Decreased erythrocyte potassium concentration associated with exercise-related myopathy in horses

To investigate the possibility that a disorder of potassium balance may have a role in the development of equine rhabdomyolysis, the potassium concentration within erythrocytes (RBC [K+]) and plasma (P [K+]) was measured in 3 groups of horses: group 1, eight 2-year-old fillies that had postexercise muscle soreness within 48 hours of sample collection; group 2, ten 2-year-old fillies subjected to identical management and training conditions (as fillies of group 1) and that did not have signs of myopathy; and group 3, 32 yearlings of both sexes on the farm of origin of groups 1 and 2 that were pastured and not in training. Creatine kinase activity in serum from horses of groups 1 and 2 was also measured. The mean P [K+] was not significantly different between groups, whereas the mean RBC [K+] was significantly (P less than 0.01) lower in group-1 fillies vs group-2 fillies and group-3 horses. Group-1 fillies also had markedly high serum creatine kinase activity. Results of the study revealed significantly lower RBC [K+] in horses that had had signs of myopathy within the preceding 48 hours. This does not prove a causal relationship between RBC potassium depletion and myopathy, but does suggest that decreased RBC [K+] may be observed in horses with exercise-related myopathy.     

A survey of equine parasite control practices in Tennessee

A weighted, random sample of 130 horse owners in Tennessee was selected from subscribers to an equine newsletter published by the Agricultural Extension Service. Data about the participants' farms, horses, parasite control practices, and sources of information regarding equine parasite control were obtained through a telephone survey. The response rate was 98%. The typical respondent kept 4 horses on 2 pastures totaling 15 acres, and did not rotate pastures as a parasite control measure. The majority (83%) of horse owners indicated that they administered anthelmintics according to a regular schedule; 9% delayed deworming until the onset of weight loss. Proportions of owners deworming the various classes of horses at least 1, 2, 3, or 4 times annually were as follows: foals (0 to 6 months) 100, 60, 15, and 0%, respectively; weanlings (6 to 12 months) 100, 91, 32, and 0%, respectively; yearlings (1 to 2 years) 100, 100, 86, and 51%, respectively; and adults (greater than 2 years) 100, 94, 56, and 24%, respectively. Median treatments of yearlings and adults were evenly spaced at 6-, 4-, or 3-month intervals when the owners dewormed 2, 3, or 4 times annually, respectively. Mean intervals between treatments of foals and weanlings were less regular. Of the horse owners who dewormed 2 or more times annually, most (53 to 80%) used the same product exclusively for all treatments. In all age classes of horses, ivermectin paste (46 to 63%) was the most common product used, followed by tube deworming (23 to 38%) and use of benzimidazoles (4 to 16%).(ABSTRACT TRUNCATED AT 250 WORDS)     

Comparative long-term efficacy of ivermectin and moxidectin over winter in Canadian horses treated at removal from pastures for winter housing

The impact of a late fall treatment on the spring rise of fecal egg counts was evaluated in a controlled study with Canadian horses treated with 2 different dewormers immediately after removal from pasture for winter housing. The horses were stabled until the end of the trial period. Seventeen weanlings, 20 yearlings, and 15 2-year-old horses located in Ontario, which were presumed to be naturally infected with cyathostomins after pasture grazing, were randomly allocated to either a group treated with 0.4 mg/kg of moxidectin and 2.5 mg/kg of praziquantel or a group treated with 0.2 mg/kg of ivermectin and 1.5 mg/kg of praziquantel. Three weeks after treatment, all strongyle fecal egg counts were reduced to zero for both treatment groups. However, at 5 months post-treatment, mean geometric fecal egg counts were statistically higher for the yearlings and 2-year-old horses treated with ivermectin than for the yearlings and 2-year-old horses treated with moxidectin (P < 0.0001).     

Glutathione peroxidase activity in whole blood and plasma of horses of different ages, sexes and different use]

GSH-Px activity in blood and plasma of 269 horses was determined and interrelated to age, sex, and type of use or breed. Furthermore values in blood were related to hematocrit and hemoglobin contents. Trotters and riding horses had higher GSH-Px activities in plasma as well as in blood (0.83 +/- 0.22 and 0.79 +/- 0.23 U/ml plasma or 27.2 +/- 4.3 and 24.0 +/- 7.0 U/ml blood) than Thoroughbreds in training and yearlings (0.61 +/- 0.,14 and 0.56 +/- 0.16 U/ml plasma or 20.6 2 +/- 6.9 and 24.6 +/- 4.3 U/ml blood). 3 to 6 years old Thoroughbreds had higher GSH-Px-activities than 1 to 2 years old ones. Colts and fillies did not have differing values.     

