Urinary markers of type I collagen degradation in the dog

Urinary assays for type I collagen metabolites provide a non invasive index of bone resorption in humans, and are widely used in the management of patients with metabolic bone diseases. The specific aims of this study were to investigate the feasibility of using commercial human assay kits for quantifying the urinary excretion of type I collagen metabolites in dogs of different ages. Urine and serum samples were collected from 35 beagle dogs in five age groups (0 to 1 years; 1 to 2 years; 2 to 3 years; 3 to 7 years; > 8 years old). Urinary concentrations of pyridinoline (Pyd), deoxypyridinoline (Dpd), and the carboxy- and amino-terminal cross-linked telopeptides of type I collagen (CTx and NTx, respectively) were measured with commercial enzyme-linked immunoassay kits. Serum concentrations of another type I collagen metabolite, the carboxy-terminal cross-linked teloptide of type I collagen (ICTP), were measured with a commercial radioimmunoassay. Dilutional studies indicated that the four urinary assays show specific cross-reactivity with canine urine. Age-related differences in urinary marker excretion were identified, with young dogs excreting the highest concentrations of Pyd, Dpd, NTx and CTx. The correlation between the individual urinary markers was excellent (r = 0.87 to 0.98), while the correlation between serum ICTP and individual urinary markers was weaker (r = 0.52 to 0.64). These results validate the usefulness of the commercial assay kits in monitoring type I collagen metabolism in dogs. Histomorphometric studies have confirmed the relationship between collagen degradation and bone resorption in humans, and similar studies are now needed in dogs.     

Response of Biochemical Markers of Bone Metabolism to Exercise Intensity in Thoroughbred Horses

We studied the response of biochemical markers of bone metabolism to exercise intensity in horses. Four horses were walked on a mechanical walker for one week (pre-exercise). Then they performed low-speed exercise on a high-speed treadmill in the first week and medium-speed exercise in the second week and high-speed exercise in the third week of training. We measured two indices of bone resorption, serum hydroxyproline concentration and the urinary deoxypyridinoline/creatinine ratio, and serum osteocalcin (OC) concentration as an index of bone formation. Both indices of bone resorption gradually decreased during the experiment. Serum OC concentration did not change in the first week but was significantly lower in the second and the third weeks compared to in the pre-exercise period and in the first week. These results suggest that the low-speed exercise decreased bone resorption but did not affect bone formation, which possibly results in increasing bone mineral content and strengthening of bones. The high-speed exercise decreased bone formation and bone resorption, i.e., bone turnover was suppressed. The low-speed exercise may be preferable for increasing bone mineral content.     

Biochemical markers of bone metabolism in growing thoroughbreds: a longitudinal study

This study describes longitudinal changes in serum levels of biochemical markers of bone cell activity in a group of 24 thoroughbred foals from birth to 18 months of age. The markers of bone formation included the type I collagen carboxy-terminal propeptide (PICP), the bone-specific isoenzyme of alkaline phosphatase (BAP), and osteocalcin (OC). Levels of the cross-linked telopeptide of type I collagen (ICTP), a marker of bone resorption, and the N-terminal propeptide of type III collagen (PNIIIP), a marker of soft tissue turnover, were also measured. Levels of all markers fell significantly between birth and 18 months of age (70-80 per cent); this decrease being most marked between 0 and 6 months. However, a transient increase in levels of the markers then occurred between 6 and 14 months of age. The timing of this increase was specific for each parameter. ICTP and OC concentrations increased between October and December. PICP concentrations increased between December and April whereas the increase in PIIINP was coincident with the peak in weight gain between April and June. Changes in BAP concentration were less distinct at this time. Season was shown to have significant effects on the biochemical markers independent from the effect of age. Concentrations of all markers decreased with increasing body weight and at any given age heavier horses had lower marker levels. These results show that biochemical markers of bone cell activity and soft tissue turnover follow characteristic patterns of change in growing thoroughbreds influenced by age, season and bodyweight. The demonstration that the reference ranges for the biochemical markers change from month to month means that single samples from individuals are of little value for monitoring bone cell activity in growing thoroughbreds.     

