Activities of gamma-glutamyltransferase, alkaline phosphatase and aspartate-aminotransferase in colostrum, milk and blood plasma of calves fed first colostrum at 0-2, 6-7, 12-13 and 24-25 h after birth

Enzyme activities of gamma-glutamyltransferase (gamma-GT), alkaline phosphatase (AP) and aspartate-aminotransferase (AST) were measured from birth to the age of 28 days in calves which were fed colostrum at 0-2, 6-7, 12-13, or 24-25 h after birth. Enzyme activities were also measured in colostrum (first to fifth milking) and in mature milk. Activities were highest in the first colostrum milking and decreased to the lowest activities in mature milk. Plasma gamma-GT activity transiently increased after first colostrum intake and was greater in calves fed first colostrum within less than 6-7 h than in those fed first colostrum later than 12 h after birth. Activity of gamma-GT reflected the absorption of colostral gamma-GT, which decreased with time after birth. The AP activity transiently increased after colostrum intake and was higher in calves fed colostrum within the first 12 h of life than in those fed later after birth. The transient rise of plasma AP activity also indicated absorption of colostral AP, although endogenous sources of AP could not be excluded. The activity of AST also transiently increased after colostrum intake but there was no association with time of first colostrum feeding, indicating that the rise of plasma AST activity was the consequence of enhanced endogenous production and was independent of colostrum intake. In conclusion, there are different causes leading to postnatal changes in enzyme activities.     

Response of plasma bone markers to a single intramuscular administration of calcitriol in dairy cows

To elucidate the effects of an exogenous calcitriol (1,25-dihydroxyvitamin D₃) on plasma bone markers, the formation item osteocalcin (OC), undercarboxylated OC (ucOC) and bone-specific alkaline phosphatase (BALP), and the resorption parameter tartrate-resistant acid phosphatase isoform 5b (TRAP5b) and hydroxyproline (HYP) were measured in conjunction with plasma calcitriol and calcium (Ca) concentrations in dairy cows receiving calcitriol or its vehicle according to a 2 × 2 crossover design. Calcitriol (0.5 μg/kg, i.m.) increased significantly its plasma level during 6 h to day 2 and plasma Ca concentration during 12 h to day 7 compared to the vehicle. Also, plasma OC and ucOC started to rise from day 3 and 1, respectively, and remained elevated until day 7. No change in plasma BALP, TRAP5b or HYP associated with calcitriol treatment was noted. These results demonstrate that exogenous calcitriol stimulates osteoblasts to biosynthesise OC, a determinant of the bone formation in cows.     

The effect of the use of milk-based feed mixtures and whole milk on the development of selected indicators in the blood plasma in calves

Two milk feeding systems were investigated as influencing the health and development of calves. After the termination of colostrum feeding, the ten animals of the experimental group were given whole milk whereas the control group (also ten calves) was given the Laktosan milk replacer. By the age of three months, blood was collected from the calves for biochemical examination in weekly intervals, later once a month. The content of urea, determined in the blood plasma of the calves of the experimental group was significantly lower in the fourth to seventh week. The plasma levels of nitrogen, potassium, calcium and magnesium were about the same in the experimental and control groups, being within the limits of the reference values. At the age of six to nine weeks, the content of inorganic phosphorus in the blood plasma of the tested animals was statistically significantly higher. Vitamin A concentration in the blood plasma was about the same in both groups. The content of vitamin E in the blood plasma of the calves of the experimental group was statistically significantly higher in the fourth to eight week of age. No significant differences between the two groups were observed in the plasmatic activities of aspartate aminotransferase (AST) and gamma-glutamyl transferase (GMT). The activities of alkaline phosphatase (ALP) were significantly higher in the third to fifth week of life. From the fifth to eighteenth week of age, the average daily weight gains were significantly higher in the calves given whole milk.     

