the stifle and power in all 3 joints were less than normal. Kinetics also identified a greater joint moment and power of the contralateral limbs compared with normal, particularly of the stifle extensor muscles group. CONCLUSION: Lameness resulting from CCL disease affected predominantly reaction forces during the braking phase and the extension during push-off. A greater contribution of the contralateral limbs to propel the dog forward was identified. CLINICAL RELEVANCE: Reductions in joint motion, loads, and muscle contraction were interpreted as modifications adopted to reduce or avoid painful mobilization of the injured stifle joint. The increased joint moment and power of the contralateral compensating side may correlate with the lameness observed, but also with the predisposition of contralateral limbs to CCL deficiency in dogs.

Different effects of spinally applied prostaglandin D2 on responses of dorsal horn neurons with knee input in normal rats and in rats with acute knee inflammation.

Prostaglandin D2(PGD2) is the most produced prostanoid in the CNS of mammals, and in behavioral experiments it has been implicated in the modulation of spinal nociception. In the present study we addressed the effects of spinal PGD2 on the discharge properties of nociceptive spinal cord neurons with input from the knee joint using extracellular recordings in vivo, both in normal rats and in rats with acute inflammation in the knee joint. Topical application of PGD2 to the spinal cord of normal rats did not influence responses to mechanical stimulation of the knee and ankle joint except at a high dose. Specific agonists at either the prostaglandin D2 receptor 1 (DP1) or the prostaglandin D2 receptor 2 (DP2) receptor had no effect on responses to mechanical stimulation of the normal knee. By contrast, in rats with inflamed knee joints either PGD2 or a DP1 receptor agonist decreased responses to mechanical stimulation of the inflamed knee and the non-inflamed ankle thus reducing established inflammation-evoked spinal hyperexcitability. Vice versa, spinal application of an antagonist at DP1 receptors increased responses to mechanical stimulation of the inflamed knee joint and the non-inflamed ankle joint suggesting that endogenous PGD2 attenuated central sensitization under inflammatory conditions, through activation of DP1 receptors. Spinal application of a DP2 receptor antagonist had no effect. The conclusion that spinal PGD2 attenuates spinal hyperexcitability under inflammatory conditions is further supported by the finding that spinal coapplication of PGD2 with prostaglandin E2 (PGE2) attenuated the PGE2-induced facilitation of responses to mechanical stimulation of the normal joint.

Bovine claw and limb disorders related to reproductive performance and production diseases.

As part of a cross-sectional study of Norwegian Red Cattle, associations of lameness, lesions at the tarsus, claw shapes, and claw lesions with reproductive performance and production diseases were examined. Fifty-five tiestall herds and 57 freestall herds were sampled by computerized systematic selection and 2,665 cows were trimmed and limb and claw disorders recorded by 13 specifically trained claw trimmers during the late winter and spring of 2002. After exclusions, 2,583 cows were included in this study. Most claw lesions were mild (score 1). Prevalence of moderate and severe lesions (score 2 + 3) did not exceed 5% for any of the lesions. Hazard ratios for independent variables were identified using Cox regression analyses incorporating herd as a random effect in a positive stable frailty model. Wounds and swellings at the tarsus were associated with more clinical mastitis [hazard ratio (HR) = 4.0] and teat injuries (HR = 2.5). Moderate and severe heel-horn erosions in first-lactation cows were associated with increased calving interval (HR = 0.60). Moderate and severe hemorrhages of the sole in first-lactation cows were associated with decreased interval from calving to first service (HR = 1.6) and moderate and severe hemorrhages of the sole were associated with more milk fever (HR = 8.6). All hemorrhages of the sole (scores = 1, 2, and 3) were associated with more reproductive hormonal treatments (HR = 2.3). All sole ulcers in first-lactation cows were associated with longer interval from calving to last service (HR = 0.59) and longer calving interval (HR = 0.61), whereas sole ulcers in older cows were associated with longer calving interval (HR = 0.62). All sole ulcers also were associated with more milk fever (HR = 4.8) in all cows. Moderate and severe sole ulcers in older cows were associated with increased interval from calving to first (HR = 0.35) and last (HR = 0.37) service. Moderate and severe white-line fissures in older cows were associated with increased return rate from previous insemination (HR = 2.4). Our study shows that claw disorders are associated with poorer reproductive performance and some production diseases.

