Effect of breed of cattle on transmission rate and innate resistance to infection with Babesia bovis and B bigemina transmitted by Boophilus microplus

OBJECTIVE: To assess the effect of breed of cattle on the transmission rates of and innate resistance to Babesia bovis and B bigemina parasites transmitted by Boophilus microplus ticks. DESIGN: Groups of 56 purebred B indicus and 52 B indicus cross B taurus (50%, F1 generation) steers were placed in a paddock seeded with and also naturally infested with B microplus which were the progeny of females ticks fed on B taurus cattle specifically infected with a virulent isolate of B bovis. The cattle were placed in the infested paddock 50 days after seeding had started. PROCEDURE: Cattle were inspected from horseback daily for 50 days. Clinically ill cattle were brought to yards and assessed by monitoring fever, depression of packed-cell volume, parasitaemia and severity of clinical signs. Any animals that met preset criteria were treated for babesiosis. Blood samples were collected from all cattle on day 28, 35 and 42 after exposure and antibodies to Babesia spp and packed cell volume measured. RESULTS: All steers, except for one crossbred, seroconverted to B bovis and B bigemina by day 35 and 75% of the crossbred steers showed a maximum depression in packed cell volume of more than 15% due to infection with Babesia spp compared with only 36% of the B indicus group. Ten of the 52 crossbreds and 1 of the 56 B indicus steers showed severe clinical signs. Two of the crossbreds required treatment of which one died 2 weeks after initial treatment. CONCLUSIONS: Pure-bred B indicus cattle have a high degree of resistance to babesiosis, but crossbred cattle are sufficiently susceptible to warrant the use of preventive measures such as vaccination. Transmission rates of B bovis and B bigemina to B indicus and crossbred cattle previously unexposed to B microplus were the same.     

Models for biomechanical analysis of jumping horses

The application of qualitative analysis techniques, currently used in sports biomechanics, may help equine biomechanics researchers identify the most appropriate directions for future research. This paper reviews existing qualitative biomechanical models that could be relevant to equine jumping research. The deterministic model approach¹ is identified as the most appropriate. This approach is used to derive deterministic models suitable for equine jumping evaluation. The horse's jump can be broken down into five discrete parts_— approach, take off, suspension, landing and departure. Each of these parts has specific determining factors, which have either a mechanical or a mathematical relationship. These models may be used to assist horse trainers identify and implement appropriate strategies for improvement in jumping horses.     

The pharmacokinetics of orbifloxacin in the horse following oral and intravenous administration

The purpose of this study was to determine the pharmacokinetics and physicochemical characteristics of orbifloxacin in the horse. Six healthy adult horses were administered oral and intravenous orbifloxacin at a dose of 2.5 mg/kg. Plasma samples were collected and analyzed by high-pressure liquid chromatography with ultraviolet detection. Plasma protein binding and lipophilicity were determined in vitro . Following i.v. administration, orbifloxacin had a terminal half-life ( t _1/2) of 5.08 h and a volume of distribution (V_d(ss)) of 1.58 L/kg. Following oral administration, the average maximum plasma concentration ( C _max) was 1.25  μ g/mL with a t _1/2 of 3.42 h. Systemic bioavailability was 68.35%. Plasma protein binding was 20.64%. The octanol:water partition coefficient (pH 7.4) was 0.2 ± 0.11. No adverse reactions were noted during this study. Dosage regimens were determined from the pharmacokinetic–pharmacodynamic parameters established for fluoroquinolone antibiotics. For susceptible bacteria, an oral dose of approximately 5 mg/kg once daily will produce plasma concentrations within the suggested range. This dose is suggested for further studies on the clinical efficacy of orbifloxacin for treatment of susceptible bacterial infections in the horse.     

Pathological changes in the mammary gland and biochemical changes in milk of the goat following oral dosing with leaf of the Avocado (Persea americana)

Two varieties of avocado leaves (Persea americana var Guatemalan and var Mexican) were administered to lactating goats. The Mexican variety was without effect. The Guatemalan variety in doses exceeding 20 g fresh leaf per kg bodyweight, produced damage to the mammary gland with decreased milk production. The lesions were characterised by oedema and reddening, with clots in the large ducts. Microscopically, there was widespread degeneration and necrosis of the secretory epithelium, the necrotic cells sloughing into the lumen. There was no significant cellular inflammatory response. Concentrations of antitrypsin in the milk, indicating changes in vascular permeability, increased rapidly 15 h after a single high dose, coinciding with palpable oedema. Concentrations of NAGase, indicating cell damage, increased after 24 h. Goats given multiple doses followed a similar pattern but the initial response was delayed. The toxic principle, and its mode of action in selectively damaging mammary secretory cells, remains to be determined.