A technique for central venous pressure measurement in normal horses

Objective – To investigate a technique of central venous pressure (CVP) measurement using a newly developed catheter in healthy adult horses. Design – Prospective experimental study. Setting – University research facility. Animals – Twenty healthy adult horses. Interventions – An equine central venous catheter was inserted into the jugular vein to a length of approximately 80 cm from the mid‐cervical region in an attempt to catheterize the pulmonary artery. Pulmonary arterial catheterization was confirmed by echocardiography. Insertion distance and pressure were measured at this location with a disposable manometer. The catheter was then withdrawn until presence in the right atrium was confirmed by echocardiography. Insertion distance and pressure were also measured at this location. The catheter was then withdrawn in 5 cm increments until exiting the jugular insertion site with pressure measured at each location. All pressure measurements were taken with the manometer zero position at the point of the shoulder. Measurements and Main Results – Pulmonary artery catheterization was successful in 16 of 20 horses. Mean pulmonary arterial pressure was 23.8 cm H₂O (17.5 mm Hg) (95% confidence interval [CI] 20.9–26.7 cm H₂O [15.4–19.6 mm Hg]). Mean right atrial pressure was 8.3 cm H₂O (6.1 mm Hg) (95% CI 7.1–9.4 cm H₂O [5.2–6.9 mm Hg]). Right atrial pressure was compared with pressures recorded at sequential insertion distances and resulted in a recommendation for catheter insertion of at least 40 cm for CVP measurement in adult horses. Jugular venous pressure measurement was statistically different from CVP measurement. Conclusions – This catheter measurement technique is well tolerated in normal horses. Routine clinical use of this equine central venous catheter may improve our ability to monitor patients and improve patient care and outcomes of ill horses in hospital.     

A lag-screw technique for bridging of the medial aspect of the distal tibial physis in horses

A lag-screw technique for transphyseal bridging of the medial aspect of the distal tibial physis in foals with tarsal valgus deformities and results of the technique in 11 foals (6 with bilateral tarsal valgus deformities and 5 with unilateral tarsal valgus deformities) are described. Briefly, horses were anesthetized, and a single stab incision was made through the skin to the underlying bone over the most distal aspect of the medial malleolus. A 20-gauge needle was placed in the incision to guide screw placement, and a lag screw was inserted parallel to the medial cortex of the tibia under radiographic guidance. Screws were removed when the tarsal valgus deformity was clinically assessed to have improved by at least 80%. Clinically, all horses had evidence of a tarsal valgus deformity of > 7 degrees prior to surgery. Mean age at the time of lag-screw implanation was 220 days (range, 116 to 364 days). Mean time the implant was in place was 62 days (range, 39 to 89 days). The tarsal valgus deformity resolved in all 11 horses with excellent cosmetic results.     

Mineral balance in juvenile horses in race training

Twenty-four long yearlings were fed rations containing differing amounts of calcium, phosphorus, and magnesium to further elucidate the requirements for these minerals during exercise-induced skeletal modeling and remodeling in juvenile racehorses. The animals were assigned randomly within gender subgroups to 1 of 4 diets. Total collections of feces and urine were performed on days 0, 64, and 128 of the trial for determination of mineral absorption and retention. Horses were maintained in a typical race-training protocol to mimic the nutritional stresses placed on long yearlings during strenuous exercise. Calcium absorption and retention were lower (P < .05) at day 64 than at day 0 and day 128. Also, the efficiency of retaining absorbed calcium was lower at day 64 than at day 0 or day 128. Thus, lower calcium retention at day 64 was due to both reduced absorption and reduced systemic demand. At day 64, calcium absorption and retention were not maximized at calcium intake of 160 mg/kg per day. At day 128, calcium absorption was maximal at a daily intake of 124 mg/kg per day, and retention was maximal at a daily intake of 123 mg/kg per day. These are in excess of current National Research Council (NRC)[1] recommendations by 38% and 36%, respectively. There was no consistent, significant effect of days on trial on phosphorus absorption or retention, which may have been due to inadvertent limited phosphorus intake. The efficiency of phosphorus retention systemically was over 94% to 98%. Phosphorus absorption and retention were not maximized at the highest intake (66 mg/kg/d), which is 32% over current NRC [1] recommendations. Similarly, there was no day effect on the efficiency of magnesium absorption or retention. Urinary excretion of magnesium was highest; thus, systemic efficiency of magnesium retention was lower on days 64 and 128 than on day 0. At day 64, magnesium retention was maximized at a daily intake of 35.6 mg/kg per day, which is 66% over NRC [1] recommendations. However, at day 128, magnesium retention was not maximized even at its highest intake (44 mg/kg/d), which is over 2 times the current NRC [1] recommendations. These data indicate that early race training affects the dietary requirements for calcium, phosphorus, and magnesium.