The influence of sex on biochemical markers of bone turnover in dogs

Biochemical markers of bone turnover have been shown to be useful as inexpensive and noninvasive tools for monitoring skeletal health. The reference range for bone markers in dogs has been set by different age groups. However, other sources of biological variations were not fully investigated in dogs. To explore whether sex influences the interpretation of bone marker data we examined serum bone markers in 33 male and 25 female dogs. The bone markers selected for this study were: bone alkaline phosphatase (BALP) and osteocalcin (OC) as indicators of bone formation, and C-terminal telopeptide (CTx) of type I collagen as marker of bone resorption. All concentrations of bone markers were lower, but still within the reference range reported for dogs. We found statistically significant differences of the median OC and CTx serum concentrations between males and females. The results of this study suggest that there are sex differences in biochemical markers of bone turnover in dogs which should be considered in interpretation of bone marker data.     

Diurnal variation in concentrations of various markers of bone metabolism in dogs.

OBJECTIVE: To evaluate diurnal variation in concentrations of selected markers of bone metabolism in dogs. ANIMALS: Ten 3- to 4-year-old ovariectomized Beagles. PROCEDURE: Blood and urine samples were obtained in the morning before dogs were fed (8 AM) and then at 2-hour intervals for 24 hours. This procedure was repeated 2 weeks later. Concentrations of osteocalcin (OC) and carboxy terminal telopeptide of type-I collagen (ICTP) were measured in serum, using a radioimmunoassay; concentrations of hydroxyproline (HYP), pyridinoline (PYD), and deoxypyridinoline (DPD) were analyzed in urine. Hydroxyproline concentration was measured by means of a colorimetric test, whereas PYD and DPD concentrations were quantified by use of high-performance liquid chromatography. RESULTS: In both parts of the study, HYP concentrations increased significantly, compared with values before feeding, until 8 hours after feeding; HYP concentrations then returned to prefeeding values. Concentrations of DPD and PYD decreased from before feeding until 2 PM and then increased until 8 PM. The ICTP concentrations slowly decreased until 4 PM but returned to prefeeding values thereafter. In both parts of the study, concentrations of OC decreased during the day and then increased to reach values similar to those obtained before feeding. CONCLUSIONS: Changes in the concentrations of bone markers were detected throughout the day in the dogs of this study. Increase in HYP concentration most likely was related to feeding. As documented for bone resorption and formation in other species, circadian rhythms were evident for concentrations of DPD, PYD, and OC. Investigators should consider the time of sample collection when measuring these markers.     

Growth, nutrient utilization, radiographic bone characteristics and postprandial thyroid hormone concentrations in weanling horses fed added dietary fat

Thirty, 19-week-old Quarter Horses were utilized in a 112-d study to compare growth, nutrient utilization and post prandial thyroid hormone concentrations in weanling horses fed fat-supplemented or conventional diets. Concentrates were formulated to contain the same nutrient-calorie ratios and were fed with Coastal Bermuda grass hay in a 70:30 concentrate:hay ratio. Initially and at 28-d intervals the horses were weighed and measured for height, heart girth circumfer ence and subcutaneous fat thickness over the rump and ribs. Radiographs were taken of the right carpal and metacarpal phalangealjoints at the beginning and end of the experimental period for evaluation of bone density and physeal maturation. A digestion trial was conducted on each horse 10 d prior to completion of the study. On d 70, blood samples were col lected from 6 females in each treatment group over a 6-h collection period for evaluation of postprandial insulin, T₄ and T₃ concentrations in response to the diets. Horses in both groups consumed an average of 2.6% of body weight daily of total feed (Dry Matter). Weanlings consuming the fat-supplemented concentrate tended to have higher (P = .10) average daily weight gains (.80 vs .74 kg) and lower (P<.05) feed:gain ratios (6.3 vs 7.3) than weanlings fed the control diet. Gain in heart girth circumference was greater (P<.05) for the fat fed weanlings (20.1 cm) than the control weanlings (17.9 cm). All other linear measurements of growth were similar between treatments. There were no radiographic indications of abnormalities in the physes of horses on either treatment. Closure of the physes occurred at normal rates in foals on both treatments. Radiographic bone density was not different between treatments, and there was an expected increase in bone density in weanlings on both treatments over time. Digestibilities of protein and energy were similar between treatments, while ether extract and neutral detergent fiber digestibilities were higher (P<.05 and P<.06, respec tively) in those horses consuming the fat-supplemented diet (65.39 vs 57.67% and40.55 vs 35.62%, respectively). These data indicate that fat can be used as an energy source to support growth and development in weanling horses.     