Plasma vitamin A status in calves fed colostrum from cows that were fed vitamin A during late pregnancy

Calves are born vitamin A and β‐carotene deficient and the β‐carotene conversion to vitamin A is limited. Colostrum, contains relatively large amounts of vitamin A and β‐carotene and the retinol and β‐carotene status of calves can be normalized with colostrum consumption. We studied whether vitamin A supplementation of cows during late gestation (dry period) increases cow plasma retinol concentrations, the retinol content of first colostrum, and the plasma vitamin A status of calves during their first month of life. Both plasma and colostrum retinol concentrations were higher in vitamin A supplemented cows than in non‐supplemented cows. In calves that were for 5 days fed colostrum (milk) from vitamin A‐supplemented cows and then mature milk, plasma retinol concentrations were higher from 14 to 30 days after birth than in calves that were fed colostrum (milk) from cows that were not vitamin A supplemented. The study shows that vitamin A supplementation of cows during the dry period can improve the vitamin A status of their calves up to 1 month, if calves ingest their colostrum/milk for up to 5 days.     

Plasma fluctuation in estradiol-17β and bone resorption markers around parturition in dairy cows

Blood samples were obtained sequentially from 10 dairy cows around the time of parturition to assess plasma fluctuations in estradiol-17β (E₂) levels in association with those of several bone resorption markers. Plasma E₂ concentration increased sharply a few days prepartum and decreased quickly after parturition. In terms of bone resorption markers, the plasma level of tartrate-resistant acid phosphatase isoform 5b (TRAP5b) rose significantly, commencing 1 week prepartum, and was maintained at this level to a few days postpartum. The plasma concentration of carboxyterminal collagen cross-links of type-I collagen (CTx) increased significantly after parturition. These observations suggest that osteoclast-mediated bone resorption was activated after parturition when plasma E₂ concentrations decreased.     

Colostral transfer of gamma glutamyl transpeptidase in calves

Serum gamma glutamyl transpeptidase (GGT) levels in blood samples taken from normal calves which bad suckled colostrum were much higher than those found in healthy adult cattle. Levels of over 60 times the normal adult level were observed. These high levels of GGT took approximately 5 weeks to decline to adult values. Calves which appeared to have not received or absorbed colostrum had GGT levels which would be considered normal in adult cattle. A calf with serum gamma globulin levels which indicated an intermediate amount of colostrum absorption had a level of GGT which was intermediate between that expected for normal adult cattle and that found in calves which had more fully absorbed colostrum. The mean GGT level observed in colostrum from 6 newly-calved cows was over 800 times the mean serum GGT level of the same 6 cows. It therefore appears most likely that GGT is concurrently absorbed with colostrum by calves and this gives rise to the very high levels seen in normal calves. Calves with very high levels of serum GGT also had raised levels of alkaline phosphatase (AP) which slowly declined but never reached normal adult levels within the 53-day period of observation. It therefore appears that high levels of both GGT and AP are achieved by calves at the time of colostrum absorption and it is concluded that clinical interpretation of serum GGT and AP levels in young calves is closely dependent upon parallel knowledge of their serum gamma globulin levels.     

Colostral transfer of gamma glutamyl transpeptidase in calves

Serum gamma glutamyl transpeptidase (GGT) levels in blood samples taken from normal calves which bad suckled colostrum were much higher than those found in healthy adult cattle. Levels of over 60 times the normal adult level were observed. These high levels of GGT took approximately 5 weeks to decline to adult values. Calves which appeared to have not received or absorbed colostrum had GGT levels which would be considered normal in adult cattle. A calf with serum gamma globulin levels which indicated an intermediate amount of colostrum absorption had a level of GGT which was intermediate between that expected for normal adult cattle and that found in calves which had more fully absorbed colostrum. The mean GGT level observed in colostrum from 6 newly-calved cows was over 800 times the mean serum GGT level of the same 6 cows. It therefore appears most likely that GGT is concurrently absorbed with colostrum by calves and this gives rise to the very high levels seen in normal calves.

Calves with very high levels of serum GGT also had raised levels of alkaline phosphatase (AP) which slowly declined but never reached normal adult levels within the 53-day period of observation.

It therefore appears that high levels of both GGT and AP are achieved by calves at the time of colostrum absorption and it is concluded that clinical interpretation of serum GGT and AP levels in young calves is closely dependent upon parallel knowledge of their serum gamma globulin levels.     