Introduction

The need for a marketable product at an early age in both competition and in sales places significant pressure on horse owners to start training or conditioning early in a horse's life. Training at an early age may exacerbate physiologic stress on young horses and increase nutritional requirements. The process of bone modeling/remodeling is necessary for the juvenile skeleton to adapt to the stresses of training. The horse must form new bone and remodel existing bone to bear the load being applied. During the demineralization process of bone remodeling, there is an increase in mineral excretion from the degradation of the bone matrix. Nielsen et al[2] reported this demineralization of the third metacarpal in conjunction with the introduction of speed in juvenile horses on a race-training regimen. The lack of time routinely given to the stressed bone of a juvenile horse to model and/or remodel according to the stresses placed upon it can cause serious and career-ending injuries. [3] While injury reduction may be achieved from a delay in the onset of training until the horse is mature, this is not feasible economically. Alterations in existing training methods and increasing physiologic stimulus to the skeleton are approaches being researched to minimize skeletal injuries to young horses.Mineral density increase and size of the third metacarpal would result in larger cortical bone mass, decreased strain on the bone, and decreased susceptibility for injury. Previous work in this area demonstrated that increased calcium and phosphorus intake above NRC[1] recommendations for juvenile horses in training enhanced bone density, but no quantitative estimates of requirements were made. [4] The NRC [1] developed an approximation of the requirements for juvenile horses in training using mineral intakes based on extrapolations from research conducted with sedentary and mature horses. This study was conducted to verify previous findings and to further quantify the dietary requirement for calcium, phosphorus, and magnesium during the bone modeling/remodeling process in juvenile athletic horses. The specific objectives of this study were to determine calcium, phosphorus, and magnesium balances in young horses during race training.

Materials and methods

Management of animals

Twenty-four long-yearling Quarter Horses were grouped according to age and sex, then randomly assigned to the diet treatments as shown in Table 1. Two horses from each group were randomly assigned to 1 of 4 diets with the condition that each treatment group would contain the same number of fillies and geldings. While at the Texas A&M University Horse Center, the horses were vaccinated against eastern and western equine encephalomyelitis, influenza, and tetanus and dewormed. All horses began the trial with a background period of at least 1 week, during which the horses were group-housed at the Texas A&M University Horse Center, fed hay ad lib, and offered concentrate at approximately 1% of body weight twice daily. Regular hoof care and deworming were provided throughout the course of the study. The horses were then moved from the Texas A&M University Horse Center in groups of 8 to Steephollow Farm in Bryan, Texas, a race-training facility, where they were separated and housed individually in 7 × 7-m stalls. The horses were moved to Steephollow Farm in 3 groups of 8 at an average age of 226 days for the group. Rations were formulated based on 60% concentrate and 40% Bermuda grass hay, with varying concentrations of calcium, phosphorus, and magnesium. The concentrate diets were provided by Consolidated Nutrition of Omaha, Nebraska (Table 1). All concentrates were mixed, pelleted, and bagged by Consolidated Nutrition and shipped to the Texas A&M University Horse Center. The horses were fed concentrate and hay at 12-hour intervals (7:00 and 7:00 ) for the duration of the trial. They were given until the next feeding to consume all concentrate and hay, and any feed refused was weighed and recorded. Refusals were very infrequent. Feed intake was adjusted weekly as needed to allow for normal growth and to maintain a body condition score of 5 to 6,[5] while maintaining a constant ratio of 60% concentrate and 40% hay. The protocol for management and treatment of the animals was approved by the Texas A&M University Agricultural Animal Care and Use Committee. Five horses were not able to complete the study because of lameness, injury, or sickness, and data from those horses were not included in the results of the study.     

Effect of dietary cation-anion balance in mineral balance in anaerobically exercised and sedentary horses