Serum IGFBP4 concentration decreased in dairy heifers towards day 18 of pregnancy

This study was conducted to determine if the main components of the somatotropic axis change during the early phase of pregnancy in the maternal blood system and whether differences exist on day 18 after pregnancy recognition by the maternal organism. Blood samples of pregnant heifers (Holstein Friesian; n = 10 after embryo transfer) were obtained on the day of ovulation (day 0), as well as on days 7, 14, 16 and 18 and during pregnant, non-pregnant and negative control cycles. The oncentrations of progesterone (P₄), oestrogen, growth hormone (GH), insulin-like growth factor-1 and -2 (IGF1, -2) and IGF-binding protein-2, -3 and -4 (IGFBP2, -3, -4) were measured. The mRNA expressions of growth hormone receptor 1A, IGF1, IGF2, IGFBP2, IGFBP3 and IGFBP4 were detected using RT-qPCR in liver biopsy specimens (day 18). In all groups, total serum IGF1 decreased from day 0 to 16. Notably, IGFBP4 maternal blood concentrations were lower during pregnancy than during non-pregnant cycles and synchronized control cycles. It can be speculated that the lower IGFBP4 in maternal blood may result in an increase of free IGF1 for local action. Further studies regarding IGFBP4 concentration and healthy early pregnancy are warranted.     

Early management of race-bred weanlings and yearlings on farms

A total of 58 Thoroughbred and Quarter Horse farms that managed 1,987 weanlings and yearlings responded to a survey designed to better characterize early management of racing prospects. Average age at weaning was 5.5 months and over half of all farms kept almost three-fourths of all weanlings to be placed in pre-race training. Variation in feeding practices was evident and while well over half of all farms provided balanced nutrient supply to young horses, 20% to 40% likely fed unbalanced diets. An obvious preference existed for semi-confinement in young horses with plenty of free exercise. The majority of farms reported that young prospects were fed and managed for a moderate rate of growth. Forced exercise occurred to a much larger extent with yearlings than weanlings and 40% of farms described the footing as soft, but not deep. Response to the prevalence of developmental orthopedic diseases appeared somewhat guarded, and average injury rate was low on farms that attributed much of injury to horses playing too hard. Technological advancements such as photoperiod manipulation in broodmares were widely used, while valuable tools such as body condition scoring were utilized to a lesser extent.     

Racing performance after arthroscopic removal of apical sesamoid fracture fragments in Thoroughbred horses age < 2 years: 151 cases (1989--2002)

REASONS FOR PERFORMING STUDY: Studies on arthroscopic removal of apical proximal sesamoid fracture fragments in Thoroughbred (TB) horses age > or = 2 years have reported a high success rate. However, there are no reports documenting the racing prognosis of TB horses that undergo such surgery as weanlings or yearlings. OBJECTIVES: To describe the incidence of apical proximal sesamoid fractures in immature TB horses, age < 2 years and determine probability and quality of racing performance after arthroscopic removal of such fractures in 151 TB weanlings and yearlings. METHODS: The medical records of TB horses age < 2 years that underwent arthroscopic surgery for removal of apical proximal sesamoid fracture fragments were reviewed. Follow-up information was obtained from race records. Student's t tests were used to compare performance variables of operated racehorses to that of their maternal siblings. RESULTS: Ninety-two percent (139/151) of fractures occurred in the hindlimbs and 8% (11/151) in the forelimbs (fracture of both fore- and hindlimb, n = 1). Horses with forelimb fractures had a greatly reduced probability of racing (55%) compared to those with hindlimb fractures (86%). Overall, 84% of the horses raced post operatively and had performance records similar to that of their maternal siblings, 78% (787/1006) of which raced. CONCLUSIONS: Arthroscopic removal of apical proximal sesamoid fracture fragments in TB weanlings and yearlings carries an excellent prognosis for racing in horses with hindlimb fractures and a reduced prognosis in those with forelimb fractures. Medial fractures of the forelimb carry the worst prognosis. POTENTIAL RELEVANCE: The determination of prognosis increases knowledge on apical sesamoid bone fractures and potential for arthroscopic restoration of the ability to race; and enables the value of yearlings for subsequent sale to be established.     