Dexamethasone and colostrum feeding affect hepatic gluconeogenic enzymes differently in neonatal calves

Plasma glucose concentrations in neonates are influenced by colostrum feeding and by glucocorticoids. We have tested whether a high-glucocorticoid status after birth, as well as colostrum feeding, influences glucose metabolism in association with changes of hepatic expression and activities of gluconeogenic enzymes phosphoenolpyruvate carboxykinase (PEPCK; EC 4.1.1.32) and pyruvate carboxylase (PC; EC 6.4.1.1) in neonatal calves. Calves (n = 14 per group) were fed either colostrum or a milk-based formula with nutrient and energy contents similar to colostrum. Half the calves in each feeding group were treated with dexamethasone (DEXA; 30 microg/[kg BW x d]). Pre- and postprandial blood samples were taken on d 1, 2, 4, and 5 and liver samples were collected on d 5 of life. Dexamethasone treatment increased (P < or = 0.05) plasma concentrations of glucose, insulin, and glucagon more in colostrum-fed than in formula-fed calves but increased (P < or = 0.05) urea concentrations and decreased (P < or = 0.05) concentrations of NEFA, ACTH, and cortisol independent of colostrum vs. formula feeding. Colostrum feeding increased (P < 0.05) plasma glucose, but decreased (P < 0.05) plasma urea concentrations. Glucagon-to-insulin ratios in DEXA-treated and colostrum-fed calves were decreased (P < 0.05). Dexamethasone treatment decreased hepatic mRNA levels and activities of PC (P < 0.001 and P < 0.10) and activities of PEPCK (P < 0.001) but increased (P < 0.001) the glycogen content. Colostrum feeding increased (P < 0.05) mitochondrial PEPCK mRNA levels and PEPCK activities in calves not treated with DEXA but decreased (P < 0.1) amounts of PC mRNA. In conclusion, increased plasma glucose concentrations after DEXA treatment were not associated with a stimulation of hepatic gluconeogenic enzyme activities; however, colostrum feeding probably raised plasma glucose concentrations because of increased hepatic gluconeogenic activities.     

The effect of clover silage treated with acrylic acid on selected indicators of metabolism in cows around the time of parturition and the status of their calves]

A trial was conducted with 16 cows divided into control and test group (eight cows in either); since day 57.6 +/- 21.1 before parturition, test cows were given feed rations for 107 days which contained 16.0 kg clover-grass silage a day, treated with 3 l acrylic acid per t ensiled matter. Control group of cows was administered feed rations containing silage treated with 4 l formic acid per 1 t ensiled matter from day 55.5 +/- 21.9. In the blood (plasma) of test cows the alkaline phosphatase activity was increasing gradually, in the time after parturition a tendency of lower glucose (P 0.05 to 0.01), thyroxine and triiodothyronine concentrations was observed, and the phagocytal activity of leucocytes and its index decreased. The levels of ketone bodies and aspartate aminotransferase activity were found to be higher. In this period in urine the pH value and net acid-base output were lower, while the inorganic phosphorus concentration was higher. No difference were observed in colostrum density, liveweight of born calves and in the target metabolic parameters in the blood (plasma) of calves. In the 30-day period of investigation the cows of test group gave an average daily milk yield lower by 1.5 l (in comparison with control cows). The residues of acrylic acid (method sensitivity of 1.0 mg acrylic acid in 1 l sample) were not detected in their colostrum and milk.     