Evaluation of serum osteocalcin and CTX-I in Ardenner horses with special reference to juvenile interphalangeal joint disease

The first aim of this study was to establish a profile of age-related normal serum concentrations of osteocalcin (OC) in Ardenner horses. For this first part, blood samples from 49 healthy Ardenner horses were collected. The second aim was to study two biochemical markers of bone metabolism, OC and a carboxy-terminal cross-linking telopeptide of type I collagen (CTX-I), in 30 young Ardenner horses during 1 year. Amongst them, 17 showed lesions of juvenile degenerative joint disease in the distal forelimbs. A specific radioimmunoassay for equine OC was used to measure the serum concentration of the marker. The serum concentration of CTX-I was measured using a commercially available human assay validated for use in the horse. The effect of age, sex, season and health status (with or without lesions) was assessed. Levels of OC fall between birth and the adult stage: this decrease being most marked between birth and 1 year of age. This age-related decrease of OC was confirmed in the 30 young Ardenner horses, but CTX-I levels remained constant in this group. The Levels of the two markers changed significantly with the season with higher concentrations during the winter. No significant difference was shown either between the two sexes or between the two health statuses.     

Evaluation of serum concentrations of biochemical markers of bone metabolism and insulin-like growth factor I associated with treadmill exercise in young horses

OBJECTIVE: To evaluate changes in serum concentrations of biochemical markers of bone metabolism and insulin-like growth factor I (IGF-I) associated with treadmill exercise in young horses. ANIMALS: 12 two-year-old Thoroughbred mares. PROCEDURE: During a 20-week study period, 6 horses were exercised on a treadmill 3 times a week (exercise group) and 6 horses received walking exercise 6 days a week (controls). Serum concentrations or activity of biochemical markers and IGF-I were assessed biweekly. Bone mineral density and content of the first phalanx were measured by dual-energy X-ray absorbiometry (DEXA) on completion of the study. RESULTS: Compared with values in controls, bone mineral density and content were higher and serum concentrations of osteocalcin (a marker of bone formation) and the carboxy-terminal telopeptide of type I collagen (a marker of bone resorption; ICTP) were lower in exercised horses. Serum concentration and activity of the bone formation markers carboxy-terminal propeptide of type I collagen and bone-specific alkaline phosphatase (BAP) were not different between the 2 groups. Serum IGF-I concentration was lower in the exercise group, compared with control values; there was a significant correlation between change in IGF-I values and changes in osteocalcin, ICTP, and BAP values at the end of the study. CONCLUSIONS AND CLINICAL RELEVANCE: Treadmill exercise over 20 weeks induced adaptive changes in bones of 2-year-old Thoroughbreds; training appears to increase bone mineral density, thereby enhancing mechanical strength of bone, but decreases bone turnover. Results indicated an association between changes in serum IGF-I concentration and bone cell activity in horses.     

Equine osteoclast-like cells generated in vitro demonstrate similar characteristics to directly isolated mature osteoclasts

We report on novel methods to isolate osteoclasts (OC s) and generate osteoclast-like cells (OCL s) from the bone and bone marrow of the equine femur. OC s were successfully isolated from bone scrapings taken from the endosteal surface of the femurs of three horses. OCL s were generated from bone marrow cells taken from the same animals. The validity of using the formation of OCL s as a method for studying OC differentiation and activity was confirmed by the similar characteristics of these two cells. In particular, they both were multinuclear, expressed the enzyme tartrate resistant acid phosphatase and the vitronectin receptor. Most importantly, both were able to resorb bone as demonstrated by the formation of extensive resorption pits when cultured on dentine slices.The generation of OCL s from bone marrow obtained from the equine femur can therefore be used to study equine OC differentiation and for studies requiring the generation of large numbers of these cells. OC s isolated directly from the same bones may be used to examine the effect of a variety of factors on bone resorption in vitro and to continually reaffirm the validity of using OCL s for large-scale studies on OC biology. Such research is essential for improved understanding of bone turnover and endochondral ossification in the horse.     