Does examination of fecal samples 24 hours after cestocide treatment increase the sensitivity of Anoplocephala spp. detection in naturally infected horses?

Fecal samples were examined immediately before and 24 to 48 h after cestocide treatment for a comparative detection of tapeworm-positive horses. In early winter, 17 weanlings, 20 yearlings, 15 2-year-old horses, 24 breeding mares, and 2 stallions were treated with praziquantel in combination with a macrocyclic lactone. The horses were presumed to be naturally infected with tapeworms after pasture grazing. Fecal samples were collected before treatment (Day 0), at 24 or 48 h after treatment (Day 1-2), and 16 to 21 d after treatment (Day 16-21). A Wisconsin test was done on all fecal samples. Odds of detection of infection for all age groups increased by a factor of 2.04 [95% confidence interval (CI): 1.30 to 3.20] from Day 0 to Day 1-2 (P = 0.002).     

Plasma plasminogen concentrations in clinically normal horses: the effect of age, sex and pregnancy

Plasma concentrations of plasminogen were determined in 28 clinically normal horses, including 13 adult geldings, five non-pregnant mares, five pregnant mares and five yearlings (two fillies, three geldings). Plasminogen was quantitated by a chromogenic assay based on activation of plasmin by excess urokinase. The overall mean plasma plasminogen for these horses was 2.94 +/- 0.54 CTA units (casein units, as defined by the Committee on Thrombolytic Agents) per ml. There were no significant differences in mean plasma plasminogen values among adult geldings, non-pregnant mares, pregnant mares or yearling horses (P greater than 0.05).     

Prevalence and distribution of radiographically evident lesions on repository films in the hock and stifle joints of yearling Thoroughbred horses in New Zealand

AIM: To characterise the prevalence and distribution of radiographic changes in the hocks and stifles of Thoroughbred yearling colts and fillies in New Zealand and compare them with other populations of young horses. METHODS: Repository radiographs taken in New Zealand for the 2003-2006 Thoroughbred national yearling sales were evaluated by two individual readers. The distribution of radiographic changes was classified as left side only, right side only, or bilateral. Lesions were categorised by type, location, and sex of the yearling. Complete sets of hock and stifle radiographs of 1,505 yearlings were evaluated. RESULTS: Osteophytes or enthesophytes were seen radiographically in the distal tarsal joints of 460/1,505 (31%) horses. Osteochondrosis was seen in the tibiotarsal joint of 66/1,505 (4%) horses, and in the femoropatellar joint of 40/1,505 (3%) horses. Radiographic lucency in the distal or axial aspect of the medial femoral condyle was seen in 247/1,505 (16%) horses, and lucencies consistent with subchondral cyst-like lesions were seen in 26/1,505 (2%) horses. No significant difference was seen in the proportion of colts and fillies with radiographic changes in the hock or stifle. The prevalence of osteochondrosis and subchondral cyst-like lesions in the stifles of the yearlings examined were similar to those reported in Thoroughbred yearling sale horses in the United States of America (USA). The prevalence of changes in the distal tarsal joints was similar to those reported in Standardbred and Thoroughbred yearlings from Scandinavia and the USA. CONCLUSIONS: There was no significant difference in the prevalence of osteochondrosis in the hock and stifle, lucencies in the distal medial femoral condyle, or radiographic changes in the distal tarsal joints between colts and fillies. CLINICAL RELEVANCE: Establishment of the normal prevalence and distribution of radiographic changes in the hocks and stifles of Thoroughbred yearlings in New Zealand will allow comparison with populations of young horses in other countries. Knowledge of the normal prevalence will assist veterinarians to identify abnormally high or low prevalences on individual farms, to further investigate the pathogenesis of the lesions.     

