R. M. Hoffman

Effect of a single dose of dexamethasone on glucose homeostasis in healthy horses by using the combined intravenous glucose and insulin test.

Sustained dexamethasone administration to horses results in insulin resistance, which may predispose them to laminitis. A single dose of dexamethasone is commonly used as a diagnostic aid, yet the effect of a single dose of dexamethasone on glucose homeostasis in horses is not well defined. The objective of this study was to characterize the change in glucose dynamics over time in response to a single dose of dexamethasone. A combined glucose-insulin tolerance test (CGIT) was performed on 6 adult geldings before and at 2, 24, and 72 h postdexamethasone (40 microg/kg of BW, i.v.); a minimum of 1 wk of rest was allowed between treatments. Before any treatment, the CGIT resulted in a hyperglycemic phase followed by a hypoglycemic phase. Dexamethasone affected glucose dynamics in 3 ways: 1) at 2 h, dexamethasone shortened the ascending branch of the negative phase (P < 0.001) of the test, indicating moderate insulin resistance; 2) at 24 h, dexamethasone impaired glucose clearance by extending the positive phase and eliminating the negative phase while insulin was elevated before the CGIT, indicating a decreased response to insulin; and 3) at 72 h, dexamethasone caused a deeper nadir value (P < 0.001) compared with predexamethasone, indicating an increased response to insulin. It was concluded that dexamethasone decreased the response to insulin as early as 2 h and maximally at 24 h. At 72 h, dexamethasone caused an increased response to insulin, which was unexpected.

Weight prediction from linear measures of growing Thoroughbreds

REASON FOR PERFORMING STUDY Monitoring weight of foals is a useful management practice to aid in maximising athletic potential while minimising risks associated with deviations from normal growth. OBJECTIVE To develop predictive equations for weight, based on linear measurements of growing Thoroughbreds (TBs). METHODS Morphometric equations predicting weight from measurements of the trunk and legs were developed from data of 153 foals. The accuracy, precision and bias of the best fitting equation were compared to published equations using a naive data set of 22 foals. RESULTS Accuracy and precision were maximised with a broken line relating calculated volumes (V(t + l)) to measured weights. Use of the broken line is a 2 step process. V(t + l) is calculated from linear measures (m) of girth (G), carpus circumference (C), and length of body (B) and left forelimb (F). V(t + I) = ([G2 x B] + 4[C2 x F]) 4pi. If V(t + l) < 0.27 m3, weight is estimated: Weight (kg) = V(t + l) x 1093. If V(t + l) > or = 0.27 m3: Weight (kg) = V(t + l) x 984 + 24. The broken line was more accurate and precise than 3 published equations predicting the weight of young TBs. CONCLUSIONS Estimation of weight using morphometric equations requires attention to temporal changes in body shape and density; hence, a broken line is needed. Including calculated leg volume in the broken line model is another contributing factor to improvement in predictive capability. POTENTIAL RELEVANCE The broken line maximises its value to equine professionals through its accuracy, precision and convenience.

The Application of the Self-Adjusting Palmar Angle Shoe for the Promotion of Sole Growth in Horse Feet

Abstract The objective of this case study was to determine if applying a self-adjusting palmar angle shoe (SAPAS) influenced sole thickness in horses as compared to using flat shoes or leaving horses unshod. Eighteen horses were allocated into 3 groups of 6 horses each. The front feet of the horses in 2 groups were shod with either a SAPAS or flat shoe in a 2 x 2 factorial crossover design with 5-wk periods. The third group remained unshod for the study. At the beginning and end of each period, the horses’ front feet were radiographed to measure the sole thickness, as determined to be the distance between the sole and the distal tip of the third phalanx, and its change over time. The sole thickness of the horses shod with either shoe increased more than the sole thickness of the unshod horses (P = 0.003). Sole thickness increased when a SAPAS was applied after the flat shoe (P = 0.003), and sole thickness decreased when a flat shoe was applied after a SAPAS (P = 0.003).