Objective—To determine whether a unique dihydropyridine
(BAY TG 1000) would be beneficial in preventing
laminitis in horses.
Animals—16 clinically normal adult horses.
Procedure—8 pairs of horses were used in a controlled
double-blind study, using sex- and agematched
horses randomly assigned to treatment or
control groups. Horses were subjected to carbohydrate
overload to induce laminitis. Treated horses
were administered BAY TG 1000 (30 mg/kg, PO, q
24 h) for 3 days. Hoof wall surface temperature
(HWST) and lameness were recorded at 4-hour
intervals. The HWST was adjusted on the basis of
time of onset of lameness and evaluated, using a
repeated-measures ANOVA. Lameness 8 hours
after onset and clinical status 72 hours after onset
of lameness were evaluated, using Mann-Whitney
Results—Analysis revealed that BAY TG 1000 did not
decrease the incidence of lameness but significantly
ameliorated prodromal hypothermia, lessened the
severity of lameness 8 hours after onset of lameness,
and improved the clinical status of horses 72 hours
after onset of lameness.
Conclusion and Clinical Relevance—Results support
the conclusion that BAY TG 1000 was protective
when used in prevention of laminitis. The drug
decreased severity and improved clinical status
(recovery) of induced lameness, which was interpreted
to mean that the drug's actions were on mechanisms
important but secondary to primary causal
mechanisms of laminitis. Therefore, drugs that
enhance digital perfusion via alteration of rheologic
activity may have potential use in the prevention and
management of laminitis in horses. (Am J Vet Res
Objective—To evaluate the use of hoof wall surface
temperature (HWST) as an indirect indicator of digital
perfusion and to describe HWST patterns during the
prodromal and acute phases of carbohydrate-induced
laminitis in horses.
Animals—30 adult horses without foot abnormalities.
Procedures—Three experiments were performed. In
the first, HWST was measured in 2 groups of horses
acclimatized to hot (n = 6), or cold (6) environments
and exposed to cold (15 C) ambient temperature. In
the second experiment, HWST were measured in
both forefeet of 6 horses before and after application
of a tourniquet to 1 forefoot to induce vascular occlusion.
In the third experiment, HWST were recorded in
12 horses before and during the prodromal and acute
phases of carbohydrate-induced laminitis.
Results—Mean HWST of hot-acclimatized cold-challenged
horses was significantly less than that of cold-acclimatized
cold-challenged horses at all times.
Transient episodes of high HWST were observed during
prolonged cold-induced vasoconstriction. Hoof
wall surface temperature significantly decreased during
arterial occlusion and increased during reperfusion.
Digital hypothermia was observed during the
prodromal phase of carbohydrate-induced laminitis.
Conclusions and Clinical Relevance—Determination
of HWST is a valid technique to evaluate digital
perfusion under appropriate controlled conditions in
horses. Digital hypothermia detected during the prodromal
phase of laminitis is consistent with decreased
digital vascular perfusion or metabolic activity. If administered
to horses during the prodromal phase, agents
that enhance digital perfusion may prevent development
of laminitis. (Am J Vet Res 2001; 62:1167–1172)
Objective—To determine the pharmacokinetics and clinical effects of a subanesthetic, continuous rate infusion of ketamine administered to healthy awake horses.
Animals—8 adult horses.
Procedures—Ketamine hydrochloride was administered to 2 horses, in a pilot study, at rates ranging from 0.4 to 1.6 mg/kg/h for 6 hours to determine an appropriate dose that did not cause adverse effects. Ketamine was then administered to 6 horses for a total of 12 hours (3 horses at 0.4 mg/kg/h for 6 hours followed by 0.8 mg/kg/h for 6 hours and 3 horses at 0.8 mg/kg/h for 6 hours followed by 0.4 mg/kg/h for 6 hours). Concentration of ketamine in plasma, heart rate, respiratory rate, blood pressure, physical activity, and analgesia were measured prior to, during, and following infusion. Analgesic testing was performed with a modified hoof tester applied at a measured force to the withers and radius.
Results—No signs of excitement and no significant changes in the measured physiologic variables during infusion rates of 0.4 and 0.8 mg of ketamine/kg/h were found. At 6 hours following infusions, heart rate and mean arterial pressure were decreased, compared with preinfusion measurements. An analgesic effect could not be demonstrated during or after infusion. Pharmacokinetic variables for 0.4 and 0.8 mg/kg/h infusions were not significantly different.
Conclusions and Clinical Relevance—Ketamine can be administered to awake horses at 0.4 or 0.8 mg/kg/h without adverse behavioral effects. The observed pharmacokinetic values are different than those reported for single-dose IV bolus administration of this drug.