Age- and gender-related variations in hematology, clinical biochemistry, and hormones in Spanish fillies and colts

In order to assess which laboratorial parameters need specific age- and/or gender-related reference values, hematological and biochemical profiles (including hormones) were performed in 205 Spanish foals of 5 groups: A (1-2 months; 20 fillies, 10 colts), B (2-3 months; 24 fillies, 18 colts), C (3-6 months; 25 fillies, 16 colts), D (6-9 months; 20 fillies, 23 colts) and E (9-12 months; 25 fillies, 15 colts). Additionally, 120 adult horses were sampled in order to establish baseline data for this breed in our laboratory. Group E had lower red blood cell number and mean cell volume than B, C and D, and neutrophil count was lower in A. Albumin was lower in A than in D, lactate was higher in B, C and D, CK, AST and K were higher in C. In D and E, cortisol was lower and adrenaline was higher. Urea progressively increases, whereas ALP decreases with age. Packed cell volume was higher in fillies of group A, creatinine was higher in colts of group E and fillies of groups B, C, and D had higher aldosterone than colts. In comparison to Spanish adult horses, mean cell volume, albumin, urea, CK, AST, LDH, and ALP requires specific ranges for foals.     

Influence of age and sex on serum osteocalcin concentrations in horses at weaning and during physical conditioning

Three experiments were conducted to evaluate serum osteocalcin concentrations in normal weanling and yearling Quarter Horses. In Experiment 1, jugular blood samples were taken at 3 hr intervals for 24 hr to evaluate diurnal changes in serum osteocalcin concentration of foals (n=3) and yearlings (n=5). In Experiment 2, twelve Quarter Horse foals were weaned at 4 months of age to determine the influence of sex, weaning and method of weaning of serum osteocalcin concentration. The third experiment utilized fifteen yearling Quarter Horses (7 geldings, 8 fillies) in a two-phase trial to evaluate normal peripheral osteocalcin concentration in sedentary and exercising horses. In Experiment 1, there was no detectable variation (P>.05) in serum osteocalcin concentration during the 24 hr sample period in either age group. In Experiment 2, colts had greater (P<.05) osteocalcin concentrations than fillies at weaning. Method of weaning did not alter mean serum osteocalcin concentration (P>.1). Serum osteocalcin concentrations declined (P<.05) in all horses following weaning but returned to preweaning levels within one week. In Experiment 3, sedentary horses had similar (P>.1) osteocalcin concentrations on d 0, 45 and 90. Serum osteocalcin concentrations of sedentary horses were not affected by sex (P>.1). During exercise, fillies had greater (P<.05) osteocalcin concentrations than geldings. Serum osteocalcin concentrations of all horses declined linearly (P<.0001) during the 90 d exercise period. Osteocalcin may be useful as a tool to assess bone metabolism during growth and physical conditioning in horses. However, variability in serum osteocalcin concentrations due to age, sex and level of activity suggest that these factors must also be considered.     

Concepts in Protein Digestion and Amino Acid Requirements of Young Horses

There are numerous industry situations in which horses are N sufficient, but amino acid deficient. Although simple formulation of diets and consideration of nutrient-to-calorie ratios against requirements may appear to produce feeding programs that are suitable for horses, other factors, such as diet, rate of intake, site of nutrient absorption, horse age, and growth rate, must be considered when determining whether or not requirements are actually met. As an example, some yearlings kept in confinement consume concentrate and hay that fail to satisfy amino acid requirements. Other yearlings grazing very high quality pastures with no supplemental feed are able to meet their lysine requirement and achieve moderate growth. Field studies have documented that trends to manage weanlings and yearlings in a similar nutritional fashion are contributing to problems associated with rapid growth. Weanlings cannot process roughage at levels used effectively in yearlings, yet farms typically provide concentrate-to-hay ratios for weanlings inconsistent with NRC requirements and recommendations. Research on protein intake, site of absorption, concentrate type and intake, and grazing behavior must all be combined to be precise regarding adequate supply of protein quality to horses.     

Emotional Response to Novelty and to Expectation of Novelty in Young Race Horses

The aim of this study was to estimate the emotional response to novelty and to expectation of novelty in young race horses. The novelty in this study was the first training on an automated horse walker at a new training center. To estimate the level of emotionality in horses, the telemetric measurement of heart rate (HR) was used. A hypothesis was developed that expectation of novelty can be as exciting for horses as a novelty test. In this study, 40 horses were studied just before and then during their first walk on an automated horse walker. They were divided into four groups, with 10 horses in each group. These groups were as follows: (1) 1.5-year-old Thoroughbred colts, (2) 1.5-year-old Thoroughbred fillies, (3) 2.5-year-old Purebred Arabian colts, and (4) 2.5-year-old Purebred Arabian fillies. HR was measured at rest before exercise, during handling and moving the horse from the stable, while walking on the automated horse walker for about 20 minutes, while moving the horse from the walker to the stable, and at rest after exercise. HR response to the anticipation of novelty was higher in colts than in fillies, particularly in the group of Thoroughbreds.     