Interactions between cutaneous afferent inputs to a withdrawal reflex in the decerebrated rabbit and their control by descending and segmental systems.

Previous studies have suggested that activation of nociceptive afferents from the heel recruits a supraspinal mechanism, which is modulated by adrenergic descending inhibition, that augments withdrawal reflexes in medial gastrocnemius (MG) motoneurones. To test this idea, we have studied the temporal evolution of reflexes evoked in MG by electrical stimulation of sural nerve A(beta)-, A(delta)- and C-fibre axons at 1 Hz, in decerebrated rabbits. Reflexes were analysed in three time bands, estimated to accord to afferent drive from A(beta)- (phase 1), A(delta)- (phase 2) and C-fibre (phase 3) inputs. Stimulation of A(delta)- and C-fibres gave significant temporal summation of all reflexes. The alpha(2)-adrenoceptor antagonist RX 821002 ((2-(2,3-dihydro-2-methoxy-1,4-benzodioxin-2-yl)-4,5-dihydro-1-H-imidazole)-HCl) (100 microg intrathecal (i.t.)) potentiated, and the alpha(2)-agonist dexmedetomidine (1-30 microg i.t.) depressed all reflexes per se, but the effects of these drugs on temporal summation were secondary to changes in baseline excitability. When C-fibres were stimulated, the N-methyl-D-aspartate (NMDA) receptor antagonist dizocilpine (1 mg i.t.) reduced temporal summation of phase 2 and 3 but not phase 1 reflexes. Spinalisation at L1 in the absence of drugs increased phase 2 and 3 reflexes but had no effect on phase 1, whereas spinalisation after RX 821002 resulted in decreased phase 1 responses with no significant change in later phases. Spinalisation in the presence of dizocilpine resulted in small reductions in phase 3 reflexes only. In all cases spinalisation virtually abolished temporal summation. In spinalised animals, dizocilpine selectively reduced late reflexes, and the opioid antagonist naloxone (100 microg i.t.) augmented all reflexes but gave rise to temporal subtraction of reflexes when C-fibres were stimulated.The present experiments have revealed a number of novel and important features of the sural-MG reflex pathway: (i) activity in fine afferent axons augments the reflexogenic potential of all subsequent afferent input, thereby allowing all afferent drive from the sural field to contribute to withdrawal of the heel; (ii) endogenous adrenergic control of this reflex pathway is completely non-selective; (iii) there is a non-adrenergic element of descending inhibition that is selective for the late components of MG reflex responses, and this element is directed particularly against transmission through NMDA receptors; (iv) temporal summation in this reflex is dependent on NMDA receptor-dependent and -independent mechanisms; and (v) this temporal summation is in some way dependent on the integrity of descending pathways.

Effects of paracetamol and aspirin on neural activity of joint mechanonociceptors in adjuvant arthritis.

1. The effects of paracetamol and lysine acetylsalicylate (L-AS) on high-threshold mechanonociceptors have been investigated by recording neural activity from the inflamed ankle joint in anaesthetized rats with mild adjuvant-induced monoarthritis. 2. Paracetamol (50 mg kg-1, i.v.) and L-AS (100 mg kg-1, i.v., equivalent to 50 mg kg-1 aspirin) both caused a maximal reduction of about 40% in mechanically-evoked discharge and of 30% in ongoing (spontaneous) activity by about 15 min after the injection: a second dose of either drug did not have any significant additional effect on discharge. 3. The prostanoid IP receptor agonist, cicaprost (0.1-0.5 micrograms), increased both mechanically-evoked and ongoing discharge to pre-paracetamol levels when injected close-arterially 30-50 min after paracetamol, whereas prostaglandin E2 (PGE2) was relatively ineffective at restoring activity. 4. The results suggest that prostacyclin (PGI2) contributes to the sensitization of high-threshold joint mechanonociceptors in adjuvant-induced monoarthritis, and that paracetamol and L-AS both act to reduce discharge by inhibiting the synthesis of prostacyclin in the joint capsule. 5. Paracetamol has a direct peripheral action affecting joint capsule mechanonociceptors in rat adjuvant-induced arthritis which is very similar to that of the soluble aspirin preparation, L-AS. These findings, together with the existing literature concerning the anti-arthritic effects of paracetamol, are relevant to the treatment of chronic inflammatory disorders such as rheumatoid arthritis.