Plasma leptin status in young calves: effects of pre-term birth, age, glucocorticoid status, suckling, and feeding with an automatic feeder or by bucket

Plasma leptin concentrations depend on energy intake and fat stores and are modified by hormones, such as glucocorticoids. We have measured plasma leptin concentrations in pre-term calves (born on day 277 of gestation) during the first week of life, in full-term calves (290 days of gestation), fed similar amounts of nutrients with colostrum or a milk-derived formula, combined with or without dexamethasone treatment (to simulate a high glucocorticoid status), during the first five days of life, and in calves fed with an automatic feeder or by bucket or suckling on dams up to day 28. Leptin concentrations increased (P<0.05) from birth to day 7 in pre-term calves. In full-term calves leptin concentrations were stable from day 1 to day 4 in colostrum-fed animals, but decreased (P<0.05) and were lower (P<0.05) if fed a formula with similar amounts of energy and macronutrients as colostrum. Concentrations increased (P<0.05) from day 1 to day 2 in calves suckling on dams and then remained elevated, but did not change and were lower in calves fed with the automatic feeder or by bucket than in suckling calves. Dexamethasone only slightly elevated leptin concentrations. There was no episodic secretion pattern, and there were no consistent associations of leptin with various metabolites and hormones. In conclusion, plasma leptin in young calves with respect to effects of nutrition (low energy intake) and hormones (glucocorticoids) and in association with metabolic changes behaved differently from what is known in mature cattle.     

Thyroid hormone concentrations in selenium deficient and selenium sufficient cattle

Selenium deficient calves when compared to selenium supplemented calves had increased plasma thyroxine concentrations and decreased plasma tri-iodothyronine concentrations. These changes in the selenium deficient calves were accompanied by significant increases in plasma urea and creatinine concentrations and decreased plasma alkaline phosphatase activity. The demonstration that low selenium status can cause imbalances in thyroid hormone metabolism may provide an explanation for some of the effects of the deficiency.     

The effects of genotype and selected environmental factors on colostrum production and intake in cattle

The aim of this study was to determine effects of genotype and selected environmental factors on colostrum production, intake, and efficiency in the cattle. The investigations were conducted on 67 dam-calf pairs. All cows were of Polish Holstein-Friesian breed, the Black-and-White variety (PHF-HO), whereas calves were sired by bulls of the following breeds: PHF-HO, Polish Holstein-Friesian of the Red-and-White variety (PHF-RW), Jersey (JE), Montbéliarde (MB) and Limousine (LI). The colostrum was collected from cows and offered to calves "from bucket" thrice a day. The amount of produced colostrum considerably exceeded the ability of its consumption by calves. Low share of HF genes in the cow, older cow's age and calving in the period from January to April appeared to be favorable factors for colostrum production. Calves born to cows with low HF gene share drank more colostrum than calves originating from cows with higher gene share of this breed. Crosses with JE drank the highest amount of the colostrum in relation to body weight, while MB-sired calves drank the highest amount in absolute terms. Colostrum intake was positively correlated with the dam's age. Furthermore, it was shown that in case of the first colostrum intake the most favorable period was from May to September, while in cases of total intake in the first day of life and mean intake in the first 5 days of life it was the period from January to April. Crosses with JE were characterized by extremely high use of colostrum per unit of body weight gain.     

Influence of feeding different amounts of first colostrum on metabolic, endocrine, and health status and on growth performance in neonatal calves

Colostrum intake is important for health and postnatal development of neonatal calves. We studied the effects of enhanced first colostrum feeding on growth, health status, and metabolic and endocrine traits in calves during their 1st wk of life. Calves of group CL (GrCL; n = 7) were fed colostrum of milkings 1 to 6 twice daily during the first 3 d of life, followed by milk replacer (MR) up to d 7. Calves of group CH (GrCH; n = 7) were fed colostrum of the first milking during the first 3 d and then colostrum (of the first milking) twice daily, which on d 4, 5, 6, and 7 was diluted with 25, 50, 75, and 75 parts of MR, respectively. Pre- and postprandial blood samples were taken on d 1, 2, 3, and 7 for the determination of various metabolic and endocrine traits, and on d 5 intestinal absorption capacity was measured using the xylose absorption test. Rectal temperatures and fecal scores were higher (P < .05) in GrCH than in GrCL. Plasma concentrations of total protein and albumin were higher (P < .05) on d 7, IgG on d 2 and 3, and urea on d 2, 3, and 7 in GrCH than in GrCL. Plasma concentrations of triglycerides were higher (P < .05) on d 2 and of phospholipids and cholesterol were higher (P < .01) on d 7 in GrCH than in GrCL. Plasma insulin and glucagon concentrations were higher (P < .05) in GrCH than in GrCL, whereas prolactin and growth hormone concentrations were higher (P < .05) in GrCL than in GrCH. Enhanced colostrum intake had no effects on xylose absorption on d 5. Higher plasma protein, urea, and lipid concentrations in GrCH partly mirrored higher protein and fat intake but additionally pointed to higher protein synthesis and lipid turnover.     

