Variations in the concentration of zinc in the blood of Icelandic horses.

The effect of factors including the horses' farm environment, their sex and age and whether they suffered from summer seasonal recurrent dermatitis (sweet itch) on the concentrations of zinc in the plasma, whole blood and blood cells of 104 Icelandic horses was investigated. Its concentration in plasma varied significantly between farms (P<0.01), but its concentration in blood and blood cells was not influenced by any of the variables. The concentration of zinc in the blood cells was 10.5 times greater than in plasma, but its concentration in plasma was not correlated with its concentration in whole blood or blood cells owing to the variability in the proportion of whole blood zinc present in plasma (relative plasma zinc), which ranged between 9 and 24 per cent. This variability was significantly influenced by a three-way interaction between farm, sex and sweet itch (P<0.05). Relative plasma zinc was positively correlated with absolute plasma zinc (r=0.78, P<0.001) and negatively correlated with whole blood and blood cellular zinc (r=-0.58, r=-0.71, P<0.001).

Acute insulin-induced hypoglycaemia does not alter IGF-1 and LH release in cyclic mares.

Lactation in the mare is associated with changes in the release of metabolic as well as reproductive hormones. Plasma glucose concentration is constantly reduced in lactating compared with non-lactating mares. Several metabolic signals have been proposed to link nutrition and somatic metabolism with reproductive function. The following experiment was performed to study the effect of acute hypoglycaemia on the release of insulin-like growth factor-1 (IGF-1) and luteinizing hormone (LH) in cyclic mares. Different doses of insulin (0.1 and 0.2 IU/kg body weight) were given to induce a decrease in plasma glucose concentration, as existent in lactating mares. All horses treated with insulin developed a hypoglycaemia over a time period of nearly 10 h. The IGF-1 and LH were analysed before and after insulin administration. At no point of time, a significant difference between the two insulin treatments and the control treatment was observed. Therefore, the hypoglycaemic horse is apparently able to provide the brain with sufficient glucose. Short-term hypoglycaemia does not affect the hypothalamo-pituitary-ovarian axis, and concentrations of IGF-1 and LH remained stable during insulin-induced hypoglycaemia. An acute change in plasma glucose concentration is thus not or at least not the only metabolic signal that links nutrition and somatic metabolism with reproductive function in the horse mare.

Effect of clenbuterol on the clearance of particles of charcoal (4 to 90 microm) from the uteri of mares.

The failure of clearance mechanisms in the mare's uterus results in persistent inflammation and is considered a major cause of subfertility. Eighteen mares, of which three were susceptible to endometritis and four had been ovariectomised, underwent charcoal clearance testing to evaluate their clearance mechanisms. This consisted of installing 500 mg of charcoal (particle size 4 to 90 microm) added to 50 ml of phosphate-buffered saline (PBS) into the uterus. Forty-eight hours later the uterus was flushed out with 0.0012 per cent methylene blue in 50 ml of PBS for determination of the diluting factor by photospectrometry. Flush volume, pH, specific gravity and pellet size were all analysed. To investigate the effect of a beta2-adrenergic agonist on the ability of genitally healthy oestrous mares to eliminate a suspension of charcoal from the uterus, four genitally healthy mares with appropriate charcoal clearance were also subjected to clearance testing following intravenous administration of 0.8 microg/kg of clenbuterol every 12 hours and 1 microg/kg of clenbuterol every eight hours. All parameters were within their normal range following clenbuterol treatment. However, minimal but significant differences in pre- and post-treatment values regarding fluid volume and extinction rate were recorded.

Efficacy of montelukast in the treatment of chronic obstructive pulmonary disease in five horses.

Five horses with moderate to severe chronic obstructive pulmonary disease (COPD) were treated with 0.11 (0.01) mg/kg bodyweight of montelukast, a cysteinyl leukotriene receptor antagonist, once a day for 26 days. The horses were evaluated clinically and endoscopically and subjected to arterial blood gas analysis and lung function tests before and after the period of treatment, and the plasma concentrations of montelukast were determined by high-performance liquid chromatography with fluorescence detection. The treatment did not result in statistically significant differences in the total scores of clinical and endoscopical signs, or in the difference in the arterioalveolar partial pressure of oxygen, maximal changes in pleural pressure, pulmonary resistance or dynamic compliance. The mean (sd) peak plasma concentration (C(max0) of montelukast was 12 (4) ng/ml and was reached 66 (13) minutes (t(max)) after its oral administration. The dose of montelukast per kg bodyweight was approximately the same as that for human beings, but the C(max) in the horses was 28 times lower and the t(max) was reached in one-fifth of the time, suggesting that its oral bioavailability may be lower.