Eight geldings and four mares were randomly assigned treatments within three 4x4 Latin square design experiments to study the effects of dietary cation-anion balance (DCAB) on mineral balance and dry matter digestibility in sedentary and anaerobically exercised horses. Four diets with an average DCAB (calculated as meq ((Na+K+) - Cl-)/kg of diet dry matter) of +24 (Low, L), +127 (Medium Low, ML), +227 (Medium High, MH) and +352 (High, H) were fed for a 21 day adjustment period followed by a 72 hour collection period. Diets consisted of a pelleted base concentrate of com, soybean meal and cottonseed hulls fed with either native prairie grass or bermuda grass hay in a 60:40 ratio. Diet L was formed by adding calcium chloride and ammonium chloride to the base concentrate, diet ML was formed by adding calcium chloride, and diet H was formed by adding potassium citrate and sodium bicarbonate. Diet MI-I received no supplementation and served as the control. Representative samples of feed, feces and urine were analyzed for mineral content and mineral balances were calculated by difference. Fecal output was greater (p <.05), and thus, dry matter digestibility was lower in exercised homes consuming diet L versus diet H. Sodium balance was greater (p <.05) in sedentary horses consuming diet MH as compared to those consuming diets ML and L Sodium balance was greater (p <.05) in exercised homes consuming diet H as compared to those consuming diets ML and L Potassium balance was greater (p <.05) in sedentary horses consuming diet H as compared to those horses consuming diet ML, however, potassium balance was not affected by DCAB in exercised horses. No significant differences were detected in chloride or magnesium balances in the sedentary horses, although chloride balance was greater (p <.05) and magnesium balance was lower (p <.05) in exercised homes consuming diet L as compared to all other diets. In sedentary homes, phosphorus balance was reflective of intake with differences (p <.05) observed between all treatments. However, in exercised homes, phosphorus balance was lower (p <.05) oniy for those consuming diet L. Calcium balance decreased significantly as DCAB decreased between all treatments in sedentary horses, while calcium balance in exercised homes was greater (p <.05) for homes consuming diet H as compared to those consum- ing diet L.Previous research from our laboratory has shown that both exercised and sedentary horses consuming diets with a low DCAB experience a nutritionally induced metabolic acidosis. The current data indicate that anaerobically exercised and sedentary horses consuming these diets excrete significantly more calcium in the urine resulting in decreased calcium balances. Prolonged consumption of diets with a low DCAB may lead to a significant demineralization of bone and a subsequent weakening of the skeleton.     

Unipodal stance influences radiographic evaluation of foot balance in horses

Lifting the contralateral forelimb (unipodal stance) is often used as a method of restraint in horses. This experimental one group pretest, posttest study was conducted to evaluate the effects of unipodal stance on quantitative radiographic parameters in equine forefeet. Seven nonlame horses were randomly selected. Lateromedial (LM) and dorsopalmar (DP) projections were acquired for both forefeet, squarely placed on blocks, using two X‐ray generators. Radiographs of each foot were acquired first in a bipodal stance, immediately followed by the same radiographic projections obtained in a unipodal stance. The following measurements were recorded for each stance: distal interphalangeal joint (DIPJ) space width on both projections; mediolateral joint balance as the difference between lateral and medial DIPJ space widths on DP projections; extensor process‐to‐middle phalangeal condyle distance; and deep digital flexor tendon angle on LM projections. A matched pairs design and Student's t‐test with a 95% confidence level were used to test for statistical significance. Compared to a bipodal stance, lateral DIPJ space width was significantly reduced on unipodal DP views, whereas mediolateral joint imbalance and to a lesser extent medial DIPJ space width were significantly increased. On unipodal LM views, there was a significant higher degree of DIPJ flexion. These findings suggest that stance should be carefully taken into consideration when measuring radiographic parameters in equine forefeet, especially if assessing foot balance and conformation, as unipodal stance significantly affects the mediolateral balance of the DIPJ on DP radiographs and significantly alters the phalangeal axis on LM radiographs.     

Mineral balance in horses fed two supplemental silicon sources

Numerous studies suggest that silicon (Si) supplementation is beneficial for mineral metabolism and bone health. Mineral balance studies have not been performed in horses to determine how these supplements affect absorption of other minerals. The purpose of these studies was to investigate the effects of two different Si supplements on mineral absorption and retention in horses. Eight geldings were randomly placed in one of two groups: control (CO) or supplemental Si, which was provided by one of two supplements. The first, sodium aluminium silicate (SA), contains a bioavailable form of Si and is high in aluminium (Al). The second supplement contains oligomeric orthosilicic acid (OSA). All horses received textured feed and ad libitum access to hay. Supplemented horses received either 200 g of SA or 28.6 ml of OSA per day. Following a 10-day adaptation period, the horses underwent a 3-day total collection. Blood samples were taken on days 0 and 13. The two balance studies were conducted 4 months apart to reduce carryover effects. Intakes of Al and Si were greater with SA supplementation (p < 0.05). Sodium aluminium silicate increased faecal and urinary Si excretion (p < 0.05). Calcium retention and apparent digestion were increased by SA (p < 0.05). It also maintained plasma Si compared with the CO which tended to have a decrease in plasma Si (p = 0.08). Supplemental OSA increased retention of Ca and B (p < 0.05) and apparent digestion of B (p < 0.01). Orthosilicic acid tended to increase Si retention (p = 0.054), apparent digestion (p < 0.065), and also increased plasma Si. Both supplements were able to alter Ca retention and B metabolism, however, only OSA was able to alter Si retention, digestibility and plasma concentration. Orthosilicic acid, an Si supplement without substantial Al, appears to be a viable option for Si supplementation as it increased Si retention and digestibility.     