Variations in the immune response to natural Schistosoma mattheei infections in calves born to infected mothers

During previous work Schistosoma antibodies and circulating antigens were detected at birth in the serum from some calves born to Schistosoma mattheei infected mothers. The objectives of the present survey were: (1) to investigate the proportion of calves, born to cows infected with S. mattheei, which have specific antibodies and circulating schistosome antigens present in their serum at birth and (2) to investigate whether the presence or absence of these specific antibodies and/or circulating antigens at birth may affect the pattern of a natural S. mattheei infection in calves from 4 to 5 months of age, when the colostral antibodies are thought to be of negligible importance. A total of 28 calves born to infected mothers were randomly selected. Faeces, serum and colostrum samples were collected from the cows at calving, serum samples were collected from the calves at birth (day 0), after intake of colostrum (day 1) and monthly thereafter up to the age of 10 months. Both serum and colostrum samples were analysed for IgG(H+L) against SWAP mattheei and schistosome circulating anodic antigen (CAA) levels. The calves were exposed to a natural challenge from the age of 4-5 months. Faecal samples were collected from the calves monthly, starting at an age of 5 months up to 10 months, and were examined for faecal egg counts. Nine (group 1) out of the 28 calves were found to have specific antibodies in their serum at birth, in 5 of them CAA levels were also detected. In the other 19 calves (group 2) no IgG(H+L) or CAA were detected. At the end of the study faecal egg counts and CAA levels were significantly lower in calves from group 1 compared to group 2. Results confirm earlier work that specific antibodies and circulating antigens may be present in serum from calves at birth, and show that these calves have lower faecal egg counts and CAA levels after exposure to a natural challenge.     

Quantification of bone alkaline phosphatase in canine serum

An assay was developed and proven accurate and precise for the quantification of canine serum alkaline phosphatase of bone origin (BAP). The assay uses wheat germ lectin (WGL) which selectively precipitates SAP but not liver alkaline phosphatase (LAP) in serum preincubated for 1 hour at 37 degrees C before conducting the assay. Although a large percentage of corticosteroid-induced alkaline phos- phatase (CAP) is also precipitated by WGL, the activity of this isoenzyme can be determined by utilizing the automated levamisole inhibition assay and BAP determined by subtraction except in those cases in which CAP is very markedly increased. Use of these two assay techniques in combination allows the quantification of LAP, BAP, and CAP activity in canine serum. In sera from adult dogs of various ages, BAP activity represents a mean of 21.27 -/+ 11.4 U/L; however, there was a statistical decrease in BAP activity with age. This allowed the determination of 95% confidence interval for a reference range dependent on age of the dog. Bone AP activity in puppies drops dramatically within the first 3 months, reaching a magnitude of activity consistent with that of the adult dog by approximately 15 months. BAP was increased over adult reference range in five of five dogs tested with osteosarcoma. This assay will now allow conducting a clinical study of the diagnostic significance of bone AP activity in neoplastic and metabolic diseases of bone.     