Behavioral and physiological responses to stabling in naive horses

The purpose of this study was to investigate the response of horses to confinement and isolation in a stable (indoor individual housing) for the first time using behavioral indices, heart rate, and salivary cortisol concentration. Six naive 2-year-old Australian Stock Horse fillies were examined at 4-hour intervals over 24 hours in an outdoor group paddock followed by 24 hours in indoor individual housing. Behavioral observations and scores and heart rates were recorded and saliva samples were taken at each interval. During stabling, all horses became agitated and demonstrated increased vocalization and movement. Behavioral scores were significantly higher in the indoor individual housing (P < .001). No significant difference in heart rates between the two environments was detected. Mean salivary cortisol did not increase significantly (2 ng/mL ± 1.4 ng/mL in outdoor group paddock vs 2.5 mL ± 1.2 ng/mL in indoor individual housing). No diurnal rhythm in salivary cortisol was evident in either the outdoor group paddock or indoor individual housing. The results of this study highlight that a combination of behavioral and physiological measures allow better understanding of stress, where one measurement may be misleading. First time stabling of horses elicited marked behavioral responses indicative of stress that were not reflected in increased heart rates or salivary cortisol concentrations. The lack of a diurnal cortisol rhythm and the comparatively high basal cortisol concentrations found in the outdoor group paddock environment may imply that the fillies were already stressed; therefore, stabling did not cause further aberrations detectable by salivary cortisol analysis.     

A Marine Mineral Supplement Alters Markers of Bone Metabolism in Yearling Arabians

This study tested whether the supplement (Aquacid), high in calcium and other minerals, can alter markers of bone metabolism and mineralization of the equine third metacarpus bone. Radiographs were taken of the left third metacarpus of 14 yearlings. Radiographic bone aluminum equivalence (RBAE) of each cortex was calculated to estimate mineral content. Blood samples were also taken at this time. Horses were ranked according to RBAE and gender, were pair-matched, and randomly assigned to two treatment groups. Each group was provided one of two mineral supplements in addition to their normal diet. The treated group (Aq) received 75 g Aquacid/horse/d, which provided an additional 15 g of calcium. The control group (Co) received 39.5 g of limestone to provide similar amounts of calcium. The study lasted for 112 days, with blood being taken every 28 days. At day 56 and 112, additional radiographs was taken to track changes in RBAE. Blood was analyzed for osteocalcin (a bone formation marker) and serum C-telopeptide crosslaps of type I collagen (a bone resorption marker) to detect alterations in bone metabolism. Using day 0 values as a covariate for bone markers, there was a trend (P = .07) for osteocalcin concentrations to be greater in Aq horses than in Co. Likewise, C-telopeptide crosslaps of type I collagen concentrations were greater (P < .0001) in Aq horses than in Co. There were minimal differences in RBAE values. These findings suggest Aquacid, while not altering bone mass, increases bone turnover and may aid in repairing damaged bone and preventing injuries.     

