No abstract

This study was conducted to determine normal rates of growth of different skeletal segments in the thoroughbred horse. Growth of body weight and eight skeletal segments (wither height, hip height, body length, knee to pastern length, hock to pastern length, shoulder to pastern length, width of chest, depth of girth) were monitored in 106 horses (60 colts, 46 fillies) during the period from 14 to 588 d of age. Body weight gains were slightly higher (30 to 40 kg) than previously reported values. Growth in wither height and hip height were similar to previous reports. During the period measured in this study hip height was consistently 2 or 3 cm larger than wither height. Growth patterns for wither height, body length, and shoulder to pastern lengths were similar to one another. Growth of the knee to pastern and hock to pastern segments reached a plateau at approximately 140 d of age, which coincided with the cessation of longitudinal bone growth. These data define skeletal growth patterns in the thoroughbred horse and are useful in determining the relationship between growth and the occurrence of orthopedic diseases in horses.

Summary The highest no effect doses (HNEDs) for the local anaesthetic (LA) effects of procaine, cocaine, bupivacaine and benzocaine were determined using the heat lamp/hoof withdrawal model of Kamerling et al. (1985b) and the abaxial sesamoid block model of local anaesthesia. The heat lamp rapidly (4 or 5 s) increased the temperature of the superficial skin layers of the pastern to about 90°C, at which point the animal sharply withdrew its hoof. Effective LA blockade precluded this response and superficial skin temperatures exceeded 120°C. Thermal stimulus experiments were routinely terminated after 10 s of exposure to prevent undue tissue damage. Following abaxial sesamoid block with bupivacaine, the HNED for that drug was about 0.25 mg/site. Increasing the dose to 2 mg/site apparently produced complete and prolonged LA blockade. Analogous work showed that the HNED for procaine was about 2.5 mg/site. Similarly, the dose response curve for procaine was parallel with that of bupivacaine but was shifted 10‐fold to the right The duration of the LA response following procaine injection was less than for bupivacaine with the statistically significant response following 40 mg/site injection lasting less than 45 min. Cocaine was less potent than procaine, showing a shallower dose response curve. The HNED for cocaine was less than 5 mg/site, although at this dose the duration of action was extremely short (<7.5 min). Benzocaine had no significant LA action when a dose of 800 mg was applied topically as a 5% preparation. These results show that the HNEDs for bupivacaine and procaine are remarkably low, that cocaine is somewhat less potent as a LA than might be expected, and that 5% topical benzocaine has no significant pharmacology. The small doses of bupivacaine and procaine producing effective local anaesthesia suggests that developing plasma thresholds for these agents is likely to be very challenging.

Effects of high dietary levels of energy, protein and Ca and deficient levels of Ca on skeletal growth and development in the equine were studied in two experiments. The weanlings were fed grain-based diets. In Exp. 1, Group 1 (Ctl) received all nutrients at NRC recommended levels for growth; Group 2 (HE) received 150% of their digestible energy (DE) requirement; Group 3 (LC) received 150% of DE and 35% of Ca requirements. In Exp. 2, Group 1 (Ctl) again received all nutrients at NRC recommended levels for growth; Group 2 (HEP) received 150% of DE and 275% of CP requirements; Group 3 (HEPC) received 150% of DE, 275% of CP and 500% of Ca requirements. In addition, all groups had access to pasture. The HE treatment resulted in greater (P less than .10) increases in BW and total cortical width. However, LC weanlings had lower (P less than .10) gains in third metacarpal length and radiographic bone density. Cumulative increases in BW and wither height were greater (P less than .10) for the HEP and HEPC weanlings than for the Ctl weanlings. Increases in third metatarsal length also were greater (P less than .10) for HEP weanlings than for Ctl weanlings. Higher planes of nutrition increased body weight gains and growth rate of several long bones. However, skeletal development (e.g., cortical area) may be compromised by a high rate of growth.

No abstract

Summary In the first study, 5 mature, unconditioned, Thoroughbred geldings performed an initial submaximal exercise test (UC) prior to any conditioning and a final test (C) following 8 weeks conditioning. Serum creatine kinase (CK) and aspartate aminotransferase (AST) activity were measured before and for 72 h after exercise. Plasma lactate concentration [La−] was used as an indicator of exercise conditioning. Serum CK and AST activity remained increased above pre‐exercise levels from 0–24 h and 0–8 h post exercise, respectively. There was a time by conditioning interaction for AST, CK and plasma [La−] resulting in an attenuated response of each variable following exercise test C as compared to following exercise test UC. These results indicate that submaximal exercise can elevate serum AST and CK and that conditioning can attenuate these changes. A second study using 8 mature Thoroughbred horses was conducted to evaluate the effect of 2 different types of exercise, short term high intensity (STHI) and repeated submaximal exercise (RS) on serum AST and CK activities. Serum AST and CK activities during the post exercise period were higher in response to the RS test compared to the STHI test.

Because exercise fatigue has been associated with the accumulation of lactic acid, factors that influence lactate metabolism during exercise can potentially enhance performance. The objective of this study was to examine the effects of supplemental betaine on eight mature Thoroughbred horses before and after 8 wk of conditioning. The effects of betaine were tested in two cross-over design experiments, allowing each horse to receive both the control and betaine treatments at each fitness level. Ingestion of 80 mg of betaine/kg of BW for 14 d before exercise testing did not alter plasma lactate, glucose, free fatty acids (FFA), or triglyceride concentrations during exercise in the untrained or trained horses. A time x treatment interaction (P < .05) was observed for plasma lactate in untrained horses during recovery from exercise, and plasma lactate concentrations were lower (P < .05) at 60 min after exercise when untrained horses received betaine. Plasma FFA concentrations were lower (P < .05) before exercise and at 720 min after exercise when untrained horses received betaine. These data indicate that betaine may influence lactate metabolism following exercise in untrained horses; however, betaine does not seem beneficial for trained horses.

Summary The purpose of this study was to determine whether a difference in roughage intake could affect electrolyte and water balance in horses during endurance type exercise. In each of 2 experiments, 2 treatments (a high hay or limited hay diet) were assigned in a crossover design so that each horse performed 2 exercise tests, 1 on each treatment. In experiment 1, diet was controlled only the night before the exercise test. Water intake was lower (P<0.001) when horses received the limited hay diet. Exercise caused a decrease in plasma chloride and potassium concentration and an increase in plasma total protein concentration, but there were no diet differences (P>0.05). Weight loss was 2.8% of body weight for both treatments. In experiment 2, horses were adapted to the diets for 7 days prior to the exercise test. Again, water intake was lower when the horses received the limited hay diet (P<0.01). During exercise, both groups lost about 4% of bodyweight, but total protein concentration was lower (P<0.05) in the horses receiving the high hay diet. Plasma potassium concentration initially increased and then decreased during exercise (P<0.05), but the horses receiving the high hay diet maintained a higher potassium concentration during exercise (P<0.05). Sodium was not affected by diet or exercise (P>0.05). Plasma chloride concentration decreased during exercise (P<0.05). The increased water intake and lower plasma protein concentration associated with the hay diet may be beneficial for horses involved in endurance type exercise.