Serum immunoglobulin G concentrations in calves fed fresh and frozen colostrum

OBJECTIVE: To determine whether serum IgG concentrations in neonatal calves are adversely affected by short-term frozen storage of colostrum. DESIGN: Prospective study. SAMPLE POPULATION: Experiment 1 consisted of 10 pairs of Holstein calves (n = 20) fed matched aliquots of either fresh (n = 10) or frozen and thawed (10) colostrum. In experiment 2, 26 Holstein calves were fed either fresh (n = 13) or frozen and thawed (n = 13) colostrum. PROCEDURE: Experiment 1 consisted of calves resulting from observed parturitions; calves were randomly assigned to treatment groups (fresh or frozen and thawed colostrum) in pairs. Calves were fed 4 L aliquots of colostrum via oroesophageal intubation at 3 hours of age. Serum IgG concentrations at 2 days of age were compared between the 2 groups by use of a paired t-test. Experiment 2 consisted of calves resulting from observed parturitions; calves were randomly assigned to treatment groups (fresh or frozen and thawed colostrum). Calves were fed 4 L aliquots of colostrum via oroesophageal intubation at 3 hours of age. Regression analysis was used to determine whether calf serum IgG concentration was a function of colostral IgG concentration and colostrum storage group. RESULTS: Significant differences were not observed between the 2 groups in experiment 1. No significant relationship was observed between colostrum storage group and serum IgG concentration in experiment 2. The model that best predicted serum IgG concentrations accounted for 20% of the variability in serum IgG concentration. CONCLUSION AND CLINICAL RELEVANCE: Frozen colostrum is an adequate source of IgG for calves.     

Blood pH, plasma carotene, vitamin A, albumin and globulin concentrations in newborn calves and in dams during the first three days of the postnatal period.

Blood pH, total plasma carotene, plasma vitamin A fractions and some plasma proteins were determined in newborn calves (n = 38) and their dams. Calves were assigned to one of two groups according to their blood pH immediately after birth: group 1 (normal) with pH above 7.2 (n = 27) and group 2 (slightly acidotic) with pH 7.0 to 7.2 (n = 11). The difference between the neonatal blood pH values of the two groups immediately post partum disappeared 24 h after birth. The blood pH of the dams was normal. The extremely low plasma carotene concentration (group 1: 32.7 micrograms/l; group 2:20.5 micrograms/l) and the low plasma globulin fractions (group 1:19.6 g/l; group 2:19.2 g/l) immediately after birth were elevated by the intake of colostrum. There was no significant change in plasma vitamin A fractions (retinol, retinyl ester) during the early postnatal period (3 days post partum) in newborn calves. The acid-base balance of newborn calves does not have any influence on the physiological alterations of plasma vitamin A, carotene and some plasma proteins during the first three days of life.     

Plasma amino acid pattern during the first month of life in calves fed the first colostrum at 0-2 h or at 24-25 h after birth

Calves are born with a mostly inadequate essential amino acid (EAA) status. Studies were designed to test the hypothesis that delaying the intake of the first colostrum for 24 h, besides its early effects, also has late effects on plasma free amino acid levels and on the protein status. There were marked and rapid elevations (within 2 h) of plasma levels of various amino acids, and especially of EAA, after the intake of the first colostrum, whereas changes after the intake of mature milk on day 28 of life were mostly absent or concentrations even decreased. The EAA and non-essential amino acid (NEAA) status was rapidly normalized after intake of the first colostrum, but normal plasma levels of some amino acids were also reached during the first 24 h of life even when the first meal was withheld. Delaying colostrum intake had only transient effects on EAA and NEAA (except hydroxyproline), in contrast to its effects on plasma immunoglobulin G and total protein levels.     

Serum enzyme changes in newborn calves fed colostrum

In 10 newborn Holstein calves, which were initially bottle-fed on pooled colostrum, there were transient increases in several serum enzymes. Within a few hours, the mean serum gamma-glutamyl transferase (gammaGT), aspartate aminotransferase (AST), alkaline phosphatase (ALP), acid phosphatase (ACP), and lactate dehydrogenase (LDH) activities increased 62.5, 2.4, 2.0, 1.8 and 1.3 fold, respectively. In two other calves given initial feeds of enzyme-free pasteurized milk, there were similar increases in serum enzymes, except serum gammaGT. Correct interpretation of serum enzyme activities in newborn calves must take into account the normal increases which occur after feeding colostrum. Serum gammaGT was the only enzyme to increase markedly as a result of its absorption from colostrum. The other serum enzymes are presumably released from the tissues of the calf. The increased activities of serum CK observed in some newborn calves probably resulted from trauma during birth or increased muscular activity after birth.     

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.