Growth of yearling fillies fed alfalfa or soybean meal

Sixteen Quarter Horse yearling fillies were used in a 112-day randomized block experiment to determine the comparative efficacy of alfalfa hay protein to support growth in young horses. The yearlings were divided into two groups of eight and paired according to weight and age, with one yearling from each pair randomly allotted to each diet. Group 1 was fed a diet of coastal Bermuda grass hay and concentrate. The corn-based concentrate was supplemented with soybean meal such that the total diet for group 1 contained approximately 13% CP. Group 2 was fed a diet that also contained approximately 13% CP and consisted of alfalfa hay and a similar concentrate without soybean meal. Yearlings were fed the diets in a 60:40 grain-to-hay ratio, and intakes between members of each pair were equalized. The calculated digestible energy density in both final diets was approximately 2.85 mcal/kg, and the protein:calorie ratio for both diets was approximately 45 gm/Mcal. Body weight, body length, heart girth, wither and hip heights, as well as forearm, gaskin and cannon bone circumferences were measured every 28 days. Rump fat thickness was measured ultrasonically every 28 days. Physical measures of growth were similar for horses eating each diet (P>0.05). Also, blood urea nitrogen was similar for horses eating each diet (P>0.05) and was not reflective of differences in nitrogen metabolism. The fillies fed the SBM-supplemented diet retained more nitrogen more efficiently than did fillies fed the alfalfa diet (P<0.05), and the SBM-fed fillies had higher concentrations of osteocalcin on days 14, 28, 42, and 112. It can be concluded that SBM and alfalfa proteins were equally effective in providing growth to young horses; however, the biological value of absorbed nitrogen appeared to be higher in the fillies fed the SBM-supplemented diet. also, differences in serum osteocalcin concentrations indicate that the SBM-fed fillies were experiencing a greater amount of osteoblastic activity than the alfalfa fed fillies.     

Serum Leptin Concentrations in Lipizzan Fillies

To determine seasonal changes in circulating leptin concentrations, as well as leptin fluctuations in various patterns of seasonal ovarian activity, blood samples were taken in 107 Lipizzan fillies aged 1–4 years over the whole year from January to December. Serum concentrations were measured in samples obtained once a month (leptin) or twice a month (progesterone), and evaluated with respect to the age of animals (yearlings, 2-, 3- and 4-year olds) and the pattern of ovarian activity (anoestrous, seasonal cycle, prolonged cyclicity, continuous cyclicity). The mean and monthly leptin concentrations in 3- and 4-year olds were significantly higher than in yearlings and 2-year olds (p < 0.001). Circulating leptin levels in 3- and 4-year olds increased significantly in summer, to peak in August and then decline significantly (p < 0.001) in autumn. The fluctuations in younger fillies were less evident. The highest mean serum leptin concentrations were observed in fillies exhibiting continuous cyclicity and the lowest in those, exhibiting seasonal cyclicity (p < 0.001). In anoestrous fillies, leptin concentrations were lower than in fillies with prolonged or continuous cyclicity but higher than in fillies with seasonal cyclic activity (p > 0.05).     

Cloning and expression of equine insulin-like growth factor binding proteins in normal equine tendon