Effects of dietary energy and phosphorus content on blood chemistry and development of growing horses

Growth and clinical biochemistry were examined over 30 wk in 42 light horse weanlings fed high-forage diets (73 to 77% alfalfa) or high-concentrate diets (63 to 65% grain and grain by-products) that were either low (.24 to .35%), normal (.68%) or high (.95 to 1.06%) in P. Body weights and blood samples were taken every 2 wk. Forage and concentrate diets contained 2.65 and 3.09 Mcal digestible energy/kg DM, respectively. Calcium and P digestibilities were highest (P less than .01) in those horses fed the low P diets, but only horses fed forage-low P diets may have absorbed insufficient P. Serum alkaline phosphatase activity, serum Ca, serum Mg and plasma Cu concentrations were unaffected by diet but varied (P less than .01) among sampling periods. The concentrations of serum Ca and P of all groups fluctuated to wk 10 before being stabilized at means of 2.77 and 2.03 mmol/liter, respectively. Plasma Zn concentrations increased quadratically with age and were 3.8% greater (P less than .05) for concentrate-fed horses than for forage-fed horses. Mild to moderate physitis and flexure limb deformities occurred in 88% of the weanlings principally between wk 6 and 8 of the study. Limb deformities had largely resolved by wk 12. Marginally deficient P intakes did not alter productivity, feed intake, blood mineral concentration in the final 20 wk or the occurrence of musculoskeletal abnormalities in weanling horses.     

Increased plasma silicon concentrations and altered bone resorption in response to sodium zeolite a supplementation in yearling horses

This study examined the effect of supplementation of a bioavailable source of silicon (sodium zeolite A) on altering systemic markers of bone metabolism in horses. Twenty yearlings (ten Quarter Horses and ten Arabians) were randomly grouped as silicon (Si) supplemented (S; n=10), in which yearlings consumed 2% of the total diet as a Si-containing supplement, and a second non-supplemented control group (C; n=10). Blood samples were taken on days 0, 15, 30 and 45. Both plasma and serum were collected; the plasma was analyzed for Si concentrations and serum was analyzed for osteocalcin (OC), carboxy-terminal pyridinoline cross-linked telopeptide region of type I collagen (ICTP), and pyridinoline and deoxypyridinoline crosslinks (PYD). Supplemented yearlings had higher plasma Si concentrations than C yearlings by day 15, and remained higher than C yearlings on days 30 and 45 (P < 0.0001 for all days). There were no differences between treatment groups for OC or PYD concentrations (P > .05); however, ICTP concentrations were lower in S yearlings on day 45 when compared to C yearlings (P = .04). Results indicate that sodium zeolite A supplementation (consumed at 2% of the total diet) increases plasma Si concentrations. Furthermore, results indicate that Si-supplemented yearlings may have decreased bone resorption, which may provide for greater net bone formations, as OC concentrations were not different between groups. Unfortunately, systemic markers give no indication as to the quality of the bone that may be formed, and further research in the area of Si supplementation, bone metabolism and bone strength is required to establish conclusive evidence as to the benefits of supplemental Si to the skeletal system.     

Biochemical markers of bone metabolism in draught andwarmblood horses

Concentrations of the cross-linked carboxyterminal telopeptide of type I collagen (ICTP) and osteocalcin (OC) have been determined in the serum of one hundred clinically healthy adult Draught or Warmblood horses. The correlation between these two markers has been evaluated and the influence of gender, age and type of horse described. No significant variations were observed between animals of different sex, but a significant inverse correlation (P<0.0001) with age was observed for both measured parameters. After correction for age, serum levels of OC were found to be lower in Draught [adjusted least square mean (LSM)=6.612μg. L⁻¹] than in Warmblood horses (adjusted LSM=8.596μg.L⁻¹), whereas levels of ICTP were higher in Draughts (adjusted LSM=8.035pg.L⁻¹) than in Warmbloods (adjusted LSM=6.643μg.L⁻¹). A significant correlation (P<0.0001) was observed between OC and ICTP. This correlation was stronger if the type of horse was taken into account in the statistical model. The ratio OC:ICTP was independent of gender and age. A higher OC:ICTP ratio in Warmbloods compared to the Draught horses might reflect a higher bone remodelling level of horses submitted to regular daily work. It was concluded that ICTP and OC are influenced by the type of horse, and probably reflect a physiological difference in bone remodelling between these animals.     

