Much can be said about the blood supply to the bone, but generally speaking the blood flow to the bone is normally centrifugal from the medulla to the periosteum.  In the event the nutrient supply is compromised, the periosteal system is able to adjust and convey an adequate supply to the compactum.   Fluids delivered bathe the crystalline component of bone and the necessary ion exchanges occur. Uptake of radionuclide in the bone is directly proportionate to blood flow. That being said, offers a partial explanation to the seemingly random incidences of poor bone uptake in the equine patient especially in the cooler weather conditions.   Significant detrimental factors appear to be age, breed, mass, and atmospheric temperature. Special attention to the these factors can improve the target (bone) to background (soft tissue) ratio of a bone scan and subsequently improve the diagnostic quality of a bone scan.  Some suggestions are: (1) to wrap the distal limbs and blanket the horse 12-24 hours prior to injection of the radionuclide. (2) Hold the patient in a heated area during colder temperatures for 12-24 hours prior to injection. and/or (3) exercise the horse to increase the heart rate and encourage profusion immediately prior to injection of the radionuclide especially for larger breeds and older horses.