Plasma l-indospicine and 3-nitropropionic acid in ponies fed creeping indigo: Comparison with results from an episode of presumptive creeping indigo toxicosis.

BACKGROUND: Creeping indigo (Indigofera spicata) toxicosis is an emerging problem among horses in Florida and bordering states. OBJECTIVES: To quantify the putative toxins l-indospicine (IND) and 3-nitropropionic acid (NPA) in creeping indigo collected from multiple sites and to measure plasma toxin concentrations in ponies fed creeping indigo and horses with presumptive creeping indigo toxicosis. STUDY DESIGN: Experimental descriptive study with descriptive observational field investigation. METHODS: Air-dried creeping indigo was assayed for IND and NPA content. Five ponies were fed chopped creeping indigo containing 1 mg/kg/day of IND and trace amounts of NPA for 5 days, then observed for 28 days. Blood samples from these ponies and from horses involved in a presumptive creeping indigo toxicosis were assayed for IND and NPA. RESULTS: IND in creeping indigo plants was 0.4-3.5 mg/g dry matter whereas NPA was <0.01 to 0.03 mg/g. During creeping indigo feeding, clinical and laboratory signs were unchanged except for significant weight loss (median 6%, range 2%-9%; p = .04) and significant increase from baseline plasma protein concentration (median 16 g/L, range 8-25 g/L; p < .001). These changes could not definitively be ascribed to creeping indigo ingestion. Plasma IND rose to 3.9 ± 0.52 mg/L on day 6. Pharmacokinetic modelling indicated an elimination half-life of 25 days and a steady state plasma concentration of 22 mg/L. Plasma IND concentration in sick horses during an incident of creeping indigo toxicosis was approximately twice that of clinically normal pasture mates. Plasma NPA was <0.05 mg/L in all samples. MAIN LIMITATIONS: Creeping indigo used in the feeding trial may not be representative of plants involved in creeping indigo toxicosis. There was no control group without creeping indigo in the feeding trial. CONCLUSIONS: Indospicine can be detected in blood of horses consuming creeping indigo and the toxin accumulates in tissues and clears slowly. The role of NPA in the neurological signs of this syndrome is unclear.

Effect of feed deprivation on daily water consumption in healthy horses.

BACKGROUND: Measurements of water consumed by fed healthy horses might not apply to horses that are unwilling or unable to drink or are not fed for any reason. OBJECTIVE: To examine the effects of feed deprivation on voluntary water consumption compared with fed conditions. STUDY DESIGN: In vivo experiment. METHODS: Eight healthy adult Thoroughbred geldings were used in a randomised crossover design so that each horse served as its own control for fed vs feed-deprived conditions. Water intake, bodyweight, physical findings and vital signs were measured during 4 days of feeding and 4 days of feed deprivation. Daily measurements during the trial periods were PCV, TPP, electrolytes, osmolality and triglycerides. Plasma and extracellular fluid volumes were measured in the last 8 hours of the trial periods. Data were analysed with a two-way analysis of variance with repeated measures, and statistical significance was P ≤ .05. RESULTS: Feed deprivation immediately and persistently reduced water consumption to ~16% of fed values, with laboratory evidence of mild dehydration on day 4. MAIN LIMITATIONS: Changes in total body water and in water and electrolyte excretion or conservation through faeces and urine were not measured. CONCLUSIONS: Feed consumption has a marked effect on water requirements in healthy horses. Because current guidelines for water needs were obtained in the fed state, they might not apply to horses that are denied feed for any reason or have reduced feed intake. This study provides new information on water consumption in horses that should apply to this essential nutrient in health and disease.