Degenerative joint disease in poultry--differences in composition and morphology of articular cartilage are associated with strain susceptibility.

The morphology and basic biochemical composition of articular cartilage from two strains of fowl were examined. Broiler breeder fowl are considered susceptible to degenerative joint disease (DJD); histological examination of one-year-old broiler breeders showed in some samples, articular cartilage thinning, fibrillation and chondrocyte cluster formation, features considered typical of DJD. Examination of similar samples from laying strain fowl showed only minor age-related changes such as some slight cartilage thinning and very mild fibrillation. The articular cartilage from the broiler breeder birds was significantly more hydrated with a higher uronic acid content than that of the laying strain birds. In addition, unloaded articular surfaces such as the proximal humerus had significantly higher amounts of uronic acid than the loaded cartilage surfaces of the proximal tarsometatarsus and the distal tibiotarsus; this suggested that the joint loading may have a role in any biochemical differences found between joints and between strains of fowl. These findings concur with other reports in mammals that showed increased hydration and uronic acid in association with early DJD and in models of osteoarthritis (OA). Thus, despite some differences between avian and mammalian articular cartilage, studies on avian DJD may give insights into mammalian disease.

Radiographic and clinical survey of degenerative joint disease in the distal tarsal joints in Icelandic horses.

The prevalence of degenerative joint disease (DJD) in the distal tarsal joints and the relation between radiographic and clinical signs compatible with the disease were estimated in a population of Icelandic horses used for riding. The material consisted of 614 horses age 6-12 years (mean age = 7.9 years). Radiographs with 3 projections of each tarsus were made and a clinical examination, including palpation of the medial aspect of the distal tarsus and motion evaluation of the hindlimbs before and after a flexion test of the tarsus, was performed. Radiographic signs of DJD in the distal tarsal joints were found in 30.3% of the horses and the prevalence was strongly correlated with age. Hindlimb lameness before and after flexion test and palpation abnormalities were significantly associated with the radiographic findings. The lameness was usually mild and, in most cases, detectable only after the flexion test. The prevalence of lameness was not significantly correlated with age. Lameness could not be predicted by details of the radiographic findings.

Gross, histological and histomorphometric features of the navicular bone and related structures in the horse.

Forelimb navicular bones and associated soft tissues were collected from 3 groups of horses and subjected to pathological examinations. The groups consisted of 38 horses with clinical navicular disease (ND) and 2 control groups, with no history of forelimb lameness, consisting of 25 age-matched mature horses (A-MC) and 9 immature horses (IC). Histological and histomorphometric studies were performed on tissue samples from 10 ND, 10 A-MC and 5 IC horses. Gross changes seen only in ND horses included: full thickness defects in the palmar surface fibrocartilage, palmar cortex erosion, medullary lysis, flexor digitorum profundus tendon (FDPT) surface fibrillation, FDPT core lesions and adhesions between the FDPT and navicular bone. Palmar surface partial thickness fibrocartilage loss and distal border fragmentation were seen with a significantly greater incidence in ND than in A-MC and not observed in IC. Remodelling of the proximal border, FDPT surface colouration, palmar surface fibrocartilage colouration and proximal border entheseous bone were identified in ND and A-MC but not in IC. Mid-ridge synovial fossae and horizontal depressions in the palmar surface were identified in all groups. Histologically palmar fibrocartilage thinning and loss were associated with reduced palmar fibrocartilage cell density and chondrocyte cluster formation. Palmar fibrocartilage fibrillation, palmar cortical bone defects, fibromyxoid stromal change in the medulla, medullary pseudocyst formation and entheseous new bone formation were all seen in ND. The adjacent FDPT showed fibrillation, tag formation and degeneration of the dorsal surface. Necrotic foci were also present within the body of the tendon. Although not always present, medullary bone pseudocysts, separate mineralised foci and most changes on the dorsal surface of the FDPT were specific to ND. Bone histomorphometric parameters were compared among groups. Cross-sectional area reduced from the sagittal ridge to the medial and lateral margins of each navicular bone. IC navicular bones had a smaller subchondral area, subchondral bone volume and a greater osteoid volume than in the AC, indicating that these differences were age-related. In ND the medullary area was decreased but the trabecular bone volume increased. The palmar subchondral area was increased but contained bone with an increased porosity and osteoid volume. Changes occurred from the medial to the lateral margins of the bone in horses with ND indicating remodelling of the bony elements throughout the bone in ND. The histological and histomorphometric changes in the navicular bone and palmar fibrocartilage were considered similar of those found in articular hyaline cartilage and subchondral bone in osteoarthritis.