Objectives—To compare limb-load distribution
between horses with and without acute or chronic
Animals—10 horses with carbohydrate-induced
acute laminitis, 20 horses with naturally occurring
chronic laminitis, and 20 horses without foot abnormalities
Procedures—Limb-load distribution was determined,
using a custom-designed system that allowed simultaneous
quantification of the mean percentage of
body weight voluntarily placed on each limb (ie, mean
limb load) and the SD of the mean load over a 5-
minute period (ie, load distribution profile [LDP]). Load
distribution profile was used as an index of frequency
of load redistribution.
Results—Mean loads on fore- and hind limbs in control
horses were 58 and 42%, respectively, and loads
were equally and normally distributed between left
and right limbs. In addition, forelimb LDP was greater,
compared with hind limbs, and was affected by head
and neck movement. In comparison, limb-load distribution
in horses with chronic laminitis was characterized
by an increase in the preferential loading of a
forelimb, a decrease in total forelimb load, and an
increase in LDP that was correlated with severity of
lameness. In horses with carbohydrate-induced acute
laminitis, mean limb loads after onset of lameness
were not different from those prior to lameness; however,
LDP was significantly decreased after onset of
Conclusion and Clinical Relevance—Quantification
of limb-load distribution may be an applicable screening
method for detecting acute laminitis, grading
severity of lameness, and monitoring rehabilitation of
horses with chronic laminitis. (Am J Vet Res 2001;
Objective—To evaluate chemotactic, phagocytic, and
bactericidal activities of bovine and porcine alveolar
macrophages (AM) exposed to tilmicosin.
Animals—12 healthy calves and 12 healthy pigs.
Procedure—Lungs were obtained immediately after
euthanasia; AM were collected by means of bronchoalveolar
lavage and density gradient centrifugation.
Chemotactic activity was evaluated by exposing
AM to lipopolysaccharide or macrophage inhibitory
peptide during incubation with tilmicosin. Phagocytic
activity was evaluated by incubating AM with tilmicosin
for 24 hours and then with tilmicosin-resistant
Salmonella serotype Typhimurium. Bactericidal activity
was evaluated by incubating AM with tilmicosin (0,
10, or 20 µg/ml for bovine AM; 0 or 10 µg/ml or 10
µg/ml but washed free of tilmicosin for porcine AM)
and then with Mannheimia haemolytica (bovine AM)
or with Actinobacillus pleuropneumoniae or
Pasteurella multocida(porcine AM).
Results—Tilmicosin had no significant effects on
chemotactic or phagocytic activities of bovine or
porcine AM. The time-course of bactericidal activity
was best described by polynomial equations. Time to
cessation of bacterial growth and area under the time
versus bacterial number curve were significantly
affected by incubation of AM with tilmicosin.
Conclusion and Clinical Relevance—Results show
that bactericidal activity of bovine and porcine AM
was enhanced by tilmicosin, but not in proportion to
the reported ability of AM to concentrate tilmicosin
intracellularly. With or without exposure to tilmicosin,
the time-course of bactericidal activity of bovine AM
against M haemolytica and of porcine AM against
A pleuropneumoniae or P multocida was too complex
to be reduced to a simple linear equation. (Am J Vet
Objective—To assess the serologic response of calves to inactivated and modified-live (ML) Mannheimia haemolytica (MH) preparations given alone and concurrently with combination viral vaccines containing ML bovine herpesvirus type 1 (BHV-1).
Animals—642 calves seronegative for BHV-1.
Procedures—In experiment 1, 192 calves received 1 of 3 MH preparations alone or concurrently received 1 of 3 MH preparations and 1 of 4 combination viral vaccines. In experiment 2, 450 calves received 1 of 4 MH preparations alone or concurrently received 1 of 4 MH preparations and 1 of 5 combination viral vaccines. Pretreatment and posttreatment blood samples were processed to obtain serum, which was analyzed to detect concentrations of antibodies against MH leukotoxin and BHV-1.
Results—In experiment 1, antibody titers against MH leukotoxin in calves receiving MH and ML virus vaccine appeared decreased, albeit nonsignificantly, compared with titers for calves receiving MH preparations alone. In experiment 2, all groups (except for 1) concurrently receiving an MH preparation and viral vaccine had a significant decrease in antibodies against MH leukotoxin. In both experiments, there was a significant decrease in the number of calves responding to MH leukotoxin when ML viral vaccine was coadministered.
Conclusions and Clinical Relevance—Coadministration of ML BHV-1 and MH preparations interfered with the serologic response to MH leukotoxin in calves seronegative for BHV-1. Serologic response to MH leukotoxin may be substantially improved in seronegative calves when MH vaccination is delayed until after calves have received a dose of ML BHV-1 vaccine.