OBJECTIVES: To define a portion of the nucleotide sequences of each of the 6 insulin-like growth factor (IGF) binding proteins (IGFBPs) in horses and describe patterns of messenger RNA (mRNA) and protein expression for IGFBPs in normal equine tendons. ANIMALS: 7 horses. PROCEDURE: Total RNA was extracted from the tensile region of normal superficial digital flexor tendons and reverse transcribed into complimentary DNA (cDNA). The cDNA was amplified via PCR, and products representing portions of each IGFBP were cloned and sequenced. Nucleotide sequences were used to deduce the amino acid sequences, and both nucleotide and predicted amino acid sequences were compared with those published for bovine, human, mouse, and ovine IGFBPs. Gene expression was quantitated by real-time PCR assay, and protein expression was evaluated by western ligand blot (WLB). RESULTS: Clones ranged in size from 262 to 522 bp and had high degrees of sequence homology with other mammalian species. Sequence homology was highest between bovine and equine IGFBPs (86% to 95%) and amongst the IGFBP-5 sequences from the various species (92% to 95%). Message for IGFBP-2 to -6, but not IGFBP-1, was expressed in normal tendon. Protein expression for IGFBP-2, -3, and -4 was detected byWLB in normal tendon and markedly increased in damaged tendons. CONCLUSIONS AND CLINICAL RELEVANCE: Results provide basic information and tools needed for further characterization of the role of the IGF system in tendon healing and may lead to the ability to potentiate the response of healing tendon to exogenous IGF-I via concurrent manipulation of IGFBPs.     

Myostatin down‐regulates the IGF‐2 expression via ALK‐Smad signaling during myogenesis in cattle

Myostatin (MSTN) is a negative regulator during muscle differentiation, whereas insulin‐like growth factors (IGFs) are essential for muscle development. MSTN and IGFs act oppositely during myogenesis, but there is little information on the mutual relationship of MSTN and IGFs. The present study was conducted to examine whether MSTN affects IGF expression during early myogenesis in cattle. IGF‐1 mRNA was similarly expressed in M. longissimus thoracis of double‐muscled (DM) and normal (NM) Japanese shorthorn cattle. IGF‐2 mRNA expression was consistently higher in the normal and regenerating muscle of DM cattle than those of NM cattle. When myoblasts were isolated from regenerating M. longissimus thoracis, IGF‐2 mRNA expression showed a significant increase in differentiating DM derived myoblasts (DM‐myoblasts) as compared with differentiating NM derived myoblasts (NM‐myoblasts). An addition of recombinant mouse myostatin (rMSTN) to myoblast cultures attenuated IGF‐2 mRNA expression and decreased myotube formation, but did not effect IGF‐1 mRNA expression. An activin‐like kinase (ALK) inhibitor, SB431542, mediates MSTN action, suppressed the translocation of Smad2/3 into the nucleus in DM‐myoblasts, and restored the attenuated IGF‐2 mRNA expression and the decreased myotube formation induced by rMSTN in myoblast cultures. The findings indicate that MSTN may negatively regulate myoblast differentiation by suppressing IGF‐2 expression via ALK‐Smad signaling.     

Onset of puberty and duration of seasonal cyclicity in Lipizzan fillies

REASONS FOR PERFORMING STUDY: The onset of puberty and duration of seasonal cyclicity in Lipizzan fillies and young mares have been determined mostly by empirical data, but very little is known about the hormonal changes at puberty and during the seasonal cyclicity in this breed. OBJECTIVES: To determine the onset of puberty and the course of the cyclicity in young Lipizzan mares from age 1-4 years. METHODS: Blood samples were collected twice a month for 2 years from 46 Lipizzan fillies age 1-4 years. Progesterone concentrations, indicating ovarian activity, were measured using an EIA kit. Values above 6.4 nmol/l were taken to indicate luteal phase and those below 3.4 nmol/l, oestrus. RESULTS: Fifty percent of Lipizzan fillies entered puberty during the first spring after their birth at mean +/- s.e. age 15.25 +/- 0.31 months and 50% during the second spring, at age 25.2 +/- 0.57 months. For several fillies of all ages, manifesting anoestrus during the winter months, the oestrus started in March and reached a peak in June to September. The duration of the oestrus activity was age-dependent, at 2.37 +/- 0.62 months in yearlings and 8.56 +/- 0.46 months in fillies age 4 years. In December, >50% of fillies age 2-4 years still exhibited oestrus activity and some entered anoestrus in January the following year. A small proportion of fillies age 3-4 years remained cyclic during the whole year, indicating that factors other than photoperiod can be involved in regulating seasonal cyclicity. CONCLUSIONS AND POTENTIAL RELEVANCE: Our results demonstrate the influence of seasonal factors on the onset of puberty and on the course of oestrus activity in the majority of Lipizzan fillies. However, certain exceptions were also demonstrated but reasons for the prolonged periods of oestrus activity in some Lipizzan fillies were not identified, and the role of the hormone leptin should be studied in future investigations.