Serial blood samples were collected and plasma concentrations of florfenicol (FLO) were measured following the administration of an intravenous bolus of 50 mg/kg FLO to five healthy non-lactating dairy cows. A triexponential equation provided the best fit of the data for four of the five cows. The mean value for beta corresponded to a half-life of 3.2 h. The mean apparent volume of distribution was 0.67 l/kg, and the mean body clearance was 0.15 l/kg/h. The extent of binding of FLO to bovine plasma proteins was determined in vitro at concentrations of 5 micrograms/ml and 50 micrograms/ml by equilibrium dialysis and ultrafiltration. The drug was 18% and 19% bound by equilibrium dialysis, and 23% and 19% bound by ultrafiltration, at 5 micrograms/ml and 50 micrograms/ml, respectively. Phagocytosis of 32phosphorus-labelled Staphylococcus aureus by bovine blood neutrophils was compared in vitro between neutrophils incubated in phosphate-buffered saline alone or in combination with 5, 125, or 1000 micrograms/ml chloramphenicol or FLO. There was no significant effect of chloramphenicol at any concentration. Florfenicol significantly inhibited phagocytosis at all concentrations, but the percentage inhibition was small. The clinical significance, if any, of this effect of FLO remains to be demonstrated.

Sodium and potassium were measured in epididymal plasma at six different levels of the epididymal duct in individual bulls, and the sperm concentration was estimated at the same levels. The sperm concentration was very low in the rete testis and the proximal part of the caput, but increased continuously to a maximum at the proximal end of the corpus. It fluctuated thereafter, being lower in the distal corpus and slightly higher in the cauda. In the rete testis the sodium content of the plasma was high and the potassium content low. The concentration ofsodium decreased in the caput and proximal part of the corpus, where the potassium concentration reached its maximum, thus indicating a selective resorption of sodium with the fluid. In the rest of the corpus the concentration of sodium and potassium remained unchanged but in the cauda the concentration of both decreased markedly.

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The peripheral plasma levels of oestrone* were measured in 127 dairy cows of the Swedish Red and White Breed. The levels recorded during the time period from the 20th to the 35th week of pregnancy were below or about 0.1 ng per ml. After the 35th week of pregnancy the levels increased gradually and maximum levels ranging from 0.5 to 2 ng per ml were found during the last week of gestation. After parturition the levels decreased significantly to about 0.1 ng per ml or less. Six cows were sampled daily from 8 days before until two days after parturition. The peripheral plasma levels of oestrone, oestradiol-17β and progesterone were measured. The oestrone level ranged from about 0.7 to 0.9 ng per ml during the last eight days preceding the delivery. The peripheral plasma levels of oestradiol-17β followed the same pattern as for oestrone. The concentration of oestradiol was only 10 to 20 per cent of the oestrone level. The mean peripheral plasma levels of progesterone were about 4 to 5 ng per ml during the last seven days before partus. A significant drop of the peripheral plasma level of progesterone to an average of 1.8 ng per ml occurred about 24 hours before parturition.