Prevalence and risk factors of bone spavin in Icelandic horses in Sweden: a radiographic field study.

The present field study was performed to estimate the prevalence of radiographic signs of bone spavin (RSBS) and to evaluate some possible risk factors for RSBS in the Icelandic horse in Sweden. The survey included horses from 11 farms involving 379 horses, comprising 238 geldings, 125 mares and 16 stallions. Age ranged from 0 to 19 years with a mean age of 8.1 years. Horses were radiographed with a dorsolateral-plantaromedial-oblique projection of both tarsi. Information about age, gender, origin, working intensity, number of gaits and age when saddle broken were obtained by interviewing the owners. Features of each horse's conformation were obtained by measurement or inspection. Radiographic signs of bone spavin were found in 23% (n = 88) of the horses. Horses younger than 5 years did not show any RSBS and the prevalence increased from zero to 33% between 4 and 8 years of age. Using a multivariate logistic regression model increasing age and sickle hock conformation were found to be significantly associated with increased risk of RSBS. Age when saddle broken in combination with height at the withers also influenced the multivariate logistic regression model significantly.

Relationship between hind limb lameness and radiographic signs of bone spavin in Icelandic horses in Sweden.

A field study was designed to estimate the prevalence of hind limb lameness in a population of Icelandic horses in Sweden. All available Icelandic horses at 11 different farms within 150 km from Uppsala were examined once during a study period of 13 months. The relationship between hind limb lameness and radiographic signs of bone spavin (RSBS) was investigated. The rate of agreement between the outcome after palpation, motion evaluation and flexion test and radiographic examination was established. A total of 379 horses including 238 geldings, 125 mares and 16 stallions, with mean age 8.1 years (range 1-19 years) were examined by palpation of the medial aspect of the tarsal joints, motion evaluation and flexion test of the hind limbs. One dorsolateral-plantaromedial oblique radiographic view was recorded from each tarsus. Palpable abnormalities were found in 118 horses (31%). Forty-three horses (12%) were lame at presentation, 94 horses (25%) were positive on flexion test and 88 horses (23%) had RSBS. There was a significant relationship between palpable abnormalities, lameness, positive flexion test and RSBS. The proportion of joints with RSBS increased with increasing severity of physical findings. The proportion of lame limbs increased with increasing radiographic changes. The presence of palpable findings or positive flexion test was not influenced by the grading of radiographic changes. Using palpation, motion evaluation, and flexion test 75% of the horses with RSBS were identified. The rate of agreement between the clinical examination and the radiographic examination was 73%.

The incidence of tibiotarsal rotation in the ostrich (Struthio camelus).

Abnormal lateral tibiotarsal rotation has been reported as one of many abnormalities affecting the pelvic appendicular skeleton of birds. In this study, lateral rotation of the tibiotarsus affected 89 out of 1,407 ostrich chicks between 2 weeks and 6 months of age raised at the Oudtshoorn Experimental Farm. There was no sexual preference, but the lesion affected the right pelvic limb almost exclusively and very rarely the left limb. Pelvic appendicular skeletal abnormalities make a significant contribution to mortalities in ostrich chicks.

Vacuum phenomenon in equine carpal, metacarpophalangeal and metatarsophalangeal joints.

In order to establish the incidence of vacuum phenomenon in horses' carpal, metacarpophalangeal and metatarsophalangeal joints, stress-flexed radiographs were made of normal joints, joints with known pathology and in anaesthetised horses with joints under traction. Focal intra-articular radiolucencies were identified in normal stress-flexed carpal, metacarpophalangeal and metatarsophalangeal joints. These radiolucencies can be confused with those associated with pathological conditions.