The course of some bone remodelling plasma metabolites in healthy horses and in horses offered a calcium-deficient diet

An inquiry was carried out to assess the concentrations of plasma metabolites related to bone remodelling in 21 saddle horses of Warmblood breed aged 4-26 years, five draught horses of Ardennes breed aged 4-10 years, and 10 Ardennes foals aged 9-11 months. They were fed according to normal feeding practice in Belgium. The changes in some bone remodelling plasma metabolite concentrations were studied when an unbalanced diet was offered and later corrected for four Warmblood horses. Bone formation was evaluated by bone alkaline phosphatase (BALP), total alkaline phosphatase (TALP) and osteocalcin (bone gla-protein, OC). Bone resorption was assessed by hydroxyproline (HYP). Total calcium, ionized calcium, phosphorus (P) and 25-hydroxyvitamin D3 [25-(OH)D] concentrations were more or less constant. The comparison of four bone remodelling factors between the Ardennes and Warmblood horses showed higher concentrations in the Ardennes breed. Bone marker concentrations decreased according to age. The correction of the unbalanced Ca : P diet induced inconsistent effects at plasma level. The interpretation of the different bone parameters appeared to be difficult if not associated with other parameters such as a complete anamnesis and clinical examination of the animal in addition to dietary evaluation.     

Repeated oral administration of a cathepsin K inhibitor significantly suppresses bone resorption in exercising horses with evidence of increased bone formation and maintained bone turnover

Our investigations evaluated the effect of VEL‐0230, a highly specific irreversible inhibitor of cathepsin K (CatK). The objectives of our study were to determine whether repeated dosing of a CatK inhibitor (CatKI) produced a desired inhibition of the bone resorption biomarker (CTX‐1), and document the effect of repeated dosing on bone homeostasis, structure, and dynamics of bone resorption and formation in horses. Twelve young exercising horses were randomized in a prospective, controlled clinical trial and received 4 weekly doses of a CatKI or vehicle. Baseline and poststudy nuclear scintigraphy, blood sampling and analysis of plasma bone biomarkers (CTX‐1 and osteocalcin), poststudy bone fluorescent labeling, and bone biopsy were performed. Bone specimens were further processed for microcomputed tomography and bone histomorphometry. Each dose of this CatKI transiently inhibited plasma CTX‐1 (reflecting inhibition of bone collagen resorption) and increased bone plasma osteocalcin concentrations, with no detectable adverse effect on normal bone turnover in the face of exercise. Bone morphology, density, and formation rate were not different between control and treated group. Further investigation of CatK inhibition in abnormal bone turnover is required in animals with bone diseases.     

Influence of starch intake on growth and skeletal development of weanling horses

Forty-four weanling horses were used in two experiments to evaluate the effect of starch intake on growth and skeletal development. In Exp. 1, the weanlings were fed either a grain-based, high-starch (31.1%, DM basis) concentrate or a by-product-based, low-starch (0.0%) concentrate with coastal bermudagrass (Cynodon dactylon) hay. Corn oil was used to equalize the energy concentration of the concentrates. The concentrate:hay ratio was 64:36 (as-fed basis), and intake was the same for both diets. Body weight gains were greater by the weanlings consuming the high-starch concentrate (0.81 vs. 0.67 kg/d; P = 0.01). Total body length gain also was greater for the weanlings consuming the high-starch concentrate (15.5 vs. 13.2 cm; P = 0.045). Other body measurements and bone mineral deposition were not influenced by diet or gender. At the end of the experiment, postprandial blood glucose concentrations suggested that the horses on the low-starch diet were less efficient in metabolizing blood glucose than were those that had been consuming the high-starch diets. In Exp. 2, the weanlings were fed either a high-starch (34.7%) or medium-starch (17.0%) concentrate plus coastal bermudagrass hay. Corn oil again was used to equalize the energy content of the medium-starch concentrate to that of the high-starch concentrate. The concentrate:hay ratio was 64:36 (as-fed basis), and the intake was the same for both diets. The diets did not influence rate of gain (0.75 kg/d; P = 0.98), body measurements (P = 0.11 to 0.93), or bone mineral deposition (P = 0.66). Animals on the medium-starch diet tended to have blood glucose concentrations that peaked earlier and were lower at later times than those consuming the high-starch concentrate. Bone osteochondrotic lesions were not related to the diet and were found to decrease during the course of the experiment for both the high-starch and the medium-starch diets (P = 0.006 and 0.016, respectively).     