Midline scrotal ablation technique for unilateral cryptorchid castration in horses

Thirty-nine unilateral cryptorchid horses were castrated, using a midline scrotal ablation technique. This approach was satisfactory to access both inguinal rings, to eliminate the need for 2 incisions, and to allow for completion of the surgery by primary closure. These horses recovered from surgery with few complications, returned to work promptly, and had excellent cosmetic results.     

Evaluation of a minimally invasive arthrodesis technique for the carpometacarpal joint in horses

Objective: To evaluate a minimally invasive technique for arthrodesis of the carpometacarpal (CMC) joint in horses. Study Design: Experimental study. Animals: Healthy horses (n=6). Methods: A 5.5 mm, 3‐drill tract arthrodesis technique was evaluated in 1 randomly selected CMC joint in each of 6 normal horses. Peak vertical ground reaction force (GRF) values were recorded before surgery and at 6, 8, and 12 months thereafter. Radiographic and clinical lameness scores were assigned at regular intervals until 12 months after surgery when the horses were euthanatized. Gross and histologic examinations were performed on the treated CMC joints. Results: After surgery, all horses were lame. Clinical resolution of lameness occurred in 2 by 12 months. Mean peak vertical GRF values significantly differed between treated and nontreated limbs at all recorded time points after surgery. Radiographic scores significantly differed from day 0 at all times after surgery, but did not change significantly after 4 months. Intraarticular bony ankylosis only occurred in 2 horses, based on gross, histologic, and microradiographic examination of sagittal sections of the operated CMC joints. Conclusion: The 5.5 mm, 3‐drill tract arthrodesis technique was considered successful in only 2 of 6 normal CMC joints treated. Greater articular damage may be necessary to achieve arthrodesis in normal horses. Better results may be achieved by technique modification or in horses affected by CMC osteoarthritis.     

Effects of dietary cation-anion balance on acid-base status in horses

Four mature, sedentary geldings were used in a 4x4 Latin square design experiment to study the effects of dietary cationanion balance (DCAB), defined as meq ((Na + K) - C1)/kg of dietary dry matter, on urine pH, blood pH and blood gasses. Four diets with actual DCAB levels of +21 (Low, L), +125 (Medium Low, ML), +231 (Medium High, MH) and +350 (High, H) were fed for a 21-day adjustment period and a 72 hour collection period. Total urine output was collected every 4 hours post feeding for 72 hours, and like times across days were combined for analyses. Arterial and venous blood samples were drawn, via indwelling catheters, hourly for 12 hours beginning at feeding. All samples were analyzed immediately after collection for pH, blood gasses and blood acid-base measures. Urine pH was lower (p<.05) at all measured intervals when geldings consumed diet L than when they consumed diets MI, MH and H. Least squares means for urine pH ranges from 5.40 to 5.86 on diet L, 6.79 to 7.30 on diet ML, 7.35 to 7.63 on diet MH and 7.52 to 8.14 on diet H. Blood pH, pCO₂ and HCO₃ values were also significantly lower in both arterial and venous samples when geldings consumed diet L than when fed diets MH and H. Results of this trial indicate that horses consuming highly anionic diets may experience a nutritionally-induced metabolic acidosis.     

Influence of furosemide treatment on fluid and electrolyte balance in horses

Alterations in electrolyte and acid-base balance were studied in 6 horses for 8 hours after furosemide administration (1 mg/kg of body weight, IM), and the results were compared with those for 5 healthy untreated horses (controls) kept under identical environmental conditions. In the treated group, decreases in plasma potassium, chloride, and calcium concentrations and increases in total plasma protein content persisted for the 8-hour observation period, whereas there was no change in plasma sodium concentration, osmolality, or packed cell volume. Plasma bicarbonate concentration and PCO2 remained high throughout the study, during which time venous blood pH was modestly increased only at the 6-hour sampling time. Furosemide treatment resulted in decreases in urine pH, specific gravity, osmolality, and potassium and calcium concentrations and increases in urine volume and total urine sodium, chloride, and calcium excretion. Body weight decreased 19.2 +/- 5.2 kg (mean +/- SD) in treated horses (4 +/- 1% of body weight), compared with a weight loss of 8 +/- 2.1 kg in untreated horses (1.5 +/- 0.4% of body weight) during the 8-hour experimental period. The increased fluid losses induced by the diuretic did not cause any obvious clinical signs in the horses. Pulse pressure, skin turgor, capillary refill time, and jugular distensibility remained unchanged throughout the experimental period.