[Hock lesions in dairy cows--an overview]. / Sprunggelenkschäden bei Milchkühen--eine Übersicht.

Hock lesions are the most common husbandry-related disease of the locomotor system in dairy cattle. These conditions are referred to as technopathies. The prevalence of tarsal lesions ranges from 40 to 70% and thus, from a welfare standpoint, clearly exceeds an acceptable level. These lesions usually indicate inadequate stall or cubicle design in dairy barns. The presence and severity of hock lesions are associated with lameness and other limb disorders as well as mastitis and reduced milk yield. Hock lesions therefore influence animal welfare and production. Epidemiological and behavioural studies have shown that a manure pack covered with straw is associated with the lowest prevalence of lesions, followed by sand bedding, provided that the lying space is adequate.

Functional evaluation in the rat sciatic nerve defect model: a comparison of the sciatic functional index, ankle angles, and isometric tetanic force.

BACKGROUND: The sciatic functional index has long been the standard method of assessing motor recovery in the rat sciatic nerve model. The relative subjective nature of the assessment has led to development of newer methods, including video gait analysis and quantitative measurement of isometric tetanic muscle force. METHODS: Forty male Lewis rats, each with a 10-mm segmental defect in the sciatic nerve, were divided randomly into two groups: rats in group I underwent repair with reversed autograft, and those in group II received a collagen conduit. Video gait analyses were performed at 0, 4, 8, and 12 weeks, and sciatic functional index and ankle angles in four different walking phases were recorded. Isometric tetanic force of the tibialis anterior muscle was also measured at 12 weeks and correlated with sciatic functional index and video gait analysis data. RESULTS: The sciatic functional index results did not correlate with isometric tetanic force. Significantly, the sciatic functional index could not be measured in 26 percent of the rats at 8 weeks and 59 percent of the rats at 12 weeks secondary to toe contractures. Among various ankle angle measurements, only the ankle angle in toe-off phase correlated well with isometric tetanic force. CONCLUSIONS: Toe contractures occurred more frequently in rats with better nerve recovery, and interfered with evaluation of the motor recovery using the sciatic functional index method. Ankle angle in toe-off phase measured from video gait analysis is a useful parameter that reflects functional recovery of the muscle force.

Cancellous bone formation response to simulated resistance training during disuse is blunted by concurrent alendronate treatment.

The purpose of this study was to assess the effectiveness of simulated resistance training (SRT) exercise combined with alendronate (ALEN) in mitigating or preventing disuse-associated losses in cancellous bone microarchitecture and formation. Sixty male Sprague-Dawley rats (6 months old) were randomly assigned to either cage control (CC), hind limb unloading (HU), HU plus either ALEN (HU + ALEN), SRT (HU + SRT), or a combination of ALEN and SRT (HU + SRT/ALEN) for 28 days. HU + SRT and HU + SRT/ALEN rats were anesthetized and subjected to muscle contractions once every 3 days during HU (four sets of five repetitions, 1000 ms isometric + 1000 ms eccentric). Additionally, HU + ALEN and HU + SRT/ALEN rats received 10 µg/kg of body weight of ALEN three times per week. HU reduced cancellous bone-formation rate (BFR) by 80%, with no effect of ALEN treatment (-85% versus CC). SRT during HU significantly increased cancellous BFR by 123% versus CC, whereas HU + SRT/ALEN inhibited the anabolic effect of SRT (-70% versus HU + SRT). SRT increased bone volume and trabecular thickness by 19% and 9%, respectively, compared with CC. Additionally, osteoid surface (OS/BS) was significantly greater in HU + SRT rats versus CC (+32%). Adding ALEN to SRT during HU reduced Oc.S/BS (-75%), Ob.S/BS (-72%), OS/BS (-61%), and serum TRACP5b (-36%) versus CC. SRT and ALEN each independently suppressed a nearly twofold increase in adipocyte number evidenced with HU and inhibited increases in osteocyte apoptosis. These results demonstrate the anabolic effect of a low volume of high-intensity muscle contractions during disuse and suggest that both bone resorption and bone formation are suppressed when SRT is combined with bisphosphonate treatment.