Bone Metabolism Markers in Arabian Horses During the First Two Years of Life

Serum markers of bone metabolism were analyzed in Arabian horses from birth through 2 yr. The marker of bone formation utilized was osteocalcin (OC), and the marker for degradation was carboxy-terminal pyridinoline cross-linked telopeptide region of type I collagen (ICTP). Blood samples were taken via jugular venipuncture the day of birth, d 15, d 30, d 45, d 60, and every 30 d thereafter through d 720. Serum was obtained and analyzed for OC and ICTP. Osteocalcin concentrations increased immediately after birth, were variable, and returned to baseline by d 300. By d 330, concentrations of OC began to decrease from d 0 and stayed at this lower concentration through d 510. From d 540 through 720, OC concentrations were similar to baseline. A decrease from baseline (d 0) in ICTP concentrations was seen on d 60, and ICTP continued to decline in concentration through d 720. Therefore, concentrations of OC and ICTP decreased over time as previously reported, and this study characterizes those changes on a monthly basis. Variability and general concentrations for OC and ICTP obtained in this study will provide valuable information for future experimental design and use of these markers in young horses and will aid researchers in determining treatment effects without being confounded by changes in concentrations caused by growth.     

Markers of bone metabolism in dog breeds of different size

Serum and urinary markers of bone turnover may be of value in animals as noninvasive tools for determining the response of the skeleton to disease and injury. Although normal values for bone markers have been reported for the Beagle, concerns remain that breed to breed differences will complicate the interpretation of bone marker data in dogs. To explore this, we examined serum bone markers in two breeds of vastly different size, Pomeranians and Irish Wolfhounds. Our hypothesis was that serum concentrations of bone markers are similar in toy and giant dog breeds and fall within the same range as those reported for Beagles. Bone alkaline phosphatase (BALP) and carboxy-terminal telopeptide of type I collagen (ICTP), respectively markers of bone formation and bone resorption, were measured in age matched Pomeranians (n=14) and Irish Wolfhounds (n=14). No statistically significant differences between the mean BALP and mean ICTP serum concentrations from Pomeranians and Irish Wolfhounds were found. All BALP and ICTP concentrations were within the reference range reported for Beagles. The results of this study suggest that serum BALP and ICTP concentrations in giant and toy breeds are the same as in Beagles and that these assays may be used for dogs of all sizes.     

Biochemical Markers of Bone Modeling and Remodeling in Juvenile Racehorses at Varying Mineral Intakes

In this study, blood-borne biochemical markers were used to track comparative rates of bone turnover in horses fed differing amounts of Ca, P and Mg. Bone turnover was tracked by serum osteocalcin; bone resorption by the carboxyterminal telopeptide of type I collagen (ICTP); and bone formation by the carboxyterminal propeptide of type I procollagen (PICP). Twenty-one longyearling Quarter Horses were blocked by gender and age, randomly assigned to one of four diets and subjected to 128 d of race training. The study was conducted in 32-d periods, each consisting of 28 d of race training followed by a 4-d fecal and urine collection, or a 4-d rest period. Blood samples were taken weekly during the training period. Serum and plasma samples were analyzed for biochemical markers of bone activity using RIA procedures. Onset of training resulted in elevated blood concentrations of ICTP, PICP and osteocalcin. Concentrations of ICTP and PICP were greater during the first 64 d of training, indicating increased bone activity during the first half of the training period. Horses with the greatest intake of minerals exhibited greater concentrations of PICP (bone formation marker) and lesser concentrations of ICTP (bone breakdown marker). Further, ICTP, PICP and osteocalcin concentrations decreased dramatically following 4-d of confinement and relative inactivity. Therefore it appears that feeding minerals at levels greater than current NRC recommendations provided a protective effect on the developing skeleton of the young racehorse. Additionally, the biochemical markers used in this study were sensitive enough to track daily changes in bone activity resulting from daily changes in stress to the skeleton.