Lameness and heart rate elevation in the exercising horse

Seven, healthy, conditioned, Quarter Horse mares with previous treadmill experience were each fitted with an adjustable heart bar shoe on the left front foot and a counterbalanced bar shoe on the right front foot. Three treatments were studied: sound, slightly lame, and obviously lame at a trot. Each subject performed one standardized exercise test (SET) daily on three consecutive days. Each subject underwent one treatment during a SET. Treatment order was randomly assigned. The SET consisted of a 5-rain exercise period at 3.2 m/sec on a treadmill at an 11% grade. Heart rate (HR) was determined at rest, 20 rain after the induction of lameness before the SET, during the last 30 sec of the SET, and at 0.5, 1, 2, 3, 4, 5, 10, 20, 30, 40, and 60 min postexercise. The Student's paired t test was used to compare HR means for the three treatments at each monitoring interval. Heart rate was higher in slightly lame trials compared to sound trials as rest and at 0.5 through 10 and 30 through 60 min postexercise (P<0.05 to P<0.001). Lame trials evidenced higher HRs than slightly lame trials at rest and at 0.5, 2, 4, and 5 rain of recovery (P<0.05). When lame HRs were compared to sound HRs, differences were noted at rest and at 0.5 through 60 min postexercise (P<0.01 to P<0.001). The heart bar shoe as designed for the treatment of laminitis was effective as a noninvasive, nonpermanent model of lameness pain in normal horses. Increases in HR at rest and during recovery from exercise were observed with experimentally induced lameness. The degree of HR increase seen with lameness was a function of the degree of lameness induced.     

In vitro heterogeneity of osteogenic cell populations at various equine skeletal sites

Bone cell cultures were evaluated to determine if osteogenic cell populations at different skeletal sites in the horse are heterogeneous. Osteogenic cells were isolated from cortical and cancellous bone in vitro by an explant culture method. Subcultured cells were induced to differentiate into bone-forming osteoblasts. The osteoblast phenotype was confirmed by immunohistochemical testing for osteocalcin and substantiated by positive staining of cells for alkaline phosphatase and the matrix materials collagen and glycosaminoglycans. Bone nodules were stained by the von Kossa method and counted. The numbers of nodules produced from osteogenic cells harvested from different skeletal sites were compared with the use of a mixed linear model. On average, cortical bone sites yielded significantly greater numbers of nodules than did cancellous bone sites. Between cortical bone sites, there was no significant difference in nodule numbers. Among cancellous sites, the radial cancellous bone yielded significantly more nodules than did the tibial cancellous bone. Among appendicular skeletal sites, tibial metaphyseal bone yielded significantly fewer nodules than did all other long bone sites. This study detected evidence of heterogeneity of equine osteogenic cell populations at various skeletal sites. Further characterization of the dissimilarities is warranted to determine the potential role heterogeneity plays in differential rates of fracture healing between skeletal sites.     

Nucleoside phosphatases of fetal and maternal blood cells: electron microscope study

Surface membranes of the blood cells located within the maternal blood sinuses of the rat placenta contain reaction products of nucleoside phosphatases. Fetal blood cells separated from maternal blood by the placental labyrinth show no activity during normal or prolonged gestation. Neonatal blood cells examined 34 hours after parturition show these enzyme activities.