The effect of number of lengthening contractions on rat isometric force production at different frequencies of nerve stimulation.

AIM: To test the effect of 3, 10, 60 and 240 lengthening contractions (LC) on maximal isometric force of rat plantar flexor muscles at different stimulation frequencies. METHODS: Using a dynamometer and electrical nerve stimulation, maximally active skeletal muscles were stretched by ankle rotation to produce LC of the plantar flexor muscles in intact female rats. After the lengthening contraction protocols, maximal isometric force was measured at different frequencies of nerve activation to obtain frequency-dependent force deficits (weakness). RESULTS: The magnitude of the force deficit, measured 1 h after the protocols at 80 Hz, increased as a function of repetition number (three LC, 33.3 +/- 1.7%; 10 LC, 37.2 +/- 2.3%; 60 LC, 67.6 +/- 1.5%; 240 LC, 77.7 +/- 1.2%). Force deficits were also measured at each stimulation frequency tested (5:120 Hz). Using a ratio of isometric force at 20:100 Hz stimulation, the relative depression of force at low frequency was determined. The relative depression of isometric force at low frequency was most prominent during the early repetitions. CONCLUSION: As low-frequency force depression appears to result primarily from excitation-contraction (E-C) coupling failure, the early LC in a series of repeated contractions probably contribute most to damage of the cellular components involved in E-C coupling.

Effect of intermittent stretch on immobilised muscle.

When muscle is immobilised in a shortened position there is a reduction in fibre length and an increase in the proportion of connective tissue. This results in reduced muscle compliance and a loss of range of joint motion. Experiments have been carried out to determine whether short periods of stretch are effective in preventing these changes. The soleus muscle of the mouse was immobilised in a shortened position for a period of 10 days by means of a plaster cast. Every two days the cast was removed and the muscle passively stretched for a 15 minute period. It was found that this treatment prevented the connective tissue changes but did not prevent the reduction in muscle fibre length, which in itself resulted in considerable loss of range of motion.

Mutable and immutable features of paw-shake responses after hindlimb deafferentation in the cat.

1. Hindlimb paw-shake responses were assessed before and after unilateral deafferentation (L3-S1) in chronic-spinal cats (n = 5), spinalized at the T12 level 1 yr earlier. Selected ankle flexor [tibialis anterior (TA)] and extensor [lateral gastrocnemius (LG)] and knee extensor [vastus lateralis (VL)] muscles were surgically implanted with chronic electromyographic (EMG) electrodes to determine mutable features of cycle characteristics and muscle synergies that are modulated by motion-dependent feedback as opposed to immutable features that are centrally programmed and not modulated by limb afference. 2. Paw-shake responses were difficult to elicit in the extensively deafferented hindlimb; this was true particularly during the first recovery weeks after deafferentation. By the end of the first month, however, brief responses of 1 or 2 cycles were commonly elicited in four of five cats, and responses of 3-7 cycles were common by the end of the second month in three of five cats. Initially, responses in the deafferented limb were elicited by stimuli applied to the dorsolateral thigh, an oval patch of skin innervated by intact S2 afferents. Over the 4-mo recovery period, however, the receptive field of the largely denervated skin expanded, and responses were also elicited by stimuli applied to the lateral aspect of the knee and shank, but usually not the paw. 3. In addition to fewer average cycles per response (5 vs. 10 cycles), paw shaking evoked in the deafferented hindlimb was characterized by longer-than-average cycle periods (124 vs. 98 ms), but the average cycle period varied widely among responses, ranging from 99 to 239 ms. Before deafferentation, the temporal organization of consecutive cycles was stereotypic; cycle periods increased linearly throughout a response. After deafferentation, however, there was no systematic relationship between cycle period and cycle number, and approximately 14% of the records with greater than or equal to 3 cycles were characterized by arhythmical sequences of EMG bursts. 4. At the ankle, LG burst duration was not altered by deafferentation, but TA onset and burst duration were affected. Before deafferentation, TA onset was invariant with respect to the beginning of the cycle, and burst duration increased linearly with cycle period. After deafferentation, however, TA onset was delayed, and the delay increased linearly with cycle period. Consequently, the TA burst duration was brief and unrelated to cycle period.(ABSTRACT TRUNCATED AT 400 WORDS)